Accepted Manuscript

Sediment dynamics and post-glacial evolution of the continental shelf around

the Blanes submarine canyon head (NW Mediterranean)

Ruth Durán, Miquel Canals, Galderic Lastras, Aaron Micallef, David Amblas,

Rut Pedrosa-Pàmies, José Luis Sanz

PII: S0079-6611(13)00144-4

DOI: http://dx.doi.org/10.1016/j.pocean.2013.07.031

Reference: PROOCE 1319

To appear in: Progress in Oceanography

Please cite this article as: Durán, R., Canals, M., Lastras, G., Micallef, A., Amblas, D., Pedrosa-Pàmies, R., Sanz,

J.L., Sediment dynamics and post-glacial evolution of the continental shelf around the Blanes submarine canyon

head (NW Mediterranean), Progress in Oceanography (2013), doi: http://dx.doi.org/10.1016/j.pocean.2013.07.031

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1

Sediment dynamics and post-glacial evolution of the continental shelf around the 2

Blanes submarine canyon head (NW Mediterranean) 3

4

Ruth Durán1, Miquel Canals1*, Galderic Lastras1, Aaron Micallef1, David Amblas1, Rut 5

Pedrosa-Pàmies1 and José Luis Sanz2 6

7

1: GRC Geociències Marines, Departament d'Estratigrafia, Paleontologia i Geociències 8

Marines, Facultat de Geologia, Universitat de Barcelona, E08028 Barcelona, Spain 9

2: Instituto Español de Oceanografía, E28002 Madrid, Spain 10

* Corresponding author: e-mail: miquelcanals@ub.edu 11

Tel: +34 934021360; Fax: +34 934021340 12

13

2

ABSTRACT 14

The Blanes submarine canyon deeply incises the Catalan continental shelf in the 15

northwestern Mediterranean Sea. As a consequence of the closeness (only 4 km) of its 16

head to the coastline and the mouth of the Tordera River, the canyon has a direct influence 17

on the shelf dispersal system as it collects large amounts of sediment, mainly during high-18

energy events. Multibeam bathymetry, backscatter imagery and very-high resolution 19

seismic reflection profiles have allowed characterizing the morphology of the continental 20

shelf around the canyon head, also identifying sediment sources and transport pathways 21

into the canyon. The morphological data have also been used to reconstruct the evolution 22

of the continental shelf during the last sea-level transgression so that the current 23

understanding of shelf-to-canyon sediment exchanges through time could be improved. 24

The continental shelf surrounding the Blanes Canyon consists of both depositional and 25

erosional or non-depositional areas. Depositional areas display prominent sediment bodies, 26

a generally smooth bathymetry and variable backscatter. These include: (i) an area of 27

modern coarse-grained sediment accumulation that comprises the inner shelf; (ii) a modern 28

fine-grained sedimentation area on the middle shelf offshore Tossa de Mar; and (iii) a 29

modern sediment depleted area that covers most of the middle and outer shelf to the west 30

of the canyon head. Erosional and non-depositional areas display a rough topography and 31

high backscatter, and occur primarily to the east of the canyon head, where the arrival of 32

river-fed inputs is very small. In agreement with this pattern, the continental shelf north and 33

west of the canyon head likely is the main source of shelf sediment into the canyon. To the 34

north, a pattern of very high backscatter extends from the coastline to the canyon head, 35

suggesting the remobilization and off-shelf export of fines. Additionally, relict near-shore 36

sand bodies developed over the Barcelona shelf that extend to the canyon head rim 37

constitute a source of coarse sediment. High-energy processes, namely river floods and 38

coastal storms, are the main controls over the river-shelf-canyon sediment exchange. River 39

floods increase the delivery of terrigenous particles to the coastal system. Storms, mainly 40

from the east, remobilize the sediment temporarily accumulated on the shelf towards the 41

3

canyon head, so that the finer fractions are preferentially removed and a coarse lag is 42

normally left on the shelf floor. Exceptionally, very strong storms also remove the coarse 43

fractions from the shelf drive them into the canyon. Processes like dense shelf water 44

cascading, which is much more intense in canyons to the north of Blanes Canyon, and the 45

Northern Current also contribute to the transport of suspended sediment from far distant 46

northern sources. 47

During the last post-glacial transgression the Blanes Canyon had a strong influence on the 48

evolution of the inner continental margin, as it interrupted the shelf sediment dispersal 49

system by isolating the shelves to its north and south, named La Planassa and Barcelona 50

shelves, respectively. 51

Key words: Continental shelf, shelf floor morphology, sediment dynamics, eastern storms, 52

Blanes submarine canyon, Western Mediterranean Sea. 53

4

54

1. INTRODUCTION 55

Sediment dynamics in many continental shelves depends on the balance between 56

sediment supply by rivers and its dispersal across the shelf (Nittrouer and Wright, 1994). 57

Among the general factors that influence the across shelf transport of particles towards the 58

shelf break are the shelf morphology and the hydrodynamic regime. Irregular shelves, with 59

promontories and changing width, can modify the along-shelf circulation thus increasing the 60

off-shelf transport of particles such as off Cap de Creus promontory (Canals et al., 2006; 61

Puig et al., 2008; Ribó et al., 2011). Similarly, submarine canyons incising the continental 62

shelf may enhance the off-shelf transport of sediment, either by funnelling fluvial sediment 63

to the deep sea, like in Sepik (Kineke et al., 2000; Walsh and Nittrouer, 2003), Monterey 64

Canyon (Xu et al., 2002; Paull et al., 2003) and Kao-ping (Liu et al., 2002; Liu and Lin, 65

2004) canyons, or by intercepting the shelf sediment dispersal system, like in La Jolla 66

(Shepard and Dill, 1966), Quinault (Cutshall et al., 1986), Eel (Mullenbach and Nittrouer, 67

2000; Puig et al., 2003; Mullenbach et al., 2004), Cap de Creus (Canals et al., 2006), 68

Nazaré (Oliveira et al., 2007) and Bari (Turcheto et al., 2007) canyons. 69

The across and off-shelf transport of sediment also changes as a function of short-term 70

high-energy events such as river floods, storms or dense shelf water cascading (DSWC). 71

River floods increase the transfer of terrigenous material to the coastal area (Granata et al., 72

1999; Ogston et al., 2000; Liu et al., 2002; Zúñiga et al., 2009) that can be subsequently 73

remobilized during storms (Xu et al., 2002; Liu and Lin, 2004; Palanques et al., 2008). 74

When a storm coincides with a period of high river discharge, suspended sediment 75

concentrations are considerably enhanced, leading to an increased export of shelf 76

sediment to submarine canyon and the continental slope at large (Mullenbach and 77

Nittrouer, 2000; Ogston et al., 2004; Ulses et al., 2008). DSWC has also been identified as 78

an efficient mechanism in promoting the dispersal of sediment over the shelf and off-shelf 79

through submarine canyons mainly (Canals et al., 2006; Turcheto et al., 2007; Bourrin et 80

5

al., 2008; Puig et al., 2008; Sanchez-Vidal et al., 2008; Pasqual et al., 2011; Ribó et al., 81

2011). 82

The characterization of the sediment dynamics on the continental shelf adjacent to a 83

submarine canyon head allows improving the understanding of the continent-shelf-canyon 84

system functioning. Continental shelves are both sinks and major sources of sediment, 85

organic matter and pollutants that can be transported towards deep areas after being 86

trapped by submarine canyons (Canals et al., 2006; Palanques et al., 2008; Puig et al., 87

2008; Salvadó et al., 2012). Several authors have reported on the effects of submarine 88

canyon hydrosedimentary processes over marine biodiversity and living resources, also in 89

the study area (Gili et al., 1999; Company et al., 2008; Sardà et al., 2009). The magnitude 90

and nature of shelf-canyon sediment exchanges have important implications for the 91

morphological and stratigraphical development of continental shelves and slopes too 92

(Walsh and Nittrouer, 2003). 93

The analysis of the fine scale geomorphology of the continental shelf can potentially 94

provide significant insight into sediment dynamics. The shape, orientation and distribution 95

of large-scale depositional features and superimposed bedforms are strong indicators of 96

the effects of cumulated sediment transport and the processes behind (Belderson and 97

Stride, 1969; Dalrymple et al., 1978; Flemming, 1980; Allen, 1982; Ashley, 1990; Li and 98

King, 2007; Barnard et al., 2011). High-resolution multibeam bathymetry systems constitute 99

nowadays a fundamental tool to achieve such an analysis because of their ability to yield 100

high quality and density seafloor data that could be displayed in various forms such as 101

bathymetry, slope gradient or backscatter maps (Barnard et al., 2012; Hughes Clarke, 102

2012). Swath mapping shelf areas requires a stronger effort in terms of time and cost as 103

the coverage per swath is less because of its shallower depth compared to slope and 104

deeper ocean regions. 105

In this paper we present a detailed geomorphologic analysis of a narrow canyon-incised 106

continental shelf using multibeam bathymetry, including backscatter data, complemented 107

by wide-spaced very-high resolution seismic reflection profiles, in order to: (i) identify the 108

6

potential sources and transport pathways of sediment across the shelf and into the canyon, 109

and (ii) reconstruct the evolution of the continental shelf since the Last Glacial Maximum to 110

understand how shelf-to-canyon sediment processes have changed in space and time. The 111

continental shelf around the Blanes submarine canyon, in the northwestern Mediterranean 112

Sea, was chosen for this study because: (i) the shelf is very narrow where it is incised by 113

the canyon head, which itself is located in the vicinity of the coastline with a fluvial source ; 114

and (ii) previous studies of the Blanes Canyon revealed an intense shelf to canyon 115

transport of sediment, particularly during episodic high-energy events (Ulses et al., 2008; 116

Zúñiga et al., 2009; Sanchez-Vidal et al., 2012; Pedrosa-Pàmies et al., this issue) 117

118

2. GENERAL SETTING 119

2.1. Geological setting 120

The study area comprises the segment of the Catalan continental shelf around the Blanes 121

submarine canyon head, between 41º30‘N and 41º45‘N (Fig. 1). The Blanes Canyon is 184 122

km long and has a nearly N–S trending course in its shelf-incised section (Amblas et al., 123

2006; Lastras et al., 2011). The continental shelf neighbouring the canyon head includes 124

the southernmost part of the La Planassa shelf to the east, the northernmost part of the 125

Barcelona shelf to the west, and a narrow shelf stretch between the coastline and the tip of 126

the canyon head to the north (Fig. 1). 127

Hercynian granitoids outcrop along the southern Costa Brava and the Maresme coastline, 128

with colluvial and alluvial deposits of Quaternary age forming a narrow coastal fringe along 129

the Maresme coastal stretch and in the Tordera delta (IGC-ICC, 2010) (Fig. 2A). According 130

to the onshore geological structure, the Barcelona and La Planassa shelves in the 131

neighbourhood of the Blanes canyon head are dominated by NE-SW structural directions 132

(Fig. 2A). In the Barcelona shelf, a large listric fault named Barcelona Fault and other 133

parallel to subparallel faults bound the NE–SW oriented Malgrat High off the Maresme 134

coast (IGC-ICC, 2010) (Fig. 2A). A vertical slip rate of 0.02-0.04 mm·yr−1 has been 135

7

estimated for the Barcelona Fault during the Plio-Quaternary (Perea et al., 2006 and 2012). 136

The coastline parallel Costa Brava Fault cutting the innermost La Planassa shelf represents 137

the north-eastern extension of the Barcelona Fault (IGC-ICC, 2010; Durán et al., 2012) 138

(Fig. 2A). The main morphological expressions of the structural offset associated to this 139

fault are the coastal cliffs of the Costa Brava, the steepness of the inner shelf, and the 140

lithological contrast between the coastal Hercynian granites and the rocky outcrops and the 141

overconsolidated Plio–Pleistocene sediment of the middle and outer shelf (Serra, 1976; 142

ITGE, 1989). 143

The Plio–Quaternary architecture of the continental shelf near the Blanes Canyon consists 144

of a vertical stacking of sequences separated by major discontinuities (Serra, 1976; ITGE, 145

1989; Liquete et al., 2008). Within these sequences, forced-regressive deposits (FRST; 146

Fig. 2B) are the predominant element comprising the outer shelf sequences, whilst 147

transgressive deposits (TST; Fig. 2B) are limited to thin units of reworked sands (Liquete et 148

al., 2008). The most recent sequence (sequence E; Fig. 2C) overlies an erosional surface 149

(SB 4; Figs. 2C and 2D) developed during the last sea-level lowstand of Marine Isotope 150

Stage (MIS) 2 and comprises the transgressive (TST) and highstand (HST) system tracts 151

(Liquete et al., 2008). In the Barcelona shelf, this TST is defined by a series of prograding 152

sediment bodies (Díaz and Maldonado, 1991; Serra and Sorribas, 1993; Liquete et al., 153

2007), whereas in the La Planassa shelf it is almost absent, with large rocky outcrops 154

dominating the middle shelf (Serra, 1976; ITGE, 1989; García et al., 2011). In both shelf 155

areas, the HST is mostly restricted to the inner shelf modern prodeltas and infralittoral 156

prograding wedges (IPW) (Serra, 1976; ITGE, 1989; Serra et al., 2003 and 2007). 157

General descriptions of the morphology of the studied continental shelf can be found in 158

Serra (1976) and ITGE (1989). Such works are based on single-beam echo sounder and 159

side scan sonar data, seismic reflection profiles and bottom samples and describe large 160

seafloor features such as prodeltas, infralittoral prograding wedges, middle-shelf sediment 161

bodies and rocky outcrops. The sparse bathymetric coverage did not allow these authors to 162

describe adequately these features in the study area. Recently, new multibeam bathymetry 163

8

data from the northern Catalan continental shelf have revealed a complex seafloor, 164

particularly near canyon heads, where large seafloor features such as modern and relict 165

sediment bodies and numerous rocky outcrops have been identified (Lastras et al., 2011; 166

Durán et al., 2012). The high-resolution swath bathymetry data presented in this study 167

allows precisely defining the morphology and shape of the above-mentioned seafloor 168

features and helps recognizing many other previously unknown and poorly known features. 169

2.2. Sediment input 170

The Tordera River and several torrents, such as the Tossa de Mar and Lloret de Mar ones, 171

fed the continental shelf of the Blanes canyons area (Fig. 2A). Their sediment input 172

depends directly of the rainfall regime, which is characterized by long dry periods 173

interrupted by short, strong events that can result in floods within a few hours, especially in 174

the case of eastern storms carrying wet air against the coastal relieves (Martín-Vide, 1982; 175

Martín-Vide et al., 2008). The Tordera River catchment area covers 879 km2 and has a 176

maximum altitude of 1684 m and a mean slope of 3.8° (Liquete et al., 2009). The Tordera 177

River headwaters are located in the Montseny-Guilleries Massif and the Pre-Littoral Chain. 178

The drainage system is incised to a large extent in the granites of the Catalan Coastal 179

Ranges (Fig. 2A). The Tordera River releases to its mouth high amounts of coarse 180

immature sands carried as bedload and fine sediment in suspension. Sand sizes represent 181

approximately 83% of the total sediment discharge of the river (Rovira et al., 2005; Liquete 182

et al., 2009). The immature character of these sediments is due to the nature of source 183

rocks, to the relatively short distances travelled and to the dominant fast flood torrential 184

regime of the river. 185

2.3. Hydrodynamic setting 186

The Catalan continental shelf is a wave-dominated, microtidal (<0.2 m) environment that 187

has a seasonal wave climate with high-energy events occurring during fall and winter 188

mostly. The cyclonic Northern Current (NC; Millot, 1999) is a quasi-permanent geostrophic 189

current flowing along the continental slope and shelf break that often develops meanders or 190

9

eddies eventually invading the continental shelf (Font et al., 1995; Rubio et al., 2005). The 191

30 km wide stream of the south-westwards flowing NC moves at speeds of up to 35 cm s-1 192

near the surface (Durrieu de Madron et al., 1990; Monaco et al., 1990), thus generating a 193

dominant south-westward transport of suspended sediment from the north-east (Canals et 194

al., 1995; Flexas et al., 2002; Arnau et al., 2004; Ulses et al, 2005; Heussner et al., 2006). 195

Northerly and easterly winds prevail over the Blanes shelf. Strong northerly winds mostly 196

occur during December and January, whilst easterly winds are more frequent during 197

February, March, April and November (Bolaños et al., 2009). Cold and dry northerly winds 198

are responsible for the formation of dense shelf water over the Gulf of Lion and the 199

northern Catalan continental shelf. This dense water mass flows southward along the shelf 200

and cascades down the continental slope through submarine canyons, thus resuspending 201

and transporting large amounts of sediment (Dufau-Julliand et al., 2004; Canals et al, 2006; 202

Puig et al., 2008; Ulses et al., 2008; Palanques et al, 2009; Ribó et al, 2011). Because of 203

the short fetch, northerly winds trigger only small waves over the inner-shelf (Gómez et al., 204

2005; Bolaños et al., 2009). In contrast, humid marine winds blowing from the east are 205

associated to large swells resulting from some hundreds of kilometres fetch that cause 206

intense sediment resuspension along the coastline (Monaco et al., 1990; Mendoza and 207

Jiménez, 2008; Sanchez-Vidal et al., 2012). The storm wave base is located at 20 m depth 208

(Calafat, 1986), but it can move down to at least 30 m during the strongest storms (Sorribas 209

et al., 1993). Because waves approach the coast at oblique angles during eastern storms, 210

they generate an intense south-westward alongshore transport of sediment that can be up 211

to 45 000 m3 y-1 (DGPC, 1986) or even 83 000 m3 y-1 (Copeiro, 1982) off the Maresme 212

Coast (Fig. 3). 213

214

3. METHODS 215

The morphosedimentary analysis of the continental shelf near the Blanes submarine 216

canyon head is based on the integration of multibeam swath bathymetry data, including 217

10

backscatter, with widely-spaced sub-bottom seismic reflection profiles (Fig. 1). Swath 218

bathymetry data cover an area of about 525 km2 and were acquired with two Simrad 219

systems, the EM-3000D and the EM-1002S, during several cruises carried out between 220

2004 and 2010. The EM-3000D is a dual system with two sonar heads, each of them with a 221

swath width of 130 degrees. This system uses 254 beams and operates at a frequency of 222

300 kHz with a maximum ping rate of 40 Hz. The EM-1002S system operates at a 223

frequency of 95 kHz with a maximum ping rate of 10 Hz, and it forms 111 beams. 224

Measurement accuracies are 5 cm and 10 cm of root mean square for the EM-3000D and 225

EM-1002S, respectively. Deep-water EM-120 multibeam data, on the other hand, were 226

acquired over the continental slope. Multibeam bathymetry data were supplemented with 227

single beam data from various sources (e.g. nautical charts, former bathymetric maps and 228

open access bathymetric databases) in the shelf areas lacking swath bathymetry coverage 229

(Fig. 1). Positioning during multibeam data acquisition was by differential GPS. Multibeam 230

bathymetry data processing was carried out with CARIS HIPS and SIPS software. 231

Backscatter strength, originally measured in decibels (dB), represents the amount of 232

energy that is scattered from the seafloor back to the receiver transducer. Backscatter is 233

influenced by several factors including surface roughness, impedance contrast and 234

volumetric heterogeneity, showing a good correlation with the mean grain size (Goff et al., 235

2000; Collier and Brown, 2005). Despite the limitations of backscatter intensity in predicting 236

seafloor texture, high backscatter intensities can be associated to larger grain sizes and 237

low backscatter intensities to smaller grain sizes (Collier and Brown, 2005; Amblas et al., 238

2006; Micallef et al., 2012). In parallel to the multibeam bathymetry data acquisition, very 239

high-resolution seismic reflection data were collected with a Simrad 018 TOpographic 240

PArametric Sonar (TOPAS). The TOPAS transmitted each 1–2 s, with a beam angle of 241

approximately 5°, and a modulated frequency sweep (chirp) ranging between 3 and 5 kHz. 242

243

4. RESULTS 244

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4.1. Morphology of the continental shelf 245

The continental shelf shoreward of the Blanes Canyon tip is just 4 km wide. Subsequently, 246

shelf width increases towards the Barcelona and La Planassa shelves (up to 15 and 18 km, 247

respectively). The shelf of the study area comprises: (i) a narrow (0.4–0.7 km) inner shelf, 248

extending from the coastline to 30-50 m depth, (ii) a wider middle shelf from 30-50 to 90 m 249

depth, and (iii) an outer shelf from 90 m depth to the shelf edge. The shelf edge is located 250

at 125–150 m water depth along the western rim of the Blanes Canyon, and at less than 251

100 m water depth along the eastern rim (Fig. 3). 252

The inner shelf shows a relatively steep seafloor (1.5º average slope gradient; Fig. 4A) that 253

ends seaward in an abrupt step (up to 20º). The inner shelf displays numerous relieves that 254

correspond to infralittoral prograding wedges (IPWs), small prodeltas and rocky outcrops 255

(Fig. 3). To the west of the canyon head, the general bathymetric trend of the Barcelona 256

middle and outer shelf is disrupted by several morphological steps and narrow ridges that 257

show gradients in excess of 2º and up to 14º (Fig. 4A). To the east of the canyon head, the 258

La Planassa shelf shows a rugged seafloor that extends down to 90 m depth showing 259

gradients of about 2.8º. This uneven topography results from a large, complex rocky 260

outcrop and several narrow ridges (Figs. 3 and 4A). The middle La Planassa shelf offshore 261

Tossa de Mar and the outer shelf show a smooth seafloor (Figs. 3 and 4A). 262

The backscatter imagery reveals marked along- and across-shelf variations around the 263

canyon head (Fig. 4B). The inner shelf shoreward of the north of the canyon head shows 264

very-high backscatter intensities (brighter areas) with elongate, shore-normal regions of low 265

backscatter returns (darker areas) that extend from the coastline down to 40–50 m depth 266

(Fig. 4B). Backscatter intensities are medium to high over most of the middle shelf 267

surrounding the canyon head, except for small areas on the Barcelona shelf and a large 268

area of very low backscatter offshore Tossa de Mar (Fig. 4B). Backscatter decreases from 269

the middle Barcelona shelf towards the outer shelf, whilst the La Planassa shelf shows an 270

opposite trend with higher values on the outer shelf. 271

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272

4.2. Seafloor features 273

Bathymetric and backscatter data and seismic reflection profiles led to the identification of 274

distinctive seafloor features over the studied continental shelf. These comprise prodeltas, 275

Infralittoral prografing wedges (IPW), rocky outcrops and sorted bedforms in the inner shelf; 276

and a widespread rocky outcrop, large morphological steps, narrow ridges, featureless 277

seafloor zones and sediment waves in the middle and outer shelf. 278

4.2.1. Prodeltas 279

The Tordera prodelta extends almost 5 km along-shelf and 0.4 km seawards ending in a 280

steep slope down to 40 m depth (Figs. 3 and 4A). The very high backscatter it shows is 281

most probably indicative of coarse sediment (Fig. 4B). To the north of the Tordera River 282

mouth, smaller prodelta-like wedges (0.7 km wide along-shelf) have been recognized at the 283

mouth of Tossa de Mar and Lloret de Mar torrents (Fig. 3). 284

4.2.2. Infralittoral prograding wedges 285

IPW develop from the lower edge of the shoreface to a strong break in slope at 30–35 m 286

water depth (Fig. 5A). Seawards, the gradient increases to a relatively steep slope down to 287

40–50 m depth (Fig. 4A). To the north of the Tordera River mouth, an IPW appears in the 288

form of isolated bodies that are best developed in bays and pocket beaches (Fig. 5A). In 289

contrast, south of the Tordera River mouth the IPW consists of a set of continuous, coast-290

parallel to coast-oblique sediment bodies that extend along the Maresme coastline (Fig. 3). 291

There, the IPW is characterized by very-high backscatter with elongate patches of lower 292

backscatter (Fig. 4B). 293

4.2.3. Sorted bedforms 294

Sorted bedforms appear in the bathymetry as slightly depressed (0.3–1 m in depth) and 295

elongate (50–250 m) features with a patchy distribution (Fig. 5A). Most of bedforms lay 296

13

normal to oblique to the general trend of the isobaths and develop at water depths between 297

10 and 40 m depth (Fig. 5A). The largest of these bedforms can exceed 700 m in length. 298

Backscatter data display an abrupt transition between high intensities in the shallow 299

depressions and low values in the adjacent shallower areas (Fig. 5B). 300

4.2.4. Rocky outcrops 301

Rocky outcrops appear sparsely in the inner shelf but become dominant on the middle shelf 302

to the north and east of the canyon head (Figs. 3 and 6A). In the inner shelf, zones with 303

rocky outcrops show a variable relief (up to 8–10 m high) and mean gradient (0.2º–7º), and 304

high backscatter (Figs. 4A and 4B). To the north and east of the canyon head, a large, 305

complex rocky outcrop occupies the entire middle shelf down to 90 m depth (Figs. 3 and 306

6A). It shows an uneven appearance determined by WNW-ESE trending, 2–3 m high and 307

1–4 km long linear crests almost normal to the isobaths (Fig. 6A). It is characterized by 308

intermediate backscatter, with crests showing higher intensities (Fig. 6B). Seismic reflection 309

profiles show an almost opaque, high amplitude seafloor reflection, with faint south-west 310

dipping outcropping strata, which are locally draped by a very thin transparent unit in the 311

deepest zones (Fig. 6C). 312

4.2.5. Morphological steps 313

Seven morphological steps, S1 to S7, have been identified in the continental shelf adjacent 314

to the canyon head. The shallower steps, S1 to S3, show a general E-W orientation and 315

appear shoreward of the canyon head to the north, at water depths of 30–45 m, 30–50 m 316

and 35–65 m (Fig. 7A). The step S4, at 74–78 m depth, is NE-SW oriented and limits a 317

very smooth depression along its shoreward side (Fig. 8). A notch located 2.5 km away 318

from the modern Tordera River mouth, likely corresponding to the remnant of a narrow 319

fluvial channel, cuts S4. The deeper steps S5 and S6 are almost parallel and appear along 320

the outer Barcelona shelf at 78–90 m and 105–115 m of water depth, respectively (Fig. 9A). 321

While S5 and S6 are ENE-WSE oriented offshore the Maresme coast, they change to 322

NNE-SSW shoreward of the canyon head. S3 to S6 run across the shelf and die at the rim 323

14

of the canyon head. To the east of the Blanes Canyon, a small step, S7, delineates a 1.5 m 324

thick sediment body that extends 3 km along the La Planassa outer shelf at 94–95 m depth 325

(Fig. 10). . 326

Backscatter data show very high values with small patches of very low reflectivity in the 327

continental shelf between the coastline and S3 (Fig. 4B and 7B). The same step S3 marks 328

an abrupt change in backscatter from very high to low reflectivity. This low backscatter 329

zone extends eastwards from the Tordera prodelta to the Blanes canyon rim (Fig. 7B). 330

Seaward from S3, the continental shelf displays medium backscatter down to S6, which 331

marks another change to low intensities in backscatter (Fig. 4B). Limited acoustic 332

penetration hinders the interpretation of TOPAS profiles in this zone. However, a semi-333

transparent unit of up to 20 m in thickness overlies a discontinuous and uneven high 334

amplitude reflector that locally crops out (Figs. 7B and 9C). 335

4.2.6. Narrow ridges 336

Narrow ridges are 40–100 m wide positive relieves up to 2.5 m above the surrounding 337

seafloor, which are either parallel or oblique to the isobaths (Fig. 3). They are straight 338

elongate features in plan view, except close to the canyon tip, where they become arcuate 339

(Figs. 6A and 7A). Their length ranges from 0.5 to 8 km. Within the study area, twelve 340

narrow ridges have been identified showing different shapes and orientations: (i) seven NE-341

SW straight ridges at depths of 48–59 m, 56–58 m, 63–65 m, 69–72m, 74 m, 74–77 m, and 342

77–78 m; (ii) a ENE-WSW straight ridge at 35–45 m depth (Fig. 7A); and (iii) four arcuate 343

ridges at 52–57 m (Figs 6A and 7A). The ridges yield medium to high backscatter (Figs. 6B 344

and 7B). In sub-bottom penetrator profiles they are associated to an irregular strong 345

reflector that prevents acoustic penetration (Fig. 7C). 346

4.2.7. Featureless shelf floor areas 347

A large almost flat (0.3–0.5º of slope gradient) and featureless area with very low 348

backscatter intensities extends along the middle La Planassa shelf offshore Tossa de Mar. 349

15

It covers 61 km2 at depths ranging from 50 to 102 m (Fig. 4B) though it probably extends 350

beyond the swath bathymetry data limit (Fig. 1). 351

East of the canyon, the outer La Planassa shelf is characterized by a relatively flat, gently 352

inclined (0.2º on average) bottom down to 98 m depth (Fig. 10A). It shows medium to high 353

backscatter (Fig. 4B), which probably corresponds to relatively coarse-grained sediment. 354

4.2.8. Sediment waves 355

To the west of the canyon, between steps S5 and S6, a field of almost contour parallel 356

sediment waves, 6 km2 in areal extent, drapes the outer shelf at 95–115 m of water depth 357

(Fig. 9B). The sediment waves are 0.2–0.5 m high with mean wavelengths of 400 m. 358

Backscatter data are of medium intensities both in the crests and troughs (Fig. 4B) 359

5. DISCUSSION 360

5.1. Seafloor morphology 361

The detailed multibeam bathymetry and backscatter data presented in this study yield a 362

new accurate image of the seabed that provides a comprehensive overview of the 363

geomorphology of the continental shelf and reveals a variety of seafloor features, some of 364

which had not been previously recognized in the study area. The interpretation of these 365

features together with the backscatter pattern provides useful insights about past and 366

present sediment dynamics. 367

5.1.1. Interpretation of seafloor features 368

5.1.1.1. Prodeltas 369

Sediment deposition by the Tordera River and smaller streams, such as Lloret de Mar and 370

Tossa de Mar torrents, has led to the formation of small submarine prodeltas off the river 371

mouths (Fig. 11). They display very high backscatter, which is indicative of the coarse 372

nature of the sediments supplied by these water courses (Fig. 2A). The bulging to elongate 373

shape of these features results from the predominant southwards littoral drift that 374

16

distributes the sediment delivered by these streams southwards along the inner shelf. This 375

alongshore transport is also evidenced by the formation of a large submerged sand spit 376

that extends southwards off the Tordera River mouth, as described by Serra et al. (2003 377

and 2007). 378

5.1.1.2. Infralittoral prograding wedge 379

Near the Blanes Canyon, the IPW develops laterally forming continuous prodeltaic wedges 380

such as those along the Maresme coastline (Liquete et al., 2007; Ercilla et al., 2010), or 381

isolated bodies, such as those to the north of the Tordera River mouth (Fig. 11). As the 382

IPW forms just below the wave-face depth of major storms (Hernández-Molina et al., 2000), 383

it is actively involved in the present day littoral sedimentary processes. This is confirmed by 384

very high backscatter corresponding to coarse-grained facies that reflect the dominant 385

influence of stormy hydrodynamic conditions along the infralittoral belt. The IPWs show a 386

predominant stretched geometry that is parallel to the coastline as a consequence of the 387

dominant south-westward littoral drift. 388

5.1.1.3. Sorted bedforms 389

The elongate patches in backscatter images observed on the IPW have been interpreted 390

as sorted bedforms (Murray and Thieler, 2004) or “rippled scour depressions” (Cacchione 391

et al., 1984). As commented above, sorted bedforms are slightly depressed features filled 392

with coarse sediments, as evidenced by backscatter data (Fig. 5). They appear between 10 393

and 40 m depth and their longitudinal axis is normal to oblique to the coastline (Fig. 11). 394

The generation and maintenance of these features arise primarily from a sediment sorting 395

feedback in shelf environments dominated by alongshore rather than cross-shore currents 396

(Murray and Thieler, 2004; Coco et al., 2007; Lo Iacono and Guillen, 2008), which is in 397

accordance to the hydrodynamic regime deduced from the prodeltas and IPWs. According 398

to their location in relation to the storm wave base level, these sorted bedforms possibly 399

become active during high-energy events. The storm wave base along the Maresme coast 400

has been estimated at 20-30 m water depth (Calafat, 1986; Sorribas et al., 1993), but 401

17

several works reported sediment remobilization down to 60 m depth under very strong 402

conditions (Puig et al., 2001; Palanques et al., 2002). 403

5.1.1.4. Rocky outcrops 404

Rocky outcrops appear in the inner and middle shelf primarily to the north and east of the 405

canyon head (Fig. 11). In the inner shelf, rocky outcrops appear as the submerged feet of 406

coastal cliffs showing continuity with the Hercynian granites outcropping inland (Fig. 2A). In 407

the middle shelf, a widespread rocky outcrop extends down to 90 m water depth covering 408

an area of 106 km2 (Fig. 11). Although it is partially capped by sediment, probably coarse 409

grained as suggested by backscatter data and sub-bottom seismic reflection profiles, the 410

structural features of the rock outcrop are clearly visible (Figs. 3 and 11). 411

5.1.1.5. Morphological steps 412

The large morphological steps observed in the middle and outer shelf near the Blanes 413

canyon belong to three main groups, according to their location and orientation (Fig. 11): (i) 414

a E-W oriented set that comprise steps S1 to S3 at 30–45, 35–55 and 35–65 m depth, 415

respectively; (ii) a NE-SW step (S4) cut by a shallow channel at 74–78 m depth; and (iii) a 416

set made of NNE-SSW oriented steps S5 and S6 at 105–115 and 78–90 m depth and an 417

arcuate step (S7) at 94–95 m depth. 418

The E-W oriented steps appear to the north of the canyon head (Fig. 11). They are 419

characterized by very high backscatter corresponding to coarse sand (see Pedrosa-Pàmies 420

et al., this issue, for more details). Step S3 marks an abrupt change in backscatter to low 421

intensities corresponding to an elongate patch of medium to fine sand (Pedrosa-Pàmies et 422

al., this issue) that extends from the Tordera prodelta to the canyon head rim (Figs. 4B and 423

11). Further south, the seafloor is characterized by medium backscatter associated to 424

medium sand (Pedrosa-Pàmies et al., this issue). 425

Based on the seismic profiles and backscatter characteristics, the morphological steps S1 426

to S3 to the north of the canyon head have been interpreted as the edges of sediment 427

18

bodies, most probably of sandy nature. S4 shows a particular morphology determined by a 428

narrow channel that likely corresponds to an old bed of the Tordera River. Samples from 429

the top of these relict sediment bodies consist of medium to coarse sand (ITGE, 1989; Díaz 430

and Maldonado, 1990), which is in agreement with the observed medium to high 431

backscatter (Fig. 4B). The basal reflector underlying these relict sand bodies corresponds 432

to a ravinement surface developed during the Versilian transgression (i.e. younger than 18 433

000 yr BP), which can be correlated across the entire study area and beyond (Serra, 1976; 434

Diaz and Maldonado, 1991; Liquete et al., 2007). Therefore, the Barcelona shelf relict 435

sediment bodies were built during the last postglacial sea-level rise. 436

5.1.1.6. Narrow ridges 437

Narrow ridges, oriented NE-SW or ENE-WSW, appear at depths between 35 and 78 m, but 438

mostly at 48–58 m and 74–78 m (Fig. 11). Based on the bathymetric and sub-bottom 439

seismic reflection data, the narrow ridges could be ascribed to relict beach-rock alignments. 440

Although no sediment cores were collected, the narrow ridges in the study area show 441

identical morphology and appear at the same position than the cemented beach-rocks 442

described further south in the same Barcelona shelf by Liquete et al. (2007). Surface 443

sediment is composed by bioclastic to siliciclastic-bioclastic, rounded to well-rounded sands 444

and gravels (Liquete et al., 2007) yielding high backscatter intensities (Fig. 7B). However, 445

further investigations are required to constrain their origin more accurately. 446

5.1.1.7. Featureless seafloor 447

Two areas of featureless seafloor have been identified in the La Planassa shelf (Fig. 11). 448

Offshore Tossa de Mar, the middle shelf displays very low backscatter suggesting that the 449

shelf floor there is covered by fines. This area corresponds to the southernmost limit of a 450

large patch of low backscatter that extends along the La Planassa middle shelf (Durán et 451

al., 2012). This pattern contrasts with the La Planassa outer shelf, where backscatter is 452

high, which would be indicative of coarse sediment pointing to erosion or non-deposition 453

and sorting of fines. 454

19

5.1.1.8. Sediment waves 455

Contour parallel sediment waves have been observed in a restricted area of the Barcelona 456

outermost shelf at 95–115 m depth (Fig. 11). The morphology of the sediment waves and 457

the local hydrodynamics suggest that they could be reactivated during energetic conditions, 458

particularly under strong storms. In the Gulf of Lion, numerical modelling showed that 459

strong energy events are able to remobilize and transport sand over the outermost shelf 460

and shelf edge (Bassetti et al., 2006). Recent observations in the Blanes Canyon head also 461

noticed that large storms were able to produce enough bottom shear stress to resuspend 462

shelf sediment including the transport of coarse sand down to 50–60 m water depth, which 463

could explain the arrival of this sediment fraction into the canyon head (Sanchez-Vidal et 464

al., 2012; Pedrosa-Pàmies et al., this issue). Such sediment remobilization over the outer 465

shelf would contribute to the activation of these sediment waves. However, the morphology 466

of these bedforms is inconclusive about their degree of present activity, so that additional 467

observations would be necessary to confirm or deny this interpretation. 468

5.1.2. Shelf zonation 469

The interpretation of the shelf floor features allows distinguishing four zones dominated by 470

erosion (or non-deposition) and deposition that illustrate the sediment dynamics of the 471

study area (Fig. 12). These are: (i) a littoral belt of modern coarse sediment transport and 472

accumulation; (ii) a zone of modern fine sediment deposition; (iii) a zone dominated by 473

erosion or non-deposition; and (iv) a relict, modern sediment depleted zone. 474

The littoral belt of modern coarse sediment transport and accumulation covers almost the 475

whole inner shelf, i.e. 30 km2 or 5.7% of the study area (Fig. 12). It is characterized by large 476

depositional features, such as prodeltas, IPWs and sorted bedforms (Fig. 11). Backscatter 477

is very high along this belt, which fits with the coarse nature of sediment inputs from the 478

Tordera River and coastal torrents, and the action of eastern waves against this exposed 479

coastal stretch. Storm waves resuspend the finest fractions of sediment deposited on the 480

20

inner shelf that can be transported offshore towards the middle-outer shelf and slope, and 481

south-westward by the induced littoral drift. 482

Modern fine sediment deposition occurs at the middle shelf offshore Tossa de Mar, as 483

evidenced by backscatter data, covering an area of 61 km2 or 11.6% of the study area (Fig. 484

12). Middle shelf fine deposition zones, like the one observed in the La Planassa middle 485

shelf, have been recognized worldwide and described in the adjacent continental shelves 486

too, such as the Ebro shelf (Palanques and Drake, 1990; Puig et al., 2001), the Barcelona 487

shelf further south (Liquete et al., 2010) and the Gulf of Lion shelf (Got and Aloïsi, 1990, 488

Durrieu de Madron et al., 2008). 489

A large zone of long-term erosion or non-deposition measuring 226 km2, or 43.1% of the 490

study area, has been identified over the La Planassa middle and outer shelf, near the 491

canyon head (Fig. 12). This zone displays a rough bathymetry and high backscatter that 492

corresponds to rocky outcrops and coarse sediment (Fig. 11). The scarce fluvial sediment 493

input reaching La Planassa shelf, which is fed (only by short ephemeral torrents (Fig. 2A), 494

and the bottom shear stress resulting from high-energy storms leads to a sediment-starved 495

shelf. The erosive or non-depositional character of the La Planassa shelf in the vicinity of 496

Blanes Canyon extends to a sharp canyon rim there, which further indicates erosion and 497

sediment depletion (Lastras et al., 2011). 498

The relict zone, markedly starved of modern sediment accumulation, extends over the 499

middle and outer shelf to the north and west of the canyon head, covering an area of 208 500

km2, or 39.6% of the study area (Fig. 12). It includes six large-scale transgressive sediment 501

bodies that occupy the entire middle and outer shelf (Fig. 11). At present, the relict 502

character of this shelf zone is attested by (i) the relatively rough topography of the seafloor 503

with isolated rocky outcrops and narrow ridges; and (ii) the medium to high values of 504

backscatter intensity corresponding to coarse sand (Pedrosa-Pàmies et al., this issue). 505

5.2. Modern sediment dynamics 506

5.2.1. Sediment sources and transport processes 507

21

The variability of seafloor morphology and sediment type, and subseafloor configuration 508

across the studied continental shelf provides significant insight on sediment sources, 509

dynamics and transport pathways from the shelf to the canyon. The deeply incised into the 510

continental shelf Blanes Canyon intercepts the alongshore and along-shelf sediment 511

dispersal paths, which results in the escape of sediment from the shelf into the canyon 512

head (Fig 12). The sorting and preferential escape of fines makes the sedimentary cover of 513

the continental shelf around the canyon head to be mainly sandy, as shown by the high 514

backscatter pattern observed there, which also indicates reworking of shelf deposits finally 515

feeding into the canyon (Figs. 4B and 12). 516

Previous works have documented a dominant south-westward littoral and inner shelf drift 517

along the North Catalan continental shelf in previous works (Copeiro, 1982; DGPC, 1986) 518

(Fig. 12). Evidences of sediment transport over the shelf floor are provided by: (i) the 519

elongated morphology of modern prodeltas and IPWs; (ii) the orientation of sorted 520

bedforms; and (iii) a complex backscatter pattern (Figs. 3 and 4). The pattern of very high 521

backscatter between the coastline and the canyon head and the elongate patch of low 522

backscatter to the south of step S3 indicate the remobilization and south-westward along-523

shelf transport of fines that are deposited southwards on the lee side of S3 or off-shelf into 524

the canyon head (Fig. 12). 525

This predominant south-westward transport of sediment along the shelf would also explain 526

the limited contribution of river inputs directly into the canyon head. Due to the closeness of 527

the Blanes Canyon to the Tordera River mouth, a direct input from this river into the canyon 528

head could be expected. However, recent works have noticed that only a small amount of 529

the sediment volume released by the Tordera River enters the Blanes Canyon during high-530

energy events (Zúñiga et al., 2009; Sanchez-Vidal et al., 2012; Pedrosa-Pàmies et al., this 531

issue). This is attributed to the predominant along-shelf sediment transport that favours the 532

dispersal of the coarse sediment delivered by the Tordera River along the shore and inner 533

shelf towards the south-west, thus feeding river prodelta itself and the beaches and IPWs 534

off the Maresme coast. This view is supported by the seafloor morphology and backscatter 535

22

imagery (Fig. 12). The finest fractions supplied by the river bypass the inner shelf and 536

disperse over the middle shelf and beyond, as indicated by medium backscatter there 537

(Figs. 4B and 12). This interpretation is further supported by bottom samples collected in 538

the continental shelf offshore the Tordera River mouth that show a high contribution of 539

terrestrial sediment in the middle shelf that decreases toward the outer shelf and slope (see 540

Pedrosa-Pàmies et al., this issue). 541

According to this, the most probable shelf sources of sediment to the Blanes Canyon 542

responding to present day hydrodynamics are located to the north and west of its head. 543

Furthermore, the large relict sediment bodies that occupy almost the entire middle and 544

outer shelf, to the north (i.e. shoreward) and west of the canyon also represent a potential 545

source of coarse sediment into its head and upper course (Fig. 12). This would be in 546

agreement with the massive arrival of sand into the canyon during the severe storm of 547

December 2008, as observed by Sanchez-Vidal et al. (2012) and other morphological 548

evidences within the canyon head that reported a retrogradation of the Blanes Canyon 549

western rim seaward of the Maresme sediment bodies (Lastras et al., 2011) at the head of 550

a gully system that cut the whole canyon wall and reach the shelf edge. East of the canyon 551

head, the continental shelf is sediment starved and mostly erosional or non-depositional, so 552

that a minor sediment contribution into the canyon should be expected from there (Fig. 13). 553

5.2.2. Hydrodynamic forcings 554

Short-lived hydrodynamic processes such as floods, storms and DSWC largely drive the 555

transport and distribution of sediment over the Catalan continental shelf and deep margin. 556

In the Blanes Canyon, the eastern storms are the most prominent oceanographic 557

processes controlling the shelf-to-canyon transport of sediment, as noticed in recent works 558

(Sanchez-Vidal et al., 2012; Pedrosa-Pàmies et al., this issue). Storm waves generate bed 559

shear stresses sufficient to resuspend fine sediment on the inner shelf, which can be 560

subsequently deposited beyond the wave-base level forming a mid-shelf mud belt, as 561

observed offshore Tossa de Mar (Fig. 4B). The most energetic storms can resuspend again 562

these fines and force their transport further offshore and also off-shelf into the submarine 563

23

canyon (Guillén et al., 2006; Palanques et al., 2008; Pedrosa-Pàmies et al., this issue). 564

This would explain the lack of fines over the continental shelf adjacent to the canyon head, 565

particularly shoreward (Fig. 4B). Extreme storms are also able to remobilize sediment from 566

the shelf and supply sand sizes to the canyon head, as demonstrated by Sanchez-Vidal et 567

al. (2012) and Pedrosa-Pàmies et al. (this issue). The role of up and down currents along 568

the canyon over the resuspension of fines and, in general, sediment remobilization in the 569

Blanes Canyon area is not known at present. 570

DSWC likely contributes to the transfer of shelf sediment into the submarine canyon too 571

(Fig. 12). Dense shelf waters form mainly over the Gulf of Lion shelf and the Roses shelf to 572

the north, and to a much lesser extent over the La Planassa shelf, which southern limit 573

marks the boundary of the span of the cold, dry and persistent northern Tramuntana wind 574

(Canals et al., 2006; Ulses et al., 2008). Direct observations and numerical simulations 575

have shown that dense shelf water is transferred to the deep basin mostly through Cap de 576

Creus, La Fonera and Blanes canyons, with a decreasing trend from north to south (e.g. 577

Canals et al., 2006; Ulses et al., 2008; Palanques et al., 2009; Lastras et al., 2011; Ribó et 578

al., 2011). Accordingly, the Blanes Canyon traps dense shelf water formed over La 579

Planassa shelf and in northernmost areas. Because of topographical constrictions these 580

waters and the sediment load they carry after resuspension and turbulent bed load 581

transport enter Blanes Canyon mostly through its northern flank, as supported by direct 582

observations too (Zúñiga et al., 2009). However, the volume of water and sediment carried 583

out by DSWC into the Blanes Canyons likely is much less than in La Fonera Canyon and, 584

especially, Cap de Creus Canyon, which is by far the main outlet for these waters into the 585

deep margin and basin along the North Catalan margin. Sediment volumes entering the 586

Blanes Canyon because of DSWC remain to be precisely quantified. 587

The permanent mesoscale NC also brings fines to the Blanes Canyon area (Fig. 12). 588

Interaction of the NC with the canyon topography may lead to eddy formation and 589

enhanced resuspension of fines. Such eddies may enter the continental shelf, eventually 590

guided by the canyon topography, thus further resuspending the finest particles 591

24

accumulated on the outer shelf (Arnau, 2000; Flexas et al., 2002; Arnau et al., 2004) and 592

easing their southward transport along the shelf and trapping into the canyon, probably 593

contributing to the development of a canyon fill sedimentary body observed at the shelf 594

edge (Lastras et al., 2011). 595

5.3. Evolution of the continental shelf during the last transgression 596

Past studies of submarine canyons established that during sea-level low-stands they are 597

particularly efficient conduits for the transport of sediment from the continental shelf to the 598

deep margin and basin (May et al., 1983). Recent studies have also shown that canyons 599

incising narrow continental shelves receive large amount of sediment regardless of sea-600

level conditions (e.g. Cutshall et al., 1986; Kineke et al., 2000; Xu et al., 2002; Puig et al., 601

2003; Mullenbach et al., 2004). With this background in mind, we have investigated the 602

evolution of the Blanes continental shelf in terms of sediment transport pathways from 603

terrestrial and shelf sources into the canyon head during the last transgression. 604

5.3.1. Seafloor features as sea-level indicators 605

The evolution of the continental shelf around the Blanes Canyon can be reconstructed after 606

several geomorphological features, such as narrow ridges and morphological steps, which 607

can be used as sea-level indicators (Fig. 11). Narrow ridges have been ascribed to beach-608

rocks and thus they are excellent indicators of paleo-coastlines. Near the canyon head, 609

narrow ridges are mainly located at 52-58 m, 63-35 m, 69-72 and 74-78 m depth. 610

Morphological steps corresponding to the front of relict sediment bodies appear at 30-65 m 611

(S1 to S3), 74-78 m (S4), 78-90 m (S5), 94-95 m (S7), and 105-115 m depth (S6). They are 612

also considered as indicators of ancient sea-level positions during the last transgression, 613

although some caution is required. Present-day depositional breaks in slope such as 614

prodelta fronts or IPWs form below the storm-wave base, i.e., some meters below the 615

current sea-level. Consequently, a difference in water depth between the morphological 616

step and the relative sea-level must be taken into account. 617

25

The morphological features observed on the Blanes shelf area have been correlated to 618

global (Siddall et al., 2003; Deschamps et al., 2012) and Mediterranean (Aloïsi et al., 1978; 619

Lambeck and Bard, 2000) sea-level curves. We naturally focus on the last sea-level cycle, 620

as most of the geomorphological features on the studied shelf floor formed during the last 621

transgression and subsequent highstand. 622

Though studies of the Barcelona shelf reported differential subsidence across and along 623

the shelf, with maximum values at the shelf break and off Besòs and Llobregat river mouths 624

(Liquete et al., 2008), tectonic subsidence in the study area is of little relevance for the 625

purpose of our paper. Perea et al. (2006 and 2012) have estimated a vertical slip rate of 626

0.02-0.04 mm·yr−1 along the Barcelona Fault (Fig. 2A) during the Plio-Quaternary, which is 627

equivalent to 0.4-0.8 m for the last 20 kyr. In other deltaic nearby shelves, such as the Gulf 628

of Lion, Quaternary subsidence has been inferred at 0.25 mm y-1 near the shelf edge 629

(Rabineau et al., 2006). This subsidence is attributed to sediment compaction in a delta 630

environment, which cannot be directly transposed to the continental shelf near the Blanes 631

Canyon. Therefore, we consider reasonable to assume that the study area has been fairly 632

stable tectonically during the last 20 kyr. Sediment compaction likely is negligible given the 633

different setting with respect to the study cases above and also the dominant coarse nature 634

and limited thickness of post-glacial units and the short time elapsed since the beginning of 635

the transgression. However, because of the lack of correction, even if minor, for tectonic 636

vertical movements and sediment compaction, our results should be considered in terms of 637

relative sea levels. 638

During the last glacial cycle, the Mediterranean Sea was connected to the global ocean and 639

therefore followed a similar pattern of sea-level changes. The sea level reached its lowest 640

position during the Last Glacial Maximun (LGM) between 26.5 and 19 kyr (Fairbanks, 1989; 641

Lambeck and Chappell, 2001). In the Western Mediterranean, a minimum sea-level at 642

about 105–115 m below present sea-level (bpsl) was inferred (Lambeck and Bard, 2000; 643

Jouet et al., 2006; Berné et al., 2007). Since the LGM, the sea-level rise was not steady 644

(Fig. 13); instead relatively short periods of rapid sea level rise were followed by periods of 645

26

slower rise with occasional brief stillstands (Fairbanks, 1989). Intervals of rapid sea-level 646

rise occurred at 14.65 kyr and 11.3 kyr, referred to as Meltwater Pulse 1A (MWP1a) and 647

Meltwater Pulse 1B (MWP1b), respectively (Bard et al., 2010; Deschamps et al., 2012). 648

Periods of short stillstands or slow sea-level rise occurred during the early deglacial, after 649

MWP1a, during the Younger Dryas cold climatic event (12.8–11.5 kyr) and at the 8.2 kyr 650

cold event (Lambeck et al., 2002; Bard et al., 2010). 651

By comparing the depths of the main seafloor features of the Blanes shelf with the timing of 652

these well-known sea-level changes during the last post-glacial transgression, we found 653

noteworthy correlations to sea-level rise, even though our water depths are uncorrected, as 654

explained above (Fig. 13B). The depth of the narrow ridges at 52–65 m bpsl would likely 655

correspond to: (i) the onset of the Younger Dryas, when the sea-level was located at a 656

water depth of approximately 50–55 m bpsl in the Western Mediterranean (Siddal et al., 657

2003; Berné et al., 2007); and (ii) a phase of decreased sea-level rise after MWP1a when 658

sea level was at about 77 m bpsl (Fairbanks, 1989; Bard et al., 1990). The depths of the 659

morphological steps, however, fall at or below three short intervals of slow sea-level rise or 660

stillstand (Fig. 13B): (i) the decrease in sea level rise during the deglacial onset; (ii) the 661

short-lived stillstands or slowdowns in sea-level rise during the Younger Dryas; and (iii) the 662

8.2 kyr cold event, when sea level was at about 20 bpsl (Siddal et al., 2003; Camoin et al., 663

2004) or 30 m bpsl in the Mediterranean (Aloïsi, 1986, Lambeck et al., 2002). The 664

difference between water depth of sediment bodies and the relative sea-level would be 665

related to the storm-wave base level or other local factors, as has been commented above. 666

Our interpretation on the relation between sea-level rise and shelf floor features in the 667

Blanes canyon area would largely benefit from age dating so that they could be confirmed 668

or better adjusted. 669

5.3.2. Morphological development of the continental shelf under a rising sea-level 670

The identification of the various morphologies left mainly during relative stillstands or 671

slowdowns is critical in reconstructing the evolution of the submerged landscape of the 672

continental shelf near the Blanes Canyon since the LGM. Such reconstruction should help 673

27

understanding the varying influence of the canyon on the shaping of the shelf and how the 674

nature of their interactions has changed through time (Fig. 14). The morphology of the 675

continental shelf model reveals a major shift in sediment dynamics likely related to the 676

flooding of the shelf stretch shoreward of the canyon head, which determined the 677

reestablishment of the littoral drift and the coastline parallel circulation over the inner shelf. 678

We hypothesize that the achievement of modern conditions occurred in three stages 679

corresponding to the lowest LGM sea-level (∼18 kyr BP, 105–115 m) and to two 680

intermediate stillstands or slowdowns during the transgression placed before (∼14.1 kyr BP, 681

74–77 m) and after (∼8.2 kyr BP, 30 m) the flooding of the continental shelf shoreward of 682

the Blanes Canyon (Fig. 14). Each stage is plotted as a function of water depth of the main 683

morphological sea-level indicators on the shelf floor over the relative sea-level curve (Fig. 684

13B). 685

The lowest sea-level position corresponds to the maximum exposure of the continental 686

shelf, when the Blanes Canyon head was deeply incised in the paleo-coastline, thus 687

preventing a shallow water connection between the La Panassa and Barcelona shelves 688

(Fig. 14A). East of the Blanes Canyon, the relatively small volumes of sediment delivered 689

by the northern coastal streams, and the sediment resuspended on the inner shelf were 690

very likely transported southwards by the littoral drift till directly entering the submarine 691

canyon. West of the canyon, the Tordera River mouth opened into the canyon rim or very 692

close to it. Consequently, the paleo-Tordera River discharged directly into the canyon, 693

which trapped most of the fluvial input with only small amounts that could be transported 694

southwards by the littoral drift (Fig. 14A). 695

With the subsequent rise of sea-level and the landward migration of the coastline, 696

extensive transgressive sediment bodies began to develop on the Barcelona shelf, shown 697

by the reconstruction corresponding to a short stillstand or slowdown at about 74-77 m bpsl 698

(Fig. 14B). At this stage, the narrow shelf stretch landwards of the Blanes Canyon head 699

was still totally emerged. Small amounts of sediment were supplied by coastal torrents to 700

the La Planassa shelf, where fines could be easily resuspended during storms and 701

28

transported towards the canyon by the dominant circulation, thus leaving an essentially 702

sediment-starved shelf. West of the canyon, the increasing distance between the Tordera 703

River mouth and the canyon head with the sea-level rise favoured the development of large 704

sediment bodies in the half flooded Barcelona shelf. However, the relative closeness of the 705

river mouth to the canyon rim still favoured the off-shelf transport of some sediment, mainly 706

the finest fractions, to the western canyon flank. The notch attributed to a fluvial channel 707

cutting S4 corresponds to this stage. 708

The most significant change in the sediment dynamics of the Blanes shelf took place when 709

the sea-level raised enough to flood of the continental shelf stretch landwards of the 710

shallowest part of the canyon head (Fig. 14C). This allowed the establishment of an 711

alongshore sediment transport between the La Planassa and Barcelona shelves 712

uninterrupted by the canyon head. Such a situation favoured the development of new 713

morphosedimentary features on the shelf stretch north of the canyon head. The change in 714

the orientation of these features with regard to the sand bodies in the Barcelona shelf can 715

be tentatively attributed to a westward migration of the Tordera delta and prodelta from the 716

canyon rim at S3 to its current position, combined with a promontory effect by the same 717

delta that favoured the accumulation of sediment to the east under the effective action of 718

the newly established littoral drift carrying loose IPW deposits along the coastline of La 719

Planassa towards the southwest while redistributing the inputs by Tordera River. In the 720

Barcelona shelf, the steady landward migration of the coastline contributed to a reduction of 721

the off-shelf export of sediment till reaching the present situation with a south-westward 722

sediment transport belt attached to the shoreline. 723

724

6. CONCLUSSIONS 725

1. The detailed study of the geomorphology and uppermost sediment cover of the 726

continental shelf surrounding the Blanes submarine canyon yields insight into the past 727

and present shelf sediment dynamics and the shelf-to-canyon sediment exchanges. 728

29

2. The continental shelf near the canyon head consists of mosaic where erosional, or non-729

depositional, and depositional zones coexist. East of the canyon and offshore Tossa de 730

Mar, the modern sediment deposition is mostly confined to the inner and middle shelf, 731

whilst most of the La Planassa shelf is sediment depleted with numerous relict 732

morphosedimentary features cropping out. Rocky outcrops, narrow ridges and relict 733

coarse sand deposits suggesting erosion or non-deposition of fine sediments in modern 734

times occupy the middle and outer shelf floor east and northeast of the canyon head. In 735

contrast, north and west of the canyon head, the middle and outer shelf comprises 736

several large relict sand bodies that point out to long-term deposition. However, the lack 737

of modern sediments on top of these bodies supports active erosion or by-pass in 738

present times. 739

3. The morphology of the continental shelf near the canyon head records the imprint of the 740

main factors controlling the shelf sediment-dispersal system and provides evidence for 741

the main sources and transport pathways of sediment from the shelf into the canyon. 742

The depletion of fine sediments on the continental shelf, as evidenced by backscatter 743

data, suggests that the Blanes Canyon acts as a sediment trap collecting the finest 744

fractions resuspended primarily from the adjacent shelf to the north. The main 745

processes that control the shelf-to-canyon transfer of sediment are eastern storms, 746

which enhance the off-shelf export of mainly fine sediment from the shelf. Particularly 747

severe storms are also able to remobilize and transport coarse sediment from the shelf 748

and also from the relict sand bodies into the canyon. Other processes, such as DSWC 749

and the Northern Current, contribute to a lesser extent to the transport of sediment along 750

the shelf and into the canyon. 751

4. During the last post-glacial transgression, the Blanes Canyon played a crucial role in the 752

shaping of the continental shelf surrounding it by cutting the littoral drift of sediment 753

between the shelf areas to the north and south, thus severely modifying the across- and 754

along-shelf sediment pathways. As a result, to the east of the canyon, the poor 755

development of transgressive deposits indicates the prevalence of erosion and non-756

30

deposition associated to a limited sediment supply and an effective action of the littoral 757

drift leading to a south-westward transport of sediment towards the canyon head. To the 758

north and west of the canyon the morphology of the continental shelf changed 759

significantly during the sea-level rise. At the early stage of the transgression, the 760

sediment supplied by the Tordera River was discharged directly into the canyon, thus 761

preventing deposition over the shelf. Later, the progressive sea-level rise favoured the 762

development of large depositional bodies on the Barcelona shelf favoured by the 763

increase of accommodation space and the augmenting distance between the river 764

mouth and the canyon head. A drastic change in the configuration of the shelf occurred 765

when the sea-level raised enough to flood the entire continental shelf. The along-shelf 766

sediment transport between the shelf areas to the north and south of the canyon head 767

was then restored and new sediment bodies were formed between the coastline and the 768

canyon tip. At present, these sediment bodies constitute the primary source of coarse 769

sediment into the Blanes Canyon. 770

5. These results confirm that the Blanes submarine canyon head is highly dynamic and 771

sensitive to a variety of processes that enhance the transport of sediment from the shelf 772

into the canyon, particularly during major storms. 773

774

ACKNOWLEDGMENTS 775

This work is a contribution to the Spanish RTD projects DOS MARES (CTM2010-21810-776

C03-01/MAR), and VALORPLAT (CTM2011-14623-E) and GRACCIE-CONSOLIDER 777

(CSD2007-00067). Generalitat de Catalunya support through its grant 2009-SGR-1305 is 778

also acknowledged. Ruth Durán thanks the Spanish Ministry of Science and Innovation for 779

a Juan de la Cierva research contract. A. Micallef was supported by a Marie Curie Intra-780

European Fellowship PIEF-GA-2009-252702 within the 7th Framework Programme of the 781

European Commission. 782

31

REFERENCES 783

Allen, J.R.L., 1982. Simple models for the shape and symmetry of tidal sand waves: (1) 784

Statically stable equilibrium forms. Marine Geology, 48, 31-49. 785

Aloïsi, J.C., 1986. Sur un modele de sedimentation deltaique. Contribution a la 786

connaissance des marges passives. Ph.D. thesis. University of Perpignan, 170 pp. 787

Aloïsi, J.C., Monaco, A., Thommeret J., Thommeret, Y. 1978. Holocene transgression in 788

the Gulf of Lions (southern France): paleogeographic and palaeobotanic evolution. 789

Geographie Physique Et Quaternaire, 32, 145-162. 790

Amblas, D., Canals, M., Urgeles, R., Lastras, G., Liquete, C., Hughes-Clarke, J.E., 791

Casamor, J.L., Calafat, A.M., 2006. Morphogenetic mesoscale analysis of the northeastern 792

Iberian margin, NW Mediterranean Basin. Marine Geology, 234, 3-20. 793

Arnau, P., Liquete, C., Canals, M., 2004. River mouth plume events and their dispersal in 794

the northwestern Mediterranean Sea. Oceanography, 17, 22-31. 795

Arnau, P.A., 2000. Aspectos de la variabilidad de mesoescala de la circulación marina en 796

la plataforma continental catalana. Ph.D. Thesis. Universidad Politécnica de Cataluña, 600 797

pp. 798

Ashley, G.M., 1990. Classification of large-scale subaqueous bedforms: a new look at an 799

old problem. Journal of Sedimentary Petrology, 60, 160–172. 800

Bard, E., Hamelin, B., Delanghe-Sabatier, D., 2010. Deglacial Meltwater Pulse 1B and 801

Younger Dryas Sea levels Revisited with Boreholes at Tahiti. Science, 327, 1235-1237. 802

Bard, E., Hamelin, B., Fairbanks, R.G., Zindler, A., 1990. Calibration of the 14C timescale 803

over the past 30,000 years using mass spectrometric U-Th ages from Barbados corals. 804

Nature, 345, 405-410. 805

32

Barnard, P., Erikson, L., Kvitek, R., 2011. Small-scale sediment transport patterns and 806

bedform morphodynamics: new insights from high-resolution multibeam bathymetry. Geo-807

Marine Letters, 31, 227-236. 808

Barnard, P.L., Erikson, L.H., Elias, E., Dartnell, P., 2012. Sediment transport patterns in the 809

San Francisco Bay Coastal System from cross-validation of bedform asymmetry and 810

modeled residual flux. Marine Geology, in press. 811

Bartrina, M.T., Cabrera, L., Jurado, M.J., Guimerà, J., Roca, E., 1992. Evolution of the 812

central Catalan margin of the Valencia trough (western Mediterranean). Tectonophysics, 813

203, 219-247. 814

Belderson, R.H., Stride, A.H., 1969. Tidal currents and sand wave profiles in the 815

northeastern Irish Sea. Nature, 222, 74-75. 816

Berné, S., Jouet, G., Bassetti, M.A., Dennielou, B., Taviani, M., 2007. Late Glacial to 817

Preboreal sea level rise recorded by the Rhône deltaic system (NW Mediterranean). Marine 818

Geology, 245, 65-88. 819

Bolaños, R., Jorda, G., Cateura, J., Lopez, J., Puigdefabregas, J., Gomez, J., Espino, M., 820

2009. The XIOM: 20 years of a regional coastal observatory in the Spanish Catalan coast. 821

Journal of Marine Systems, 77, 237-260. 822

Bourrin, F., Durrieu de Madron, X., Heussner, S., Estournel, C., 2008. Impact of winter 823

dense water formation on shelf sediment erosion (evidence from the Gulf of Lions, NW 824

Mediterranean). Continental Shelf Research, 28, 1984-1999. 825

Cacchione, D.A., Drake, D.E., Grant, W.D., Tate, G.B., 1984. Rippled scour depressions on 826

the inner continental shelf off central California. Journal of Sedimentary Petrology, 54, 827

1280-1291. 828

Calafat, A., 1986. Morfo-sedimentología de las playas del Maresme (sector Calella-829

Blanes). Master Thesis. University of Barcelona, Spain. 830

33

Camoin, G.F., Montaggioni, L.F., Braithwaite, C.J.R., 2004. Late glacial to post glacial sea 831

levels in the Western Indian Ocean. Marine Geology, 206, 119-146. 832

Canals, M., Monaco, A., Dinet, A., Heussner, S., Buscail, R., Calafat, A.M., Durrieu de 833

Madron, X., Nyffeler, F., Sánchez-Cabeza, J.A., Thunus, V., Casamor, J.L., Gadel, F., 834

Palanques, A., Grehan, A. Puig, P., 1995. Transfer of matter and benthic response in the 835

Northwestern Mediterranean continental margins. In: Weyder M, Lipiatou E, Go& R, 836

Fragakis C, Bohle-Carbonell M. and Barthel K. G. (Eds.), MAST Days and EUROMAR 837

Market. Brussels. European Communities 1, 419-431. 838

Canals, M., Puig, P., de Madron, X.D., Heussner, S., Palanques, A., Fabres, J., 2006. 839

Flushing submarine canyons. Nature, 444, 354-357. 840

Coco, G., Murray, A.B., Green, M.O., Thieler, E.R., Hume, T.M., 2007. Sorted bed forms as 841

self-organized patterns: 2. Complex forcing scenarios. Journal of Geophysical Research: 842

Earth Surface, 112, F03016.Collier, J.S., Brown, C.J., 2005. Correlation of sidescan 843

backscatter with grain size distribution of surficial seabed sediment. Marine Geology, 214, 844

431-449. 845

Collier, J.S., Brown, C.J., 2005. Correlation of sidescan backscatter with grain size 846

distribution of surficial seabed sediments. Marine Geology, 214, 431-449. 847

Company, J.B., Puig, P., Sardà, F., Palanques, A., Latasa, M., Scharek, R., 2008. Climate 848

Influence on Deep Sea Populations. PLoS ONE, 3, e1431. 849

Copeiro, E., 1982. Playas y obras costeras en España. Revista de Obras Públicas, 3205, 850

531-547. 851

Cutshall, N.H., Larsen, I.L., Olsen, C.R., Nittrouer, C.A., DeMaster, D.J., 1986. Columbia 852

River sediment in Quinault Canyon, Washington — Evidence from artificial radionuclides. 853

Marine Geology, 71, 125-136. 854

34

Dalrymple, R.W., Knight, R.J., Lambiase, J.J., 1978. Bedforms and their hydraulic stability 855

relationships in a tidal environment, Bay of Fundy, Canada. Nature, 275, 100-104. 856

Deschamps, P., Durand, N., Bard, E., Hamelin, B., Camoin, G., Thomas, A.L., Henderson, 857

G.M., Okuno, J., and Yokoyama, Y., 2012, Ice-sheet collapse and sea-level rise at the 858

Bølling warming 14,600 years ago. Nature, 483, 559–64. 859

DGPC (Direcció General de Protecció Civil), 1986. Investigación tecnológica de las 860

acciones a tomar para la estabilidad de las playas del Maresme. Generalitat de Catalunya, 861

Barcelona, Spain. 862

Díaz, J.I., Maldonado, A., 1990. Transgressive sand bodies on the Maresme continental 863

shelf, western Mediterranean Sea. Marine Geology, 91, 53-72. 864

Dufau-Julliand, C., Marsaleix, P., Petrenko, A., Dekeyser, I., 2004. Three-dimensional 865

modeling of the Gulf of Lion's hydrodynamics (northwest Mediterranean) during January 866

1999 (MOOGLI3 Experiment) and late winter 1999: Western Mediterranean Intermediate 867

Water's (WIW's) formation and its cascading over the shelf break. Journal of Geophysical 868

Research C: Oceans, 109, C11002. 869

Durán, R., Canals, M., Sanz, J.L., Lastras, G., Amblas, D., Micallef, A., 2012. Morphology 870

and sediment dynamics of the northern Catalan continental shelf, northwestern 871

Mediterranean Sea. Geomorphology, in press. 872

Durrieu de Madron, X., Nyffeler, F., Godet, C.H., 1990. Hydrographic structure and 873

nepheloid spatial distribution in the Gulf of Lions continental margin. Continental Shelf 874

Research, 10, 915-929. 875

Durrieu de Madron, X., Wiberg, P.L., Puig, P., 2008. Sediment dynamics in the Gulf of 876

Lions: The impact of extreme events. Continental Shelf Research, 28, 1867-1876. 877

35

Ercilla, G., Estrada, F., Casas, D., Durán, R., Nuez, M., Alonso, B., Farrán, M., 2010. The 878

El Masnou infralittoral sedimentary environment (Barcelona province, NW Mediterranean 879

Sea): morphology and Holocene seismic stratigraphy. Scientia Marina, 74, 20. 880

Fairbanks, R.G., 1989. A 17,000-year glacio-eustatic sea level record: influence of glacial 881

melting rates on the Younger Dryas event and deep-ocean circulation. Nature, 342, 637-882

642. 883

Flemming, B.W., 1980. Sand transport and bedform patterns on the continental shelf 884

between Durban and Port Elizabeth (southeast African continental margin). Sedimentary 885

Geology, 26, 179-205. 886

Flexas, M.M., Durrieu de Madron, X., Garcia, M.A., Canals, M., Arnau, P., 2002. Flow 887

variability in the Gulf of Lions during the MATER HFF experiment (March–May 1997). 888

Journal of Marine Systems, 33–34, 197-214. 889

Font J., García-Ladona, E., Gorriz, E.G., 1995. The seasonality of mesoscale motion in the 890

Northern Current of the western Mediterranean: several years of evidence. Oceanologica 891

Acta, 18, 207-219. 892

García, M., Maillard, A., Aslanian, D., Rabineau, M., Alonso, B., Gorini, C., Estrada, F., 893

2011. The Catalan margin during the Messinian Salinity Crisis: Physiography, morphology 894

and sedimentary record. Marine Geology, 284, 158-174. 895

Gili, J.M., Bouillon, J., Pagès, F., Palanques, A., Puig, P., 1999. Submarine canyons as 896

habitats of prolific plankton populations: three new deep-sea Hydroidomedusae in the 897

western Mediterranean. Zoological Journal of the Linnean Society, 125, 313-329. 898

Goff, J.A., Mayer, L.A., Traykovski, P., Buynevich, I., Wilkens, R., Raymond, R., Glang, G., 899

Evans, R.L., Olson, H., Jenkins, C., 2005. Detailed investigation of sorted bedforms, or 900

“rippled scour depressions,” within the Martha's Vineyard Coastal Observatory, 901

Massachusetts. Continental Shelf Research, 25, 461-484. 902

36

Gómez, J., Espino, M., Puigdefabregas, J., Jerez, J., 2005. Xarxa d’Instrumentació 903

Oceanogràfica i Meteorològica de la Generalitat de Catalunya (XIOM), Boies d’onatge 904

dades obtingudes l’any 2004. Technical report (catalan). 905

Got, H., Aloisi, J.C., 1990. The Holocene sedimentation on the Gulf of Lions margin: a 906

quantitative approach. Continental Shelf Research, 10, 841-855. 907

Granata, T.C., Vidondo, B., Duarte, C.M., Satta, M.P., Garcia, M., 1999. Hydrodynamics 908

and particle transport associated with a submarine canyon off Blanes (Spain), NW 909

Mediterranean Sea. Continental Shelf Research, 19, 1249-1263. 910

Guillén, J., Bourrin, F., Palanques, A., Durrieu de Madron, X., Puig, P., Buscail, R., 2006. 911

Sediment dynamics during wet and dry storm events on the Têt inner shelf (SW Gulf of 912

Lions). Marine Geology, 234, 129-142. 913

Hernández-Molina, F.J., Fernández-Salas, L.M., Lobo, F.J., Somoza, L., Díaz del Río, V., 914

Alveirinho Dias, J.M., 2000. The infralittoral prograding wedge: a new large-scale 915

progradational sedimentary body in shallow marine environments. Geo-Marine Letters, 20, 916

109-117. 917

Heussner, S., Durrieu de Madron, X., Calafat, A., Canals, M., Carbonne, J., Delsaut, N., 918

Saragoni, G., 2006. Spatial and temporal variability of downward particle fluxes on a 919

continental slope: Lessons from an 8-yr experiment in the Gulf of Lions (NW 920

Mediterranean). Marine Geology, 234, 63-92. 921

Hughes Clarke, J.E., 2012. Optimal use of multibeam technology in the study of shelf 922

morphodynamics. International Assocciation of Sedimentologists. Special Publication, 44, 923

1-28. 924

IGC-ICC, 2010. Atles geològic de Catalunya. Institut Geològic de Catalunya - Institut 925

Cartogràfic de Catalunya, Barcelona, Spain. 926

37

Imbrie, J., Duffy, A. et al., Brown University, 1990. SPECMAP Archive #1, IGBP 927

PAGES/World Data Center for Paleoclimatology, Data Contribution Series # 90-001 928

[online]. Web page of the NOAA/NGDC Paleoclimatology Program, 929

ftp://www.ncdc.noaa.gov/paleo/paleocean/specmap/S. Last revision in 1994. 930

ITGE, 1989. Mapa Geológico de la Plataforma Continental Española y Zonas Adyacentes 931

1:200 000. Hoja 35/42E (Barcelona). Instituto Tecnológico GeoMinero de España, Madrid, 932

mem. expl. 117 pp. 933

Jouet, G., Berné, S., Rabineau, M., Bassetti, M.A., Bernier, P., Dennielou, B., Sierro, F.J., 934

Flores, J.A., Taviani, M., 2006. Shoreface migrations at the shelf edge and sea level 935

changes around the Last Glacial Maximum (Gulf of Lions, NW Mediterranean). Marine 936

Geology, 234, 21-42. 937

Kineke, G.C., Woolfe, K.J., Kuehl, S.A., Milliman, J.D., Dellapenna, T.M., Purdon, R.G., 938

2000. Sediment export from the Sepik River, Papua New Guinea: evidence for a divergent 939

sediment plume. Continental Shelf Research, 20, 2239-2266. 940

Lambeck, K., Bard, E., 2000. Sea level change along the French Mediterranean coast for 941

the past 30 000 years. Earth and Planetary Science Letters, 175, 203-222. 942

Lambeck, K., Chappell, J., 2001. Sea level Change Through the Last Glacial Cycle. 943

Science, 292, 679-686. 944

Lambeck, K., Yokoyama, Y., Purcell, T., 2002. Into and out of the Last Glacial Maximum: 945

sea level change during Oxygen Isotope Stages 3 and 2. Quaternary Science Reviews, 21, 946

343-360. 947

Lastras, G., Canals, M., Amblas, D., Lavoie, C., Church, I., De Mol, B., Duran, R., Calafat, 948

A.M., Hughes-Clarke, J.E., Smith, C.J., Heussner, S., 2011. Understanding sediment 949

dynamics of two large submarine valleys from seafloor data: Blanes and La Fonera 950

Canyons, northwestern Mediterranean Sea. Marine Geology, 280, 20-39. 951

38

Li, M.Z., King, E.L., 2007. Multibeam bathymetric investigations of the morphology of sand 952

ridges and associated bedforms and their relation to storm processes, Sable Island Bank, 953

Scotian Shelf. Marine Geology, 243, 200-228. 954

Liquete, C., Canals, M., De Mol, B., De Batist, M., Trincardi, F., 2008. Quaternary stratal 955

architecture of the Barcelona prodeltaic continental shelf (NW Mediterranean). Marine 956

Geology, 250, 234-250. 957

Liquete, C., Canals, M., Lastras, G., Amblas, D., Urgeles, R., De Mol, B., De Batist, M., 958

Hughes-Clarke, J.E., 2007. Long-term development and current status of the Barcelona 959

continental shelf: A source-to-sink approach. Continental Shelf Research, 27, 1779-1800. 960

Liquete, C., Canals, M., Ludwig, W., Arnau, P., 2009. Sediment discharge of the rivers of 961

Catalonia, NE Spain, and the influence of human impacts. Journal of Hydrology, 366, 76-962

88. 963

Liquete, C., Lucchi, R.L., García, J., Canals, M., Masqué, P., Pascual, C., Lavoie, C., 2010. 964

Modern sedimentation patterns and human impacts on the Barcelona continental shelf (NE 965

Spain). Geologica Acta, 8, 169-187. 966

Liu, J.T., Lin, H.-l., 2004. Sediment dynamics in a submarine canyon: a case of river–sea 967

interaction. Marine Geology, 207, 55-81. 968

Liu, J.T., Liu, K.-J., Huang, J.C., 2002. The effect of a submarine canyon on the river 969

sediment dispersal and inner shelf sediment movements in southern Taiwan. Marine 970

Geology, 181, 357-386. 971

Lo Iacono, C., Guillén, J., 2008. Environmental conditions for gravelly and pebbly dunes 972

and sorted bedforms on a moderate-energy inner shelf (Marettimo Island, Italy, western 973

Mediterranean). Continental Shelf Research, 28, 245-256. 974

Maillard A., Mauffret A., 1999. Crustal structure and riftogenesis of the Valencia Trough 975

(north-western Mediterranean Sea). Basin Research, 11, 357-379. 976

39

Martín-Vide, J., 1982. Característiques climatològiques de la precipitació en la franja 977

costera mediterrània de la Península Ibèrica. PhD Thesis, Universitat de Barcelona, Spain. 978

Martin-Vide, J., Sanchez-Lorenzo, A., Lopez-Bustins, J.A., Cordobilla, M.J., Garcia-Manuel, 979

A., Raso, J.M., 2008. Torrential rainfall in northeast of the Iberian Peninsula: synoptic 980

patterns and WeMO influence. Advances in Science and Research, 2, 99-105. 981

Mauffret, A., Pascal, G., Maillard, A., Gorini, C., 1995. Tectonics and deep structure of the 982

north-western Mediterranean Basin. Marine and Petroleum Geology, 12, 645-666. 983

May, J.A., Warme, J.E., Slater, R.A., 1983. Role of submarine canyons on shelfbreak 984

erosion and sedimentation: modern and ancient examples. In: Stanley, D.J., Moore, G.T. 985

(Eds.), The Shelfbreak: Critical Interface on Continental Margins, SEPM Special 986

Publication, 33, 315– 332. 987

Mendoza, E.T., Jiménez, J.S., 2008. Vulnerability assessment to coastal storms at a 988

regional scale. Proceedings 31st International Conference on Coastal Ingenierring, ASCE, 989

Hamburg, pp. 4154-4166. 990

Micallef, A., Le Bas, T.P., Huvenne, V.A.I., Blondel, P., Hühnerbach, V., Deidun, A., 2012. 991

A multi-method approach for benthic habitat mapping of shallow coastal areas with high 992

resolution multibeam data. Continental Shelf Research, 39-40, 14-26. 993

Millot, C., 1999. Circulation in the Western Mediterranean sea. Journal of Marine Systems, 994

20, 423-442. 995

Monaco, A., Courp, T., Heussner, S., Carbonne, J., Fowler, S.W., Deniaux, B., 1990. 996

Seasonality and composition of particulate fluxes during ECOMARGE—I, western Gulf of 997

Lions. Continental Shelf Research, 10, 959-987. 998

Mullenbach, B.L., Nittrouer, C.A., 2000. Rapid deposition of fluvial sediment in the Eel 999

Canyon, northern California. Continental Shelf Research, 20, 2191-2212. 1000

40

Mullenbach, B.L., Nittrouer, C.A., Puig, P., Orange, D.L., 2004. Sediment deposition in a 1001

modern submarine canyon: Eel Canyon, northern California. Marine Geology, 211, 101-1002

119. 1003

Murray, A.B., Thieler, E.R., 2004. A new hypothesis and exploratory model for the 1004

formation of large-scale inner-shelf sediment sorting and “rippled scour depressions”. 1005

Continental Shelf Research, 24, 295-315. 1006

Nittrouer, C.A., Wright, L.D., 1994. Transport of particles across continental shelves. 1007

Reviews of Geophysics, 32, 85-113. 1008

Ogston, A.S., Cacchione, D.A., Sternberg, R.W., Kineke, G.C., 2000. Observations of 1009

storm and river flood-driven sediment transport on the northern California continental shelf. 1010

Continental Shelf Research, 20, 2141-2162. 1011

Ogston, A.S., Guerra, J.V., Sternberg, R.W., 2004. Interannual variability of nearbed 1012

sediment flux on the Eel River shelf, northern California. Continental Shelf Research, 24, 1013

117-136. 1014

Oliveira, A., Santos, A.I., Rodrigues, A., Vitorino, J., 2007. Sedimentary particle distribution 1015

and dynamics on the Nazaré canyon system and adjacent shelf (Portugal). Marine 1016

Geology, 246, 105-122. 1017

Palanques, A., Puig, P., Guillén, J., Jiménez, J., Gracia, V., Sánchez-Arcilla, A., Madsen, 1018

O., 2002. Near-bottom suspended sediment fluxes on the microtidal low-energy Ebro 1019

continental shelf (NW Mediterranean). Continental Shelf Research, 22, 285-303. 1020

Palanques, A., Drake, D.E., 1990. Distribution and dispersal of suspended particulate 1021

matter on the Ebro continental shelf, northwestern Mediterranean Sea. Marine Geology, 95, 1022

193-206. 1023

41

Palanques, A., Guillén, J., Puig, P., Durrieu de Madron, X., 2008. Storm-driven shelf-to-1024

canyon suspended sediment transport at the southwestern Gulf of Lions. Continental Shelf 1025

Research, 28, 1947-1956. 1026

Palanques, A., Puig, P., Latasa, M., Scharek, R., 2009. Deep sediment transport induced 1027

by storms and dense shelf-water cascading in the northwestern Mediterranean basin. Deep 1028

Sea Research Part I: Oceanographic Research Papers, 56, 425-434. 1029

Pasqual, C., Lee, C., Goñi, M., Tesi, T., Sanchez-Vidal, A., Calafat, A., Canals, M., 1030

Heussner, S., 2011. Use of organic biomarkers to trace the transport of marine and 1031

terrigenous organic matter through the southwestern canyons of the Gulf of Lion. Marine 1032

Chemistry, 126, 1-12. 1033

Paull, C.K., Ussler, W., Greene, H.G., Keaten, R., Mitts, P., Barry, J., 2003. Caught in the 1034

act: the 20 December 2001 gravity flow event in Monterey Canyon. Geo-Marine Letters, 22, 1035

227-232. 1036

Pedrosa-Pàmies, R., Sanchez-Vidal, A., Calafat, A., Canals, M., Durán, R.. Storm-induced 1037

changes in organic carbon and the mineral fraction of sediment from the Blanes Canyon, 1038

NW Mediterranean Sea. Progress in Oceanography, this issue. 1039

Perea, H., Masana, E., Santanach, P., 2006. A Pragmatic Approach to Seismic Parameters 1040

in a region with Low Seismicity: The Case of Eastern Iberia. Natural Hazards, 39, 451-477. 1041

Perea, H., Masana, E., Santanach, P., 2012. An active zone characterized by slow normal 1042

faults, the northwestern margin of the València trough (NE Iberia): a review. Journal of 1043

Iberian Geology, in press. 1044

Puig, P., Ogston, A.S., Mullenbach, B.L., Nittrouer, C.A., Sternberg, R.W., 2003. Shelf-to-1045

canyon sediment-transport processes on the Eel continental margin (northern California). 1046

Marine Geology, 193, 129-149. 1047

42

Puig, P., Palanques, A., Guillén, J., 2001. Near-bottom suspended sediment variability 1048

caused by storms and near-inertial internal waves on the Ebro mid continental shelf (NW 1049

Mediterranean). Marine Geology, 178, 81-93. 1050

Puig, P., Palanques, A., Orange, D.L., Lastras, G., Canals, M., 2008. Dense shelf water 1051

cascades and sedimentary furrow formation in the Cap de Creus Canyon, northwestern 1052

Mediterranean Sea. Continental Shelf Research, 28, 2017-2030. 1053

Rabineau, M., Berné, S., Olivet, J.-L., Aslanian, D., Guillocheau, F., Joseph, P., 2006. 1054

Paleo sea levels reconsidered from direct observation of paleoshoreline position during 1055

Glacial Maxima (for the last 500,000 yr). Earth and Planetary Science Letters, 252, 119-1056

137. 1057

Ribó, M., Puig, P., Palanques, A., Lo Iacono, C., 2011. Dense shelf water cascades in the 1058

Cap de Creus and Palamós submarine canyons during winters 2007 and 2008. Marine 1059

Geology, 284, 175-188. 1060

Rovira, A., Batalla, R.J., Sala, M., 2005. Fluvial sediment budget of a Mediterranean river: 1061

the lower Tordera (Catalan Coastal Ranges, NE Spain). CATENA, 60, 19-42. 1062

Rubio, A., Arnau, P.A., Espino, M., Flexas, M.M., Jordà, G., Salat, J., Puigdefàbregas, J., 1063

Sanchez-Arcilla, A., 2005. A field study of the behaviour of an anticyclonic eddy on the 1064

Catalan continental shelf (NW Mediterranean). Progress in Oceanography, 66, 142-156. 1065

Salvadó, J.A., Grimalt, J.O., López, J.F., Palanques, A., Heussner, S., Pasqual, C., 1066

Sanchez-Vidal, A., Canals, M., 2012. Role of Dense Shelf Water Cascading in the Transfer 1067

of Organochlorine Compounds to Open Marine Waters. Environmental Science & 1068

Technology, 46, 2624-2632. 1069

Sanchez-Vidal, A., Canals, M., Calafat, A.M., Lastras, G., Pedrosa-Pàmies, R., Menéndez, 1070

M., Medina, R., Company, J.B., Hereu, B., Romero, J., Alcoverro, T., 2012. Impacts on the 1071

Deep-Sea Ecosystem by a Severe Coastal Storm. PLoS ONE, 7, e30395. 1072

43

Sanchez-Vidal, A., Pasqual, C., Kerhervé, P., Calafat, A., Heussner, S., Palanques, A., 1073

Durrieu de Madron, X., Canals, M., Puig, P., 2008. Impact of dense shelf water cascading 1074

on the transfer of organic matter to the deep western Mediterranean basin. Geophysical 1075

Research Letters, 35, L05605. 1076

Sardà, F., Company, J.B., Bahamón, N., Rotllant, G., Flexas, M.M., Sánchez, J.D., Zúñiga, 1077

D., Coenjaerts, J., Orellana, D., Jordà, G., Puigdefàbregas, J., Sanchez-Vidal, A., Calafat, 1078

A., Martín, D., Espino, M., 2009. Relationship between environment and the occurrence of 1079

the deep-water rose shrimp Aristeus antennatus (Risso, 1816) in the Blanes submarine 1080

canyon (NW Mediterranean). Progress in Oceanography, 82, 227-238. 1081

Serra, J., 1976. Le précontinent catalan entre le Cap Begur et Arenys de Mar (Espagne): 1082

structure et sédimentation récente. PhD Thesis, Université Paul Sabatier, Toulouse III. 1083

Serra, J., Montori, C., Valois, X., 2003. Tordera River delta relict lobes and Holocene Sea 1084

level rise (Maresme Coast, Spain, NW Mediterranean). Project IGCP 437 Final 1085

Conference, Puglia. GI2S Coast Research Publication, 4, 211-212. 1086

Serra, J., Sorribas, J., 1993. Las barras de arena infralitorales del Maresme, formación y 1087

cronología. Geogaceta, 14, 28-31. 1088

Serra, J., Valois, X., Parra, D., 2007. Estructura del prodelta de la Tordera (costa del 1089

Maresme, NO Mediterráneo) a partir del análisis sísmico de alta resolución. Geogaceta, 1090

41, 3. 1091

Shepard, F.P., Dill, R.F., 1966. Submarine Canyons and Other Sea Valleys. Rand McNally, 1092

Chicago. 1093

Siddall, M., Rohling, E.J., Almogi-Labin, A., Hemleben, C., Meischner, D., Schmelzer, I., 1094

Smeed, D.A., 2003. Sea level fluctuations during the last glacial cycle. Nature, 423, 853-1095

858. 1096

44

Sorribas, J., Serra, J., Calafat, A.M., 1993. Límites dinámicos y modos de transporte en el 1097

litoral del Maresme (Barcelona). Geogaceta, 14, 24–26. 1098

Turchetto, M., Boldrin, A., Langone, L., Miserocchi, S., Tesi, T., Foglini, F., 2007. Particle 1099

transport in the Bari Canyon (southern Adriatic Sea). Marine Geology, 246, 23. 1100

Ulses, C., Estournel, C., Durrieu de Madron, X., Palanques, A., 2008. Suspended sediment 1101

transport in the Gulf of Lions (NW Mediterranean): Impact of extreme storms and floods. 1102

Continental Shelf Research, 28, 2048-2070. 1103

Ulses, C., Grenz, C., Marsaleix, P., Schaaff, E., Estournel, C., Meulé, S., and Pinazo, C., 1104

2005. Circulation in a semi-enclosed bay under influence of strong freshwater input: 1105

Journal of Marine Systems, 56, 113-132. 1106

Waelbroeck, C., Labeyrie, L., Michel, E., Duplessy, J.C., McManus, J.F., Lambeck, K., 1107

Balbon, E., Labracherie, M., 2002. Sea level and deep water temperature changes derived 1108

from benthic foraminifera isotopic records. Quaternary Science Reviews, 21, 295-305. 1109

Walsh, J.P., Nittrouer, C.A., 2003. Contrasting styles of off-shelf sediment accumulation in 1110

New Guinea. Marine Geology, 196, 105-125. 1111

Xu, J.P., Noble, M., Eittreim, S.L., Rosenfeld, L.K., Schwing, F.B., Pilskaln, C.H., 2002. 1112

Distribution and transport of suspended particulate matter in Monterey Canyon, California. 1113

Marine Geology, 181, 215-234. 1114

Zúñiga, D., Flexas, M.M., Sanchez-Vidal, A., Coenjaerts, J., Calafat, A., Jordà, G., García-1115

Orellana, J., Puigdefàbregas, J., Canals, M., Espino, M., Sardà, F., Company, J.B., 2009. 1116

Particle fluxes dynamics in Blanes submarine canyon (Northwestern Mediterranean). 1117

Progress in Oceanography, 82, 239-251. 1118

45

FIGURE CAPTIONS 1119

Figure 1. Location and general bathymetric map of the Blanes Canyon area. The 1120

shadowed area on the continental shelf indicates the swath coverage area available for this 1121

study. Contours are every 100 m. The location of figures 4 to 11 is also shown. 1122

Figure 2. (A) Geological map of the Blanes coastal area. The offshore structural elements 1123

have been synthesized from Serra (1976), Bartrina et al. (1992), Mauffret et al. (1995) and 1124

Maillard and Mauffret (1999) and the onshore structure is adapted from IGC-ICC (2010). 1125

BF: Barcelona Fault. CBF: Costa Brava Fault. MF: Montseny Fault. (B) Across-shelf and 1126

(C) along-shelf and across-canyon sections showing the seismostratigraphic configuration 1127

of the study area synthesized from Serra (1976) and Liquete et al. (2008). FRST: Forced 1128

Regressive System Tracts. TST: Transgressive System Tracts. HST: Highstand System 1129

Tracts. (D) Main sequence boundaries (SB1 to SB4) and units (A to E) correlated to Marine 1130

Isotopic Stages MIS1 to MIS10 (Liquete et al., 2008). 1131

Figure 3. Shaded relief and bathymetry map of the study area showing the main seafloor 1132

features identified on the continental shelf adjacent to the Blanes Canyon head. Contours 1133

are at 10 m intervals down to 200 m and every 100 m in the slope and canyon. Onland 1134

orthophotomap from “Institut Cartogràfic de Catalunya”. See Fig. 1 for location. 1135

Figure 4. (A) Shaded relief and slope gradient map of the study area. (B) Shaded relief and 1136

backscatter intensity map of the study area. Onland orthophotomap from “Institut 1137

Cartogràfic de Catalunya”. See Fig. 1 for location. 1138

Figure 5. (A) Shaded relief and bathymetry map showing the infralittoral prograding wedge 1139

(IPW) offshore Tossa de Mar. Note the presence of sorted bedforms normal to contours 1140

atop of the IPW. Contours every 2 m. (B) Backscatter intensity map showing elongated 1141

patches of low backscatter normal to contours. Onland orthophotomap from “Institut 1142

Cartogràfic de Catalunya”. See Fig. 1 for location. 1143

46

Figure 6. (A) Shaded-relief and bathymetry map showing the large rocky outcrop to the 1144

east of the Blanes Canyon head occupying the La Planassa middle shelf. Contours every 1145

10 m. (B) Backscatter intensity map of the same area. Onland orthophotomap from “Institut 1146

Cartogràfic de Catalunya”. (C) Very-high resolution seismic reflection profile across the La 1147

Planassa middle shelf large rocky outcrop. Vertical scale in milliseconds two-way travel 1148

time (TWTT). See Fig. 1 for location. 1149

Figure 7. (A) Shaded-relief and bathymetry map showing steps S1 to S4 identified in the 1150

middle shelf stretch between the canyon rim and the coast of Blanes and Lloret de Mar. 1151

Contours every 10 m. (B) Backscatter intensity map of the same area. Onland 1152

orthophotomap from “Institut Cartogràfic de Catalunya”. (C) Very-high resolution seismic 1153

profile across steps S3 and S4. Vertical scale in milliseconds two-way travel time (TWTT). 1154

See Fig. 1 for location. 1155

Figure 8. (A) Bathymetry map showing the location and morphology of step S4 identified 1156

off the Tordera River mouth. Note the pronounced notch cut in the step. Contours every 10 1157

m. Bathymetric sections across (B and C) and along (D) S4. See Fig. 1 for location. 1158

Figure 9. (A) Shaded relief and bathymetry map showing steps S4 and S5 in the middle 1159

shelf and S6 in the outer shelf, close to the western rim of the Blanes Canyon. Contours 1160

every 10 m. (B) Detailed map of sediment waves on the outer shelf. Contours every 2 m. 1161

(C) Very-high resolution seismic reflection profile across steps S4 and S5. Vertical scale in 1162

milliseconds two-way travel time (TWTT). See Fig. 1 for location. 1163

Figure 10. (A) Detailed shaded-relief bathymetry map of the La Planassa outer shelf. 1164

Contours every 2 m. (B) Very-high resolution seismic reflection profile across step S7 1165

identified in the outer shelf. Vertical scale in milliseconds two-way travel time (TWTT). See 1166

Fig. 1 for location. 1167

Figure 11. General shaded relief map of the study area showing the main geomorphic 1168

elements commented in the text. Onland orthophotomap from “Institut Cartogràfic de 1169

Catalunya”. See Fig. 1 for location. 1170

47

Figure 12. 3D iamge of the study area illustrating the main domains in terms of sediment 1171

dynamics and sediment transport pathways across the shelf and into the canyon. See text 1172

for explanation. 1173

Figure 13. (A) Relative sea-level curves for the past 120 kyr (Waelbroeck et al., 2002; 1174

Siddall et al., 2003; Imbrie et al. 1990). (B) Global (Siddall et al., 2003) and Mediterranean 1175

relative sea-level curves of the last transgression (Aloïsi et al., 1978; Lambeck and Bard, 1176

2000). Vertical scale is in meters with respect to present sea-level (zero value). The steps 1177

and narrow ridges identified in the study area have been placed in the sea-level plot 1178

according to their present water depth. 1179

Figure 14. Reconstruction of the evolution of the continental shelf in the Blanes Canyon 1180

area during the last transgression. Schematic diagrams illustrate the coastline configuration 1181

and the main processes shaping the continental shelf at three different relative sea-level 1182

stages: (A) during the last lowstand and initial phases of the transgression (105–115 m); 1183

(B) at about 74–77 m bpsl; and (C) at about 30 m bpsl. 1184

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

48

Highlights: 1185

1186

The Blanes Canyon severely narrows the continental shelf close to the Tordera river 1187 delta. 1188

The shelf morphologies provide insights into sediment sources and transport pathways. 1189

Most of sediment export from the shelf into the canyon occurs through the Barcelona 1190 Shelf. 1191

Severe storms strongly impact the shelf enhancing off-shelf sediment export. 1192

The Blanes Canyon controlled the shaping of the shelf during the last transgression. 1193

1194

1195