Evidence of strong storm events possibly related to the little Ice Age in sediments on the...

Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2014) xxx–xxx

PALAEO-06799; No of Pages 7

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Palaeogeography, Palaeoclimatology, Palaeoecology

j ourna l homepage: www.e lsev ie r .com/ locate /pa laeo

Evidence of strong storm events possibly related to the little Ice Age insediments on the southerncoast of Brazil

F.M. Oliveira a, K.D. Macario a,⁎, J.C. Simonassi b, P.R.S. Gomes a, R.M. Anjos a, C. Carvalho c, R. Linares a,E.Q. Alves a, M.D. Castro a,d, R.C.C.L. Souza e, A.N. Marques Jr. e

a Instituto de Física, Universidade Federal Fluminense, Av. Gal. Milton Tavares de Souza, S/N, Niterói, 24210-346, RJ, Brazilb Núcleo de Estudos do Mar, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina, Florianópolis, 88040-900, SC, Brazilc Departamento de Ciências da Natureza, Universidade do Estado do Rio de Janeiro, Rua Santa Alexandrina, 288, Rio de Janeiro, 20261-232, RJ, Brazild Instituto Superior de Tecnologías y Ciencias Aplicadas, InSTEC, Quinta de los Molinos, Ave. Salvador Allende y Luaces, Plaza de la Revolución, Ciudad de La Habana, Cubae Departamento de Biologia Marinha, Instituto de Biologia Universidade Federal Fluminense, Niterói, RJ, Brazil

⁎ Corresponding author. Tel.: +55 2126295892.E-mail address: kita@mail.if.uff.br (K.D. Macario).

Please cite this article as: Oliveira, F.M., etsoutherncoast of Brazil, Palaeogeogr. Palaeoc

a b s t r a c t

Article history:Received 22 May 2013Received in revised form 22 February 2014Accepted 6 March 2014Available online xxxx

Keywords:Carbon and Nitrogen Stable IsotopesLittle Ice Age (LIA)Radiocarbon Accelerator Mass SpectrometrySouthern Brazilian CoastMarine shellsMarine sediments

Late Holocene environmental changes on the southeastern Brazilian coast were assessed using a high-resolutionpaleoproductivity proxy record from a sediment core collected at 14 m water depth in the Pântano do Sul Inlet.Mollusk shells from the corewere AMS dated, and sediment grain size, concentrations of organic carbon and totalnitrogen, and δ13C and δ15N values were determined to investigate changes in paleoceanographic and paleocli-matic conditions over the depositional period. Most of the parameters showed strong fluctuations in the depthinterval corresponding to the Little Ice Age, between 1560 and 1700 AD, that were marked by first an increaseand then a decrease of input of terrigenous sediments to the inlet. Proxies also indicate that sedimentary condi-tionsweremore stable, before and after this period. The strong sedimentary changes observed in the Pântano doSul Inlet may be related to climatic changes reported elsewhere in South America during 1550 and 1800 AD andto severe storm events associatedwith the enhanced cold fronts that occurred in the southern littoral region dur-ing this period.

The existence of late Holocene rapid climate shifts has become pro-gressively better documented during the last decade. During the LittleIce Age (LIA) (1400–1800 AD), extratropical NorthernHemisphere con-tinents experienced significant cooling. Both El Niño and the NorthAtlantic Oscillation–Arctic Oscillation were affected, leading to a stronglatitudinal gradient of temperature between the cooled North hemi-sphere and the heated tropics (Mann et al., 2009). The trade windstrengthened, the Intertropical Convergence Zone (ITCZ) shifted south-ward, and low latitude continental areas became more arid (Goniet al., 2009; Gutierrez et al., 2009). In such conditions, both the El-Niño–Southern Oscillation (ENSO) and the Indian Monsoon systemswere affected. Eastern Africa and Chile experienced wetter conditions,Benguela Current sea surface temperatures (SSTs) were cooler, andSouthern Africa experienced a cool and dry episode (Mayewski et al.,2004).

Knowledge about the effects of these climate shifts on the Atlanticcoast of South America remains limited, although several studies sug-

al., Evidence of strong storlimatol. Palaeoecol. (2014), h

gest that significant changes occurred in the coastal dynamics duringthe LIA. Arid conditions in low latitudes induced a low frequency of in-undation on the Amazonian coast, which also experienced a sea-levelregression (Cohen et al., 2005). The Antarctic Peninsula became cooland windy, the Patagonia Ice field increased (Davies and Glasser,2012; Aniya, 2013), and the Pacific upwelling weakened during theLIA (Gutierrez et al., 2009). In contrast, Souto et al. (2009) report in-creases in foraminiferal fluxes that suggest a gradual increase of upwell-ing in the southeastern Brazilian continental shelf from 1500 to 1830that appears to have been linked to regional atmospheric factors. Simi-larly, Mahiques et al. (2005), using SST reconstruction by alkenones,document an increase of the Cabo Frio upwelling in the last 700 years,likely due to intensification of atmospheric systems.

The present studywas carried out in the Pântano do Sul Inlet, whichis on Santa Catarina Island on the southern Brazilian coast (Fig. 1). Thepurpose of the study was to investigate late Holocene environmentalchanges on the southern Brazilian coast as recorded in a high-resolutionsedimentary sequence. Paleoproductivity proxies (organic carbonand nitrogen concentrations and isotopic compositions) togetherwith grain-size variations were used to evaluate temporal climatechanges that affected sedimentation patterns during the lastmillennium.

m events possibly related to the little Ice Age in sediments on thettp://dx.doi.org/10.1016/j.palaeo.2014.03.018

Fig. 1. Location of the Pântano do Sul Inlet on Santa Carolina Island, showing the coring site (star).

2 F.M. Oliveira et al. / Palaeogeography, Palaeoclimatology, Palaeoecology xxx (2014) xxx–xxx

1. Study area

The Pântano do Sul Inlet (PSI) is located on the south-facing oceanicside of the Santa Catarina Island (27°30′S–48°30′ W) on the southernBrazilian coast. The tidal regime is semidiurnal with an average rangeof 50 cm (Soriano-Sierra, 1988). The main oceanographic features ofPSI waters are defined by the five water masses that occur in the north-ernmost part of the arc-shaped Southern Brazilian Bight (SBB), which isalso known as São Paulo Bight (23°S and 29°S) (Zembruscki, 1979).These water masses are (i) Tropical Water (TW) that is characterizedby temperatures N20.0 °C and salinities N36.0; (ii) Coastal Water(CW)with temperatures N22.0 °C and salinities b35.0; iii) South Atlan-tic Central Water (SACW) with temperatures b18.0 °C and salinities34.4–36.0, (Valentin et al., 1987; Matsuura, 1996); (iv) Plata PlumeWater (PPW) that reaches the region from the Rio de La Plata to thesouth during winter; and (v) Subtropical Shelf Water (STSW), a coldwater with temperatures N14.0 °C and salinities 33.5–36.0 that origi-nates from a mixture of PPW and TW (Moller et al., 2008; Piola et al.,2008; Simonassi et al., 2010). Sedimentation processes on the innershelf are highly controlled by the PPW (Moller et al., 2008), and localand regional climate and hydrometeorological conditions are mainlycontrolled by the South Atlantic Convergence Zone (SACZ) (Carvalhoet al., 2011;Marengo et al., 2012). The climate in the region has a regulardistribution of rainfall throughout the year without a rainy season(Cruz, 1998).

The São Paulo Bight constitutes one of the most productive fishinggrounds of Brazil. Apart from local estuarine inputs from southernBrazilian lagoons, its biological productivity is mainly controlled bythe wind-dependent northward displacement of waters from theRio de La Plata (Moller et al., 2008). Nevertheless, the productivityof the SBB is also influenced by local upwelling, which is stronger

Please cite this article as: Oliveira, F.M., et al., Evidence of strong storsoutherncoast of Brazil, Palaeogeogr. Palaeoclimatol. Palaeoecol. (2014), h

in the northernmost part of the SBB near the Arraial do Cabo region(22°57′S–42°01′W).

The PSI is flanked by rocky shores on both sides. The rocky shore onthe eastern side, which is ~1000 m in length, plays an essential role inthe protection of the inlet from waves. Due to its location, the southwinds have a major influence on the oceanographic conditions (GallucciandNetto, 2004). The particular positioning of the PSI subjects it to south-ern fronts that play a major role in determining both oceanographic andmeteorological conditions (Campos et al., 1996). The shoreline of PSI con-sists of a beach and sand ridges with coastal vegetation typical of theAtlantic Brazilian seaboard (“restinga”), characterized by plants withhigh diversity of life forms and both C3 and CAM photosynthetic path-ways (Braz et al., 2013). The transitional area between the coastal plainand inland is covered by wetlands.

2. Methods

2.1. Sampling

Sediment sampling was carried out in 2008 in the PSI (Fig. 1). Thecore was collected in 14mwater depth with a 1m PVC tube (7.5 cm in-ternal diameter) by SCUBA diving at a location off Pântano do Sul beach(27°78′S–48°52′W). Special care was taken during sampling to keepsediment layers undisturbed. Two sediment cores up to 60 cm depthin the sediment were collected, and sliced into thin sections of approx-imately 1 cmwith a plastic cutter by extruding the sediment up throughthe core tube. One profile was used for grain size analyses and the otherone for radiocarbon dating and geochemical analyses. The sedimentsamples were transported to the laboratory in polyethylene bags andstored at 4 °C until analysis.

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2.2. Age determination

For radiocarbon dating, samples were prepared at the RadiocarbonLaboratory at the Universidade Federal Fluminense (LAC-UFF) in Brazilto be dated by AMS. Each sediment layer was screened for molluskshells under a microscope which were identified at the lowest possibletaxonomic level. The shells showed evidence of transportation andmostwere very fragmented, making identification difficult. Shell sampleswere etched with 0.5 M HCl to remove the outer layer, which couldbe contaminated. For each set of samples, calcite blanks and IAEA C2carbonate were prepared as control samples. Phosphoric acid wasinjected with a syringe into evacuated vials (10−3 Torr) to obtainCO2.

Gas sampleswere purified bymeans of dry ice/ethanol and liquid ni-trogen traps. Graphitization was performed using zinc and titanium hy-drate, with iron catalyst in Pyrex tubes in amuffle oven at 520 °C for 7 has described in Xu et al. (2007). Graphite targets were measured in anNEC 250 kV SSAMS compact system using the 1+ charge state. Typicalcurrentswere 50 μA 12C−1measured at the low energy Faraday cup. Theisotopic fractionation was corrected by measuring the δ13C on-line inthe accelerator. Background was measured using processed calciteblanks for carbonate samples. Calcite processed blanks yielded average14C/13C ratios of 7 × 10−13. Average machine background was 10−13

for unprocessed graphite. Accuracy was checked by measuring refer-encematerialswithin the 2 sigma range of consensus values. Calibrationwas performedwithOxford software Oxcal (BronkRamsey, 2009) usingthe marine13 curve (Reimer et al., 2013) with an offset of (8 ± 17) 14Cyr (Angulo et al., 2005) to account for local corrections for shell samples(Fig. 2).

Fig. 2. Individual calibration of dates in the OxCal software (Bronk Ramsey, 2009) using themarine13 curve (Reimer et al., 2013) with local marine reservoir correction ΔR= (8 ± 17)14C yr versus depth. Results for non-identified species samples are presented in gray andthose of known species samples are presented in black.

2.3. Grain size, isotopic compositions, organic carbon and nitrogenconcentrations

Grain-size analyses were performed using standard sieve (2 mm–

63 μm) and pipette techniques (b63 μm) after organicmatter destructionwith H2O2 (Suguio, 1973). Dried and homogenized sediment sampleswere acidified to remove carbonate and the carbonate-free residueswere weighed in tin capsules. The total organic carbon (TOC), nitrogen(TN) and their stable isotopes signatures were determined using aElementarVario EL Cube elemental analyzer (ElementarAnalysensystemeGmbH, Hanau, Germany) interfaced to a PDZ Europa 20–20 isotope ratiomass spectrometer (Sercon Ltd., Cheshire, UK) at the UC Davis Stable Iso-tope Facility, University of California Davis (SIF, 2013). C/N concentrationratios are expressed as molar. Isotopic values are expressed in delta nota-tion (δ) defined as parts per mil (‰) expressed relative to internationalstandards V-PDB (Vienna PeeDeeBelemnite) and air for carbon andnitro-gen, respectively (http://stableisotopefacility.ucdavis.edu/13cand15n.html). Detection limits for these determinations are 20 μg N and 100 μgC in natural abundance samples. Long term replicate analyses yield stan-dard deviations of 0.2‰ for 13C and 0.3‰ for 15N.

3. Results

3.1. Sedimentary environment

Sediments of the core are mostly sandy (70–90%) (Fig. 3a), and theaverage particle sizes varied from 0.1 to 0.4 mm, showing the PSI to bea high energy depositional environment. Silt and clay profiles aremarked by an increase from the core top to 12 cmdepth and by an irreg-ular downward decrease from this depth (12 cm) to the base of the core(Fig. 3b, c). In contrast, sand contents tend to increase with depth in thecore. These vertical variations in particle size suggest that tidal currentsandwave-energy regimes of the PSImight removemost of the fine frac-tions from the surface layers of bottom sediments (down to 12 cmdepth). The patterns showed by granulometry in the vertical profilesuggest three distinct sequence boundaries in the PSI core: (I) a toplayer (L1) from 0 to ~20 cm depth, marked by a silt and clay increase;(II) an intermediate layer (L2) from 20 cm to ~35 cm depth, markedby irregularities in both silt and clay contents; and (III) the bottomlayer from 35 and downwards (L3), characterized by increase in sandand high fluctuations in silt and clay contents (Fig. 3).

3.2. Sediment chronostratigraphy

The chronology was obtained from shell samples collected atspecific depths in the core. The types of shell found within thecore were both bivalves such as Anadaranotabilis, Cucculearca can-dida and Erodonamactroides and gastropods such as Tegulaviridula,Lotiasubrugosa and Fissurelarosea. Most of these mollusk shells arecharacteristically found in coastal sediments at water depths upto 50 m. Individual shells used for dating purposes are from differ-ent species, but all were from a shallow marine environment andwere therefore likely not to have grown in upwelling waters thatcould deliver aged carbon because upwelling is seasonal in this region.Radiocarbon dates and calibrated age intervals of shells are presentedin Table 1. Calibration was performed with Oxford software Oxcal(Bronk Ramsey, 2009) using the marine13 (Reimer et al., 2013) curvewith an offset of (8 ± 17) 14C yr (Angulo et al., 2005) to account forlocal corrections for marine samples. Fig. 2 shows the probability distri-butions for the calibrated ages. Results for non-identified species sam-ples are presented in gray and those of known species samples arepresented in black. No major differences are observed for shells of dif-ferent species in Layers 2 and 3.Moreover, the dispersion of the calibrat-ed results is not large among different depths, indicating a relativelyshort time scale event for most of the depth profile. Layer 1 contains a

Fig. 3. Vertical profiles of sand, silt and clay in the PSI core.

mixture ofmodern and of older shells thatmight have been transportedfrom other places.

3.3. Organic carbon and nitrogen concentrations and isotopic compositions

TOC and TN concentrations show similar variations in the profile andare marked by regular downward decreases from the top to 15 cm

Table 1LACUFF ID formollusk shell samples, calibration of dates in theOxCal software (Bronk Ramsey, 2ΔR = (8 ± 17) 14C yr, radiocarbon ages, depth within the core (uncertainty in depth is estima

Sample ID Cal AD min (2 σ) Cal AD max (2 σ) 14C Age y

LACUFF 12022 1851 Modern 32LACUFF 12021 1724 Modern 162LACUFF140013 1892 1944 124LACUFF 12020 1522 1676 124LACUFF140014 1646 1820 605LACUFF140015 1890 1977 165LACUFF140016 1675 modern 552LACUFF 12019 1501 1665 707LACUFF140017 1894 1942 114LACUFF 12018 1353 1496 114LACUFF140019 1467 1637 780LACUFF140020 1630 1827 610LACUFF 12017 1724 modern 481LACUFF140021 1637 1870 595LACUFF 12016 1482 1637 595LACUFF140022 1642 1833 600LACUFF140023 1668 modern 558LACUFF 12015 1636 1817 615LACUFF 12014 1334 1465 943LACUFF140024 1537 1801 652LACUFF12013 1522 1686 72LACUFF140025 1418 1631 832LACUFF12012 1480 1660 3565LACUFF140026 1536 1686 687LACUFF12011 1434 1563 225

depth (Fig. 4a, b) stabilizing throughout the core at 0.7 and 0.1 mg g−1,respectively. Below this depth, both TOC and TN concentrations start toincrease gradually down the core, forming two peaks around 21 cm and31 cmdepth. In this part of the core, TOC andTNconcentrations are on av-erage 10 and 20 times higher than those of the upper layer, and these ex-treme values are also coincident with higher values of δ13C and δ15N(Fig. 4c, d). Below the 31 cmpeak, TOC and TNprofiles gradually decrease

009) using themarine13 curve (Reimer et al., 2013)with localmarine reservoir correctionted in 0.5 cm) and taxon.

r BP Uncertainty (14C yr) Depth(cm)

77 5.64 Not identified111 7.52 Not identified36 9.40 Fissurella rosea36 9.40 Not identified28 13.16 Ostreidae37 15.04 Fissurella rosea35 15.04 Erodona mactroides29 15.04 Not identified35 16.92 Arca imbricata35 16.92 Not identified31 20.68 Chione cancellata32 20.68 Leptopecten bavayi30 20.68 Not identified39 22.56 Mytilidae39 22.56 Not identified32 24.44 Protothaca sp.42 31.96 Tellina sp.28 35.72 Not identified31 37.60 Not identified32 39.48 Felaniella viladerboana35 39.48 Not identified53 41.36 Bostrycapulus aculeatus40 52.64 Not identified28 56.40 Bostrycapulus aculeatus34 58.28 Not identified

Fig. 4. Vertical profiles of TOC, TN, the C/N ratio, δ13C, and δ15N, in the PSI core.

downward until 35 cmdepth. This “anomalous” depth interval (from~15to 35 cm) is also characterized by large fluctuations in silt and clay con-tents (Fig. 3). Below 35 cm depth, TOC and TN concentrations are stablealmost to the bottom of the core, diverging only in the deepest interval.TOC concentrations below 35 cm are on average two times higher thanin the topmost layer (Fig. 4a).

The patterns exhibited by themeasured productivity parameters re-inforce the three distinct sequences in the PSI core described by thegranulometric parameters. In this case, the top layer (L1), from 0 to20 cm depth, is marked by a gradual decrease of TOC and TN concentra-tions and large δ13C and δ15N variations, all being features possibly influ-enced by diagenetic processes. The L2 intermediate layer (between20 cm and 35 cm depth) shows extremely high fluctuations in all pa-rameters, and the bottom layer (L3) is more stable but has relativelyhigher TOC concentrations and smaller variations in δ13C values (Fig. 4).

4. Discussion

4.1. Preservation of C, N and isotopic compositions

The systematic changes observed in grain size parameters; elemen-tal C, N and their isotopic abundances in the core may reflect temporalchanges in the coastal dynamics of the PSI environment. Variations inC and N abundances in sediments can be related to temporal changesin rates of algal production in the water column and in delivery of or-ganic matter from catchments, to dilution effects of other detrital mate-rials, to bacterial decomposition of organic matter within the watercolumn and sediment, and to preservation within sediment layers(Emerson et al., 1985; Meyers and Ishiwatari, 1993). The C and N com-positions of sediments of coastal areas seem to be particularly influ-enced by two general sources—local photosynthetic production in thewater column itself and delivery of terrestrial detrital materials by run-off and rivers. Thus, sedimentary δ13C signaturesmay be determined bythe mixing of marine and terrestrial particulate organic carbon (POC)that has originated from dissolved inorganic carbon (CO2 + HCO3

−) as-similation by phytoplankton, by changes in themix of terrestrial carbonsupplied from C3 and C4 plants, and by post-depositional changes

(Bratton et al., 2003). Mixing of terrestrial and marine organic δ13Cend members would result in values between −28%o (C3 plants) and−20%o (marine phytoplankton). Thus the δ13C of the PSI sediments,ranging from−23 to−20%o, appears to bemostly indicative of marinePOC, but it is sometimes somewhat overprinted by a terrestrial C3source. In contrast to the δ13C values, the sediment δ15N values aremore related to N cycling in the water and in surface sediments ratherthan terrestrial or marine pools. An increase in 15N/14N ratios canoccur during early burial, and the extent of fractionation is related towater depth and oxygen exposure time, but the degree of alteration isusually uniform through time (Robinson et al., 2012).

Despite the possible differences in sources and biogeochemical pro-cesses, our results suggest that the organic matter source signatures arewell preserved in the PSI core. In part, this assumption is based on var-iations of the C and N isotopic ratios. The diagenetic alteration of N issimilar to that of C, resulting in δ15N (or δ13C) values becoming isotopi-cally larger in the bulk sediment inasmuch as 14N (or 12C) would bepreferentially removed during decomposition of organic matter (Sachsand Repeta, 1999). This change is not found for the PSI core becauseboth δ13C and δ15N values decrease concomitantly in the first 10 cmdepth, indicating no preferential loss of 14N. Additionally, vertical pro-files of both isotopic ratios are generally similar in the whole core. Onthe other hand, our interpretation about the good preservation of or-ganic matter in the PSI core is based largely on C and N concentrations.Another aspect observed in several sedimentary environments is thatpreferential mineralization of N relatively to C can occur during earlydiagenesis, which would lead to increased C:N ratios (Meyers andIshiwatari, 1993). This change is also not observed in the PSI core, be-cause C and N concentrations decrease proportionally from 0 to 15 cmdepth and covary through the whole core (Fig. 4). If we assume thatthe small decreases in carbon and nitrogen concentrations in theupper layers are related to diagenesis, these processes affected thetwo elements with the same intensity, which is not usual (e.g. Meyersand Ishiwatari, 1993). All these findings reinforce the conclusion thatdiagenetic alteration of organic matter is minimal in the PSI core.

A striking feature in the organic matter proxy signatures of the PSIcore is the strong variations in the L2 layer. In this part of the core,

Fig. 5. Crossplot of organic δ13C values versus C/N ratios in the PSI core.

TOC and TN concentrations are marked by two successive downwardincreases and decreases. These consistent patterns are also reflected inthe δ13C and δ15N signatures. Higher TOC and TN concentrations occurtogether with higher δ13C and δ15N values (Fig. 4a, b, c, d), indicatingthat gradual and significant changes from terrestrial to marine sourcesof organic matter occurred in the PSI. In contrast, C:N ratios tend to in-crease gradually downward in the L2 layer, changing from 3 to 21 andindicating a larger input of terrestrial organic matter deeper in the PSIcore. The C:N ratios and the δ13C of the PSI core are shown as a crossplotin Fig. 5 in order to better identify changes in organic matter sources(Meyers, 1994). Values of these parameters from the L2 and L3 layersform separate clusters indicating larger contributions frommarine phy-toplankton and C3 influences, respectively, in these core sections.

4.2. Age model and storm events

The curiously strong shifts in geochemical profiles in the L2 layer arepartially explained by the 14C chronology of the PSI core (Fig. 2). Deter-mining “when” these strong changes occurred enables us to hypothe-size about “why” they occurred. These geochemical shifts correspondto unexpected age inversions in L2 layer, which are coincident withshifts in particle sizes, CaCO3 and TOC, TN, and δ13C and δ15N profiles.These changes collectively suggest that major reworking of older

Fig. 6.Modelled ages for layers L2 and L3, considered as sequent

sediments into the sequences occurred several times during fairlyshort time intervals.

In order to understand better the period of sediment accumulationbetween 20 and 35 cm, we assumed two sequential phases in the cali-bration software: (a) before and (b) during such events. Calibrationwas performed with Oxford software Oxcal (Bronk Ramsey, 2009)using curve marine13 (Reimer et al., 2013) with an offset of (8 ± 17)years (Angulo et al., 2005) to account for local corrections. Accordingto this model, the transition from L3 to L2 events lays between 1560and 1700 AD (Fig. 6), a time of an anomalously cold and less humid pe-riod of climate history known as the Little Ice Age (LIA). The LIA is one ofthemost prominent examples for a short term climatic anomaly duringthe late Holocene, beginning about 1550 AD and ending between 1850and 1890 AD. Most of the conventional records for the LIA were obtain-ed in the Northern Hemisphere, especially in Europe and North America(Lamb, 1965; Grove, 1988; Fagan, 2000; Glaser, 2001). However, thiscold period has been also recognized in South America (Politis, 1984;Cioccale, 1999), and recent studies have shown a climatically anoma-lous period between 1550 and 1800 AD for southern South America,where the Southern Hemisphere winds play an important role in con-trolling precipitation patterns and variability. With regard to the LIA inBrazil, studies performed in bothnortheastern and southeastern regionsin mangrove areas report that the coast experienced a sea-level regres-sion and/or drier conditions with less rainfall during the LIA (Cohenet al., 2005; Pereira et al., 2009). Based on these considerations and onresults from the present study, we hypothesize that reworking of theL2 layer sequences of the Pântano do Sul Inlet core could be related tointensification of meteorological processes that are presently commonin this area. Cold fronts coming from the south can influence sea condi-tions, increasing the size of the waves in the PSI, which is especially vul-nerable to suchwaves because it faces south. It is reasonable to supposethat during the LIA, the intensity and the frequency of cold fronts wereenhanced and sowere the height ofwaves. Events of severe stormswithhigherwaves striking the PSI areamay have encroached into inner litto-ral areas, depositingmarine sediments in the coastal area. In thework ofAbrantes et al. (2005), it was shown that even at 90mdepth evidence ofa tsunami in the coast of Portugal could be found in a sediment core. Onesuch event, with smaller magnitude, occurred during summer 2009 atthe Pântano do Sul Inlet, and videos are available on the internet(Youtube, 2009a,b).

5. Conclusions

Our study of geochemical proxies and granulometry of sediments inthe Pantano do Sul Inlet has identified three layers in the 60 cmcore that

ial phases using the OxCal software (Bronk Ramsey, 2009).

we collected at 14mwater depth: L1 between 0 and 20 cm; L2 between20 and 35 cm, and L3 from 35 cm and downwards. The L3 layer is char-acterized by organicmatter from terrestrial sources as indicated by highC:N ratios, and it has large values of the sand fraction. The L2 layer ischaracterized by anupwarddecrease in C:N ratios and largefluctuationsin grain size fractions and TOC and TN concentrations. The L1 layer ischaracterized by low and stable C:N ratios indicating marine sourcesand by large values of the silt and clay fractions. The chronology of thesediments in the Pântano do Sul Inlet was obtained from AMS datingof mollusk shell samples collected in the core. Results of dating of theshells indicate that several age inversions occur in both the L1 and L2layers. According to the age calibrationmodel, assuming two sequentialphases (L3 and L2) in the OxCal calibration software, the transition be-tween L3 and L2 falls between 1570 and 1700 AD,which corresponds tothe anomalously cold and less humid period of climate history known asthe Little Ice Age. The fluctuations in geochemical proxies, grain size,and sediment ages are evidence of severe storms with higher wavesimpacting the Pantano do Sul Inlet and that may have encroached intoinner littoral areas during the Little Ice Age.

Acknowledgments

The authors would like to thank FINEP, CNPq, CAPES and FAPERJfor the financial support and CIRAM/EPAGRI-SC for collaboration. Weare grateful to the two reviewers for their valuable comments andsuggestions.

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