Magnetic properties of deep-sea sediments off southwest Greenland: Evidence for major differences between the last two deglaciations

High-resolution rock magnetic data, atomic mass spectroscopy ¹⁴C dates, δ¹⁸O, and grain-size analyses from a piston core (HU90-013-013) located off southwest Greenland provide a record of the last two deglaciations. During Termination I, a welldefined interval having high volumetric magnetic susceptibility (k) and a low ratio of anhysteretic susceptibility to volumetric magnetic susceptibility (k_ARM/k) postdates the Younger Dryas and the δ¹⁸O change marking the stage 2/1 boundary and correlates with sedimentological and geomorphological evidence for Greenland ice-sheet retreat from the coastline to the continental interior. During Termination II, a very similar magnetic signal coincides with the δ¹⁸O shift marking the stage 6/5 glacial-interglacial transition and continues throughout substage 5e. We suggest that this magnetic signal, during both Termination I and Termination II, marks continental meltwater–carried detritus from Greenland. If so, the synchronous changes in magnetic and oxygen isotopic records at Termination II indicate very early and rapid deglaciation of Greenland, in contrast to the relatively late deglaciation observed for Termination I. Distinct fluctuations in k and k_ARM/k occur below the onset of the δ¹⁸O change at Termination I (where they occur at ∼16 900 yr B.P.) and at Termination II. These fluctuations are interpreted as due to sudden influxes of detritus into the basin caused by unpinning of ice from the continental shelf at the inception of deglaciation.