COG3

Title: Southern Ocean biogeochemistry during ice ages

Abstract:
The Southern Ocean represents the largest leak in the global ocean’s “biological pump,” the sequestration of CO2 in the deep ocean due to phytoplankton production, sinking, and decay. On this basis, it has been hypothesized that Southern Ocean changes drove the observed lowering of the atmospheric CO2 concentration during ice ages. Two distinct but related changes have been proposed: a reduction in circulation-driven venting of deeply sequestered CO2 and an increase in phytoplankton growth in surface waters. In this talk, I will present our ongoing work to reconstruct Southern Ocean biogeochemical conditions over glacial cycles, which benefits from novel methods for nitrogen isotopic analysis of the organic matter trapped within sedimentary microfossils (those of diatoms and foraminifera). The new data constitute additional support for reduced physical venting of CO2 from the Antarctic Zone of the Southern Ocean, and they provide what I consider to be extremely strong evidence of iron fertilization of phytoplankton growth in the Subantarctic Zone.