Enhanced δ13C and δ18O differences between the South Atlantic and South Pacific since the last glaciation gives us clues on how the ocean exhaled: The deep gateway hypothesis

Date & time

12–1pm 14 March 2018

Location

Hales Seminar room, J7

Speakers

Dr Elisabeth Sikes (Rutgers University)

Enhanced vertical gradients in benthic foraminiferal δ13C and δ18O in the Atlantic and Pacific during the last glaciation have revealed that ocean overturning circulation was characterized by shoaling of North Atlantic sourced interior waters; nonetheless, our understanding of the specific mechanisms driving these glacial isotope patterns remains incomplete. Comparing high-resolution depth transects of benthic foraminiferal  δ13C and δ18O from the Southwest Pacific and the Southwest Atlantic, examines the relative changes in northern and southern sourced deep waters during the Last Glacial Maximum (LGM) and deglaciation. During the LGM, our transects show that water mass properties and boundaries in the South Atlantic and Pacific were significantly different from one another below 2500 m. The compositional difference between the deep portions of the basins implies independent deep water sources during the glaciation. We attribute these changes to a “deep gateway” effect whereby northern sourced waters shallower than the Drake Passage sill were unable to flow southward into the Southern Ocean because a net meridional geostrophic transport cannot be supported in the absence of a net east-west circumpolar pressure gradient above the sill depth. We surmise that through the LGM and early deglaciation, shoaled northern sourced waters were unable to escape the Atlantic and contribute to deep water formation in the Southern Ocean

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