High-resolution isotopic and micropaleontological studies of upper Pleistocene sediments at ODP Site 645, Baffin Bay

Abstract

The oxygen and carbon isotopic compositions of the planktonic foraminifer, Neogloboquadrina pachyderma (sinistral), were determined at 20-cm intervals through the "composite' top ~22 m of sediments at ODP Site 645 (Holes 645B, 645C, 645F, and 645G) and at 10-cm intervals through a 9-m piston core (85-027-016) collected during the Hudson site survey. Quantitative analyses of palynomorphs, notably dinocysts, and of planktonic foraminifers were performed. Organic and nitrogen contents and isotopic composition of nitrogen and carbon in organic matter also were determined. These data provide a high-resolution record of changes that occurred in surface-water masses during the last glacial cycle in Baffin Bay. The basin experienced low planktonic productivity during most of the late Pleistocene, either from dilution in surface water by meltwater discharges from the surrounding ice-sheet or from the presence of a relatively dense sea-ice cover. Peaks of meltwater discharge are indicated by δ18O values as low as about 1.5‰, correlative δ13C-δ18O shifts, low concentration of planktonic foraminifers, high concentrations of glacially reworked pre-Quaternary palynomorphs, and low-salinity dinocyst assemblages. As a whole, δ18O values ranging between 4.5 and 2.5‰ allow the establishment of an 18O stratigraphy spanning isotopic stages 5 to 1. Because of the poor core recovery, the general paucity of microflora and microfauna, and the possible occurrence of slumping or debris flow at Site 645, further interpretation remains problematic. -Authors