Last Glacial Maximum surface water properties and circulation over Laurentian Fan, western North Atlantic

摘要

Millennial scale events marked by the contribution of detrital sand are recorded in North Atlantic sediments during the Last Glacial Maximum (LGM), between Heinrich events (HE) 1 and 2, and left their imprint on Laurentian Fan (LF - 43 degrees N) sediments off eastern Canada. The LF counterpart of the well-known detrital events consist of glacial red-brick sediments resulting from subglacial flows separated by olive-grey sediments appears at similar to 21.4-19.9 and similar to 19.5-18.65 cal kyr BP. High-resolution analyses of diatom assemblages and lithic grains coupled with planktonic oxygen isotopic records reveal that while the red sediment is almost barren of diatoms, foraminifera and lithics (150 mu m), they are abundant in the olive-grey sediment. Diatom assemblages reveal three phases during these events: (1) initial relatively warm temperate conditions followed by (2) very cold surface water and drifting ice, and (3) a final phase characterized by relatively warmer waters and the appearance of detrital carbonate. Although these events possibly reflect the variability specific to the slope water region, they are likely the response to Atlantic Meridional Overturning Circulation perturbations and ice-sheet instability. Through a chain of mechanisms, meltwater inputs into the North Atlantic led ultimately to an increased volume of tropical waters and part of the heat stored in the subsurface was flushed by a brief convective episode that was not sustained, accounting for the return of cold conditions after the events. The sequence of mechanisms deduced from the paleo data here and elsewhere is consistent with previous modeling results. These data suggest that the detrital events between Heinrich event 1 and 2 may be synchronous across the North Atlantic, and that the LGM was probably not a time of prolonged steady state in the climate system. (C) 2018 Elsevier B.V. All rights reserved.