Thursday, April 07, 2011, 4:30PM - 5:30PM
Full title: "New insights into glacial deep ocean circulation and carbon storage: A multi-proxy approach using benthic foraminiferal elemental ratios."
Paleoatmospheric measurements generated from Antarctic ice cores have revealed the intriguing and oft-cited correlation between levels of carbon dioxide and air temperature over the past 800,000 years. This has sparked considerable debate over the extent of the role of this greenhouse gas in controlling or amplifying the glacial-interglacial transitions. Since the Vostok measurements only provide a “snapshot” of past climatic conditions and don’t reveal causal mechanisms, more data is required to understand natural carbon cycle variability in the past. The deep ocean is widely recognized to have been the repository of excess carbon during glacial episodes, accounting for the observed ~90 ppm drawdown of atmospheric pCO2. So how might ocean biogeochemical processes have naturally changed such that the ocean became an even larger carbon “sink”? One way to increase the surface ocean’s uptake capacity for atmospheric CO2 is to shift the speciation of the dissolved inorganic carbon pool in seawater away from aqueous CO2 and towards the carbonate ion (CO32-). Very simply put, we may consider average ocean CO32- concentrations and atmospheric pCO2 to be inversely related.
My research investigates the link between the marine carbonate system and atmospheric CO2 during the last glacial cycle. It is hypothesized that changes in the carbonate system reflective of increased deep ocean carbon storage will be recorded in deep ocean [CO32-]. The boron content of the calcite tests of bottom dwelling, single-celled protists called benthic foraminifera has been shown to reliably record deep water ΔCO32- with respect to calcite (ΔCO32- = [CO32-]in situ – [CO32-]saturation) over glacial-interglacial timescales. In other words, benthic foraminiferal B/Ca allows us to investigate the timing and magnitude of CO2 rearrangement to the extent that it was represented at the location of a particular deep ocean sedimentary core. I will present my preliminary B/Ca records from 3 cores spanning ~2.2 to 3.6 km water depth in the deep eastern equatorial Pacific. Additionally, I will introduce a recent approach to investigate both chemical and physical aspects of the glacial ocean using a full suite of benthic foraminiferal trace metal measurements. This “multi-proxy” method utilizes measured concentrations of boron (B), magnesium (Mg), cadmium (Cd), and zinc (Zn) as proxies for ΔCO32-, bottom water temperature, labile nutrient status, and refractory nutrient status, respectively.