Received 20 February 2002; received in revised form 19 June 2002; accepted 27 June 2002

Transcription

1 Marine Micropaleontology 47 (2002) 143^176 Millennial-scale glacial variability versus Holocene stability: changes in planktic and benthic foraminifera faunas and ocean circulation in the North Atlantic during the last years Tine L.Rasmussen a;, Erik Thomsen b, Simon R.Troelstra c, Antoon Kuijpers d, Maarten A.Prins c c a b Institute of Geology, Lund University, Tornavaegen 13, SE Lund, Sweden Department of Earth Sciences, Aarhus University, DK-8000 Aarhus C, Denmark Institute of Earth and Life Sciences, Amsterdam Free University, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands d Geological Survey of Greenland and Denmark, Òster Voldgade 10, DK-1350 Copenhagen K, Denmark Received 20 February 2002; received in revised form 19 June 2002; accepted 27 June 2002 Abstract Two piston cores, DS97-2P from the Reykjanes Ridge in the central North Atlantic Ocean (1685 m water depth) and ENAM33 from southwest of the Faeroe Islands in the NE Atlantic (1217 m water depth), have been investigated for their planktic and benthic foraminiferal content.ds97-2p is situated near the Subarctic Front and productivity measured by accumulation rates of benthic and planktic foraminifera has been generally high during the Holocene. The productivity shows a clear decrease from an early Holocene maximum to a late Holocene minimum.coeval changes in the benthic faunas indicate that the food supply changed from large, irregular pulses during the early Holocene to a more sustained flux during the late Holocene.Presumably in concert with decreasing bottom current activity oxygen conditions in the bottom water became poorer.another feature of the late Holocene is an increasing instability of the North Atlantic thermohaline circulation regime.nevertheless, the changes in faunal composition and productivity during the Holocene were gradual as compared to the discontinuous distribution patterns and abrupt productivity shifts during the glacial.the glacial shifts were on a millennial time scale and correlate with the interstadial^stadial phases of the Dansgaard^Oeschger cycles in the Greenland ice cores.the faunas of the warm interstadial phases resembled the Holocene faunas, and both surface and bottom productivity was high.the faunas suggest that the interstadial circulation pattern was very similar to the modern system with convection in the Nordic seas and generation of North Atlantic Deep Water.The planktic faunas during the cold stadials and Heinrich events were completely dominated by the polar species Neogloboquadrina pachyderma s, and surface conditions were cold and the productivity low.the benthic faunas were dominated by species that presently thrive in areas with a low amount of food and reduced oxygen content.the water column was probably stratified with low saline, cold surface water overlying poorly aerated, intermediate water masses. * Corresponding author.present address: The University Courses on Svalbard, P.O.Box 156, N-9171 Longyearbyen, Norway. Tel.: ; fax: address: tine.rasmussen@unis.no (T.L. Rasmussen) / 02 / $ ^ see front matter ß 2002 Elsevier Science B.V. All rights reserved. PII: S (02)

2 144 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^176 ß 2002 Elsevier Science B.V. All rights reserved. Keywords: Glacial and Holocene variability; North Atlantic Ocean; planktic and benthic foraminifera faunas; productivity; ocean circulation 1. Introduction The last glacial period was characterised by high-amplitude atmospheric temperature oscillations.the cycles are recorded in the Greenland ice core records (Dansgaard et al., 1993), and they are generally known as Dansgaard^Oeschger cycles (D^O cycles) (Broecker et al., 1992).Each cycle lasted from 500^2500 years and consisted of a warm interstadial phase and a cold stadial phase (Johnsen et al., 1992).More prominent and longer lasting stadials correlate with North Atlantic Heinrich events (Bond et al., 1993) during which icebergs released from the Laurentide Ice Sheet traversed the North Atlantic resulting in the deposition of thick layers with Ice Rafted Detritus (IRD) (Heinrich, 1988).It was demonstrated by Bond et al.(1993) that sea surface temperature (SST) in the North Atlantic Ocean varied in pace with the D^O cycles in the Greenland ice cores.compared to the last glacial period, the Holocene interglacial appears to be very stable climatically (Dansgaard et al., 1993). The imprint of the D^O cycles in the deep marine sediments has been investigated in high-resolution cores from many di erent locations (e.g. Fillon and Duplessy, 1980; Broecker et al., 1992; Bond et al., 1993; Keigwin and Lehman, 1994; Fronval et al., 1995; Oppo and Lehman, 1995; Maslin et al., 1995; Rasmussen et al., 1996a; Moros et al., 1997; Labeyrie et al., 1999; Cannariato and Kennett, 1999; van Kreveld et al., 2000; Knutz et al., 2001).The composition of the benthic foraminifera assemblages in the deep sea deposits varies on suborbital time scales (e.g. Streeter, 1973; Schnitker, 1974, 1982; Streeter and Shackleton, 1979; Fillon and Duplessy, 1980; Scott et al., 1989; Thomas et al., 1995; Rasmussen et al., 1996a,b; Cannariato and Kennett, 1999). In this study we investigate variations in the composition and productivity of benthic and planktic foraminifera at two North Atlantic sites from intermediate depth, DS97-2P from 1685 m water depth, and ENAM33 from 1217 m (Fig.1). Today, the two sites are located close to the North Atlantic (surface) Current, derived from the Gulf Stream system, transporting warm and saline waters into the North Atlantic high latitudes (Fig.1).DS97-2P from the Reykjanes Ridge is located south of the Irminger Current core owing in a northwesterly direction to areas west of Iceland (Fig.1).ENAM33 is located southwest of the Faeroe Islands (Fig.1).Both sites have summer SSTs from 9^12 C (Wright and Worthington, 1970).The main bottom water mass in the vicinity of the two sites is the Upper North Atlantic Deep Water composed primarily of Labrador Sea Water, Central Water and Mediterranean Out ow Water and found between ca. 1 and 2 km water depth (e.g. Dickson et al., 1985; McCartney, 1992; van Aken and Becker, 1996; Sy et al., 1997).The sites lie close to the pathway of the Norwegian Sea Over ow Water and the Iceland Sea Over ow Water (ISOW) crossing over the Iceland^Scotland Ridge (Fig.1).These water masses are generated by convection in the Nordic seas (Aagaard et al., 1985) and contribute to Lower North Atlantic Deep Water.Bottom currents are relatively weak along the Reykjanes Ridge and over the DS97-2P core site (Bersch, 1995; Hansen and Òsterhus, 2000).ENAM33 in the NE Atlantic is located in close vicinity of the out ow from the Nordic seas through the Faeroe Bank Channel and is a ected by much stronger bottom currents (Kuijpers et al., 1998a; Hansen and Òsterhus, 2000) (Fig.1).The bottom temperatures are from 3.5^3.7 C at the Reykjanes Ridge site (Wright and Worthington, 1970; Bersch, 1995) and from ca. 3.6^4.0 C at the NE Atlantic site (Kuijpers et al., 1998a).For surface water masses, the two cores have a di erent oceanographic setting.the Reykjanes Ridge core is located near the Subarctic Front in the central

3 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^ North Atlantic (Ruddiman and McIntyre, 1973, 1981; Krauss, 1986, 1995; van Aken and Becker, 1996) and close to highly productive surface waters (Yoder et al., 1994).The ENAM33 core is from a more infertile area with lower and more seasonal surface productivity (Thiel, 1983; Gooday, 1986; Mackensen, 1987). The aim of this study is to investigate variations in the properties and ow of the surface and deep water masses in the North Atlantic during the last ca years by means of benthic and planktic foraminifera, IRD and benthic and planktic oxygen isotopes.a main goal is to compare living conditions and productivity patterns during the glacial regime of short-term oceanic changes with the relatively stable conditions having prevailed in the Holocene. 2. Materials and methods The materials consist of two cores, DS97-2P (position 58 56P327 N, 30 24P590 W; water depth 1685 m) and ENAM33 (position 61 15P884 N, 11 06P545 W, water depth 1217 m) from the central and eastern North Atlantic, respectively (Fig. 1).The study comprises the whole of the DS97-2P core, which is m long (see Prins et al., 2001), and the upper 4.30 m of the ENAM33 core (see Kuijpers et al., 1998b). DS97-2P was sampled at every 10 cm except for the interval 5.1^6.5 m, which was sampled at every 2 cm because of a suspected low temporal resolution in that section of the core.each sample consists of a 1-cm thick slice with a volume of 10 cc.the samples were washed over 63-Wm sieves, dried and weighed, and thereafter dry sieved over 106-Wm sieves for faunal and IRD analyses.at least 300 planktic and 200^300 benthic specimens of foraminifera were counted in the s 106-Wm fractions and identi ed in each sample.the concentration of planktic and benthic foraminifera per g dry weight sediment was calculated.from the same fractions a total of 200^300 mineral Fig.1.Map of the northern part of the Atlantic Ocean showing locations of studied cores and other cores referred to in the text.main surface and deep currents are indicated.position of the Subarctic Front modi ed after Bode n and Backman (1996).

4 146 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^176 Table 1 AMS 14 C dates and age model for core DS97-2P with calculated linear sedimentation rates (LSR) Depth 14 C ages LSR (cm) (corr. 3400) (cm/ka) 0 0 a a a a a a a a a a a b ,140 a a b b b c 5.6 a Radiocarbon ages published in Prins et al.(2001). b Inferred radiocarbon ages obtained by correlation to core ENAM33. c Ice core age of Ash Zone II (Gro«nvold et al., 1995). grains were picked and counted.tephra grains of rhyolitic and basaltic composition were counted separately and the concentration per g dry weight sediment calculated.the percent of IRD was calculated as the proportion of grains s 106 Wm relative to the total number of foraminifera and particles (excluding tephra particles).diatoms larger than 106 Wm from diatom mats were weighed, and their wt% calculated relative to the total material s 106 Wm.The accumulation rates of benthic foraminifera (BF^AR = Benthic Foraminifera Accumulation Rates) and planktic foraminifera (PF^ AR = Planktic Foraminifera Accumulation Rates) were calculated using the equations given by Thiede et al.(1986) (data available only for core DS97-2P).The age model used for the calculations is based on accelerator mass spectrometry (AMS) 14 C dates, the ages of identi ed tephra horizons and the ages of known Heinrich events (Table 1).The accumulation rates are used as an indication of the surface and bottom productivity levels and of the export of food to the sea oor (e.g. Thiel, 1983; Altenbach, 1988; Herguera and Berger, 1991; Herguera, 1994; Schmiedl and Mackensen, 1997; Altenbach et al., 1999; Jian et al., 1999; Wollenburg and Kuhnt, 2000; Altenbach and Struck, 2001). A low-resolution study of ENAM33 was performed by Kuijpers et al.(1998b).the core has been re-sampled at 2.5-cm intervals (5-cm intervals for the 20^16 ka BP section) for this study.in these new samples Neogloboquadrina pachyderma s and Melonis barleeanum were picked for analysis of planktic and benthic oxygen isotopes.the analyses were performed at Woods Hole Oceanographic Institution using standard techniques (Ostermann and Curry, 2000).The samples were otherwise treated as in core DS97-2P using the s 106 Wm fractions for the foraminifera analyses and the s 150 Wm fractions for the IRD counts.the distribution of tephra grains in ENAM33 is published in Kuijpers et al.(1998b). The majority of the AMS 14 C dates have already been published for both cores, i.e. DS97-2P by Prins et al.(2001) (Table 1) and ENAM33 by Kuijpers et al.(1998b) (Table 2). A taxonomic list of the most common planktic and benthic foraminifera species is given in Ap- Table 2 AMS 14 C dates for core ENAM33.Samples were dated at the AMS Laboratory, University of Aarhus Depth AMS 14 C age AAR-number a (cm) (corr years) þ 50 AAR þ 65 AAR þ þ þ þ þ þ 80 AAR þ þ þ 130 AAR þ 160 AAR þ 180 AAR þ 240 AAR þ 350 AAR þ 600 AAR-5385 a AAR-number is only given for previously unpublished dates.published dates are to be found in Kuijpers et al. (1998b).

5 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^ pendix 1.The data for cores DS97-2P and ENAM33 are given in Appendices 2 and 3, respectively. 3. Stratigraphy Basaltic and rhyolitic ash particles in DS97-2P occur in discrete peaks (Fig.2).A very conspicuous peak ( s 9000 grains/g) of both rhyolitic and basaltic grains appears at 994 cm down-core.we correlate this peak with Ash Zone 2 dated to ca. 52 ka BP (see Gro«nvold et al., 1995; van Kreveld et al., 2000) (Table 1).Ash Zone 2 is also very prominent ( s grains/g) in core SO82-05 from the Reykjanes Ridge taken slightly north of our site (van Kreveld et al., 2000; Ha idason et al., 2000) (Fig.1).A smaller event occurring above a sample dated to ka BP probably represents Ash Zone 1 (Mangerud et al., 1984) (Fig.2).Most tephras correlate with peaks in IRD and are apparently ice rafted (e.g. Ruddiman and Glover, 1972; Lacasse et al., 1996; Lackschewitz and Wallrabe-Adams, 1997) (Fig.2).The recognition of Ash Zone 2 at 994 cm in DS97-2P has given an age model that di ers from the Fig.2.Relative abundance of most common planktic foraminifera, concentrations of planktic and benthic foraminifera in number of specimens per gram dry weight sediment, percentage of IRD, percentage of diatoms s 106 Wm by weight, and number of tephra shards (both rhyolitic and basaltic grains) per gram dry weight sediment in core DS97-2P.Position of Ash Zones 1 and 2 (ASH I and ASH II) are indicated.interstadial and stadial numbers and AMS 14 C dates are indicated.bars mark Heinrich events and stadials.marine isotope stages are indicated to the right.

6 148 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^176 preliminary age model proposed by Prins et al. (2001).The two age models deviate in the interval older than ca calendar years (ca C years) (see Prins et al., 2001) (Table 1). In both cores variations in the relative abundance of the polar planktic foraminifera Neogloboquadrina pachyderma s in combination with variations in the concentration of IRD, de ne a number of SST cycles (Figs.2 and 3).Compared with the ages of Ash Zones 1 and 2 (see Gro«nvold et al., 1995), and the 14 C dates, it is clear that the cycles correlate with the D^O cycles of the Greenland ice cores (Dansgaard et al., 1993) (Figs.2 and 3).In ENAM33, the marine oxygen isotope stages (MIS) 1^3 are identi ed according to the standard procedures de ned by Martinson et al. (1987) (Fig.3).In DS97-2P, the identi cation of the isotope stages is based on a correlation to ENAM33 (Fig.2).The records cover the last ca years. The more prominent cold periods share the characteristics of the North Atlantic Heinrich events, namely a high content of IRD, a high relative abundance of Neogloboquadrina pachyderma s, a low concentration of foraminifera, and low planktic N 18 O values (e.g. Heinrich, 1988; Bond et al., 1992; Andrews and Tedesco, 1992) (Figs.2 and 3).The investigated section of ENAM33 includes H1^H6, while DS97-2P includes H1^H5 (Figs.2 and 3).In DS97-2P, Heinrich events 4 and 5 have been recognised exclusively by correlation to the ENAM33 record and their identi cation is somewhat uncertain.events younger than H3 have been identi ed by the AMS 14 C Fig.3.Planktic N 18 O record measured on Neogloboquadrina pachyderma s, relative abundance of most common planktic foraminifera, concentration of planktic and benthic foraminifera in number of specimens per gram dry weight sediment, and percentage of IRD in core ENAM33.Legend as in Fig.2.

7 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^ dates as well as by correlation to ENAM33 (Tables 1 and 2; Figs.2 and 3).The ages of the dated Heinrich events are similar to the ages obtained by e.g. Bond et al.(1992), Elliott et al.(1998), Voelker et al.(1998), and van Kreveld et al. (2000).H1 usually dates 14.5^13 ka BP; H2, 22^20 ka BP; H3, 27^26 ka BP; H4, 35^33 ka BP; and H5, ca.45 ka BP.The smaller IRD events correlate with stadial events (e.g. Bond and Lotti, 1995; Fronval et al., 1995; Rasmussen et al., 1996a,b; Elliot et al., 1998; Voelker et al., 1998; van Kreveld et al., 2000) (Figs.2 and 3). The warm events with low abundances of N. pachyderma s correlate with the warm interstadials of the Greenland ice cores and have been numbered accordingly (Johnsen et al., 1992; Dansgaard et al., 1993) (Figs.2 and 3).The warm events correlate with high levels of carbonate in the sediment (Prins et al., 2001). In core DS97-2P, the Last Glacial Maximum (LGM) and the early deglaciation corresponding to the later part of MIS 2 is very thin (485^515 cm) and of low temporal resolution (Fig.2; Table 1).Crystals of calcite covering many of the foraminifera indicate stops in sedimentation and the deposits seem disturbed or signi cantly reworked. This section will therefore not be treated. 4. Distribution of planktic foraminifera and interpretation of surface conditions 4.1. Holocene (10^0 ka BP) The polar planktic foraminifera Neogloboquadrina pachyderma s is generally absent indicating summer SST at both sites close to 12 C or higher (Be and Tolderlund, 1971; P aumann et al., 1996). Turborotalia quinqueloba is the most abundant species (Figs.2 and 3).In core DS97-2P, it constitutes 60% of the fauna in the early Holocene deposits and decreases to ca.35% in the late Holocene (Fig.2). Globigerinita uvula is relatively rare but increases towards the core tops. Turborotalia quinqueloba and G. uvula are small planktic forms often related to upwelling or oceanic fronts (Parker, 1971; Kellogg, 1976; Hemleben et al., 1989; Kroon, 1991; Johannessen et al., 1994). They indicate high surface productivity especially during the early and late Holocene (Figs.2 and 3).In DS97-2P, the relative abundance of T. quinqueloba follows closely the changes in the PF^AR in good accordance with the status of this species as an indicator of surface productivity (Fig.4). The calculated average productivity of planktic foraminifera for the Holocene is 150U10 3 individuals/cm 2 /ka.the late Holocene is characterised by the deposition of numerous layers of mat-forming diatoms correlating with minima in concentration of planktic foraminifera (Figs.2 and 4) Interstadials and stadials (ca. 60^10 ka BP) The distribution of planktic foraminifera during the glacial is similar in the two cores (Figs.2 and 3).The relative abundance of Neogloboquadrina pachyderma s varies between 20% and s 95%. Maximum summer temperatures are higher than 9 C if the relative abundance of N. pachyderma s is below 20% and lower than 4 C if it exceeds 80^ 95% (Be and Tolderlund, 1971; Kellogg, 1980; Johannessen et al., 1994; P aumann et al., 1996).Thus, maximum summer SST during the glacial varied with a magnitude of at least 5 C. Turborotalia quinqueloba, and mostly also Globigerina bulloides, are abundant in the warm interstadials (Figs.2 and 3) probably indicating increased surface productivity.the warm interstadials have higher concentrations of planktic foraminifera and higher PF^AR than the cold stadials (Figs.2 and 3) indicating relatively increased surface productivity (Fig.4).Peak interstadial values are often close to or above the average value for the Holocene.The content of IRD is low indicating very limited or no iceberg drifting. The BÖlling and AllerÖd interstadials di er from the other interstadials by an increase in the relative abundance of Globigerinita uvula and Turborotalia quinqueloba (Figs.2 and 3).This suggests that the surface conditions probably resembled the late Holocene and present conditions in the area, where G. uvula also is present. The stadials and Heinrich events are dominated by Neogloboquadrina pachyderma s(figs.2 and 3).All cold events have low concentrations of

8 150 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^176 foraminifera and high concentrations of IRD.The PF^AR (site DS97-2P) is also low indicating low surface productivity of foraminifera (Fig.4).The PF^AR values lie between ca.10^30u10 3 individuals/cm 2 /ka (Fig.4).The planktic N 18 O values in core ENAM33 (Fig.3) show that the surface waters during the cold periods were depleted in 18 O.Such depletion is well known from other cores in the North Atlantic realm and generally attributed to the presence of meltwater from melting icebergs (Figs.2 and 3) The Last Glacial Maximum The LGM is only well represented in ENAM33 (Fig.3).The planktic faunas are dominated by Neogloboquadrina pachyderma s and Turborotalia quinqueloba.the concentration of planktic foraminifera is low.the IRD content is high.the high sedimentation rates suggest that the faunas may be diluted.thus, the surface conditions and SST were more similar to the interstadial conditions than to the stadial ones. 5. Distribution of benthic foraminifera and interpretation of bottom conditions The benthic faunas of the two records are slightly more di erent than the planktic faunas which can be expected given the di erence in water depth between the two sites of nearly 500 m(fig.1).the cores are therefore described separately and then compared Holocene (10^0 ka BP) Core DS97-2P The Holocene interval is dominated by Bolivina pseudopunctata and Bulimina exilis (Fig.5).Their combined relative abundance increases slightly throughout the Holocene to a maximum in the late Holocene (4.8 ka BP to the core top). The maximum relative abundances coincide with maximum concentrations of diatoms (Fig.2). Bolivina and Bulimina species are deep infaunal foraminifera generally adapted to a high supply of organic matter to the sediment (e.g. Corliss and Chen, 1988; Corliss, 1991; Kaiho, 1994; Jorissen et al., 1995; Ohga and Kitazato, 1997; de Stigter et al., 1998).They are tolerant of reduced oxygen concentration in the pore water. Bolivina pseudopunctata is abundant in the Gullmar Fjord in areas with a high supply of organic material and low oxygen conditions (Gustafsson and Nordberg, 2001). Bulimina exilis ourishes in the oxygen minimum zone in productive areas with high supplies of freshly settled phytodetritus (Caralp, 1989; Jannink et al., 1998).According to Thomas et al.(1995), Bolivina and Bulimina species typify areas of high organic productivity and a sustained ux of organic matter to the sea bottom, i.e. under areas of upwelling. Subdominant species are Globocassidulina subglobosa, Trifarina angulosa, Cassidulina laevigata, and Gavelinopsis praegeri, which we term below the G. subglobosa^t. angulosa group.at present, G. subglobosa is most abundant in sandy sediments and in areas with relatively strong bottom currents (Mackensen et al., 1993, 1995; Schmiedl et al., 1997). Trifarina angulosa is also associated with coarser sediments under the in uence of bottom currents (Sejrup et al., 1981; Mackensen et al., 1985, 1993, 1995; Mackensen, 1987; Harlo and Mackensen, 1997).In core DS97-2P, Epistominella exigua occurs together with the G. subglobosa^t. angulosa group (Fig.5). Epistominella exigua is an epifaunal species characteristic of areas with seasonal food ux to the sea bottom (Gooday and Lambshead, 1989; Gooday, 1993; Smart et al., 1994; Smart and Gooday, 1997). Thomas et al.(1995) characterise it as an opportunistic species thriving in regions with strong unpredictable pulses of organic matter into organic-poor sediments. Cassidulina laevigata is adapted to similar conditions (Gooday, 1986, 1988; Gooday and Lambshead, 1989 (recorded as C. teretis)).this is apparently also true for G. praegeri, although this epifaunal species probably prefers more oxic conditions (Scho«nfeld, 2001).The G. subglobosa^ T. angulosa group shows close a nity to modern benthic faunas from mid-depth in the NE Atlantic Ocean.These faunas are generally associated with low productivity areas with seasonal uxes of food to the sea oor (Mackensen, 1987; Gooday, 1986; Gooday and Lambshead, 1989).

9 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^ Overall, Bulimina exilis and Bolivina pseudopunctata increase in relative abundance during the Holocene, but the two species uctuate strongly, in particular during the late Holocene (Fig.5).The Globocassidulina subglobosa^trifarina angulosa group and Epistominella exigua decrease in relative abundance.the faunas indicate a reduction in bottom currents and in oxygen content of the benthic environment with time. The productivity changed from seasonal to more sustained food supply.the average benthic accumulation rate during the Holocene is 6.6U10 3 individuals/cm 2 /ka (Fig.4).The overall trend is a decrease from an early Holocene maximum to a late Holocene minimum (Fig.4).The diversity varies between ca.25 and 45 species per sample, except for a minimum value correlating with the diatom layers near the core top ca.2^3 ka BP (Fig.5) Core ENAM33 The Holocene interval in ENAM33 is dominated by the Globocassidulina subglobosa^trifarina angulosa group. Cassidulina laevigata is rare and replaced by Cassidulina obtusa and Bolivina pygmaea (Fig.6).These species are all common in the area today (Gooday, 1986; Gooday and Lambshead, 1989; Mackensen, 1987; Coles et al., 1996; Rasmussen et al., 2002b).Together, they indicate a seasonal food supply to the sea oor and relatively strong bottom currents (see Gooday, 1986; Gooday and Lambshead, 1989; Mackensen, 1987).The diversity is low Interstadials (ca. 60^10 ka BP) Core DS97-2P The interstadial deposits are dominated by the Globocassidulina subglobosa^trifarina angulosa group and Nonionella spp.and Pullenia bulloides (Fig.5). Bulimina exilis and Bolivina pseudopunctata are abundant during the AllerÖd interstadial, otherwise they are rare.the G. subglobosa^t. angulosa group is most abundant in the lower part of the core in the older interstadials 17^8 and in the BÖlling interstadial (Fig.5). Pullenia species are shallow to deeper infaunal foraminifera mostly found in areas with a relatively high supply of organic material (e.g. Schnitker, 1974, 1982; Corliss and Chen, 1988; Corliss and Emerson, 1990; Mackensen et al., 1994). Nonionella species are opportunistic, epifaunal species known to invade formerly anoxic sea bottoms (e.g. Barmawidjaja et al., 1992; Hohenegger et al., 1993; Rathburn et al., 2001).They were more abundant during the glacial interstadials than during the Holocene, when they apparently were replaced by B. exilis and B. pseudopunctata. Overall, the bottom conditions during the interstadials were fairly similar to the Holocene conditions with enhanced bottom currents and a high food supply to the bottom.the food supply was probably irregular and causing temporal anoxia. A few details may be added to this general picture. Epistominella vitrea and Fursenkoina fusiformis are rare in the older interstadials with the exception of interstadial 9.They increase in relative abundance upwards through interstadials 7^2 (ca.30^22 ka BP) (Fig.5).They also increase within each interstadial toward the stadial.today, E. vitrea is abundant in the Labrador Sea on the lower slope and rise in newly formed North Atlantic Deep Water (NADW; Schafer and Cole, 1982; Schafer et al., 1985).It is a small thin-shelled form probably with a life-form intermediate between those of Epistominella exigua and Epistominella arctica. Epistominella arctica is a small thin-shelled species living in the Arctic Ocean (e.g. Lagoe, 1977; Scott and Vilks, 1991; Bergsten, 1994; Wollenburg and Mackensen, 1998a).It has an opportunistic life style similar to that of E. exigua, but is adapted to a lower and more irregular, seasonal supply of organic substances, and living in colder bottom water with little current activity (Wollenburg and Kuhnt, 2000).In the Gullmar Fjord, west Sweden, F. fusiformis multiplied by seven times after a spring bloom with high input of phytoplankton (Gustafsson and Nordberg, 2001).It is suggested that F. fusiformis and other species were competing against E. vitrea and similar species. Fursenkoina fusiformis is tolerant to low oxygen levels and can survive anoxia (Alve, 1994; Bernhard and Alve, 1996) and indicates prolonged anoxia. Epistominella vitrea may be less tolerant to low oxygen (Gustafsson and Nordberg, 2001).Alto-

10 152 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^176 Fig.4.Relative abundance of Turborotalia quinqueloba, accumulation rates of planktic and benthic foraminifera (PF^AR and BF^AR), and percentage of IRD in core DS97-2P.Legend as in Fig.2. gether, the composition of the interstadial faunas indicates a high, but irregular, food ux. Epistominella vitrea and F. fusiformis may have been competing, with F. fusiformis dominating when the oxygen content was low.the decline and subsequent disappearance of the Globocassidulina subglobosa^trifarina angulosa group from interstadial 7 indicate lower current activities. The interstadial BF^AR averages 5.9U10 3 individuals/cm 2 /ka (Fig.4).Thus, the average productivity of the interstadials and the Holocene is almost the same.the peak productivity of the interstadials is often higher than the Holocene average.during the late MIS 3 and MIS 2, productivity was generally lower (about 2^3U10 3 individuals/cm 2 /ka).this is probably an indication of increasingly irregular surface blooms Core ENAM33 The interstadials contain diverse faunas.the Globocassidulina subglobosa^trifarina angulosa group constitutes up to 20% of the fauna (Fig. 6). Cibicides species and Astrononion gallowayi are also present (not shown in Fig.6).The faunas suggest that bottom conditions resembled the modern conditions, especially during the early MIS 3. Cibicides species live attached to rm substrates and are indicative of bottom currents. They often occur together with T. angulosa (e.g. Sejrup et al., 1981; Mackensen et al., 1985, 1995; Mackensen, 1987; Schro«der-Adams et al., 1990; Hald and Steinsund, 1992). Astrononion gallowayi is infaunal with a typical infaunal life style (e.g. Hunt and Corliss, 1993; Wollenburg and Mackensen, 1998a,b).It is probably attracted to areas

11 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^ Fig.5.Relative abundance of Neogloboquadrina pachyderma s, relative abundances of most common benthic foraminifera, and number of benthic species per sample in core DS97-2P.Legend as in Fig.2. with a relatively high organic matter content (Hald and Korsun, 1997).As in DS97-2P, the concentration of specimens was high during the interstadials (Figs.3 and 6).We cannot calculate the interstadial productivity in ENAM33 due to the lack of dry bulk density data.however, comparison to the very similar DS97-2P suggests that it was high.as in DS97-2P, the relative abundance of Epistominella vitrea increases from a minimum during interstadial 9 to a maximum during interstadial 3 (Figs.5 and 6).In contrast to DS97-2P, Fursenkoina fusiformis is rare.the relative success of E. vitrea over F. fusiformis suggests that the food ux was lower and the oxygen level higher than at the location of DS97-2P (see description for DS97-2P above).however, the overall rise in the relative abundance of E. vitrea during the late MIS 3 and MIS 2 is similar in the two study areas indicating similar bottom conditions with irregular food supply. The benthic oxygen isotope values are low at the beginning of each interstadial.the values increase to maximum values just prior to the stadials and Heinrich events (Fig.6) Younger Dryas, Heinrich events, and stadials Core DS97-2P The Younger Dryas cold period, the stadials and Heinrich events show a more uniform faunal distribution than the interstadials.they are all dominated by the Atlantic species group (Fig. 5).This group is composed of a large number of relatively rare species that have been lumped to-

12 154 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^176 Fig.6.Relative abundance of Neogloboquadrina pachyderma s, relative abundances of most common benthic foraminifera, number of benthic species per sample, and benthic N 18 O record measured on Melonis barleeanum in core ENAM33.Legend as in Fig.2. gether because of their unique common distribution pattern (Rasmussen et al., 1996a).The most abundant species are Sigmoilopsis schlumbergeri, Eggerella bradyi/tosaia hanzawaia, Bulimina costata, Sagrina subspinescens, Epistominella decorata/weddellensis, Anomalinoides minimus, Hoeglundina elegans, Sphaeroidina bulloides, Nummoloculina irregularis and other miliolid species (e.g. Discospirina italica, Spirophtalmidium acutimargo, Sigmoilina tenuis, Pyrgoella sphaera), Cibicides a. C. oridanus, and various species of Gyroidina/ Gyroidinoides a.o. (Appendix 1).The species included in the Atlantic species group occur at mid-depth along the west European seaboard to the south of the Faeroe Islands, in the Gulf of Mexico, in the Labrador Sea and in the Mediterranean (see references in Rasmussen et al., 1996a, 2002a).They are relatively abundant on the Reykjanes Ridge, today, constituting about 10% of the species in the core top sample of DS97-2P (Fig.5) (Hermelin and Scott, 1985).The majority are epibenthic or shallow infaunal species such as recorded by Scho«nfeld (1997, 2001) from the Portuguese margin at water depths between ca.800 and 1900 m.epifaunal and potentially infaunal species dominate in the oligotrophic conditions of the Mediterranean Sea (Jorissen et al., 1995; de Stigter et al., 1998; Jorissen, 1999; Schmiedl et al., 2000), in the central Arctic Ocean (Wollenburg and Mackensen, 1998b) and on the Walvis Ridge in the South Atlantic (Schmiedl et al., 1997).

13 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^ The species of the Atlantic species group are probably adapted to low food conditions.this is known for e.g. Gyroidina spp., various Milioline species, and Cibicides spp.(mackensen et al., 1995; Altenbach et al., 1999; Schmiedl et al., 2000). Eggerella bradyi is epifaunal (Scho«nfeld, 2001) and found in sediments with a low organic carbon content in the South Atlantic (Harlo and Mackensen, 1997).They are among the Atlantic benthic colonisers that are able to survive in the fairly infertile and slightly suboxic bottom water environments of the Mediterranean slopes (e.g. Parker, 1958; Colom, 1970; Wright, 1978; Bizon and Bizon, 1984; see also de Rijk et al., 1999, 2000; Schmiedl et al., 2000).In fact, Gyroidina spp.and Anomalinoides minimus are among the few species in the Mediterranean that are able to cope with the extremely oligotrophic lower slopes and abyssal sea oor, comparable to the mid-oceanic deserts (e.g. Massiota et al., 1976; Cita and Zocchi, 1978; Vismara-Schilling and Parisi, 1981).Several of the species are also known to be tolerant to slightly reduced oxygen levels, e.g. Bulimina spp., Sagrina spp., Gyroidinoides neosoldanii, and Eponides weddellensis (see Kaiho, 1994; Loubere, 1996; Scho«nfeld, 2001). The high diversity of the benthic foraminifera during the stadials and Heinrich events is mainly due to the high diversity of the Atlantic species group (Fig.5).The BF^AR is very low as are the concentrations of both planktic and benthic species (Figs.2 and 4).The average productivity is 1.1U10 3 individuals/cm 2 /ka, well below the Holocene and interstadial averages.thus, bottom conditions favoured faunas adapted to oligotrophic and slightly under-oxygenated water Core ENAM33 The benthic faunas of the Younger Dryas, the stadials, and Heinrich events are dominated by the Atlantic species group as in core DS97-2P. Their peak abundance coincides with the peak diversity of the benthic assemblages as a whole in parallel with the observations in DS97-2P (Figs.5 and 6).The concentration of benthic specimens is likewise low and the bottom conditions were probably similar to the stadial conditions in DS97-2P. The benthic oxygen isotopes show a gradual decrease from high N 18 O values at the beginning of the stadials and Heinrich events to low values at the stadial/interstadial transition (Fig.6).The benthic N 18 O values vary almost inversely with the relative abundance of the Atlantic species group (Fig.6) The Last Glacial Maximum Core ENAM33 The LGM 20^16 ka BP is well represented in ENAM33 (Figs.3 and 6).The concentration of benthic foraminifera is low, but the sedimentation rates were very high suggesting dilution of the faunas. Cassidulina teretis, Elphidiumexcavatum, and Cassidulina reniforme are the dominant species (see Rasmussen et al., 2002b).The diversity is low.the fauna is typical of polar regions (e.g. Sejrup et al., 1981; Aksu and Mudie, 1985; Vilks, 1989; Korsun and Hald, 2000).At present, C. teretis is found at water temperature down to 31^2 C (Mackensen and Hald, 1988; Wollenburg and Mackensen, 1998a).Altogether the fauna indicates colder bottom water.the fauna is unique for the LGM period in the ENAM33 record. 6. North Atlantic palaeoceanography and palaeoproductivity The changes in the distribution and productivity of the planktic and benthic foraminifera in DS97-2P and ENAM33, as discussed above, demonstrate profound di erences in surface and bottom conditions between the Holocene and the glacial period and, within the glacial, between the warm interstadials and the cold stadials and Heinrich events (Figs.2^7).Below we compare our results from the two cores with other records from the central and eastern North Atlantic Holocene The discussion of Holocene conditions is based almost exclusively on DS97-2P from the Reykjanes Ridge due to the low resolution of the Holocene interval in ENAM33 (Figs.3 and 6).

14 156 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^176 Fig.7.Accumulation rates of most common planktic and benthic species and species groups in core DS97-2P. Legend as in Fig.2. The overall distributional pattern of the benthic faunas during the Holocene shows an increase in abundance of Bulimina exilis and Bolivina pseudopunctata and a decrease in the Globocassidulina subglobosa^trifarina angulosa group and Epistominella exigua.during time periods dominated by B. exilis and B. pseudopunctata the bottom environment was probably characterised by a high amount of organic material in the sea oor sediment, slow bottom currents and temporarily poor oxygen conditions.time periods dominated by the G. subglobosa^t. angulosa group and E. exigua, on the other hand, were probably characterised by less organic material in the sediments, higher current velocities, and better ventilated bottom water.the decrease in planktic species Turborotalia quinqueloba and weaker bottom currents may suggest a general decrease in the Irminger Current and a decrease in the deep over- ows from the Nordic seas from a maximum in the early and mid-holocene to a late Holocene and Recent minimum. An increase in the relative abundance of Bulimina exilis and Bolivina pseudopunctata and a decrease in Epistominella exigua during the Holocene has been observed in core 14K from 1756 m water depth on the Hatton Bank about 700 km east of DS97-2P (Thomas et al., 1995) (Fig. 1).Thus, the general trend in food ux during the Holocene in the North Atlantic ranged from an irregular, though mainly zonal, ux with good oxygenation of the bottom environment to a more sustained ux with a poorer oxygenation. However, during the late Holocene this general trend is disturbed by several episodes of great instability indicated by the highly uctuating foraminifera faunas and the numerous diatom beds dated to 3^2 ka BP (Figs.2, 4, 5, and 7).The instability could be the result of the Subarctic Front migrating back and forth over the area (e.g. Yoder et al., 1994; Bode n and Backman, 1996) concomitant with an expansion of the East Greenland Current and a shift of the Irminger Current towards the south.furthermore,

15 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^ the most recent samples, which are dated to younger than 2000 years, contain a small proportion of the opportunistic species Fursenkoina cf. F. tenuis, probably indicating prolonged anoxic episodes (Fig.5).In fact, the late Holocene productivity of foraminifera at the DS97-2P site is low and sometimes as low as the glacial productivity (Fig.4).A general decrease in BF^AR during the Holocene is also recorded in the 14K core on the Hatton Bank (Thomas et al., 1995). The overall changes in the species composition of the benthic faunas during the Holocene suggests that the amount of organic material incorporated into the sediments was increasing and the oxygen content decreasing.this seems surprising considering that the planktic fauna and the benthic and planktic accumulation rates indicate that benthic food supply was highest during the early Holocene and generally decreasing during the remainder of the Holocene.We attribute this apparent paradox to slower bottom currents combined with a more sustained ux of organic matter leading to poorer oxygenation and higher content of organic matter in the sea oor sediments. The time interval around 6.5 ka BP is generally described as the peak warm period of the Holocene correlating with an expansion of warm North Atlantic surface water into the Nordic seas (e.g. Koc et al., 1993; Sarnthein et al., 1995).We have not found a clear temperature optimum on the southern Reykjanes Ridge.However, in DS97-2P, the Neogloboquadrina pachyderma d^globigerina bulloides fauna shows a small increase in relative abundance during the mid^ late Holocene ca.6.5^3.5 ka BP indicating higher SST (Figs.2 and 7).This increase occurs somewhat later than the temperature optimum in the Nordic seas (Fig.2) The glacial Interstadials The interstadials resemble the Holocene interval in many aspects with equally high productivity, although they show consistently somewhat lower SST (Figs.3 and 4). van Kreveld et al. (1996), in a low-resolution study of core T88-9P from the NE Atlantic, also found that the planktic foraminiferal productivity for the intervals between Heinrich events H1^H6 equalled that of the Holocene. In nearby core SO82-05 (Fig.1), summer SST reached an average of 8 C during all interstadials (van Kreveld et al., 2000).This is lower than the recent average summer temperature (11 C) at the site.in DS97-2P and ENAM33, interstadial SST was s 9 C as indicated by the proportion of Neogloboquadrina pachyderma s, and thus also lower than the present SST of about 12 C.At both DS97-2P and ENAM33, SST jumped from 6 4 to s 9 C between interstadials and stadials.a similar magnitude in interstadial/stadial SST shifts based on transfer functions was calculated by van Kreveld et al.(2000).in the eastern North Atlantic Bond et al.(1993) also found SST jumps of 5^6 C for the Dansgaard^Oeschger cycles of MIS 3. During the interstadials, species connected to sustained food ux such as Bulimina exilis and Bolivina pseudopunctata are absent (except for the BÖlling/AllerÖd interstadials; Fig.5).They are replaced by Nonionella spp.and Pullenia spp., two genera that are adapted to irregular, high organic uxes and probably episodic anoxia in the sediments.thus, bottom conditions during the interstadials were not very di erent from those of the Holocene, only the deep currents may have been more sluggish. The conclusions above agree well with previous studies of the interstadial palaeoceanography in the area.on the basis of analyses of foraminifera, oxygen isotopes and sediments from cores in the SE Norwegian Sea, Rasmussen et al.(1996a,b, 1998) suggested that the interstadial circulation pattern closely resembled the modern pattern in the area, which is characterised by cold out ow water from the Nordic seas and formation of NADW.Convection and modern-like deep water formation in the Nordic seas during interstadials are also indicated by high N 13 C values in benthic foraminifera in a core from the VÖring Plateau (Dokken and Jansen, 1999). However, distinctive changes in the composition of the benthic faunas suggest that the bottom conditions of the various interstadials were not uniform, but changed over time (Figs.5 and 6). The increase in Epistominella vitrea during MIS 2

16 158 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^176 indicates colder bottom water, reduction in food supply and improved oxygenation as compared to intervals with high abundances of Fursenkoina fusiformis.overall, the changes in the benthic faunas during MIS 3 and MIS 2 suggest a deterioration of the bottom conditions over time.it is interesting to note that in both the SE Norwegian Sea and the Labrador Sea E. vitrea also attains maximum relative abundance during late MIS 3 and MIS 2 (Rasmussen et al., 1996a, 2002a).The simultaneous spreading of E. vitrea across the North Atlantic region suggests that bottom conditions at mid-depths during the late MIS 3 and MIS 2 interstadials became more and more alike Younger Dryas, stadials and Heinrich events In contrast to the interstadials, productivity was low during the Younger Dryas, stadials and Heinrich events (Figs.4 and 7). Thomas et al. (1995) suggest that the variations in productivity were caused by movements in the polar front. During the stadial periods the front moved south to a position south of our core sites (Fig.1).The results of both the DS97-2P and ENAM33 cores corroborate this interpretation.the low SST, the abundant IRD and the low N 18 O values during stadials clearly indicate polar conditions with glacial meltwater at the surface.it was inferred by van Kreveld et al.(2000) that during the stadials the East Greenland Current expanded causing SSTs in the central North Atlantic to drop below 4 C. However, the front movements also induced some signi cant changes in the bottom water as indicated by the uctuations in the benthic faunas and N 18 O values (Figs.5 and 6).Modelling of grain-size distributions indicates decreased ow strength of the ISOW during ice rafting events (Prins et al., 2001, 2002).Grain size investigations of stadial and interstadial sediments from ENAM33 and ENAM93-21 indicate strong reductions in current velocities during the stadial events (Kuijpers et al., 1998b; Rasmussen et al., 1998).The benthic faunas indicate oligotrophic bottom conditions during the stadials, very low productivity, and slightly reduced oxygen content. Investigations of N 13 C variations at mid-depth from the Portuguese margin (Zahn et al., 1997), the north central North Atlantic (Curry et al., 1999), and the SE Labrador Sea (Rasmussen et al., 2002a) demonstrate low values during Heinrich events.this indicates that the intermediate depth water in the North Atlantic region was old and poorly ventilated, in agreement with the evidence from the benthic faunas. Rasmussen et al.(1996a,b) suggested that the water mass was similar to the Glacial North Atlantic Intermediate Water (GNAIW) present at intermediate depth in the North Atlantic Ocean during the LGM (Oppo and Lehman, 1993).However, the benthic conditions during the stadials and Heinrich events differed profoundly from those of the LGM as they are represented in ENAM33.The faunas of the LGM indicate lower bottom temperatures and the productivity both at the surface and at the bottom was relatively high (Rasmussen et al., 2002b). Furthermore, the GNAIW had high N 13 C values and was well oxygenated (Oppo and Lehman, 1993). The increase in the Atlantic species group probably also indicates a gradual warming of the bottom water during stadials and Heinrich events (Rasmussen et al., 1996a,b, 1997, 2002a) (Figs.5 and 6).Rasmussen et al.(1996a,b, 1997) interpret similar changes in the SE Norwegian Sea to indicate intrusion of Atlantic intermediatedepth water below a layer of meltwater, causing a gradual warming of the bottom water.the intrusion was possible because convection ceased during Heinrich events and out ow from the Nordic seas stopped.the very high abundance of the Atlantic species group at intermediate depth in the central and NE Atlantic seems to corroborate this interpretation.still, the origin of this middepth water mass remains controversial (e.g. Rasmussen et al., 1996b; Vidal et al., 1998; Curry et al., 1999; Dokken and Jansen, 1999; Bauch et al., 2001; Rasmussen et al., 2002a). 7. Conclusions During the Holocene period, subpolar species dominated the planktic foraminifera at the locations of cores DS97-2P and ENAM33 from the central and eastern North Atlantic, respectively.

17 T.L. Rasmussen et al. / Marine Micropaleontology 47 (2002) 143^ Turborotalia quinqueloba was the dominant species, in particular during the early Holocene, when it constituted more than 60% of the planktic fauna.it decreased in relative abundance during the Holocene to an average of about 35% during the latest part. At the location of core DS97-2P on the Reykjanes Ridge, the surface and bottom productivity decreased from a maximum in the early Holocene to a minimum in the late Holocene.Among the benthic species, Bulimina exilis and Bolivina pseudopunctata increased, while Globocassidulina subglobosa, Trifarina angulosa, Cassidulina laevigata, Gavelinopsis praegeri and Epistominella exigua decreased.the faunistic changes re ect changes in food supply, current activity, and oxygen conditions.food supply was generally high, but it seems to have decreased slightly during the Holocene.However, due to decreasing currents and, possibly, more sustained food uxes oxygen conditions at the bottom became increasingly less favourable.a weakly developed SST maximum occurred 6.5^3.5 ka BP. Living conditions for the planktic and benthic foraminifera became increasingly unstable during the late Holocene with stronger variations in productivity both at the surface and the bottom.this was probably due to greater thermohaline instability caused by migrations of the Subarctic Front moving closer to the site. The surface and deep circulation during the interstadial periods of MIS 3 to MIS 2 was similar to the modern and Holocene circulation with convection in the Nordic seas and generation of NADW.However, SSTs were somewhat lower than at present. Turborotalia quinqueloba dominated the planktic fauna, whereas Globocassidulina subglobosa, Trifarina angulosa, Gavelinopsis praegeri, Epistominella exigua, Nonionella spp., Pullenia bulloides, Epistominella vitrea and Fursenkoina fusiformis dominated the benthic faunas. Two of these, namely E. vitrea and F. fusiformis are almost totally absent from the Holocene and modern faunas in the areas. The planktic and benthic faunas during the stadials and Heinrich events were very di erent from the interstadial and Holocene faunas. Neogloboquadrina pachyderma s was totally dominating at the surface indicating low SSTs.The Atlantic species group dominated the benthic faunas. The group consisted of epifaunal species adapted to low food conditions and reduced oxygen content.the productivity was extremely low and comparable to oligotrophic areas today.numerous icebergs delivered IRD to the sediments, and the surface water had probably low salinity due to a high input of meltwater.the NADW was replaced by an old, poorly ventilated, intermediatedepth water mass. While the benthic faunas of the various stadials and Heinrich events are almost identical, the interstadial faunas show a distinct change through time from early MIS 3 to late MIS 2.The faunas of the early interstadials were very similar to the Holocene fauna.from mid-mis 3 and during MIS 2 opportunistic species such as Fursenkoina fusiformis and Epistominella vitrea increased in relative abundance suggesting more extreme environmental conditions with irregular food supply and episodic anoxia. The changes in fauna composition and productivity during the glacial period were abrupt and distinct.markedly di erent faunas replaced each other on a millennial time scale.this pattern is completely di erent from the gradual changes that characterise the Holocene period.the Holocene fauna has existed almost unchanged for a time period of nearly years.except for moderate uctuations, the only noticeable modi- cation has been the appearance of Fursenkoina cf. F. tenuis and Globigerinita uvula during the late Holocene. Acknowledgements Core DS97-2P was collected in 1997 during a cruise of R/V Professor Logachev, nanced by the Netherlands Geoscience Foundation (GOA/ NWO^ALW).Additional support was provided by the Free University of Amsterdam and the Geological Survey of Denmark and Greenland (GEUS).GOA/NWO^ALW also supported further work, i.e. AMS 14 C dating and stable isotope stratigraphy.core ENAM-33 was collected in 1993 during a cruise of R/V Pelagia conducted