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Contrasting Glacial/Interglacial Regimes in the Western Arctic Ocean As Exempli¢Ed by a Sedimentary Record from the Mendeleev Ridge

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Contrasting Glacial/Interglacial Regimes in the Western Arctic Ocean As Exempli¢Ed by a Sedimentary Record from the Mendeleev Ridge Palaeogeography,Palaeoclimatology,Palaeoecology 203 (2004) 73^93 www.elsevier.com/locate/palaeo Contrasting glacial/interglacial regimes in the western Arctic Ocean as exempli¢ed by a sedimentary record from the Mendeleev Ridge Leonid Polyak a;Ã,William B. Curry b,Dennis A. Darby c,Jens Bischof c, Thomas M. Cronin d a Byrd Polar Research Center, Ohio State University, Columbus, OH 43210, USA b Woods Hole Oceanographic Institution, Woods Hole, MA02543, USA c Old Dominion University, Norfolk, VA23529, USA d US Geological Survey, Reston, VA20191, USA Received 1 August 2002; received in revised form 14 August 2003; accepted 19 September 2003 Abstract Distinct cyclicity in lithology and microfaunal distribution in sediment cores from the Mendeleev Ridge in the western Arctic Ocean (water depths ca. 1.5 km) reflects contrasting glacial/interglacial sedimentary patterns. We conclude that during major glaciations extremely thick pack ice or ice shelves covered the western Arctic Ocean and its circulation was restricted in comparison with interglacial,modern-type conditions. Glacier collapse events are marked in sediment cores by increased contents of ice-rafted debris,notably by spikes of detrital carbonates and iron oxide grains from the Canadian Arctic Archipelago. Composition of foraminiferal calcite N18O and N13C also shows strong cyclicity indicating changes in freshwater balance and/or ventilation rates of the Arctic Ocean. Light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca. 12 14C kyr BP. The prolonged period with low N18O and N13C values and elevated contents of iron oxide grains from the Canadian Archipelago in the lower part of the Mendeleev Ridge record is interpreted to signify the pooling of freshwater in the Amerasia Basin,possibly in relation to an extended glaciation in arctic North America. Unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the Mendeleev Ridge and other mid-depth locations throughout the Arctic Ocean such as the Northwind and Lomonosov Ridges. This correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for Arctic Ocean sediments. ß 2003 Elsevier B.V. All rights reserved. Keywords: Arctic Ocean; Quaternary; stratigraphy; paleoceanography; glaciation; ice rafting; Foraminifera; Ostracoda; stable isotopes; provenance 1. Introduction * Corresponding author. Tel.: +1-614-292-2602; Fax: +1-614-292-4697. The Arctic Ocean plays a major role in the late E-mail address: [email protected] (L. Polyak). Cenozoic evolution of the Earth’s environmental 0031-0182 / 03 / $ ^ see front matter ß 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0031-0182(03)00661-8 PALAEO 3228 5-1-04 74 L. Polyak et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 203 (2004) 73^93 system,including the modern climatic change Ocean sedimentary archives for understanding (e.g., Aagard et al.,1999 ). The most important the Earth’s Quaternary climatic evolution,rela- aspects of the interaction between the Arctic tively few sedimentary records have become avail- Ocean and the global climate are (1) vast ice cover able for detailed investigation because of opera- that increases albedo and controls a signi¢cant tional constraints in the ice-bound Arctic Ocean part of the global energy balance,and (2) the interior. In addition to logistical problems of ob- control on the oceanic thermohaline circulation taining sediment cores,it is di⁄cult to develop an through the water exchange with the Atlantic unequivocal stratigraphy of late Cenozoic sedi- and Paci¢c oceans (Delworth et al.,1997; Smith ments because of the meagerness of biotic re- et al.,2002 ). The Quaternary history of the Arctic mains,low sedimentation rates of mostly below Ocean features multiple dramatic changes associ- 1 cm/kyr,and the unique history of the Arctic ated with glaciations and deglaciations of the arc- Ocean. In recent years,several late Cenozoic sedi- tic periphery and sea level £uctuations. During mentary records with a moderate temporal reso- glacial periods and low sea levels,extensive areas lution have been investigated from the Arctic of shallow arctic shelves were exposed and par- Ocean interior,mainly from intermediate water tially covered by ice sheets,which drastically re- depths,such as on the Northwind and Lomono- duced the circulation within the Arctic Ocean and sov Ridges (Fig. 1; Poore et al.,1993,1994; Phil- the inter-oceanic water exchange. This,together lips and Grantz,1997; Spielhagen et al.,1997; with more severe ice conditions in the ocean in- Jakobsson et al.,2000,2001 ). However,di¡erent terior,had a dramatic e¡ect on sedimentary envi- stratigraphic approaches employed in these stud- ronments. Despite the importance of the Arctic ies result in di¡ering age models and contrasting Fig. 1. (A) Map of the Arctic Ocean with bathymetry in 1-km contour lines. Inset area (B) is shaded. Black circle shows the lo- cation of NP26 cores; un¢lled circles show locations of cores from Northwind and Lomonosov Ridges used for stratigraphic cor- relation (Fig. 10). Arrows show major current systems: Beaufort Gyre and Transpolar Drift. (B) Map of the Mendeleev Ridge and Chukchi Borderland with bathymetry in 500-m contour lines (from Perry and Fleming,1986 ). Black circles show location of NP26 cores 5 and 32; un¢lled circles indicate other cores referred to in the paper; triangles indicate hydrographic pro¢les shown in Fig. 2. PALAEO 3228 5-1-04 L. Polyak et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 203 (2004) 73^93 75 paleoceanographic interpretations. This under- layer with a core at depths of ca. 200^500 m scores the necessity to investigate more sedimen- originates from the North Atlantic Drift; this tary records from the Arctic Ocean aiming at mul- water retains fairly high heat content resulting in ti-proxy studies of sea£oor areas with relatively temperatures s 0‡C throughout the Arctic Ocean high sedimentation rates. In this paper,we present (Fig. 2). The water column above this Atlantic- results of a multi-proxy investigation of a sedi- derived layer contains the Paci¢c water that in- ment core record from intermediate water depths £ows via the Bering Strait and is characterized at the Mendeleev Ridge in the western part of the by high nutrient contents and relatively low salin- Arctic Ocean (Amerasia Basin). ity of 6 33 psu. The balance of Atlantic and Pa- ci¢c waters £owing into the Arctic Ocean varies with time (Carmack et al.,1997; Steele and Boyd, 2. Study area 1998). Currently,the front between Atlantic and Paci¢c components in subsurface waters is located Mendeleev Ridge is an elevated portion of the along the Mendeleev Ridge (Jones et al.,1998 ), Arctic Ocean £oor extending from the East Sibe- which underscores the signi¢cance of this area for rian shelf towards the North Pole (Fig. 1). On the studying the long-term changes in the Arctic cir- shallow southern part of the Mendeleev Ridge culation. The surface water of the Arctic Ocean and adjacent Chukchi Borderland (Chukchi Pla- receives the voluminous river runo¡ that keeps teau and Northwind Ridge),sedimentation rates the salinity low and thus maintains the sea ice are higher than in the interior of the Amerasia cover. Ice and the sur¢cial waters are involved Basin (Poore et al.,1993; Phillips and Grantz, in a wind-driven circulation which forms the anti- 1997),probably because of sediment transport cyclonic Beaufort Gyre over the Amerasia Basin from the adjacent shelves and more frequent (Fig. 1). The major gateway for out£owing low- summer ice melt. Modern sedimentation rates salinity surface water is the Fram Strait; addition- were estimated to be as low as 0.2^0.3 mm/kyr throughout the Amerasia Basin by 230Th and pore water chemistry methods (Cranston,1997; Huh et al.,1997 ); however, 14C data from the Chukchi Borderland show up to two orders of magnitude higher sedimentation rates during the deglaciation and the Holocene (Darby et al., 1997). The strati¢ed water mass structure of the Arctic Ocean includes the low-salinity surface water,sev- eral intermediate water layers,and the bottom waters (Aagard et al.,1985 ). Cold and saline bot- tom waters are formed by the exchange with the Norwegian-Greenland Sea via the Fram Strait and by cascading of dense water ejected by ice formation on the shelves. The Amerasia and Eur- asia Basins of the Arctic Ocean are separated by Fig. 2. Hydrographic pro¢les from the Mendeleev Ridge area the Lomonosov Ridge with a sill depth of ca. (Fig. 1; data from Ekwurzel et al.,2001 ). Shown are poten- 1500 m; as a result,their deep waters have some- tial temperature,salinity,and equilibrium calcite N18O (vs. what di¡ering thermohaline properties and resi- PDB) estimated from temperature and water N18O using the dence times. The deep water of the Amerasia Ba- equation of Shackleton (1974). Halocline and thermocline 3 levels are highlighted. Right panel shows details of the upper sin is relatively warm ( 0.5‡C) and may have a portion of the water column. Gradient in surface salinity and notably old age of almost 1000 years (Macdonald N18O re£ects the contribution of runo¡ related to the dis- and Carmack,1991 ). The major intermediate water tance from the shelf. PALAEO 3228 5-1-04 76 L. Polyak et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 203 (2004) 73^93 Table 1 3. Materials and methods Geographic position of sediment cores under study Core No. Latitude Longitude Water depth Sediment cores used in this study were collected (‡N) (‡W) (m) with a gravity corer in 1983 from a Russian drift- NP26-5 78‡58.7P 178‡09P 1435 ing ice camp ‘Severnyj Polyus (North Pole) 26’ NP26-32 79‡19.4P 178‡04P 1610 (further referred to as NP26).
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