The climate-sensitive Vesterisbanken area (central Greenland Sea): Depositional environment and paleoceanography during the past 250,000 years MARTIN ANTONOW1, PETER MARTIN GOLDSCHMIDT2j3and HELMUT ERLENKEUSER2 1. Freiberg University of Mining and Technology, Institute of Geology, Bernhard-von-Cotta-Str. 2, D-09596 Freiberg, Germany 2. SFB 313, University of Kiel, Heinrich-Hecht-Platz 10, D-24118 Kiel, Germany 3. present address: PCD, Eckernforder Str. 259, D-24119 Kiel, Germany ABSTRACT Sedimentological, micropaleontological and geochemical studies of sediment cores from the Vesterisbanken region were used to reconstruct the sedimentation pattern, depositional history and paleoceanography for this area over the last 250,000 years. The dating and correlation of the sediments were based on oxygen isotope stratigraphy and absolute ages. The hemipelagic deposits near the Vesteris Seamount are characterised by biogenic, ter- restrial and volcanogenic sediment input that varies through time. The area was influenced by sporadic turbidity currents and thermohaline-induced contour currents. Ice-rafted debris occurred nearly throughout the investigated time interval. Primary production was higher during interglacial periods. Filter-feeding epifauna (C. zi~~~t~llt~rst~rji),an indicator of bottom cur- rents, dominated in isotope stages 7 and 5. During deglaciation (stage boundaries 8/7, 6/5 and 2/1, events 3.3 and 3.1), enorinous meltwater inp~~tstabilised the water column, leading to periodic interruptions in deep water renewal. The influence of water masses from the Polar and Atlantic Domains in the Greenland Sea were very variable over time. The oceanic fronts in the Vesterisbanken area were always close together, allowing only a narrow Arctic Domain to exist. Although the area is rather unique in relation to other parts of the Greenland Sea, climatic data can be compared favourably to the established Late Pleistocene/Holocene sedimentation pattern in the northern North Atlantic. Due to their good correlation to ice core records from Greenland and Antarctica, the Vesterisbanken sediments present a high-resolution picture of global climate change. INTRODUCTION: THE VESTERIS SEAMOUNT bathylnetry and gave rise to strong basaltic volca- IN THE GREENLAND SEA nism that event~lally generated the Vesteris The Greenland Sea is one of the few links between Seamount (73"301N,9"101W, Fig. 1).Vesterisbanken the Arctic Ocean and the northern North Atlantic. rises from the Greenland abyssal plain up to 133 in This area is reinarkably sensitive to oceanographic water depth (Johnson & Campsie, 1976), thus for- and climatic changes because Polar and Atlantic ming the only intra-plate volcano in the ~~orthern water masses mix here. Morphologically, the North Atlantic. Greenland Sea is framed by major fracture zones The goal of this investigation is to provide a and ridges such as Knipovich and Mohns Ridges to reconstruction of the climatic development and the the east and the Greenland continental slope/shelf sedimentary environment of an area of the to the west (Vogt, 1986). Tectonically, sea-floor Greenland Basin that has been studied relatively spreading since the Paleocene led to a complex little due to a thck ice cover linliting access. The In: Hass, H.C. & Kaminski, M.A. (eds.) 1997. Contributions to the Micropaleontology and Paleoceanogra- phy of the North Atlantic. Grz!ybozoski Fo~lildatio~lSpccinl Pllblicntion, no. 5, pp. 101-118 a - P6hocny Atlantyk Antonow, Goldschmidt and Erlenkeuser central reasons and questions to be answered for this study are: 1. The determination of sedimentation in the Vesterisbanken area. - What depositional processes affected the study area? -Was there a temporal variation of different sedimentation patterns? 2. Paleoceanographic determination for the central Greenland Sea area. - Which paleo-surface water masses influenced the area around the Vesterisbanken and how variable is the position of the oceanic fronts? - When did meltwater pulses change the isotopic character of the Greenland Sea? 3. The integration of these results into the pattern of Late Pleistocene-Holocene sedimentation and paleoceanography of the Greenland-Jceland- 1WW 0" 1WE I Norwegian Seas. -+Vlskris Sralnoulll 1.01) Polar "'3nl;lin N41, NorlI~Athtl~lic l)riKl - Does the paleoceanographic development of Pelur Fr,,nl ARD Arclic Lk,mi,in yVC;l Na~~-rrgi;n~~IU,anrla~ll Cx#rrsnl 1Vr.t SpiI.l>wgcn Cnmrrem~l - ~~~~i~ AND ~~l~,,~i~~,,,,,~i~I<SC I.**SpiIrlrl.gcn C<lr~.r.nl the central Greenland Sea agree with that of 1I"&c vr,,,,, WAC Retu1'83 Altdttlic C#8r1'cnl 1 other parts of the northern North Atlantic Ocean (e.g. the Norwegian and Iceland Seas)? - Did unique sedimentary or paleoceanographic events occur? Figure 1. Recent surface circulation and different hydro- 4. A comparison with global climate variations. graphic regimes of the Greenland-lceland-Norwegian - Can the marine climate information from the Seas (from Jiinger, 1994; modified after Paq~~ette1.t a/., Vesterisbanken sediments be correlated with 1985; Johaimessen, 1986; Bourke ct a/., 1987; Dickson ('t terrestrial signals from ice cores? 01. 1988). - How do the changes in the central Greenland Sea fit into the global framework of climate waters of the EGC represents the southward-flow- changes? ing Return Atlantic Current (RAC, Paquette et nl., 1985). RECENT CIRCULATION OF SURFACE AND DEEP WATERS Deep waters Surface waters Arctic Ocean Deep Water (AODW) enters the The modern hydrography of the Greenland Sea is Greenland basin from the north. There it mixes dominated by water masses of the Arctic Domain with the Greenland Sea Deep Water (GSDW) that is that contrast with those from the Polar and Atlantic formed due to surficial freezing processes: as a Domains (Figs. 1, 2). The region around the sub- result of the genesis of sea-ice, the surface water marine Vesterisbanken mountain complex is main- masses cool down and reach a high density (salt ly influenced by the East Greenland Current enrichment). They therefore sink, following the (EGC),which carries polar waters southwards. The convection of little "chimneys" (Aagaard ef nl., Jan Mayen Current branches off from the EGC and 1985; Rudels, 1990). Depending on the stratifica- moves southeastward, representing the southern tion of the water colulnn, these waters reach the flank of the cyclonic Greenland Sea Gyre (Figs. 1, bottom or stagnate as intermediate water lnasses 2). During winter, nearly the whole Greenland Sea (Fig. 2). The GSDW is assumed to cross the Mol~ns is ice-covered, whereas the summer ice distribution Ridge, moving southeast to the adjacent Lofoten retreats far to the west with strong interannual Basin (Koltermam, 1987). Temporary Greenland variations. Large amounts of sediment-laden Sea Deep Water renewal is described by Arctic sea ice are transported via Fram Strait into Koltermam (1987) and Jiinger (1994). the Norwegian-Greenland Seas (Vinje & Finne- kasa, 1986). Summer ice melting regionally produ- MATERIAL AND METHODS ces surface salinities below 29%0 (Koltermann, During the expedition ARK VII/l of the German 1987).Atlantic Intermediate Water (AIW) recircula- ice-breaking research vessel Polnrsfrr~z,short box ting in parts of the Fram Strait beneath the polar cores (GKG) and long kastenlot cores (KAL) were Vesterisbanken (central Greenland Sea) during the past 250,000 years 103 - Central Greenland Sea Influence of from the East --- NAW- North Atlantic Water NSDW - Norwegian c;,. 5" \v Deep Water Temperature Salinity Reference Surface Waters Polar Water < 0°C < 34.4 %< Swift (1986) EGC - East Greenland Current (EGC. JMC) -I°C 33 %< Hopkills (1991) JMC - Jan Maycn Current RAC- Return Atlantic Current Intermediate Water Pnquette et al. ( 1985) AIW (IIAC) 0.5 to 3OC 34.9 to 35 Ic(. Berner (1 99 1) ADW- Arctic Deep Water Deep Waters GSDW- Greenland Sea Deep Water AI)W -0.5 to -0.8"C 34.93 to 34.95 %r Hopkins (1991 ) AIW- Atlantic lntermediatc Water GSDW -I. l to -I.3"C 34.88 to 34.90 Tr Swift (1986) PW- I'olar Water Figure 2. Recent oceanography of the Greenland Sea after several authors (see text). recovered from the vicinity of the Vesteris Coarse fraction analysis Seamount (Thiede & Hempel, 1991). The present The analysis of the sediment composition of the study investigates sedimentation processes at sites two subfractions 125-250 pm and 250-500 pm was PS1878, PS1882, and PSI892 (Fig. 3, Table 1). To carried out according to the method of Sarnthein answer the questions raised in section 1, these sedi- (1971). When the sample had more than ca. 400 ment cores from the Greenland Sea were analysed particles per subfraction, a microsample splitter in terms of sedimentology, micropaleontology and was used to generate representative subsamples. geochemistry. The sampling interval was 4 cm. The presence and frequency of the coarse fraction analysis is represented in grain percent for each Granulometry subfraction. A Zeiss GSZ microscope was used for A combination of two size-dependent methods the analyses. was used to determine the total grain size. The Ca. 600-700 sediment particles were assigned to the boundaries of the grain size subfractions are based following groups: on the scale of Krumbein (1936). The weighed sediment sample was wet-sieved A terrigenous particles (quartz, rock fragments) to separate the fine (<63pm) and the coarse B volcanogenic particles (>631un) material. The coarse fraction was divided (brown and transparent, porous and amor- into five subfractions (63-125, 125-250, 250-500, phous glass, volcanic