Sack Lunch Seminar (SLS)

SLS - Katherine Allen (Rutgers University) The Ocean's Role in Ending an Ice Age: A View from the South Pacific
Date Time Location
May 20th, 2015 12:10pm-1:00pm 54 915
Abstract: During the termination of the last ice age, atmospheric CO2 increased by ~30% and global temperature rose by several degrees, yet the mechanism(s) driving these major changes remain elusive. Marine and terrestrial records indicate that the amount of CO2 stored in the deep sea is greater during glacial periods than interglacial periods. The implied net transfer of carbon into and out of the ocean is likely the result of changes in ocean circulation and/or the efficiency of the biologic pump. The resulting atmospheric CO2 fluctuations may play some role in amplifying temperature shifts across ice age cycles. In this study, we reconstruct past variations in seawater carbonate ion concentration in order to gain insight into the relative roles of different oceanic CO2 storage mechanisms and to place constraints on the timing, magnitude, and location of subsequent deep ocean ventilation. Our reconstruction is based on the trace element and stable isotopic composition of calcite shells of the epi-benthic foraminifer Cibicidoides wuellerstorfi from a sediment core in New Zealand's Bay of Plenty. The sediment core site (1,627 m water depth) lies within the upper limit of modern Circumpolar Deep Water (CDW), ~500 m below the local Antarctic Intermediate Water (AAIW) salinity minimum. A record of ΔCO32- derived from the foraminiferal boron to calcium ratio (B/Ca) provides evidence for greater ice-age storage of respired CO2 and also reveals abrupt deglacial shifts in inorganic carbon chemistry up to 30 µmol/kg (5 times larger than the difference between average LGM and Holocene values). The rapidity of these deglacial changes in the ocean interior suggests 1) fluctuations in the intermediate-deep water boundary near the core site, and/or 2) rapid changes in deep water composition. Additional records are currently being reconstructed to probe these possibilities.