Late Quaternary sedimentation patterns on the Meriadzek Terrace, Bay of Biscay (ESSCAMP 02 core: 47°N 9°W

ELSEVIER Marine Geology 152 (1998) 57–73

Late Quaternary sedimentation patterns on the Meriadzek Terrace,Bay of Biscay (ESSCAMP 02 core: 47ºN 9ºW)

Neven Loncaric a,*, Gerard A. Auffret b, Fatima Abrantes a, Jaco H. Baas c, Luis Gaspar a,Claude Pujol d

a Instituto Geologico e Mineiro, Departamento de Geologia Marinha, Estrada da Portela, Zambujal, Apartado 7586,2720 Alfragide, Portugal

b Departement DRO=GM, IFREMER, B.P. 70, 29280 Plouzane cedex, Francec GEOMAR, Research Center for Marine Geosciences, Wischhofstr. 1–3, 24148 Kiel, Germany

d Universite de Bordeaux I, Departement de Geologie et Oceanographie, URA 197, 33405 Talence cedex, France

Received 24 January 1998; accepted 26 March 1998

Abstract

Foraminiferal assemblage changes, size and mineralogy of lithic grains, oxygen isotopes, CaCO3, and dolomite contentwere studied along a 9-m-long core from the Meriadzek Terrace to gain insight into climate, productivity, and sedimentsource changes at this part of the Northeast Atlantic margin during the late Quaternary. An age model has been generatedon the basis of radiocarbon dating, downcore foraminiferal assemblages, and Ž18O values. High sedimentation rates atthis site allow very detailed records for the last glacial period down to late isotopic stage 3. Sea surface temperature(SST) inferred from the foraminiferal assemblages, Ž18O curve, and the temperature estimation by the SIMMAX analogtechnique reveal three distinctive periods during isotopic stage 2, with late stage 2 (15.3–13.4 ka) being the coldest periodof the last 26 ka. A northward retreat of the polar front at 13.4 ka based on the SST record coincides with the strongestpeak of primary productivity as indicated by the foraminiferal fluxes. Levels rich in large lithic grains (LLG) interpretedas ice-rafted debris (IRD) correspond to periods of low SST and are coeval with Heinrich layers 1, 2 and 3. However, thehematite-stained quartz found in the detrital fraction and the scarce dolomite and detrital carbonate content in our corepoint to an Iceland and=or Fenno-Scandian rather than a Laurentian or Greenland origin of this material. 1998 ElsevierScience B.V. All rights reserved.

Keywords: late Quaternary; Bay of Biscay; Meriadzek Terrace; foraminiferal fluxes; SST

1. Introduction

One of the major objectives of the EuropeanNorth Atlantic Margin (ENAM) project was to study

Ł Corresponding author. Fax: C351 (1) 471-9018; E-mail:[email protected]

the evolution of the sedimentary fluxes along theeastern North Atlantic European continental marginfrom Norway to Portugal. Much work has been doneat both ends of this north–south transect (e.g. thisissue), but the central part, between 43ºN and 60ºN,has been studied only to a limited extent. ESSCAMPcore 02 (Fig. 1), taken on the Meriadzek Terrace(47º27.50N; 8º32.70W at 2192 m depth), provides

0025-3227/98/$ – see front matter 1998 Elsevier Science B.V. All rights reserved.PII: S 0 0 2 5 - 3 2 2 7 ( 9 8 ) 0 0 0 6 4 - 4

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Fig. 1. Location of the ESSCAMP 02 core (depth 2192 m; length 905 cm; latitude 47º27.50N; longitude 8º32.70W) in relation to regional bathymetryand geographic features. Inset: surface current system of the area; Gulf Stream Branch (GSB); Winter Iberian Current (WIC). GSB and WIC arrows arepresent-day currents after Keffer et al. (1988) and Haynes and Barton (1990) and bold arrows are currents during the LGM after Pantin and Evans (1984).

N. Loncaric et al. / Marine Geology 152 (1998) 57–73 59

therefore an important link between the northern andthe southern pole of the ENAM studies.

The goal of our study is to gain insight intochanges of climate, productivity, and sedimentsources on this part of the Celtic margin duringthe late Quaternary. High sedimentation rates (upto 112 cm=ka) allow the establishment of a verydetailed record of these changes over the last 26 ka.

2. Morphological and environmental setting

The Meriadzek Terrace, bounded by the north-east–southwest trending Shamrock and Black-Mudcanyons, constitutes an outstanding topographic fea-ture at the southern limit of the Celtic margin. Thenorthern, shallower part of the terrace, from wherethe piston core ESSCAMP 02 was retrieved on boardR=V l’Atalante (Fig. 1), is bathed by North AtlanticDeep Water (NADW) (Tchernia, 1969, in: Auffretand Sichler, 1982). As inferred from the texturalparameters of the surface sediments, this area corre-sponds to a low-energy zone, with maximum bottomcurrents flowing northwards (Auffret et al., 1975;Auffret and Sichler, 1982). The Meriadzek Terrace ispresently characterized by low terrigenous supply incontrast to the south Biscay Bay margin marked bylarge terrigenous input (Cremer et al., 1992). Thus,the ESSCAMP 02 site should be characterized byrelatively undisturbed and continuous hemipelagicsedimentation.

The present surface current system in the areais dominated by the northeast flowing Gulf Stream,which diverges into two branches roughly off Ireland(Keffer et al., 1988). One branch flows into the Bayof Biscay (Fig. 1) and another flows northeastwardalong the Irish margin. Haynes and Barton (1990)observed the existence of a warm poleward currentflowing along the Iberian coast during autumn andwinter. This poleward-flowing current is suppressedduring the summer when the wind-driven upwellingoccurs along the Portuguese coast.

Several authors noticed the significance of cli-matic variations as a factor influencing the sedimentdistribution in the Bay of Biscay, either directly orthrough oceanic circulation, eustatic variations, andfluvial input (e.g. Grousset, 1977; Cremer et al.,1992; Auffret et al., 1996a). The CaCO3 contents at

the regional scale display a clear latitudinal gradientaccording to the mean polar front position and inten-sity of carbonate biogenic production, but could alsobe related locally to reworking by bottom currents(Cremer et al., 1992).

The Quaternary foraminiferal assemblages of thearea were also subject of numerous studies (e.g. Pu-jol, 1980; Caralp et al., 1982; Caralp, 1985; Pujol andDuprat, 1985) and the assemblages composition hasbeen used as a tool for deciphering the local stratig-raphy. Pujol (1980) studied the coiling directionof three planktic foraminiferal species, Neoglobo-quadrina pachyderma (Ehrenberg), Globorotalia hir-suta (d’Orbigny) and Globorotalia truncatulinoides(d’Orbigny), and distinguished four different strati-graphic periods in the last 18,000 years. The Ž18Orecord and the coiling direction of N. pachydermaformed the stratigraphic framework in Caralp’s studyof sediments from the Bay of Biscay older than theLast Glacial Maximum (LGM) (Caralp et al., 1982).

Also on the base of foraminiferal assemblages,the CLIMAP project members (1976) and Ruddimanand McIntyre (1977) located the polar front duringthe LGM ca. 2–5º south of the Meriadzek Terrace.

During glacial times, the Gulf Stream was shiftedsouthward from its present position; at the LGM itflowed approximately parallel to the 40ºN latitude,towards the Iberian Peninsula (Keffer et al., 1988).Robinson et al. (1995) suggested the existence ofthe southwest-flowing Norwegian Sea Current dur-ing the LGM carrying drifting icebergs, between theFaeroe Islands and Iceland. After the anti-clockwisespin through the central North Atlantic, this cur-rent approaches the European margin as the North-east Atlantic Current. Based on the observations ofRuddiman and McIntyre (1977), Molina-Cruz andThiede (1978), and Pantin and Evans (1984), theBay of Biscay was, during glacial times, exposedto the northeast-flowing Iberian Current (IC), which,after entering the Bay of Biscay, turned clockwiseand flowed back southward along the Iberian coast(Fig. 1). Pantin and Evans (1984) have suggested theexistence of a divergence zone west of the CelticSea between the IC and the Northeast Atlantic Driftflowing northward along the Irish margin.

During the last two decades, beginning with thepioneer works of Kudrass (1973) and Ruddiman andMcIntyre (1977) till the more recent papers of Hein-

60 N. Loncaric et al. / Marine Geology 152 (1998) 57–73

rich (1988), Bond et al. (1992), Grousset et al. (1993),Revel et al. (1996), Auffret et al. (1996b), and Le-breiro et al. (1996) among others, many sites of ice-rafted debris (IRD) have been recognized in the NorthAtlantic. This ocean-wide IRD input occurred at spe-cific, short time intervals fed by the huge glacier in-stability. The maximum deposition occurred at thesouthern limit of the cold surface waters between45º and 50ºN, but IRD have also been reported asfar south as 37ºN (Baas et al., 1997; Zahn et al.,1997). Although within the latitude of Ruddiman’sIRD belt, little has been published about IRD distri-bution within the Bay of Biscay.

3. Material and methods

The upper 148 cm of the 1053-cm-long core (10cm in diameter) consists of coarser grain sediments,initially described as turbiditic, but later identifiedas a coring artifact. Therefore, this part is not con-sidered in our study and the former 148-cm-level isassumed to be the core top (D0 cm). The remain-ing 905 cm of the core are hemipelagic sedimentswithout disturbances or apparent discontinuities. Thecore was subsampled every 10 cm for isotope stud-ies and every 20 cm for the establishment of theforaminiferal assemblages, grain size analysis, andCaCO3 content. Samples were prepared accordingto the following procedure: each sample, contain-ing ca. 20 cm3 of sediment (10 cm3 for the isotopeanalysis) was treated with sodium polymetaphosphateand then washed and sieved through a 63-µm meshsieve. The sand fraction (>63 µm) was oven-driedat 40ºC, sieved through a 150-µm mesh sieve, andweighed. Forams were picked dry from a split fractionof the>150-µm size fraction, large enough to provideca. 300 foraminifera per sample. All picked foramswere identified, counted, and stored in slides. Theforaminiferal species determination is mainly basedon the taxonomy of Kennett and Srinivasan (1983).

To quantify dissolution rates of foraminiferaltests, the core was divided into eight units, basedon the relative abundance of N. pachyderma (s.). Foreach unit one sample was chosen to evaluate themass percentage of broken foraminiferal test parti-cles compared to whole tests. From a split fractioncontaining ca. 300 whole planktic foraminiferal tests,

all broken particles and whole tests were picked,each category weighed, and expressed as percentage.Ž18O analysis was performed on the planktic

foraminiferal species Globigerina bulloides. In inter-vals containing insufficient numbers of G. bulloides(112–312 cm and 842–904 cm), Neogloboquadrinapachyderma (s.) was picked. Where G. bulloides andN. pachyderma (s.) were both present, both specieswere analyzed so that the N. pachyderma (s.) Ž18Ovalues could be converted to the standard isotopiccurve of G. bulloides. All picked specimens werecleaned by ultrasound to separate impurities fromthe internal parts of the foraminiferal tests. Ž18Oanalysis was not performed on benthic foraminiferaltests due to their very low abundance.

To determine the approximate stratigraphic posi-tion of the upper part of our core, following Pujol(1980)’s Holocene stratigraphy of the Bay of Bis-cay, we have studied the coiling directions of theplanktic forams N. pachyderma, G. hirsuta, and G.truncatulinoides.

The age model of the core ESSCAMP 02 (Ta-ble 1) is based on five AMS14C-dated control points.AMS14C dating was performed on tests of N. pachy-derma (s.) except for the uppermost sample wheretests of N. pachyderma (d.) have been used. All14C dates are corrected for the reservoir effect of�400 years (Bard, 1988). The quantitative analysisof foraminiferal assemblages and analysis of oxygenisotopes from tests of planktic foraminiferal speciesG. bulloides and N. pachyderma (s.) complementedthe age model. Ages between control points areobtained by linear interpolation.

The percentages of carbonates (calcite anddolomite) were determined following the gasometricmethod of Hulsemann (1966) in combination withX-ray diffraction. Sand, silt, and clay percentageswere calculated by the traditional sieving and pipet-ting methodologies (Folk, 1980).

The large lithic grains (LLG) determination(>150 µm) and mineralogical analysis of six sam-ples corresponding to the maximum in the detritalgrain record have been performed by binocular mi-croscope observation.

For the quantitative palaeo-sea surface tempera-ture (SST) estimation, the modern analog techniqueSIMMAX was applied. Developed by Pflaumann etal. (1996), this technique uses the similarity index


Table 1The stratigraphic model for the ESSCAMP 02 core with the summary of results presented in Fig. 2

Depth interval Stratigraphic level Characteristics

0–52 cm Holocene – depleted Ž18O values– high values of CaCO3 and number plankton=g; onset of decreasing trends– absence of polar species– rel. abundant subtropical species

8.0 ka – low dolomite content; increasing trend

52–67 cm Termination Ib – rapid increase in Ž18O values– rapid decrease in CaCO3 percentages; first negative spike– still relative high abundance of subtropical species; decreasing trend– first appearance of Arctic species

10.0 ka – increase in dolomite % till its main value

67–90 cm Younger Dryas – stagnation in increasing trend of Ž18O curve; first max. at 72 cm– stagnation of decreasing trends of CaCO3 and number plankton=g sed.– Arctic species compose ca. 20% of planktic assemblages

11.6 ka – strong decreasing trend for subtropical species

90–122 cm Termination Ia – similar trends like in T Ib for CaCO3 and Ž18O– decrease in number plankton=g sed.– very rapid increase in Arctic species; at the base of T Ia they compose 95%

of planktic assemblages– subtropical species still present; they disappear at the base of T Ia

13.4 ka – increase in number of LLG; peak at the base of T Ia

122–322 cm stage 2 upper: – dominated by N. pachyderma (s.) (>95%)– absence of subtropical species– double-peaking LLG curve– drastic decrease in numb. plankton=g sed.; absolute minimum for the whole

period covered in the study at 202 cm– Ž18O curve reached the highest value with max. at 142, 222 and 292 cm

15.3 ka – low values for CaCO3

322–622 cm middle: – reappearance of subtropical species with spike at 522 cm– polar species less abundant– no LLG– Ž18O lower than in upper part– more plankton=g than in upper stage 2

19.8 ka – LGM probably at ³550 cm622–782 cm lower: – two significant peaks in abundance of Arctic species (>95%) followed by

peaks in number of LLG and in Ž18O, and negative spikes of subtropical23.7 ka species

below 782 cm stage 3 – presence of subtropical species– low abundance of N. pachyderma (s.) with increasing trend downwards– peak in abundance of LLG followed by peak in Ž18O and N. pachyderma (s.)– slightly increased numb. plankton=g sed

based on the scalar product of the normalized fau-nal percentages and weighing of the best analogsites by their inverse geographical distance from thelocation of the subject site. In contrast to the clas-sical CLIMAP transfer technique (Imbrie and Kipp,1971), this method can also be applied at the re-gional scale and is quite insensitive to dissolution

problems. In our study, a set of 738 samples ofplanktic foraminiferal percentage data from the At-lantic between 40ºS and 87ºN is used. From thatdata set, the five best analogs with a similarity indexbetween 91 and 100% are chosen.

The data gathered in the study are availablefrom the first author upon request and it is go-


ing to be accessible via the Internet address http://www.marine.ie.

4. Results

4.1. Stratigraphy

The stratigraphic model presented in Table 1, gen-erated using the AMS14C-dated control points com-bined with the Younger Dryas (YD) and LGM datesinferred from the isotopic record for G. bulloidesand N. pachyderma (s.) and foraminiferal assemblagecurves, agrees well with the standard oxygen isotopicstratigraphy of Prell et al. (1986), Bard et al. (1987)and Martinson et al. (1987). However, the very highsedimentation rate (up to 112 cm=ka) observed be-low 122 cm (D13.4 ka) permits a much more detailedcurve for the stage 2 interval. In this interval, the res-olution for the isotopic record is ca. 100–250 years,and 200–500 years for other measurements.

We are aware of the fact that the linear interpo-lation between stratigraphic control points does notprovide a perfect solution for calculating sedimen-tation rates. Nevertheless, considering the availabledata, it appears to be the most convenient method.

4.2. Biogenic and terrigenous components

Planktic foraminiferal species identified in thisstudy are grouped according to their ambient tem-perature preferences following works of Be andTolderlund (1971) and Imbrie and Kipp (1971)(Table 2). The downcore distribution of these groups,together with the Ž18O curve of G. bulloides and N.pachyderma (s.), the percentage of total CaCO3 anddolomite, number of planktic foraminifera per gram

Table 2Bioclimatic assemblages of the planktic foraminifera after Beand Tolderlund (1971) and Imbrie and Kipp (1971)

Bioclimatic group Species

Arctic Neogloboquadrina pachyderma (s.)Subarctic Neogloboquadrina pachyderma (d.)

Globigerina bulloidesGlobigerina quinqueloba

Subtropical Globigerinoides ruberGlobigerina falconensis

of sediment, the relative abundance of lithogenicgrains larger than 150 µm, and the lithology arepresented in Fig. 2. Table 1 presents a detaileddescription of these measurements for each strati-graphic interval. Sediments of the ESSCAMP 02core (Fig. 2a) are essentially calcareous mud withminor variations in lithology.

The relative abundance of benthic species is low,ranging between 0.3 and 28.5%. The only twospecies appearing in abundance higher than 2%are Globobulimina affinis (d’Orbigny) (between 14.4and 13.7 ka with a maximum in relative abundanceof 9.2% at 14.3–14.2 ka) and Cassidulina leavigata(d’Orbigny) (between 20.1 and 15.2 ka: double-peaking at 19.8 ka and 16.2–15.3 ka with relativeabundance of ca. 21.1 and 25%, respectively).

The mass percentages of broken tests from eightchosen levels are low, ranging between 3 and 20.5%(on average ca. 9%). Intervals with high abundanceof N. pachyderma (s.) have, on average, a lowerpercentage of broken tests. That result was expectedsince N. pachyderma (s.) belongs to the group ofspecies more resistant to dissolution and mechanicaldestruction effects (Sautter and Thunell, 1991).

The increase in the number of IRD follows theincrease in Ž18O values and increase in relative abun-dance of the Arctic species (N. pachyderma (s.))(Fig. 2). Mineralogy of the IRD shows no obviousdifferences from peak to peak (Fig. 3). In general,the number of red, hematite-stained quartz grains isrelatively high, while the detrital carbonate grainsare nearly absent.

The dolomite record of the core is monotonous. Itranges between 3 and 5% and shows no correlationwith the IRD curve (Fig. 2) or any other measuredparameter.

4.3. Palaeotemperature estimates

As expected, the SIMMAX SST estimate agreeswell with the relative abundance of the Arcticforaminiferal species N. pachyderma (s.) (Fig. 4).Intervals with a very high abundance of this plank-tic species (>95% at 15.0–13.4 ka, 20.8 ka and22.8–22.3 ka) have an estimated SST of �0.3 to1.3ºC (mean SST 0.3ºC) for winter and 3.9–5.3ºC(mean SST 4.2ºC) for summer. For the interval be-tween 20.6 and 15.3 ka, the estimated temperatures


are much higher (mean winter SST 9.6ºC; meansummer SST 14.4ºC) and are characterized by verystrong fluctuations; the SST range lies between 3.4and 13.9ºC in winter, and 8 and 19.4ºC in summer.All IRD spikes coincide with low SST: between0ºC in winter and 4ºC in summer. The seasonality(difference between mean summer and mean wintertemperature) is always higher in the warmer periods(5.2ºC in the interval 2.0–12.7 ka; 4.8ºC in the inter-val 15.3–20.6 ka) than in the cold periods (2.9ºC at9.3 ka; 4.0ºC in the interval 13.4–14.9 ka).

5. Discussion

5.1. Preservation of foraminiferal tests

One might argue that the abundance of certainspecies in the sediment reflects a partial dissolu-tion effect rather than the composition of livingassemblages. The low mass percentages of the bro-ken test particles, with slightly increased values inintervals marked by low abundance of N. pachy-derma (s.) and dominance of less solution-resistantspecies, argues against partial dissolution and its sig-nificant imprint on the foraminiferal assemblages inthis core. Furthermore, the dominance of an Arcticspecies, not abundant at present times, points to aclimatic shift rather than a dissolution effect. An-other, although less quantitative, argument againstsignificant foraminiferal dissolution effects is the ex-perience of ultrasound cleaning. Foraminiferal testswere cleaned following the standard procedure (timeinterval and power level) that usually produces somedamage to tests from the Portuguese margin samples(Otero, pers. commun., 1995); in our study it did notproduce any damage. According to several authors(e.g. Sarnthein et al., 1982; Crowley, 1983) the CCDshallowed during the glacials, but apparently wasnever shallower than 2200 m, the depth of the ESS-CAMP 02 core, and thus it could not have influencedthe preservation of calcareous foraminiferal tests inthis core.

5.2. Sea surface temperature reconstruction

The relative abundance of N. pachyderma (s.) de-fines very distinctive intervals with either a very low

or very high number of specimens. Since this plank-tic foraminifer belongs to the cold water speciesand prefers SST between 0 and 5ºC (Be and Told-erlund, 1971), the intervals where it is dominantcan be interpreted as periods of very low SST. Lowsurface water temperature might be due to severecold climate and=or to significant melt water input.To distinguish these two signals, Bond et al. (1992)and Labeyrie et al. (1995) compared an independentSST record (composition of planktic foraminiferalcommunities can be used as one) to the plankticforaminifers Ž18O record. Negative Ž18O spikes atperiods of low SST were interpreted as salinity dropsdue to large inputs of Ž18O depleted melt water.

In this core, with the exception of two smallnegative Ž18O peaks during the upper stage 2, allthe intervals with high abundance of N. pachyderma(s.) correspond to heavier Ž18O values (Fig. 4). Eventhough meltwater input might have occurred, produc-ing a negative shift on the Ž18O record, its magnitudeis likely to have been smaller than the positive shiftcaused by the SST decrease.

The SST record of the Meriadzek Terrace asinferred from these parameters and the SIMMAXtemperature estimation for the Holocene, YoungerDryas and both Terminations shows the expectedhistory. The coldest period within the last 26 kaoccurred between 15 and 13.4 ka, with a meanwinter temp. of 0.3ºC and a mean summer temp. of4.2ºC. For the isotopic stage 2, three subperiods canbe distinguished (see Table 2). The coldest periodoccurred during late stage 2. The middle part ischaracterized by strong and abrupt oscillations andhigher mean SST, while early stage 2 is characterizedby two remarkable cold events which reach thelowest temperatures comparable to those during theperiod of 15–13.4 ka.

Palaeo-SST at LGM estimated by the SIMMAXmodern analog technique for the ESSCAMP 02 siteagrees approximately with the summer SST mapof the North Atlantic at LGM created by CLIMAPproject members (1976). However, according to theSIMMAX estimate, SST increases abruptly immedi-ately after the LGM (Fig. 4).

Labeyrie et al. (1995) estimated SST on twoNorth Atlantic cores using the classic Imbrie andKipp (1971) method: core SU 90-08 (43ºN; 30ºW)situated close to the LGM polar front position as

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Fig. 2. (a) Summary of planktic Ž18O, CaCO3 and dolomite, foraminiferal and lithic data plotted vs. depth. Five AMS14C-dated stratigraphic control points are marked in graph 1.Bioclimatic groups of planktic forams used in graphs 4 and 5 are listed in Table 2. The relative abundance of lithogenic grains larger than 150 µm (graph 6) defines IRD peaks.Depth of lithological boundaries on the right side of the lithological column is given in cm.

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57–7365Fig. 2. (cotinued). (b) Same data of (a) plotted vs. age.


Fig. 3. Mineralogical composition of the most significant IRD spikes. Number of counted grains: 142 cm, n D 217; 302 cm, n D 213;562 cm, n D 219; 642 cm, n D 235; 722 cm, n D 217; 866 cm, n D 209.

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Fig. 4. Sea surface temperature indicators (planktic Ž18O curve, planktic foraminiferal assemblage composition, and SIMMAX temperature estimations) compared with the distributionof IRD spikes. Bioclimatic groups of planktic forams used in graphs 2 and 3 are listed in Table 2. The temperature estimations in graph 4 are produced by the SIMMAX modernanalog technique (Pflaumann et al., 1996); dw D distance weighted SST estimate. (For detailed explanation and discussion see Pflaumann et al., 1996.)


defined by the CLIMAP project members (1976),and core SU 90-39 located ten degrees further north(53ºN; 22ºW) (fig. 1 in Labeyrie et al., 1995). TheESSCAMP 02 core (47ºN; 9ºW) is placed exactlybetween these two cores. Labeyrie’s northern coredoes not show many temperature oscillations duringstage 2. SST is low, constant, and similar to theESSCAMP SST estimated for the late stage 2. CoreSU 90-08 shows oscillating SST with a trend similarto that of the ESSCAMP 02 core. Nevertheless, themean ESSCAMP estimated temperature oscillateswith a larger amplitude: for late stage 2, ESSCAMPSST are ca. 3ºC lower than at SU 90-08, while forthe middle stage 2 they are ca. 2ºC higher.

Based on this record, the CLIMAP polar frontposition, south of the Meriadzek Terrace (CLIMAPproject members, 1976; Ruddiman and McIntyre,1977), must in fact have been situated in the vicinityof the ESSCAMP 02 during early and middle stage2 (23.7–15.3 ka), causing the large SST oscillationsobserved at our station. However, the similar temper-atures observed at the ESSCAMP 02 and core SU90-39, situated far behind the polar front, may beindicative of a southward shifting during late stage2 (15.3–13.4 ka). A northward retreat of the polarfront from the Meriadzek Terrace is likely to be syn-chronous with the onset of an increasing SST trendafter 13.4 ka.

5.3. Ice-rafted debris record

Layers enriched in LLG in the North Atlantichave often been interpreted as having been caused by

Fig. 5. Summary of published ages for the Heinrich events 1 to 3 from numerous NE Atlantic cores after Bond et al. (1992), Revel etal. (1996), Lebreiro et al. (1996) and Vidal et al. (1997) (dashed bars), compared with the ages of IRD spikes at the Meriadzek Terrace(bold bars). Ages match well except for the slightly earlier appearance of IRD spike 3 at M.T. The difference contrast to the reported HL3 ages can be attributed to the lack of stratigraphic control points prior to 24.8 ka and a possible overestimation of sedimentation rate inthe lowest part of the ESSCAMP core.

a sudden input of ice-rafted debris (IRD) attributedto the discharge of glacial material from the meltingicebergs produced by the Laurentide, Greenland, andpresumably Fenno-Scandian ice sheets and desig-nated by Broecker et al. (1992) as Heinrich layers(HL) (Heinrich, 1988). Distinctive features of theHLs are high accumulation rates, dominance of N.pachyderma (s.), low flux of planktic foraminifera,and low sea surface salinity (Bond et al., 1992).

Periods of lowest SST in the ESSCAMP 02 coreare always accompanied by a simultaneous increasein IRD (at 15–13.4 ka, double-peaking at 20.6=22.3ka, and at 25.7 ka) (Fig. 4). Ages of these IRD peaksagree well with reported ages for HL1 (³14.5 ka),HL2 (³23–20 ka), and HL3 (³30–26 ka) in this partof the northeast Atlantic (Fig. 5) (Bond et al., 1992;Lebreiro et al., 1996; Revel et al., 1996; Vidal et al.,1997). Still, the origin of this material is uncertain.IRD found within the Ruddiman’s IRD belt and onthe Portuguese margin are characterized by the pres-ence of detrital carbonate and increased percentageof dolomite (Bond et al., 1992; Auffret et al., 1996b;Lebreiro et al., 1996; Baas et al., 1997, 1998a). Inour core detrital carbonate is absent and dolomiteshows a monotonous record, with no relation toIRD (Fig. 2). That excludes the Laurentide ice sheetas a possible source of the material, but the highnumber of red, hematite-stained quartz may point toinput from an European source (with continental RedBeds).

We are thus not able to relate the source forthe IRD found in this core to the accepted causefor Heinrich events at the present stage of research.


However, the synchronous occurrence of these IRDpeaks and the Heinrich layers in the North Atlanticsuggests a global climate change which triggers a(European) source at the same time. In such a sce-nario, the North Atlantic glacial current system, assuggested by Robinson et al. (1995) and the IberianCurrent could be an alternative ‘carrier’ to bringthe Iceland- and possibly Fenno-Scandian-originatedicebergs close to the central European continentalmargin.

5.4. Foraminiferal accumulation rates

Foraminiferal accumulation rates (AR) (Fig. 6)are highest in the Holocene, during the first phaseof Terminations Ia and Ib and at the end of stage 3.The minimum in foraminiferal flux is synchronousto the period of lowest SST (late stage 2 at ca. 14ka). Inferred from the total plankton flux (Thunelland Sautter, 1992), primary productivity attained itsmaximum at the time of suggested northward retreatof the polar front (at ca. 13.4 ka), increasing againduring the Holocene.

The number of benthic forams counted in thisstudy is below the minimum required for a crediblestatistical calculation. Still, two peaks of near-sur-face dwelling infaunal species Cassidulina leavigata(de Stigter, 1996) during the middle part of stage2 are notable. At those levels, up to 25% of totalforaminiferal assemblage is composed of this benthicspecies (Fig. 6). C. leavigata is the superior competi-tor in food- and oxygen-rich surface microhabitats(de Stigter, 1996), and periods of its dominance maybe indicative of relatively high food fluxes.

North Atlantic Deep Water is formed by the sink-ing of dense, cold surface water in very limitedhigh latitude areas (i.e. Greenland and Iceland seas,Arctic Ocean). Its formation is therefore exposed tosignificant variations during the Pleistocene causedby the glacial–interglacial changes in the conditionsprevailing at the surface (e.g. temperature, currentdistribution, wind) (Duplessy et al., 1988, 1992; Im-brie et al., 1992; Sarnthein et al., 1994; Sarnthein andAltenbach, 1995). During Heinrich events, when agreat amount of continental ice was launched into theNorth Atlantic, the resulting salinity drop was prob-ably enough to drastically reduce the North Atlanticthermohaline circulation and the NADW formation

(Broecker and Denton, 1989; Bond et al., 1992;Keigwin and Lehman, 1994; Labeyrie et al., 1995;Maslin et al., 1995; Cortijo et al., 1997; Vidal et al.,1997). This reduction of the thermohaline circula-tion resulted in a nutrient-enriched, oxygen-depleteddeep water that can be traced trough the compositionof benthic foraminiferal communities (Kaiho, 1994).Baas et al. (1998b) infer a dysoxic bottom environ-ment prevailing during the Heinrich events 1 and 4from the high abundance of Globobulimina affinis,a deep-dwelling (6–13 cm) infaunal foraminiferalspecies very tolerant to low-oxygen bottom waterconditions (Corliss, 1985).

In our core, a significant maximum in benthicforaminiferal AR between 14.2 and 12.8 ka is al-most entirely dominated by the species G. affinis(it dominates between 14.4–13.7 ka). The peak ofthis species matches with the onset of the strongestIRD peak (Fig. 6) and agrees in age with Heinrichevent 1 (Fig. 5). This may suggest the presenceof oxygen-depleted bottom water at the MeriadzekTerrace associated with the reduced NADW forma-tion at that time. After the re-establishing of NorthAtlantic thermohaline circulation and oxygenatedbottom water conditions (end of G. affinis peak),and increased productivity (as revealed from the to-tal planktic foraminiferal AR) probably associatedwith the northward retreat of the polar front, otherless opportunistic species take advantage of nutri-ent-enriched sediments and the community becomesmore diverse, until ca. 12.3 ka when AR of benthicspecies drops to the standard low value. The matchof G. affinis peak with the onset of the strongest IRDspike is more likely due to the original microhabitatdepth of this species in a dysoxic environment ratherthan due to low-oxygen conditions preceding periodsof IRD accumulation (Baas et al., 1998b). In otherwords, a small discrepancy observed between thetwo maxima is probably due to the preferred livingdepth of G. affinis within the sediment.

6. Conclusions

The high sedimentation rates observed in the ES-SCAMP 02 core allow a very high-resolution record,in particular for the isotopic stage 2 and late stage 3:

(1) During isotope stage 2, SST was not uniform.

70N

.Loncaric

etal./M

arineG

eology152

(1998)57–73

Fig. 6. Accumulation rates of plankton, benthos, low-temperature planktic species, benthic species G. affinis and C. leavigata, and IRD plotted vs. age, compared with the Ž18Ocurve.


Three intervals can be distinguished: the coldestperiod occurred during the upper part (15.3–13.4ka) when the average SST ranged between 0.3ºCin winter and 4.2ºC in summer; the middle part(19.8–15.3 ka) was characterized by higher SSTwith strong and abrupt oscillations, while the base ofthe stage was marked by two notable negative SSTspikes congruous with the IRD spikes.

(2) Late stage 2 (15–13.4 ka) was the coldestperiod in the last 26,000 years.

(3) The polar front was located in the vicinityof the Meriadzek Terrace during early and middlestage 2, shifting southward during late stage 2, andretreating northward from the ESSCAMP 02 site at13.4 ka.

(4) All IRD peaks correspond to periods of lowSST as inferred from the Ž18O, foraminiferal assem-blages composition, and SIMMAX SST estimations.Levels rich in IRD are synchronous with the reportedages of Heinrich layers 1, 2 and 3. However, thecomposition of detrital grains and dolomite record ofthe core argue against the Laurentian or Greenlandorigin for most of this material. An alternative expla-nation could be the IRD transported by Iceland- orFenno-Scandian-originated icebergs.

(5) The strongest peak of primary productivity, asrevealed by fluxes of planktic and benthic forams,coincides with the northwards retreat of the polarfront over the site.

(6) High AR of benthic species G. affinis duringthe Heinrich event 1 may suggest low-oxygen bottomwater conditions associated with the reduced deepwater formation in the North Atlantic at that time.

Acknowledgements

We wish to acknowledge the technicians of theLaboratorio de Geologia Marinha, Lisbon, for prepa-ration of samples used in this study and for X-raydiffraction and CaCO3 analyses. Personnel at theKiel University laboratory are thanked for the Ž18Oanalyses, P. Guyomard at IFREMER, Brest, for apreliminary study of core ESSCAMP 02, and M.Arnold at Centre des Faibles Radioactivites, Gif-sur-Yvette, for the AMS14C dating. Further, we wouldlike to express our thanks to U. Pflaumann, Kiel Uni-versity, for the SST estimations using his SIMMAX

modern analog technique. The first author is gratefulto A. Baltzer (BGS) for helping him in collectingregional literature and to H. de Stigter (NIOZ) andJ.W. Zachariasse (Utrecht University) for the taxo-nomic consultations. We thank T. van Weering, J.Schonfeld, and two anonymous reviewers for valu-able comments on an earlier draft of this paper. Thisstudy was carried out as a part of the ENAM project(MAST II), contract No. MAS2 CT-93-0064.

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Late Quaternary sedimentation patterns on the Meriadzek Terrace, Bay of Biscay (ESSCAMP 02 core: 47°N 9°W