229 Recent Advances in Paleoclimatology/Paleoceanography

Wednesday, 3 November 2010
8:00 AM - 12:00 PM
Room 607

REVVING THE ENGINE OF OCEAN CIRCULATION: ANTARCTIC CIRCUMPOLAR CURRENT DEVELOPMENT, LATE EOCENE-EARLY OLIGOCENE

Paper number: 229-7
Program: Technical Sessions
Time: 9:30 AM – 9:45 AM

Authors

Abstract

A critical climate and oceanographic transition occurred during the late middle Eocene to mid-Oligocene (~38-28 Ma), marked by global cooling and development of continental-scale Antarctic ice sheets. Progressive development of the Antarctic Circumpolar Current (ACC) and reorganization of global ocean circulation accompanied this climate transition. The ACC “engine” began to develop in the middle Eocene with shallow flow through the Drake Passage, followed by rapid deepening of the Tasman gateway (late Eocene to early Oligocene), and more gradual deepening of the Drake Passage through the remainder of the Oligocene. The ACC is a dominant feature of present-day ocean circulation and climate, influencing the strength of meridional overturning circulation, transition depth from surface to deep ocean, gas exchange rate between atmosphere and deep ocean, and global surface heat distribution.

Here, we present high-resolution benthic foraminiferal d18O and d13C records with Mg/Ca data from Atlantic Slope Project corehole 5 (ASP-5; ~600 m paleodepth, southeast US continental slope) and d18O and d13C records from ODP Site 1053 (~1500-1750 m paleodepth; Blake Nose), with comparisons to published isotopic records (Cramer et al. 2009). We show that strengthening of interbasinal deepwater thermal differentiation during the early Oligocene was accompanied by the development of a significant carbon isotopic (d13C) offset between mid-depth (~600 m) and deep (>1000 m) waters in the western North Atlantic. We interpret the d13C offset to indicate development of low O2 conditions associated with vertical stratification of nutrients, analogous to the modern low O2 zone (~700-1000 m deep) that results from ventilation by Antarctic Intermediate Water. These records show that the engine of modern ocean overturning circulation, the ACC, gradually, but significantly, impacted global ocean circulation even while it was in the early development stage in the late middle Eocene to mid-Oligocene.