Radiocarbon chronology of depositional regimes in the western Arctic Ocean

The foraminiferal abundance and percentage of coarse ice-rafted detritus (IRD) define glacial, deglacial, and interglacial depositional regimes in AMS radiocarbon-dated box cores from the western Arctic Ocean. Sediment deposition rates are generally less than 0.5 cm/ka for glacial regimes, greater than this for deglacial regimes and greater than 1-2 cm/ka for interglacial regimes. These differences in deposition rates might account for the much lower average sedimentation rates for the last 780 ka of 1-3 mm/ka in cores from the central Arctic Ocean if glacial regimes dominated this interval. Foraminiferal abundances are less than 500/g during glacial maxima and mostly higher than 2000/g during deglacial and interglacial regimes. Slightly higher coarse IRD percentages occur in deglacial intervals (> 5-10% up to 30%) compared with interglacial intervals (mostly less than or equal to 5%), which characterize the last 10-12ka in the western Arctic Ocean. Glacial regimes occurred from about 40 to 11 ka except for a brief interglacial or deglacial interval around 24-28 ka in the central Arctic Ocean. The coarsest deglacial events occurred prior to 45 ka. The Late Wisconsin deglaciation sediments (approximately 9-16 ka) are difficult to detect in the central Arctic Ocean sediments because they are only slightly coarser than the Holocene and, in some box cores,less coarse than the Holocene. A previously unrecognized coarse IRD event occurred near the core tops (0-3 cm) between 1500 and 3500 radiocarbon years ago in the western Arctic Ocean. Only sediment older than 40 ka is coarser than this recent IRD event, which might correspond to a Neoglaciation recognized in the North Atlantic and elsewhere. (C) 1998 Elsevier Science Ltd. All rights reserved.