Glacial-interglacial environmental changes in the Drake Passage over the past 600 kyrs

Abstract

Oceanographic conditions in the Southern Ocean are closely related to the oceanic frontal system. Glacial-interglacial changes in cryosphere influence variations in oceanic fronts in the Southern Ocean and vice versa, causing changes in surface water productivity, nutrient utilization, bottom water chemistry, and/or bottom current intensity. Here, we documented geochemical, nitrogen isotope, and grain size records over the last 600 kyrs from the Drake Passage with previously published data to compare between glacial and interglacial oceanic conditions from surface to bottom. Biogenic opal (diatom) and export productions were high during interglacial periods and low during glacial periods. Surface water production was dominated by open ocean species during both glacial and interglacial periods without a clear glacial-interglacial change in sea ice species. After Marine Isotope Stage (MIS) 9, interglacial biogenic opal and diatom abundance increased distinctively with decreased terrestrial influence. Nutrient utilization increased (decreased) during interglacial (glacial) periods with increased (decreased) surface water production, particularly after MIS 9. This indicates that surface water production was regulated by light availability in association with sea ice duration/extent. According to good correlation between sortable silt mean grain size (SS MGS) and %sortable silt, SS MGS can be used for bottom current intensity indicator in this study; increased (decreased) bottom current during glacial (interglacial) periods. Increased glacial bottom current is likely related to southwestward flowing bottom current. Interglacial bottom current intensity became also significantly weakened after MIS 9. However, outstanding interglacial warmth in the Drake Passage occurred from MIS 9, not following the global trend to occur after MIS 11. This implies that more studies from the Southern Ocean in response to the Mid-Brunhes Event are required in the future.