y 62 (2007) 91–114www.elsevier.com/locate/marmicro

Marine Micropaleontolog

Present-day and past (last 25000 years) marine pollensignal off western Iberia

F. Naughton a,e,⁎, M.F. Sanchez Goñi a,b, S. Desprat a,b, J.-L. Turon a, J. Duprat a,B. Malaizé a, C. Joli a, E. Cortijo c, T. Drago d, M.C. Freitas e

a Environnements et Paléoenvironnements Océaniques (UMR CNRS 5805 EPOC), Université Bordeaux 1, Av. des Facultés, 33405 Talence, Franceb Ecole Pratique des Hautes Etudes, Environnements et Paléoenvironnements Océaniques (UMR CNRS 5805 EPOC),

Université Bordeaux 1, Av. des Facultés, 33405 Talence, Francec Laboratoire des Sciences du Climat et de l'Environnement (LSCE-Vallée), Bât. 12, avenue de la Terrasse, F-91198 Gif-sur-Yvette cedex, France

d Centro Regional de Investigação Pesqueira do Sul , Instituto Nacional de Investigação Agrária e Pescas (INIAP) (IPIMAR-CRIPSUL),Av. 5 de Outubro, 8700-305 Olhão, Portugal

e Departamento e Centro de Geologia-Universidade de Lisboa, Bloco C6, 3° piso, Campo Grande, 1749-016 Lisboa, Portugal

Received 11 May 2006; received in revised form 17 July 2006; accepted 19 July 2006

Abstract

The comparison between modern terrestrial and marine pollen signals in and off western Iberia shows that marine pollenassemblages give an integrated image of the regional vegetation colonising the adjacent continent. Present-day Mediterranean andAtlantic forest communities of Iberia are well discriminated by south and north marine pollen spectra, respectively. Results fromTotal Pollen Concentration together with recognized conceptual models of fine particle dynamics in the Iberian margin haveallowed us to establish the present-day pattern of pollen dispersion in this region.

The 25000 year-long record of continental (pollen) and marine (δ18O of Globigerina bulloides, Ice-rafted detritus—IRD andNeogloboquadrina pachyderma s.) proxies, from the Galician margin composite core (MD99-2331 and MD03-2697), show thatvegetation cover in north-western Iberia has responded contemporaneously to the climate variability of the North-Atlantic. Thevegetation response to the well known North Atlantic Heinrich events 2 and 1 (H2 and H1) is however complex and characterisedby two vegetation phases at low and mid-altitudes of north-western Iberia. The beginning of each Heinrich event is marked on landby an important pine forest reduction and the expansion of heathers which are synchronous with the heaviest planktic δ18O valuesand the maxima of N. pachyderma (s.) suggesting that these first phases were cold and wet. Pinus forest expansion characterisingthe second phase of each Heinrich event indicates a less cold episode associated, during H1, with an increase of dryness assuggested by the development of semi-desert associations. The comparison of our Galician margin multi-proxy record with severalpollen sequences from in and off Iberia allows us to demonstrate that H1 event is the marine equivalent of the Oldest Dryas on thecontinent.

The occurrence of temperate trees during the last glacial maximum (LGM) and the rapid expansion of deciduous Quercus duringthe Bölling-Allerød period in our Galician margin composite sequence show that not only the southern but also north-western Iberiawas a refugium zone for deciduous trees during the last glacial period, especially at low and mid-altitude zones. Furthermore, thecomparison between southern and northern marine and terrestrial sequences allows us to confirm that vegetation responded to the

⁎ Corresponding author. Environnements et Paléoenvironnements Océaniques (UMR CNRS 5805 EPOC), Université Bordeaux 1, Av. desFacultés, 33405 Talence, France. Tel.: +33 540008832; fax: +33 556840848.

E-mail address: f.naughton@epoc.u-bordeaux1.fr (F. Naughton).

0377-8398/$ - see front matter © 2006 Elsevier B.V. All rights reserved.doi:10.1016/j.marmicro.2006.07.006

92 F. Naughton et al. / Marine Micropaleontology 62 (2007) 91–114

Bölling-Allerød warming, the Younger Dryas cold event and the Holocene more quickly in low and mid-altitudes of north-westernIberia and in the south than in the high altitude northern region most likely as the result of the higher density of refugia for temperatetrees in these zones during the LGM.© 2006 Elsevier B.V. All rights reserved.

Keywords: Marine palynology; Pollen transport; Iberian margin; Heinrich events; LGM; Last glacial–interglacial transition

1. Introduction

During the last decade several studies had been carriedout in marine deep-sea cores off Iberia (Hooghiemstraet al., 1992; Sánchez Goñi et al., 1999, 2000, 2002, 2005;Boessenkool et al., 2001; Roucoux et al., 2001, 2005;Turon et al., 2003; Tzedakis et al., 2004; Desprat, 2005;Desprat et al., 2005, 2006, in press) to understandvegetation responses to the climate variability detected inthe North Atlantic. Among these sequences, those cover-ing the last 25000 years show similar vegetation changesto those recorded by the available 25000-year-long ter-restrial records. However, no experimental studies havebeen conducted in order to demonstrate that pollen grainspreserved in those marine sequences represent the re-gional vegetation of the nearby continent or to understandthe mechanisms involved in the transport and dispersionof these grains from the continent to the sea. To fill thesegaps, we have compared present-day continental (includ-ing coastal systems) pollen signatures with modern ma-rine (including shelf and slope) pollen assemblages. Wehave also determined total pollen concentration (TPC) ofthose surface samples to recognize present-day patterns ofpollen dispersion in the Iberian margin.

Having assessed the reliability of the present-daypollen signal in the upper layer sediments ofMD99-2331deep-sea core, we will compare their 25000-year high-resolution pollen record with other marine and terrestrialpollen sequences (Pons and Reille, 1988; Hooghiemstraet al., 1992; Peñalba, 1994; Pérez-Obiol and Julià, 1994;Allen et al., 1996; Muñoz Sobrino et al., 1997, 2001,2004; Peñalba et al., 1997; Von Engelbrechten, 1998;Combourieu Nebout et al., 1999, 2002; Sánchez Goñiand Hannon, 1999; Santos et al., 2000; Boessenkoolet al., 2001; Roucoux et al., 2001, 2005; Gil García et al.,2002; Ruiz Zapata et al., 2002; Turon et al., 2003) todocument accurately western Iberian vegetation changesover this period. Furthermore, the direct correlation be-tween sea surface temperature and vegetation changes inand off Iberia from the multiproxy study of MD99-2331and MD03-2697 deep-sea cores will allow us to linkseveral well known terrestrial climate events with thosedetected elsewhere in the North Atlantic and overGreenland.

2. Environmental setting

2.1. Study area and present-day vegetation and climate

Western Iberia including Portugal and the north-westernpart of Spain extends from 37°N to 43°N and comprisesessentially theMinho and Sado basins and the western partof the Douro and Tagus basins (Fig. 1). North-westernSpain, including theMinho basin, is influenced by the wet,relatively cool and weakly seasonal Atlantic climate(annual precipitation mean: 900–1400 mm and tempera-ture range: −7 to 10 °C) and is dominated by deciduousQuercus forest (Q. robur, Q. pyrenaica and Q. petraea),heath communities (Ericaceae and Calluna) and Ulex.There are also locally birch (Betula pubescens subsp. cel-tiberica) and hazel (Corylus avellana) groves, and brooms(Genista) (Alcara Ariza et al., 1987).

In the south, the Tagus and Sado basins, influencedby Mediterranean climate (mean annual precipitation:200–600 mm and temperature range: 4 to 14 °C), aredominated by evergreen sclerophyllous forests.Q. rotundifolia and Q. suber forests with Phillyreaangustifolia and Pistacia terebinthus colonise the west-ern basins while Q. rotundifolia and Q. coccifera wood-lands associated with Juniperus communis and Pinushalepensis occupies the eastern part. In the warmestzones, thermophilous elements such as Pistacia lentiscusand Olea sylvestris form the forests. Middle altitudes(700–1000 m a.s.l.) are dominated by deciduousQuercus forest (Q. pyrenaica and Q. faginea) associatedwith northern European species such as Taxus baccata.The degradation of this forest produces two types ofbrush communities: rockrose shrublands (Cistaceae) inzones with precipitation between 600 and 1000 mm andheath communities (Ericaceae) in wetter zones.

Between both regions, there is a transitional zonewhich includes the hydrographic basin of the Douro.This zone is characterised by high precipitation values(700 to 1000 mm/year) and winter temperatures be-tween 4 and −4 °C. At high altitudes, the wettest andcoldest zones reach 1600 mm/year and −8 °C, respec-tively (Polunin and Walters, 1985). The oceanic in-fluence is particularly important in the northwest of thebasin, where the Q. robur and Q. suber association

Fig. 1. Study area. Dashed line divides the Atlantic and Mediterranean biogeographical zones (Walter, 1954 in Blanco Castro et al., 1997). Whitecircles with a dark point represent the top samples analysed in this study; white circles represent the modern samples from the European PollenDatabase; white circles with a cross represent the studied cores sites (MD03-2697 and MD99-2331); dark circles represent marine and terrestrial coresites used for comparison with our study. Continental sequences: (a) Square A locates sequences 1 to 5: (1) Laguna de la Roya (Allen et al., 1996),(2) Sanabria March (Allen et al., 1996), (3) Laguna de las Sanguijuelas (Muñoz Sobrino et al., 2004), (4) Lleguna (Muñoz Sobrino et al., 2004),(5) Pozo do Carballal (Muñoz Sobrino et al., 1997); (b) Sites 6 to 13 correspond to: (6) Laguna Lucenza (Santos et al., 2000); (7) Lagoa Lucenza(Muñoz Sobrino et al., 2001); (8) Lago deAjo (Allen et al., 1996); (9) Los Tornos (Peñalba, 1994); (10) Saldropo (Peñalba, 1994); (11) Belate (Peñalba,1994); (12) Atxuri (Peñalba, 1994); (13) Banyoles (Pérez-Obiol and Julià, 1994); (c) Square B includes sequences 14 to 19: (14) Quintanar de la Sierra(Peñalba et al., 1997); (15) Sierra deNeila–Quintanar de la Sierra (Ruiz Zapata et al., 2002); (16) Hoyos de Iregua (Gil García et al., 2002); (17) LagunaMasegosa (Von Engelbrechten, 1998); (18) Laguna Negra (Von Engelbrechten, 1998); (19) Las Pardillas lake (Sánchez Goñi and Hannon, 1999);(20) Padul (Pons and Reille, 1988); (21) Mougás (Gomez-Orellana et al., 1998); (22) Charco da Candieira (Van der Knaap and van Leeuwen, 1995).The marine cores represented on the map are: 8057 B (Hooghiemstra et al., 1992), SO75-6KL (Boessenkool et al., 2001), SU81-18 (Turon et al., 2003)and ODP 976 (Combourieu Nebout et al., 1999; 2002) and MD95-2039 (Roucoux et al., 2001; 2005).

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predominates (Braun-Blanquet et al., 1956). The spreadof both Pinus pinaster and Eucalyptus globulus hasbeen favoured by anthropic impact. The understoryvegetation is largely dominated by Ulex, in associationwith heaths. The river margins are colonised by Alnusglutinosa, Fraxinus angustifolia, Ulmus spp., Salix spp.and Populus spp.

2.2. Oceanography

The western Iberian margin is dominated by the sur-face Portugal Current system (PCS) which is composedof the slow equatorward current in the open ocean

(Arhan et al., 1994) and the fast, seasonally reversingcoastal current (Ambar and Fiúza, 1994; Barton, 1998)(Fig. 2). During the summer, the Azores high pressurecell is located in the central North Atlantic and theGreenland low is weak. This situation generates north-erly and northwesterly prevailing winds (Fig. 1) whichfavour the occurrence of upwelling events and a south-ward surface circulation (Fiúza et al., 1982; Haynes andBarton, 1990) near the shelf break in the upper 50–100m(Álvarez-Salgado et al., 2003). The resultant upwelledcold and nutrient-rich Eastern North Atlantic CentralWater of subpolar sources (ENACWsp) is transportednorthward of 45°N. Warm, salty and nutrient-poor

Fig. 2. West to east scheme of the different water masses from the westernIberian margin (adapted from Sprangers et al., 2004). White circles with adark point represent southward water flow and white circle with a crossrepresent northwardwater flow. PCS—Portugal Current System; ENACWst—Eastern North Atlantic Central Water of subtropical origin; ENACWsp—Eastern North Atlantic Central Water of subpolar origin; MSW—Mediterranean Sea Water; LSW—Labrador Sea Water; NADW—NorthAtlantic Deep Water.

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Eastern North Atlantic Central Water of subtropical ori-gin (ENACWst) is transported to the south of 40°N(Fiúza, 1984; Rios et al., 1992) (Fig. 2). During thewinter the Azores high pressure cell is located off thenorthwest African coast and the Greenland low is deepand situated off south-eastern Greenland. The pressuregradient between the two systems results in an onshoreand slightly northward wind off Iberia (Fig. 1) triggeringdownwelling processes and a northward surface circu-lation (Frouin et al., 1990; Haynes and Barton, 1990).This reversion of hydrological paths starts in the end ofsummer in September–October and it persists untilMarch–April representing the well known PortugalCoastal Counter Current (PCCC) (Ambar et al., 1986).This poleward flow is narrow (30 km wide) and it tran-sports warm and salty waters (ENACWst) in the upper200–300 m to the North (Pingree and Le Cann, 1990).

Below the Central Waters system, between 550 m and1500 m depth, the Mediterranean Sea Water (MSW)consisting of high salinity and relatively warmwater massis transported northward (Mazé et al., 1997) (Fig. 2).However, the salinity of the MSW decreases highly atlatitudes higher than 41°N by mixing with the underlyinglow-salinity Labrador Sea water (LSW) (McCave andHall, 2002). This LSW is one of the three water massesincluded in the North Atlantic DeepWater (NADW) overthe western Iberian margin (Huthnance et al., 2002).

2.3. Morphology and recent sedimentation

The Iberian margin is characterised by a relativelynarrow shelf (30–50 km wide) with a steep irregularslope plunging to the oceanic abyssal plain (Fig. 3a).This margin is cut off by deep canyons like Mugia,Porto, Aveiro, Nazaré, Cascais, Lisbon, Setúbal and S.Vicente. The largest canyons (Nazaré, Setúbal) dissectthe entire continental shelf, capturing sediments carriedover the shelf and upper slope by alongshore currents,providing a direct conduit of particles from the uppershelf to the deep-sea (Vanney and Mougenot, 1981).Some canyons, e.g. Setúbal, start close by the present-day coastline and have a direct connection to the rivermouth, while others, such as the Porto Canyon, beginonly at the shelf edge and play a minor role in theinterception of shelf material at the present-day sealevel. All Iberian canyons were probably more activeduring the period of low sea-level (Van Weering andMcCave, 2002). The lower and upper slopes are alsointersected by several seamounts as Vigo (VS), Vasco daGama (VDGS), Porto (PS), Tore (TS), by the GaliciaBank and several tectonic depressions (Vanney andMougenot, 1981).

2.3.1. North-western Iberian marginIn north-western Iberia, five rivers (Douro, Ave,

Cávado, Lima and Minho) release large amounts ofsediments to the adjacent continental margin. The Dourois the main sediment supplier to the adjacent shelf(∼8.2×109 m3 annual mean discharge) followed by theMinho river (Dias et al., 2002; Jouanneau et al., 2002;Oliveira et al., 2002) (Fig. 3b). They are 927 km and300 km long, draining a catchment area of 97700 km2 and17100 km2, respectively (Loureiro et al., 1986). Above42°N, rivers are replaced by rias (Vigo, Pontevedra,Arousa and Muros), which act essentially as sedimenttraps, preventing particle input to the adjacent margin(Dias et al., 2002; Jouanneau et al., 2002).

The northern Portuguese continental shelf is com-posed of (a) an inner shelf zone (b30 m depth) with fineand well sorted sands, (b) a mid-shelf zone of coarsesands and gravels, and (c) a carbonate-rich outer shelfzone with medium sand (Van Weering et al., 2002).Within the shelf, there are two mud patches (Douro andGalicia) located offshore from the river inlets separatedby a mud free zone (Lopez-Jamar et al., 1992) (Fig. 3b).The mud patch growth depends on the sediment supply,morphological barriers and hydrological conditions(Dias et al., 2002; Jouanneau et al., 2002).

Sedimentation on the north-western Iberian margin iscomplex and essentially sustained by episodic flood events(Dias et al., 2002) and/or during maximal episodes of riveroutflow (Araújo et al., 1994; Drago et al., 1998). Fine

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sediments, after being released by rivers, are transported innepheloid layers (Bottom—BNL, intermediate—INL andsurface—SNL) to the outer shelf. Oliveira et al. (1999)have shown a seaward decrease of sediment concentra-tions in all nepheloid layers and that currents and wavesinduce resuspension of bottom sediments from Douro andMinho muddy deposits, especially during extreme stormevents. During these extreme events, such as southwest-erly storms (downwelling conditions), the spread of BNLsmight be blocked by rocky outcrops (Drago et al., 1999)that operate as a barrier to cross-shelf transfers (Jouanneauet al., 2002; Van Weering et al., 2002) stimulating apoleward sediment transport (Drago et al., 1998; Diaset al., 2002; Jouanneau et al., 2002; Van Weering et al.,2002). Sporadically, waves associated with those stormsare able to induce resuspension of fine deposits spreadingoffshore the BNL (Vitorino et al., 2002) nourishing theINL (Oliveira et al., 2002). These extreme eventscontribute to an important export of fine sediments(Vitorino et al., 2002) and occasionally of coarse fraction(Dias, 1987) to the upper slope. Current reversals, prob-ably caused by the presence of local slope eddies, can alsoallow some down-slope transport of particles (Pingree andLe Cann, 1992). During upwelling conditions, finesediment export is restricted to the shelf edge (McCaveand Hall, 2002; Van Weering et al., 2002). However,lateral sediment exchange can be favoured by offshorefilaments stretching westward (Huthnance et al., 2002).

MD99-2331 and MD03-2697 twin deep-sea cores,located north-western of the Mesozoic and Cenozoicoutcrops, mostly receive sediments coming from theDouro and Minho rivers, especially during downwellingconditions.

2.3.2. South-western Iberian marginIn the south-western Iberian margin, the Tagus river is

the primary sediment supplier followed by Sado river tothe shore (Dias, 1987; Jouanneau et al., 1998)(Fig. 3a, c). The Tagus river is 1110 km long draininga catchment area of 80600 km2 with 400 m3 s−1 ofannual mean flow (Vale, 1990). The Sado river is 175 kmlong, drains a catchment area of 7640 km2 and yields lessthan 10m3 s−1 of annual mean discharge (Loureiro et al.,1986). Differences between both river discharge andlittoral currents influence the sediment distribution alongthe shelf (Jouanneau et al., 1998). The mud patch islocated offshore of Tagus river basin and covers theentire continental shelf (Araújo et al., 2002). Duringsummer, suspended particulate matter (SPM) concen-tration in the mouth of the Tagus estuary is four timeshigher than that of the Sado, and the nepheloid layer canextend 30 km westward (Jouanneau et al., 1998). Fine

sediments are essentially exported to the slope and ad-jacent abyssal plains through the canyons of Cascais,Lisbon and Setúbal (Jouanneau et al., 1998) and byoffshore filaments (Huthnance et al., 2002).

3. Material and methods

3.1. Deep-sea cores: MD99-2331 and MD03-2697

MD99-2331 (42°09′00N, 09°40′90W; 2110 m depth)and MD03-2697 (42°09′59N, 59°42′10W; 2164 m depth)deep-sea coreswere retrieved in theGalicianmargin (north-west of Iberia) using a CALYPSO corer during theGINNA(IMAGES V) and PICABIA oceanographic cruises onboard the R/V Marion Dufresne (Fig. 1). MD99-2331 andMD03-2697 are 37.2 m and 41.23 m long, respectively,covering Marine Isotopic Stages (MIS) 1 to 11.

X-ray analysis using SCOPIX image-processing(Migeon et al., 1999) has shown a well preservedsedimentary sequence in core MD03-2697 while coreMD99-2331 sees a sediment mixing zone between1.10 m and 1.90 m of core depth. In order to obtain adetailed palaeoclimatic sequence for the last 25000 yearsin and off NW Iberia, we have built a composite recordassembling the MIS 1 interval of core MD03-2697 withthe MIS 2 interval of core MD99-2331.

3.1.1. Radiometric datingSeven levels of MD03-2697 and twenty levels from

MD99-2331 were dated by AMS 14C on Globigerinabulloides and Neogloboquadrina pachyderma (s.) at BetaAnalytic Inc (Beta), at Gif-sur-Yvette (Gif) and atLaboratoire de Mesure du Carbone 14-Saclay (LMC),indicating that this sequence covers the last 25000 years(Table 1). All radiocarbon dates were corrected for marineage reservoir difference (400 years) (Bard et al., 2004).The samples presenting conventional AMS 14C youngerthan 21786 BP were calibrated by using CALIB Rev 5.0program and “global” marine calibration data set (marine04.14c) (Stuiver and Reimer, 1993; Hughen et al., 2004;Stuiver et al., 2005). We use 95.4% (2 sigma) confidenceintervals and their relative areas under the probabilitycurve as well as the median probability of the probabilitydistribution (Telford et al., 2004). 14C radiometric agesolder than 21786 years BP were calibrated by matchingthe obtained conventional AMS 14C with the calendarages estimated for MD95-2042 deep-sea core by Bardet al. (2004).

In this paper, we will use 14C ages (year BP) correctedfor the marine reservoir effect (of 400 years) instead ofcalibrated ages (cal yearBP) because inmost of the Iberianterrestrial sequences, calendar ages are not available.

Fig. 3. (a) Morphology of the Iberian margin. Location of the surface samples from (b) north-western Iberian margin and (c) south-western Iberianmargin. White arrows indicate the present-day pattern of pollen dispersion in the western Iberian margin.

96 F. Naughton et al. / Marine Micropaleontology 62 (2007) 91–114

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3.1.2. Marine proxy analysesThe planktic isotopic record of MD99-2331 covering

MIS 6 toMIS 1 has been published inGouzy et al. (2004).However, additional stable isotope measurements ofplanktic foraminifera have been done to refine theplanktic isotopic record of the MIS 2 interval. In total,56 measurements have been made at 2 to 10 cm sampleresolution. For MIS 1, 29 levels with a sample spacing of5 to 10 cm have been analysed in the MD03-2697 se-quence. These measurements have been carried out on the250–315 μm fraction of G. bulloides previously cleanedwith distilled water. Each aliquot, including 8–10 speci-mens and representing a mean weight of 80 μg, wasprepared in the Micromass Multiprep autosampler, usingan individual acid attack for each sample. The CO2 gasextracted has been analysed against NBS 19 standard,taken as an international reference standard. Isotopicanalysis of MD99-2331 has been carried out using anOptimaMicromassmass spectrometer in theUMRCNRS5805 EPOC (Environnements et PaléoenvironnementsOcéaniques) at Bordeaux 1 University and, those ofMD03-2697 were performed using a delta plus Finniganat the Laboratoire des Sciences du Climat et del'Environnement (LSCE). The mean external reproduc-ibility of powdered carbonate standards is ±0.05‰ foroxygen. Results are presented versus PDB.

Polar foraminifera, N. pachyderma (s.), counting in-clude 79 levels (2 to 10 cm of sample spacing) and40 levels (5 to 10 cm of sample spacing) from MD99-2331 and MD03-2697, respectively. IRD semiquantita-tive analysis has been carried out in 78 levels (2 to 10 cmsample spacing) and 30 levels (5 to 10 cm sample spacing)from MD99-2331 and MD03-2697, respectively. In thisstudy, only the total concentrations of the lithic grainswere considered. Both analyses were performed on theN150 μm sand-size fraction which was obtained accord-ing to classic sedimentological procedure.

3.1.3. Pollen analysis110 and 22 samples with a sample spacing of 2 to

10 cmand 5 to 10 cmwere analysed fromMD99-2331 andMD03-2697, respectively. In each 1 cm-thickness sample,3 to 5 cm3 of sediment were treated for pollen analysis.

The treatment of the samples from both deep-sea cores(MD99-2331 and MD03-2697) followed the proceduredescribed by de Vernal et al. (1996), slightly modified atthe UMR CNRS 5805 EPOC (Desprat, 2005).

Palynological treatment consists of pollen concentra-tion by chemical digestion using cold HCl (at 10%, 25%and 50%) and cold HF (at 40% and 70%) to eliminatecarbonates and silicates, respectively. A Lycopodiumspike of known concentration has been added to each

sample to calculate total pollen (including spores) con-centrations. The residue was sieved through a 10 μmnylon mesh screen (Heusser and Stock, 1984) andmounted in bidistillate glycerine. A Zeiss microscopewith ×550 and ×1250 (oil immersion) magnificationswas used for pollen observation and counting.

Pollen identifications were achieved via comparisonwith specialised atlases (Moore et al., 1991; Reille,1992) together with the pollen reference collection of theUMR CNRS 5805 EPOC. At least 100 pollen grains(excluding Pinus, aquatic plants and spores) and 20pollen types were counted in each of the 142 samples(deep-sea cores and modern samples, cf. Section 3.2.)analysed to obtain statistically reliable pollen spectra(McAndrew and King, 1976). Pollen percentages werecalculated based on the main pollen sum which excludesaquatic plants, spores, indeterminate and unknownpollen grains. Because Pinus grains are usually over-represented in marine sediments (Heusser and Balsam,1977), they are also excluded from the main sum andtheir percentages are determined by using the total sum(pollen+spores+ indeterminable+unknowns).

3.2. Modern pollen samples

We have analysed the pollen grains of 10 top samplesfrom several estuarine, shelf and marine sedimentarysequences retrieved in and off western Iberia (Fig. 1,Table 2). The high percentages of Pinus detectedin these top samples confirm that they represent the last0–350 years, since it is well known that Pinusreforestation in western Iberia started in the seventeenthcentury (Valdès and Gil Sanchez, 2001). Because majorvegetation changes are not detected in percentage pollendiagrams for the last centuries in this region (Despratet al., 2003), we assume that our modern samples re-present present-day pollen signatures. The resultingmarine and coastal modern pollen assemblages havebeen compared with 12 terrestrial pollen samplesincluding moss samples, surface sediments and top ofpeat bog and lake sequences, of both the MediterraneanandAtlantic parts of western Iberia stored in the EuropeanPollen Database, http://www.imep-cnrs.com/pages/EPD.htm, (Peyron et al., 1998; Barboni et al., 2004) (Fig. 1).

4. Results and discussion

4.1. Present-day pollen signature

4.1.1. Western Iberian terrestrial sitesFig. 4 shows pollen spectra from several modern

samples collected in western Iberian Peninsula. Pollen

Table 1Radiocarbon ages of MD99-2331 and MD03-2697 deep-sea cores

Lab code Core–depth (cm) Material ConventionalAMS 14Cage BP

Conv. AMS 14Cage BP(−400 years)

Error 95.4% (2σ) calBP age ranges

Cal BP agemedianprobability

Beta-2131134 MD03 2697-20 G. bulloides 2880 2480 40 2501:2739 2656Beta-2131135 MD03 2697-40 G. bulloides 4760 4360 40 4866:5198 5008Beta-003257 MD03 2697-70 G. bulloides 7435 7035 50 7783:7998 7895Beta-2131136 MD03 2697-80 G. bulloides 7470 7070 40 7835:8014 7930Beta-2131137 MD03 2697-110 G. bulloides 9940 9540 40 10705:11084 10896Beta-003258 MD03 2697-150 G. bulloides 11920 11520 60 13233:13486 13353Beta-003259 MD03 2697-200 G. bulloides 12520 12120 60 13816:14111 13965LMC14-001231 MD99 2331-200 N. pachyderma 13640 13240 80 15303:16099 15679LMC14-001232 MD99 2331-205 N. pachyderma 13810 13410 80 15524:16359 15922GIF-102377 MD99 2331-220 N. pachyderma 14130 13730 120 15898:16828 16342LMC14-001233 MD99 2331-222 N. pachyderma 13920 13520 90 15658:16520a 16067a

LMC14-001235 MD99 2331-228 N. pachyderma 13930 13530 80 15686:16521a 16081a

LMC14-001236 MD99 2331-235 N. pachyderma 15130 14730 90 17250:18182 17848LMC14-001237 MD99 2331-242 N. pachyderma 15060 14660 90 17170:18038 17722LMC14-002445 MD99 2331-260 G. bulloides 15540 15140 90 18405:18723 18520GIF-101109 MD99 2331-290 G. bulloides 16170 15770 130 18787:19265 18983GIF-102373 MD99 2331-570 G. bulloides 19770 19370 170 22534:23622 23038LMC14-002446 MD99 2331-590 G. bulloides 22290 21890 170 ∼25,950b, c ∼25950b,c

LMC14-001845 MD99 2331-595 G. bulloides 20860 20460 250 23931:25369 24542LMC14-001846 MD99 2331-600 G. bulloides 20550 20150 240 23450:24803 24119LMC14-001847 MD99 2331-607 G. bulloides 20460 20060 140 23652:24405 24016LMC14-001849 MD99 2331-620 G. bulloides 21620 21220 160 25301:26000 25626LMC14-001850 MD99 2331-623 G. bulloides 21740 21340 160 25439:26000 25730GIF-102378 MD99 2331-630 N. pachyderma 22690 22290 180 ∼26350b,c ∼26350b,c

LMC14-001851 MD99 2331-637 G. bulloides 22150 21750 170 ∼25800c ∼25800c

LMC14-001852 MD99 2331-650 G. bulloides 22440 22040 170 ∼26000c ∼26000c

LMC14-001853 MD99 2331-655 G. bulloides 22430 22030 180 ∼26000c ∼26000c

a Not acceptable dating (bioturbated layers).b Radiocarbon dates too old (not used).c Dates calibrated by matching conventional AMS 14C with calendar ages estimated for MD95-2042 deep-sea core by Bard et al. (2004).

98 F. Naughton et al. / Marine Micropaleontology 62 (2007) 91–114

assemblages from surface samples located above 42°N(COV1, MUN1, MUN3, ES09, E258 and ES62), recordtheAtlantic deciduous forest (Figs. 1 and 4).However, thedominant tree species differs fromplace to place reflectingthe heterogeneity of the vegetation cover of this region(Fig. 4). For example, deciduous Quercus is the mostimportant tree pollen in samples ES09, ES258, MUN3and ES62 while Corylus dominates COV1 pollenspectrum and Betula that of MUN1. The pollen signalfrom the southern samples (FRA1, FRA4, GAT1, EXT1and EXT2) represents Mediterranean plant communities,essentially composed of evergreen Quercus (Quercusilex-type) and Olea (Figs. 1 and 4). However, FRA4sample also includes relatively high percentages of pollenof deciduous trees, similar to those found in pollen spectrafrom north-western Iberia. This sample, though located inthe Mediterranean region, comes from a high altitudedeciduous oak forest zone. Within this southern region,sample ESO6 collected in the coastal area reflects openvegetation resulting of saline conditions and sandy soils,

preventing the development of deciduous and perennialforests. These southern samples also reflect the mosaic ofthe vegetation colonising present-day southern Iberia.

We notice that, the southern pollen samples showhigher percentages of Mediterranean plants than thenorth-western Iberian samples (Fig. 4), clearly discrim-inating between Mediterranean and Atlantic plant com-munity sources, respectively.

4.1.2. Western Iberian estuarine and margin sitesEstuarine pollen samples VIR-18 (Ría de Vigo) and

Laquasup (Douro estuary), are marked by relativelyhigh percentages of deciduous forest reflecting thepresent-day vegetation of north-western Iberia (Figs. 1and 5). Shelf and slope samples (MD99-2331, CG11, Po287-13-2G and MD04-2814 CQ), located in theadjacent margin, reproduce the same pollen signal asthat of these northern estuarine samples. Southernsamples from estuarine (Barreiro) and margin (MD99-2332, FP8-1 and MD95-2042) sites present in turn

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higher percentages of Mediterranean plants than north-ern sites (Fig. 5). As in terrestrial samples, Mediterra-nean and Atlantic plant communities are welldiscriminated in the pollen signal from estuarine andmargin sites (Figs. 1 and 5). It is important to note thatthe estuarine pollen assemblages are more similar to themarine ones than to the terrestrial pollen spectra. Indeed,estuarine sediments contain pollen from the regionalvegetation which colonises the hydrographic basinwhile terrestrial samples mainly reflect local vegetation(Figs. 4 and 5). This indicates, as previous studies havealready shown for the south-western French margin(Turon, 1984), that pollen spectra off north-westernIberia reflect an integrated image of the regionalvegetation of the adjacent continent.

Pinus percentages from western Iberian samples arerelatively low when compared with estuarine, shelf andslope samples off this region (Fig. 5). This is in agree-ment with the observed overrepresentation of Pinuspollen in marine sediments in general and, in particular,off south-western Europe (Turon, 1984). Other workshave further shown that Pinus pollen percentages in-crease seawards (Heusser and Balsam, 1977; Heusserand Shackleton, 1979). Our study confirms this patternin the north and south-western margins. However,MD95-2042 site, representing the farthest sample fromthe coast line, presents weaker percentages of Pinuspollen than estuarine and the other marine samples.

Despite the generalPinus overrepresentation inmarinesediments, the good correlation between both terrestrialand marine present-day pollen signatures in and offwestern Iberia confirm the reliability of past vegetationand climate change reconstructions of this regionproposed by previous works on western Iberian margincores (Hooghiemstra et al., 1992; Sánchez Goñi et al.,1999, 2000, 2002, 2005; Boessenkool et al., 2001;Roucoux et al., 2001, 2005; Turon et al., 2003; Tzedakiset al., 2004; Desprat et al., 2005, 2006, in press).

Table 2Location, water depth and year of sample sampling from coastal, shelf and s

Sample name Depth (cm) Latitude L

MD95-2042 Top (0–1) 37°48′N 11FP8-1 Top (0–1) 38°01′N 0MD99-2332 Top (0–1) 38°33′N 0Barreiro Top (0–1) 38°40′N 0MD04-2814 CQ Top (0–1) 40°37′N 0Laquasup Top (0–5) 41°09′N 0Po 287-13-2G Top (0–1) 41°09′N 0CG11 Top (0–1) 41°48′N 0MD99-2331 3–4 42°09′N 0Vir-18 Top (0–1) 42°14′N 0

4.2. Present-day pollen transport patterns

Previous works on coastal zones with complex fluvialsystems have shown that pollen is mainly transported tothe sea by rivers and streams (Muller, 1959; Bottema andvan Straaten, 1966; Peck, 1973; Heusser and Balsam,1977). The western Iberian margin, close to several im-portant hydrographic basins such as Tagus and Sado in thesouth and Douro and Minho in the north, mainly receivespollen through fluvial transport (Fig. 3). Furthermore,north-western prevailing winds in both north and southernregions probably impede substantial direct airborne tran-sport of pollen seaward. This pattern of fluvial transportcontrasts with others, e.g. north-western Africa, associatedwith an arid environment, where pollen grains are mainlyseaward transported by the wind (Dupont et al., 2000;Hooghiemstra et al., 2006). Indeed, the distribution of theTPC shows (Fig. 5) that the highest TPC values are foundin samples from coastal areas such as the Douro estuary(Laquasup: 44399×103 grains/cm3) and the Ría de Vigo(VIR-18: 65443×103 grains/cm3). Barreiro sample is anexceptional case with low TPC (18×103 grains/cm3)probably because it was collected far away from the Tagusmain channel and likely receiving pollen only from thelocal vegetation. Shelf surface samples present intermediateconcentration values (CG11: 30468×103 grains/cm3,Po 287-13-2G: 42600×103 grains/cm3 and MD99-32b:56396×103 grains/cm3) and finally slope samples attainthe lowest TPC values (MD99-2331: 1924×103 grains/cm3, MD04-2814 CQ: 1886×103 grains/cm3, MD95-2042: 2153×103 grains/cm3 and IFP8: 3489×103 grains/cm3). Our work shows that a seaward decrease of totalpollen concentrations occurs on the Iberian margin fol-lowing the estuary-shelf-slope transect (Fig. 3). This patterncoincides with that observed in other margin zones aroundthe world showing a seaward decrease in total pollenconcentration with maximum values close to the mouth ofthe river systems (Muller, 1959; Bottema and van Straaten,

lope sequences of the Iberian margin

ongitude Water depth (m) Year of sampling

0°10′W 3148 19959°20′W 980 20039°22′W 97 19999°07′W 0 19999°52′W 2449 20048°38′W 0 20019°01′W 81 20029°04′W 107 19929°42′W 2120 19998°47′W 45 1990

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1966; Cross et al., 1966; Groot and Groot, 1966, 1971;Koreneva, 1966; Stanley, 1966;Mudie, 1982; Turon, 1984;Van der Kaars and de Deckker, 2003).

Based on several studies of sedimentary dynamics onthe north-western Iberian margin (Araújo et al., 1994;Drago et al., 1998; Dias et al., 2002; Huthnance et al.,2002; Jouanneau et al., 2002; Oliveira et al., 2002; VanWeering et al., 2002; Vitorino et al., 2002), we propose apattern of pollen dispersion for this region (Fig. 3b). Thispattern is similar to the distribution model of fineterrigenous particles proposed by Dias et al. (2002).Pollen and spores, once immersed behave in a similarmanner to fine sedimentary particles (Chmura andEisma, 1995). After being released by rivers (mainlyDouro followed by Minho), pollen grains, are enclosedin nepheloid layers and transported to the shelf untilgetting blocked by the rocky outcrops. In winter, duringdownwelling conditions pollen grains are then trans-ported polewards, firstly deposited in the Douro mudpatch (S–N direction) then in the Galicia mud patch, andfinally they flow westward to the deep-sea. Only smallquantities of pollen grains can be transported directly tothe outer shelf and upper slope under extreme stormyevents. In summer, under upwelling conditions, pollentransfer to the slope must be restricted to offshore fila-ments as suggested by Huthnance et al. (2002) for thefine sediments.

In the southern Iberian margin, TPC values alsodecrease seawards as in the northern region (Fig. 5). Ourstudy suggests that pollen grains released by the Tagus andto a lesser extent by the Sado river, are partially depositedin the shelf and transported to the south and seaward bylittoral and oceanic currents probably during upwellingconditions (Fig. 3c). Pollen grains are probably transportedby the southern canyons from the shelf to the slope andabyssal plain following the fine particle pathway suggestedby several works on sedimentary dynamics in this region(Dias, 1987; Jouanneau et al., 1998; Araújo et al., 2002).

4.3. Climatic and vegetational response in westernIberia to North Atlantic climatic events over the last25000 years

The comparison of the high resolution pollen com-posite record from the Galician margin (Fig. 6; Table 3),with other marine and terrestrial pollen sequences

Fig. 4. Pollen spectra from western Iberian modern samples. Total temperatedeciduous Quercus and other temperate and humid species (Acer, Fagus,Mediterranean (Tot. Mediter.) plants include: evergreen Quercus, Olea andrepresent the ubiquist group. Semi-desert plants include Ephedra, CPP: precipitation; MTCO: mean temperature of the coldest month; MTWA:

(Figs. 1 and 7; Tables 4 and 5) document the vegetationchanges that occurred in the Iberian Peninsula over thelast 25000 years. Moreover, the direct correlation be-tween marine proxies and vegetation changes from thisrecord will allow us to accurately evaluate the vege-tation response to the climatic events detected elsewherein the North Atlantic Ocean and over Greenland.

4.3.1. Marine isotopic stage 2

4.3.1.1. Heinrich events (H2 and H1). Our Galicianmargin composite record reveals two periods marked bythe dominance of herbaceous communities (Poaceae,Ericaceae, Calluna, Cyperaceae, Aster-type, Taraxa-cum-type) along with a Pinus forest reduction indicatingtwo major cold events in north-western Iberia. Theseevents, pollen zones MD31-2-2 and MD31-2-4, arecentred at around 21700 years BP and 14700 years BP,respectively. In the ocean, our record identifies H2 andH1 events on the basis of, as usual in other NorthAtlantic cores, peaks in ice rafted detritus (IRD), highpolar foraminifera (N. pachyderma s.) percentages andheavy planktic δ18O values (e.g., Heinrich, 1988; Bondet al., 1993; Duplessy et al., 1993; Grousset et al., 1993;Bond and Lotti, 1995; Lebreiro et al., 1996; Baas et al.,1997; Abrantes et al., 1998; Cayre et al., 1999; Bardet al., 2000; Shackleton et al., 2000; Thouveny et al.,2000; Broecker and Hemming, 2001; de Abreu et al.,2003; Hemming, 2004). Radiocarbon ages obtained forH2 (∼22000 to ∼20000 years BP) and H1 (∼15350 to∼13000 years BP) intervals in our Galician marginrecord are in agreement with the age limits of theseevents, proposed by Elliot et al. (1998) for the NorthAtlantic.

Direct correlation between pollen and marine proxiesperformed in this record (Fig. 6; Table 3) shows thatthese major cold events in north-western Iberia are onlyassociated with the first part of H2 and H1. Indeed, H2and H1 encompass two vegetational phases. Besides thePinus forest contraction, the first part of H2 (∼22000 to21500 years BP; MD31-2-2 pollen zone) and H1(∼15350 to 14500 years BP; MD31-2-4 pollen zone) ischaracterised by the expansion of Calluna. Callunavulgaris is a light demanding species (Calvo et al.,2002) favoured by forest regression and moist condi-tions. This indicates that the first part of both Heinrich

and humid (Tot. Temp./Hum.) trees include: Alnus, Betula, Corylus,Fraxinus, Salix, Tilia, Ulmus, Hedera helix, Myrica and Vitis). TotalCistus. Taraxacum-type, Asteraceae, Poaceae, Ericaceae and Callunahenopodiaceae and Artemisia. Climate parameters: Alt: altitude;mean temperature of the warmest month; TANN: annual temperature.

Fig. 5. Pollen assemblages of top samples from coastal and marine western Iberian sites (see also caption of Fig. 4). TPC: total pollen concentration.

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Fig. 6. Galician margin composite record (MD99-2331 and MD03-2697 deep-sea cores). From the left to the right: corrected radiocarbon ages; marine proxies: δ18O of G. bulloides, % N. pachyderma(s.), ice-rafted detritus (IRD), Marine and Greenland climatic events; % pollen taxa; pollen zones and chronostratigraphy. Pollen zones were established using qualitative and quantitative fluctuations ofa minimum of 2 curves of ecologically important taxa (Pons and Reille, 1986). They are defined by the abbreviated name of the core (MD31 or MD97) followed by the number of the marine isotopicstage (1 or 2) and numbered from the bottom to the top (MD31-2-1 to MD31-2-5 and MD97-1-1 to MD97-1-6).

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events was cold and humid. Furthermore, the first part ofH1 is marked by the continuous presence of the Isoetesfern suggesting also moist conditions.

Table 3Description of the pollen zones in the Galician margin composite core and r

Pollen zones Pollen signature

MD97-1-6 Strong increase of Pinus (15–70%)Continuous decrease of deciduous QuercusEricaceae (55%), Poaceae (10%) and Taraxacum-type (10%

MD97-1-5 Continuous decline of Pinus (40–15%), deciduous Quercuspresence of Alnus (8–12%)Ericaceae increase (30–55%)

MD97-1-4 Gradual decline of Pinus (60–40%) and deciduous Quercu(6–10%), beginning of Alnus continuous presenceGradual increase of Ericaceae (10–30%) and decrease of herCalluna (b2%), Aster-type (b1%) and Cyperaceae (b2%)Semi-desert (b3%)Spores presence (pislete triletes and Isoetes)

MD97-1-3 Pinus decline (∼60%)Maximum expansion of deciduous Quercus (60–80%),presence of evergreen QuercusHerbaceous pollen percentages decrease: Ericaceae (b10%),(b1%) and Cyperaceae (b2%)Semi-desert (b3%)

MD97-1-2 Pinus (80–90%)Decrease of deciduous Quercus (40%) and increase of BetuPoaceae increase (20–30%), Ericaceae (10–20%), TaraxacuIncrease of semi-desert associations: Artemisia (∼5–15%),

MD97-1-1 Pinus (80–90%)Strong increase of tree percentages: deciduous Quercus (40Decrease of ubiquist associations: Poaceae (10–20%), Eric(b5%)Presence of pioneer species: Betula, Cupressaceae and Hip

MD31-2-5 Pinus (∼80%)Poaceae (30%), Ericaceae (10–15%), Calluna (b10%),Taraxacum-type (∼10%)Semi-desert associations: Artemisia (2–12%), ChenopodiacPresence of pioneer species (Betula and Hippophae) (b5–1

MD31-2-4 Strong decrease of Pinus (∼20–40%)Poaceae (20–45%), Ericaceae (∼20%), Calluna (10–20%)Taraxacum-type (15–20%)Semi-desert associations: Artemisia (b5%), Chenopodiacea

MD31-2-3 Pinus (∼60%)Poaceae (20–40%), Ericaceae (20–45%), Calluna (2–15%Taraxacum-type (5–30%)Semi-desert associations: Artemisia (b5%), ChenopodiaceaPresence of temperate trees (b5–10%) and pioneer species

MD31-2-2 Pinus (30–40%)Poaceae (20–40%), Ericaceae (20–30%), Taraxacum-type(10%)Semi-desert associations: Artemisia (b5%), Chenopodiacea

MD31-2-1 Pinus (∼60%)Poaceae (0–20%), Ericaceae (20–30%), Calluna (10%),Taraxacum-type (10–20%)Semi-desert associations: Artemisia (1–5%), Chenopodiace

The second part of H2 (21500 to 20000 years BP;first 1500 years of the MD31-2-3 pollen zone) and thatof H1 (14500 to 13000 years BP, MD31-2-5) are

espective chronostratigraphy

Chronostratigraphy

Holocene

)(40–15%), Corylus and evergreen Quercus,

s (60–40%), maximum expansion of Corylus

baceous pollen percentages: Poaceae (b10%),

beginning of Corylus continuous presence,

Poaceae (b10%), Calluna (b2%), Aster-type

YoungerDryas (YD)

LateGlacialperiod

la (10%)m-type (b10%)Chenopodiaceae (∼3%), Ephedra (∼2%)

Bölling-Allerød (B-A)–60%)

aceae (b20%), Cyperaceae (∼10%); Calluna

pophae

Oldest DryasCyperaceae (5–10%), Aster-type (∼10%),

eae (∼3%), Ephedra (b2%)0%)

, Cyperaceae (b10%), Aster-type (10–20%),

e (b5%), Ephedra (∼2%)

LatePleniglacial), Cyperaceae (5–10%), Aster-type (2–15%),

e (b3%), Ephedra (b2%)

(10–20%), Calluna (15–20%), Aster-type

e (1–2%)

Cyperaceae (5–10%), Aster-type (b10%),

ae (0–3%), Ephedra (b2%)

Fig. 7. Comparison between continental (Quintanar de la Sierra; Peñalba et al., 1997) and marine (MD99-2331 and MD03-2697) pollen sequences.

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Table 4Description of pollen zones from the well-dated reference sites of Quintanar de la Sierra (Peñalba, 1994; Peñalba et al., 1997), Laguna de la Roya (Allen et al., 1996) and Padul (Pons and Reille, 1988)

Years 14 C BP/continentalsequences

Laguna de la Roya (1608 m a.s.l.) (Allen et al., 1996) Quintanar de la Sierra (1470 m a.s.l.) (Peñalba, 1994;Peñalba et al., 1997)

Padul (785 m a.s.l.) (Pons and Reille, 1988)

year BP year BP year BP

1200–present day Local increase of Betula (30–50%) Pinus, Fagus and herbs (Ericaceae, Cerealia) –Poaceae (20–30%), Ericaceae (5–10%), Rumex (∼2%)Culture presence: Olea, Castanea and CerealiaAbsence of Pinus and Quercus decrease

3000–1200 Poaceae (30–40%) well represented, spread of Ericaceae(10%)

Spread of Fagus –

Decrease of Pinus, Betula and slight decrease of Quercus6000–3000 Succession of Juniperus, Betula, Quercus, Corylus and

Alnus3060 Spread of Corylus 4450 Deciduous Quercus, Quercus ilex, Quercus suber,

PistaciaMaximum percentages of trees(Betula, Pinus, deciduous Quercus,Quercus ilex and Corylus)

Pinus is almost absent (b5%)

10000–8200 8200 Succession of Juniperus, Betulaand deciduous Quercus and Quercus ilex

8200 Deciduous Quercus, Quercus ilex, PistaciaPinus is almost absent (b5%)

Younger Dryas 10290 Pinus presence (10–40%) 10120 Pinus presence (20–40%) 10000 Decrease of trees until 40%Poaceae (20–30%), Artemisia (10%), Chenopodiaceae,Plantago, Caryophyllaceae, Anthemis-type and Calluna)

Poaceae (20–30%), Artemisia (10%), Apiaceae(10–15%), Plantago (5%), Aster (2%),Cyperaceae (2–10%),Chenopodiaceae and Calluna

Artemisia (N10%), Poaceae (20%),Chenopodiaceae (N10%), Ephedra (5%),Cyperaceae (20–30%)Slight increase of Pinus

Late Glacial interstadial Succession of Juniperus, Betula, Quercus 11050 Succession of Juniperus, Salix, Betula Juniperus, Betula, deciduous Quercus,Quercus ilex and PistaciaPinus well represented (40–60%) Pinus well represented (60–80%)

Late Glacial (Q S and LR)/Oldest Dryas (Padul)

12940 Pinus presence (10–30%) 13350 Pinus presence (10–15%)Poaceae (20–40%) , Artemisia (20–40%),Chenopodiaceae (2–5%), Plantago (∼2%),Caryophyllaceae (2%), Aster-type (2%) and Calluna (2%)

Poaceae (20–40%), Artemisia (15–30%),Chenopodiaceae (∼5%), Plantago (0–7%),Cyperaceae (5–10%), Aster (2–5%)

13200 Pinus decrease (b40%)Artemisia (20%), Poaceae (20–40%),Chenopodiaceae (N10%),Cyperaceae (60–100%)

Late Pleniglacial – – 15200 Pinus increase (50–75%)Artemisia (10–20%), Poaceae (10%),Chenopodiaceae (b10%),Cyperaceae (0–30%). Presence of trees (5%)

– – 19800 Alternation of coldest episodes: Artemisia(30–60%),Chenopodiaceae (10%), Cyperaceae (b20%),Poaceae (b10%)and Pinus presence (10–20%)with less cold episodes: Artemisia (10–20%),Chenopodiaceae (b5%), Cyperaceae (50–80%)

23600 Poaceae (20%) and Pinus increase (50–70%)

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Table 5Holocene tree succession in north-western Iberia

Quintanarde la Sierra(42°02′N,3°W)1608 m a.s.l.

LagunadeLa Roya(42°6′N,6°44′W)1085 m a.s.l.

Lago de Ajo(43°3′N,6°9′W)1570 m a.s.l.

LagunaMasegosa(42°57′N,2°49′W)1600 m a.s.l.

Laguna Negra(42°0′N,2°52′W)1760 m a.s.l.

BanyolesLake(42°08′N,2°45′E)173 m a.s.l.

Las PardillasLake(42°2′N,3°2′W)1850 m a.s.l.

LagunaLucenza(Sierrade Queixa)(Galicia)1420 m a.s.l.

Hoyosde Iregua(42°01′N,2°45′W)1780 m a.s.l.

Pozo doCarballal(42°42′N,7°07′W)1330 m a.s.l.

LagoaLucenza(42°35′N,7°07′W)1375 m a.s.l.

Lagunade lasSanguijuelas(42°08′N,6°42′W)1080 m a.s.l.

Holocenesub-phases

Pinus Betula Betula Pinus Pinus Pinus Pinus Betula Pinus Betula Betula Fagus LateHolocene5000–4000–3000yearsBP untilpresent day

Fagus Fagus Fagus Fagus Fagus Abies Fagus Salix Fagus Fagus

Taxus Taxus TaxusCorylus Alnus Ulmus Alnus Alnus Alnus Alnus Alnus Alnus Alnus Fraxinus Ulmus Mid-

Holocene9000–8000years BP to5000–4000years BP

Ulmus Alnus Ulmus Ulmus Corylus Ulmus Ulmus Salix Ulmus Alnus AlnusFraxinus Fraxinus Taxus Fraxinus Fraxinus Corylus Corylus Corylus Ulmus FraxinusCorylus Corylus Fraxinus Corylus Corylus Corylus Corylus

CorylusEve. Quercus Dec.

QuercusQuercus Eve.

QuercusEve.Quercus

Eve.Quercus

Eve.Quercus

Dec.Quercus

Eve.Quercus

Eve.Quercus

Eve.Quercus

Eve.Quercus

EarlyHolocene10500 yearsBP to9000–8000years BP

Dec. Quercus Dec.Quercus

Dec. Quercus Dec.Quercus

Dec.Quercus

Dec.Quercus

Dec.Quercus

Dec.Quercus

Dec.Quercus

Pinus Betula Betula Pinus Pinus Acer Salix Salix Pinus Salix Betula SalixSalix Juniperus Juniperus Salix Salix Betula Betula Betula Betula Betula Pinus JuniperusBetula Betula Betula Pinus Pinus Pinus Juniperus Juniperus PinusJuniperus Juniperus Juniperus Juniperus Juniperus Pinus Betula

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marked by a Pinus expansion, indicating less coldconditions than the previous phases. Furthermore,during the second part of H1, a gradual increase ofsemi-desert plants (Artemisia, Chenopodiaceae andEphedra) reflects a gradual dryness on land. Ourmultiproxy palaeoclimatic record (Fig. 6; Table 3)indicates therefore that H2 and H1 events display acomplex pattern on the adjacent continent.

This two-phase climatic succession on land withinH2 and H1 agrees with the changes detected in themarine proxy data from the same record (Fig. 6). Thefirst phase is represented by the heaviest δ18O values ofG. bulloides and the increase of N. pachyderma (s.)percentages, suggesting a strong decrease in sea surfacetemperatures (SST), and the absence of IRD in thisregion. In contrast, the second phase records thelightening of the planktic isotopic signal and thedecrease in the polar foraminifera population althoughthe presence of IRD testifies to iceberg melting offGalicia. This complex marine pattern within H2 and H1events has already been detected further south in theSU81-18 deep-sea record (Fig. 1) (Bard et al., 2000).

Comparison between our multiproxy palaeoclimaticrecord (Fig. 6) and the available terrestrial and marinepollen sequences in and off Iberia (Fig. 1) indicates thatthe impact of H2 and H1 events in Iberia is spatiallyvariable. The Pinus reduction associated with H2, datedin the Galician margin record between 22040±180 and21340±160 years BP, has been already detected byterrestrial and marine pollen sequences in and offnorthern Iberia (Fig. 1) (Pérez-Obiol and Julià, 1994;Roucoux et al., 2005). In north-eastern Spain, thedecrease in Pinus percentages before 19900 years BPdetected in the Banyoles sequence and explained as theresult of local factors (Pérez-Obiol and Julià, 1994) cannow be interpreted as the consequence of the climaticchange associated to H2. The slight expansion of Cal-luna recorded in the Galician margin sequence duringthe first phase of H2 has not been detected, however, atlow altitude in north-eastern Spain where Poaceae wasthe dominant taxa. This suggests that heathers growpreferentially in the north-western Iberia favouredprobably by Atlantic wet conditions.

Southern Iberian margin cores (Fig. 1) reveal theexpansion of semi-desert associations (Artemisia, Che-nopodiaceae,Ephedra), suggesting an increase of drynessduring the entire H2, 22000–20000 years BP, althoughno decrease ofPinus forest was detected (SU81-18, Turonet al., 2003; ODP 976, Combourieu-Nebout et al., 2002and SO75-6KL, Boessenkool et al., 2001). In contrast, thePadul record (Pons and Reille, 1988; Fig. 1; Table 4)shows between 23600 and 19800 years BP an alternation

between periods of high Pinus pollen values and periodsof high percentages of semi-desert plants. This suggestsdryness variability in Sierra Nevada at that time orchanges in pollen-input related with local factors.

The two-phase climatic succession of H1 eventcharacterised in our Galician margin record (MD31-2-4and MD31-2-5 pollen zones, Fig. 6, Table 3) by a firstcold and humid episode followed by a dry and coolphase is contemporaneous, as H2, with a unique aridityinterval and no Pinus forest reduction in south-westernIberia (Fig. 1) (Boessenkool et al., 2001; Turon et al.,2003). Seemingly, high altitude sites of northern Iberiaand eastern Iberian sites (Padul and Banyoles) detectone event of dryness between 15000 and 13000 (Table4, Figs. 1 and 7; Laguna de la Roya, Allen et al., 1996;Quintanar de la Sierra, Peñalba et al., 1997; LagunaMasegosa, Von Engelbrechten, 1998; Lagoa Lucenza,Muñoz Sobrino et al., 2001; Laguna Lleguna andLaguna de las Sanguijuelas; Muñoz Sobrino et al.,2004). The westernmost sequences record the expansionof Calluna and Isoetes, as we observed in the first partof H1 of our record, showing that these sites are alsoaffected by wet Atlantic influence (Lagoa Lucenza,Muñoz Sobrino et al., 2001; Laguna Lleguna andLaguna de las Sanguijuelas, Muñoz Sobrino et al., 2004;Mougás, Gomez-Orellana et al., 1998). Pinus forestcover around all high altitude sites remains weak overthis time-interval while our Galician margin record(Figs. 6 and 7; Tables 3 and 4) representing also thevegetation of low and mid altitudes sees a Pinusexpansion in the second part of H1. This suggests thatthe temperature increase was not enough to trigger Pi-nus expansion in high altitude areas (Fig. 1). Thesevegetational changes related with cold conditions inIberia coincide with the Oldest Dryas originallyidentified in Danish deposits one century ago anddated older than 13000 years BP (Mangerud et al.,1974) and not with the Older Dryas as erroneouslycorrelated by Turon et al. (2003). Therefore, our workdemonstrates that the Oldest Dryas is the terrestrialcounterpart of the H1 event.

4.3.1.2. The LGM. In our record, the Last GlacialMaximum (LGM), bracketed by H2 and H1 events asestablished by the EPILOG program (Environmentalprocesses of Ice age: Land, Oceans, Glaciers) (Mix et al.,2001), is characterised by the expansion of Pinus in anherbaceous-dominant environment along with scatteredpockets of deciduous trees (MD31-2-3 pollen zone) (Fig.6, Table 3). Planktic δ18O values are slightly lower thanduring H2 and H1 events and N. pachyderma s. decreaseto very low percentages. Pinus percentages stay constant

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over this interval and there is an almost continuous slightpresence of deciduous tree pollen (deciduous Quercus,Betula, Corylus and Alnus) over this period. Neverthe-less herbaceous communities remain the dominantgroup. The presence of deciduous trees has also beendetected in and off southern Iberia between 20000 and15000 years BP (Table 4; Pons and Reille, 1988;Boessenkool et al., 2001; Combourieu-Nebout et al.,2002) associated with the LGM (Turon et al., 2003). Ourrecord clearly shows that not only southern but alsonorth-western Iberia acted as a refugium zone for certaintemperate trees (deciduous Quercus, Corylus, Alnus andBetula) during the last glacial maximum corroboratingwhat has been suggested by previous studies (Roucouxet al., 2005). However, it must be noted that deciduoustrees presence is weak and that they attain theirmaximum expression in southern Iberia. Anotherinteresting feature within the LGM concerns thesustaining of Ericaceae communities in north-westernIberia indicated by our Galician margin core and theirslight expansion in southern Iberia detected by marinecores SU81-18 (Turon et al., 2003) and ODP 976(Combourieu-Nebout et al., 2002). This is contempora-neous with the slight decrease of semi-desert associa-tions in the middle altitudes of Sierra Nevada (Padul),indicating an increase of humidity in Iberia at that time.

4.3.2. Marine isotopic stage 1

4.3.2.1. The Bölling-Allerød. Following the H1 event,a drastic change in the pollen assemblage and plankticstable oxygen isotopic values identifies the Bölling-Allerød (B-A) temperate period (Greenland Interstadial1—GIS 1, Late glacial interstadial). Our Galicianmargin pollen record (Fig. 6, Table 3) (MD97-1-1pollen zone) detects a fast deciduousQuercus expansionand the slight development of pioneer species (Betula,Cupressaceae andHippophae), a decrease of herbaceousassociations and Pinus percentages reach maximumvalues. In the ocean, surface waters show an importantlowering of the δ18O values suggesting, in absence offreshwater input, an oceanic warming at these NorthAtlantic mid-latitudes.

In the northern Iberian Peninsula, the Late glacialinterstadial (B-A) is characterised by the succession ofpioneer associations (Juniperus–Betula–Pinus) and themore or less important expansion of deciduous trees(Fig.1 and 7; Table 4; Allen et al., 1996; Peñalba et al.,1997; Von Engelbrechten, 1998). High altitude sites ofnorthern Iberia such as Laguna Masegosa (VonEngelbrechten, 1998), Laguna de la Roya (Allen et al.,1996), Hojos de Iregua (Gil García et al., 2002) and

Laguna de las Sanguijuelas (Muñoz Sobrino et al.,2004) record a deciduous Quercus expansion between13000 and 11000 years BP above 1000 m a.s.l. Ourpollen analysis records higher pollen percentages ofdeciduous Quercus than the high altitude sequencessuggesting that deciduous Quercus woodlands expand-ed preferentially in the lowlands and mid-altitudes ofnorthern Iberia. Brewer et al. (2002), based on a smallnumber of high altitude northern and low altitudesouthern sequences, suggested that only southern Iberiaacted as a refugium zone for deciduous oak during thelast glacial period. However, as previously shown byour Galician record, the mid and low-altitudes of north-western Iberia were a refugium zone for deciduousQuercus species allowing the fast spread of these taxaduring B-A climate improvement.

In southern Iberia, a rapid expansion of deciduousand evergreen Quercus and other Mediterraneanelements is recorded in the Late glacial interstadial ofthe Padul peat-bog sequence and marine records SU81-18 (Turon et al., 2003), 8057 B (Hooghiemstra et al.,1992), SO75-6KL (Boessenkool et al., 2001) and ODP976 (Combourieu Nebout et al., 1999, 2002). Indeed, adistinct phase of pioneer trees is not reflected at thebeginning of this interstadial neither in southern Iberianor in low and mid altitudinal sites of the north-westernIberia as shown by our Galician margin pollen record.

4.3.2.2. The Younger Dryas cold event. Following theB-A warm phase, our Galician margin pollen record(MD97-1-2 pollen zone) sees the increase of pioneerspecies (Betula), grasses and semi-desert associations(Artemisia and Ephedra) at the expense of the temperateforest. These vegetational features characterise theYounger Dryas cold event (Fig. 6, Table 3).

This cold episode has been detected in and off Iberia(Pons and Reille, 1988; Pérez-Obiol and Julià, 1994;Allen et al., 1996; Peñalba et al., 1997; Von Engel-brechten, 1998; Gil García et al., 2002; Turon et al.,2003) (Fig. 1, Table 4) and is associated with a slightincrease of the planktic δ18O values (Hall and McCave,2000; Schönfeld and Zahn, 2000; Löwemark et al.,2004; Turon et al., 2003).

The slight decrease of deciduous Quercus, theincrease of pioneer species (Betula) and the expansionof semi-desert and herbaceous plants are also repre-sented in north-eastern Iberia as well as in continentaland offshore southern Iberian sequences (Pons andReille, 1988; Pérez-Obiol and Julià, 1994; Boessenkoolet al., 2001; Turon et al., 2003). Vegetation changesrelated to this short event appear more drastic at highaltitudinal sites of northern Iberia than at low and mid

110 F. Naughton et al. / Marine Micropaleontology 62 (2007) 91–114

altitude sites of north-western Iberia (this study) andthose from the south as indicated by the slight decreaseof temperate trees in terrestrial and marine pollensequences in and off southern Iberia (Fig. 7).

4.3.2.3. The Holocene. After the YD, the treesuccession of deciduous Quercus, Corylus and Alnusdefines the Holocene in our Galician margin record(Fig. 6, Table 3). Remarkably, during the onset of theHolocene (MD97-1-3 pollen zone), the increase ofdeciduous Quercus pollen percentages tightly parallelsthe lightening of δ18O values (Fig. 6). However,deciduous forest attains its maximum expressionslightly before sea surface water experiences its lightestδ18O values. Pinus pollen values decline steadily in thepollen zones MD97-1-3 through MD97-1-5. The end ofthe maximum expansion of deciduous Quercus treesand the beginning of the Corylus increase (MD97-1-4)occur contemporaneously with the beginning of thelightest δ18O isotopic values in the ocean. DeciduousQuercus gradually decreases until the end of theHolocene (from MD97-1-4 to MD97-1-6).

The expansion of heaths (Ericaceae and Calluna)and ferns (as indicated by psilate Trilete spores) alongwith the reduction of trees (deciduous Quercus, Corylusand Betula) mark the late Holocene phases (MD97-1-5and MD97-1-6). The minimum pollen values of Pinusare recorded in zone MD97-1-5 while maxima pollenpercentages of this tree, in the successive zone MD97-1-6, probably reflect the reforestation of the last 350 years.

In Iberia, vegetation response to climate ameliorationthat characterises the Holocene period looks quite similarto that of the B-A event. The settlement of theMediterranean forest occurred very fast in southern sites(Fig. 1) as illustrated by the pollen sequences of Padul(Table 4, Pons and Reille, 1988), Charco da Candieira(Van der Knaap and van Leeuwen, 1995), SU81-18(Turon et al., 2003), ODP 976 (Combourieu-Nebout et al.,2002), 8057 B (Hooghiemstra et al., 1992), and SO75-6KL (Boessenkool et al., 2001). In the north, vegetationresponse to the Holocene climate appears slower than inthe south. The expansion of pioneer trees (Juniperus,Betula and Pinus) marks the beginning of this period inthe high altitude sites of northern Iberia followed by thedevelopment of deciduous Quercus, Corylus and Alnus(Table 5; Fig. 1). This succession is also clearly detectedby our Galician marine record synchronously with thedecrease of planktic δ18O values which are contempora-neous with the sea surface gradual warming detected byde Abreu et al. (2003) and Schönfeld et al. (2003) in theIberian margin. However, this vegetation succession,recorded in our Galician sequence, begins earlier, during

the Younger Dryas event, in the low and mid altitude sitesthan in the high altitudinal sites of north-western Iberia.The Galician margin record further suggests that themaximum development of deciduous Quercus forestleads the lightest values of planktic δ18O during theHolocene. Finally, the late Holocene interval of all Iberianmarine and terrestrial sequences indicates the decline ofthe temperate forest during the last 5000 years.

5. Conclusions

The comparison of present-day terrestrial and marinepollen samples in and off western Iberia shows that thepollen signature from the Iberian margin is similar to thatof the Iberian terrestrial deposits, and, in particular, tothat of the estuarine samples which recruit pollen fromthe vegetation colonising the adjacent hydrographicbasins. Therefore, western Iberian margin pollen spectrareflect an integrated image of the regional vegetation ofthe adjacent continent. Furthermore, our study showsthat marine pollen spectra clearly discriminate both theMediterranean and the Atlantic plant communitiescolonising southern and northern Iberian Peninsula,respectively. It also identifies the present-day pattern ofpollen transport in northern and southern Iberian marginduring downwelling and upwelling conditions.

High resolution pollen and marine proxies analysisfrom the Galician margin composite core (MD99-2331and MD03-2697) shows a synchronicity of the vegeta-tion response to the North Atlantic climatic variabilityduring H2, LGM, H1, B-A, YD events. Comparison ofthis palaeoclimatic record with other marine andterrestrial pollen records shows that the beginning ofboth H2 and H1 cold events are associated with Pinusforest reduction in northern Iberia. It also shows thepresence of two vegetation phases within H1 and H2events, associated with an initial cold and wet episodefollowed by a cool and, particularly, dry episode duringH1. Furthermore this comparison allows us to demon-strate that the Oldest Dryas event on the continentcorresponds to the H1 event in the ocean.

The slight presence of deciduous Quercus, Corylusand Alnus during the Last Glacial Maximum shows thatnot only southern Iberia but also northern Iberia acted as arefugium zone for these trees, though at a smaller scale.Bölling-Allerød interstadial in our sequence, whichmainly represents low and mid-altitude zones, show amore rapid and great expansion of deciduous Quercusthan the high altitude sites of north-western Iberia,indicating that the vegetation of low and mid-altitudesresponded more rapidly to the climate variability of theNorth Atlantic during this interstadial. Because deciduous

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forest attained it maximum expression during the B-Ainterstadial in low and mid-altitudes of the north-westernIberia, the climate reversal characterising the YoungerDryas event is less marked in these zones than in the highaltitude ones. The response of deciduous forest to theclimate improvement that characterises the onset of theHolocene at low and mid altitudes of north-western Iberiaseems to lead those observed in the high altitude sites,although the same succession of trees is observed in allthese northern regions.

This study confirms that marine pollen sequencesfrom western Iberian margin are a powerful tool foraccurate reconstruction of vegetation response tooceanic and atmospheric climate changes within areliable chronological framework. Furthermore, itdemonstrates the importance of including vegetationreconstructions from marine pollen sequences in futureefforts to refine and model vegetation and climatedynamics in the Iberian Peninsula.

Acknowledgements

This study is a contribution to ARTEMIS, RESO-LUTION, IDEGLACE and ECLIPSE projects and hasbeen partially supported by the FCT research projectPDCTM/PP/MAR/15251/99) and by two projectsintegrated in a French–Portuguese bilateral collabora-tion (PESSOA and ICCTI-IFREMER).

We would like to thank Jean-Marie Jouanneau andAnne de Vernal, for their valuable comments whichgreatly improved this manuscript and also WilliamFletcher for the English revision. We also gratefullyacknowledge Pierre Anschutz, Frans Jorissen, Jean-MarieJouanneau and Carlos Vale for the top core samplescontribution, Marie-Hélène Castéra for palynologicaltreatments and Michel Cremer and Sébastien Zaragozifor the core X-ray interpretations. Finally, we are gratefulto referees L. Dupont and H. Hooghiemstra for theirconstructive criticisms which greatly improve this paper.

This paper is Bordeaux 1 University, EPOC, UMR-CNRS 5805 Contribution no. 1605.

Appendix A. Supplementary data

Supplementary data associated with this article can befound, in the online version, at doi:10.1016/j.marmicro.2006.07.006.

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