Mean sortable silt values from Holocene and glacial Scotia Sea sediments

The Antarctic Circumpolar Current is key to the mixing and ventilation of the world's oceans. This current flows from west to east between about 45° and 70° S connecting the Atlantic, Pacific and Indian oceans, and is driven by westerly winds and buoyancy forcing. High levels of productivity in the current regulate atmospheric CO2 concentrations. Reconstructions of the current during the last glacial period suggest that flow speeds were faster or similar to present, and it is uncertain whether the strength and position of the westerly winds changed. Here we reconstruct Antarctic Circumpolar Current bottom speeds through the constricting Drake Passage and Scotia Sea during the Last Glacial Maximum and Holocene based on the mean grain size of sortable silt from a suite of sediment cores. We find essentially no change in bottom flow speeds through the region, and, given that the momentum imparted by winds, and modulated by sea-ice cover, is balanced by the interaction of these flows with the seabed, this argues against substantial changes in wind stress. However, glacial flow speeds in the sea-ice zone south of 56° S were significantly slower than present, whereas flow in the north was faster, but not significantly so. We suggest that slower flow over the rough topography south of 56° S may have reduced diapycnal mixing in this region during the last glacial period, possibly reducing the diapycnal contribution to the Southern Ocean overturning circulation.

Age determination of Lake Melkoe sediments

The formation of Lake Melkoe (64°51'30''N, 175°14'E, altitude 36 m), one of the largest lakes of the Anadyr Lowland, is related to the moraine left by the Tyellakh Glacier, which originated on the Pekul'nei Ridge. The lake (6 km long and 4.4 km wide) extends in the northwestern direction. The Kholmy Priozernye moraine (16 km long along the arc, 1.5 km wide, and 92-103 masl) surrounds the lake in the west and south. The lake coasts are covered by sand with pebbles and shingle. The flat lake bottom dips toward its central part to a depth of 160 cm. In distinction from many other lakes of the Anadyr Lowland, the thickness of the upper layer of water-saturated sediments overlying compact aleurites in Lake Melkoe is only 5-6 cm. Such a peculiarity of the bottom is explained by the large size of the lake, low sedimentation rates, and frequent storms caused by strong winds. Regional and local vegetation corresponds to a mosaic tundra represented by high shrubs Pinus pumila, Duschekia fruticosa , and hummocky Betula - Ericales - Eriophorum communities. Pinus pumila and Alnus form thickets on the banks of the Anadyr River, coasts of lakes, and moraine slopes.