Surface and deep-water hydrography on Gardar Drift (Iceland Basin) during the last interglacial period

Abstract

Changes in surface and deep-water hydrography were inferred from variations in stable isotopes and sortable silt mean grain size, respectively, on the southern Gardar Drift in the subpolar North Atlantic. The bathymetric δ 13C gradient during the penultimate glaciation was similar to the last glaciation with high- δ 13C Glacial North Atlantic Intermediate water above ∼ 2000 m, and low- δ 13C water derived from the Southern Ocean below. During Termination II, low- δ 13C water was present throughout the water column with minimum values at intermediate depths (∼ 1500–2000 m) and below 3000 m. This pattern continued well into the early part of the Last Interglacial (LIG) period. Sortable silt mean size at 3275 m suggests that deep-water circulation on Gardar Drift was relatively weak during the earliest part of the LIG (128 to 124.5 ka) when planktonic δ 18O was at a minimum, reflecting warming and/or reduced salinity. We suggest that low- δ 13C water and slow current speed on Gardar Drift during the early part of the LIG was related to increased melt water fluxes to the Nordic Seas during peak boreal summer insolation, which decreased the flux and/or density of overflow to the North Atlantic. The resumption of the typical interglacial pattern of strong, well-ventilated Iceland Scotland Overflow Water was delayed until ∼ 124 ka. These changes may have affected Atlantic Meridional Overturning Circulation.