Late Quaternary paleoceanography in the Fram Strait

Abstract

Four sediment cores from the Fram Strait (78°N) have been studied to reconstruct the paleoceanography of this major connection of the Arctic Ocean to the world ocean. Back to oxygen isotope stage 5 (128 kyr ago) the stratigraphic interpretation of the cores is based on oxygen isotope and accelerator mass spectrometry data; the identification of oxygen isotope stage 6 is based on paleomagnetic and coccolith data. Parameters indicative for contrasting environmental conditions such as high input of ice‐rafted detritus (IRD) or seasonally open waters display characteristic sequences by which the paleoce anography of this region can be reconstructed for the last 180 kyr. The geographic setting of Fram Strait and the sediment data indicate a permanent meridional circulation pattern throughout the last 180 kyr, as it is typical, for example, for the present‐day circulation. Depending on the strength of advection, Atlantic waters appeared in Fram Strait as surface waters, resulting in seasonally ice‐free conditions, or as subsurface water masses, underlying polar waters perenially covered by ice. Sustained periods of seasonally ice‐free waters were largely restricted to interglacial stages 5.5, 5.1, and the Holocene. However, a few short events characterized by seasonally ice‐free conditions at 78°N are recorded during glacial stages as well, for example, stage 6, late stage 3, and stage 2 (“Nordway” events). These events provide for supply of moisture, and therefore they are closely related to the history of the European Arctic ice sheets. Strong input of IRD, reflecting severe glaciations on surrounding landmasses, occurred during most of stage 6, in early stage 3, and during stage 2. Variations in IRD input allow differentiation between three major source areas: (1) Svalbard/Barents Sea during major glacier advances in stages 2 to 5; (2) most likely Siberia during stage 6; and (3) Fennoscandia during the short events in glacial periods marked by seasonal open waters. Thus the circulation pattern in the Fram Strait remained rather stable throughout the last 180 kyr, while variations in the sediment composition are mainly due to the intensity of Atlantic water advection and to the prevailing IRD input pathway.