Surface and Intermediate Water Orbital Scale Variability in the Southern Hemisphere Before Northern Hemisphere Glaciation

Abstract:

Very few records depicting orbital timescale variability exist for the Southern Hemisphere during the Pliocene Warm Period (pWP, ~ 2.8-4.1 Ma.). The pWP is of particular interest as it poses a natural laboratory in which to understand climate variability in a world with only a permanent Southern Hemisphere polar ice sheet, poised near a fundamental shift in the Earth system. We report here proxy records that monitor sea surface temperature (alkenone unsaturation), surface productivity (C₃₇total), and intermediate water density and chemistry (benthic foraminifera stable isotopes) from ODP Site 1125 and DSDP 594 (North and South of Chatham Rise, respectively) for the pWP.

Surface thermal gradient between sites suggests the Subtropical Front was in place and stationary between sites for most of the pWP, much like it has been during the late Quaternary. All datasets surrounding the northernmost edge of the Southern Ocean show pacing by short Eccentricity (~100kyr) in the pWP at this location. The presence of a substantial ~100 kyr component in paleoclimatic variability contrasts with prior reports of ~ 41 kyr dominance in Pliocene climate cyclicity.