Reports: AC247576-AC2: A Refined Chronology of Late Eocene to Late Oligocene Coral Reefs: Implications for Coral Calcification Under a Regime of Declining Atmospheric Carbon Dioxide and Changing Ocean Chemistry
Gregoery E. Ravizza
, University of Hawaii (Manoa)
ActivitiesFrom September 2010 through April 2011 ACS-PRF funds supported 1 Ph. D. student with both salary and research support. This student, Francois Paquay, defended his dissertation 25 February 2011 and received Ph.D. degree in May of 2011. During this time ACS-PRF funds were used to support Paquay while he was writing and revising his dissertation, and also completing the last phases of his analytical work. This award also supported two other research projects related to Eocene ocean chemistry which Paquay initiated, but are not included in Paquay's dissertation. Results from the first research project "The Eocene Azolla Event and the Arctic Carbon research" were outlined in our previous year's report. These results remain robust with Os isotope data displaying a clear North-South gradient from high 187Os/188Os in the Arctic (0.8-0.9), low ratios in the South Atlantic (0.45-0.55) and intermediate values at ODP 913 (0.55-0.65). The high ratios in Arctic sediments are fully consistent with basinal restriction and large Os inputs from weathering of surrounding land masses. The second project involved Re-Os analyses of late Eocene sediments from the Atlantic sector of the Southern Ocean. Our results demonstrate an episode of unusual Re enrichment several hundred thousand years before the Eocene-Oligocene transition. These results are of interest because they imply a decrease in oxygen concentrations in deep ocean sediments, and thus greater carbon storage in the deep ocean, prior to this important climate transition. Results from these two studies have not yet been submitted for publication. One chapter from Paquay's dissertation was partially supported by ACS funds. This research involved Re and Os analyses of recently deposited organic-rich sediment from the Gulf of California and Cariaco Basin which are compositionally similar to the organic-rich Eocene sediments studied in our Azolla project. These results show that these modern semi-enclosed/silled basins record Os isotope composition that are only slightly offset from open ocean values. In summary Paquay's research provides data demonstrating two new applications of the Os isotope system to Eocene ocean chemistry; as tracers of basin ventilation and as a paleoredox proxy.Starting in late June of 2011 Jessica Zaiss-Bowmann began to work in our laboratory as a research assistant, and in September of 2011 she entered our graduate program as an M.S. Candidate. During the summer, Zaiss-Bowmann was trained in our lab and learned to operate the ICPMS instrument. She also also contributed to analytical efforts supported by ACS funds.