Millennial-scale variability in late Pleistocene ice-rafting to the South Atlantic Ocean

Variability of ice discharge to the South Atlantic Ocean has been reconstructed on the basis of ice-rafted debris (IRD) concentration within marine sediments at three sites along a transect from 41° to 53°S, spanning the Polar Frontal Zone (PFZ). Discrete IRD layers recur on millennial timescales during the last glaciation (marine isotope stages (MIS) 2–4). Peaks in IRD are synchronous north and south of the PFZ. Therefore, such layers are not the result of temperature-controlled shifts in the locus of iceberg melting. Rather their synchroneity implies that the IRD layers represent increases in Antarctic ice discharge.; Downcore phase relationships and marine-ice core correlations suggest that millennial South Atlantic (SA) IRD events occur on the cooling limb after millennial-scale warming events on Antarctica. SA IRD events coincide with near-peak warmth of interstadial events recorded in Greenland ice, indicating an anti-phase relationship compared to Antarctic ice. Comparison of SA events with sea-level records suggests existence of sea-level linkage whereby melting of Greenland ice associated with enhanced North Atlantic Deep Water (NADW) formation and interstadial-warmth elevated sea level and “un-pinned” Weddell Sea ice shelves.; The millennial-scale pulses in IRD delivery to the South Atlantic that marked the last glaciation are characteristic of the last four glacial periods (MIS 2-4, MIS 6, MIS 8 and MIS 10) at Site 1094 (53°S). Suborbital variability in ice rafting also characterizes each of the last five interglacial periods (the Holocene, MIS 5, MIS 7, MIS 9 and MIS 11). An early hypsithermal period, characterized by low IRD and high foraminiferal abundance, is followed by a reversal of these conditions interpreted as a neoglaciation. Millennial IRD variability between glacial and interglacial periods is fundamentally different with respect to character (magnitude and recurrence interval) as well as cause. Whereas millennial IRD events of glacial periods are interpreted to represent times of increased Antarctic ice discharge, IRD deposition during interglacial periods is instead a manifestation of changes in iceberg and sea ice survivability controlled by fluctuations in sea-surface temperature resulting from north-south migration of the PFZ and winter sea-ice margin.