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44069-GB2
The Role of Reactive Phosphorus Regeneration in Cretaceous Oceanic Anoxic Events
High oceanic productivity and ocean anoxia, or some combination of the two, are often cited as causes of high organic carbon burial during Cretaceous Oceanic Anoxic Events (OAEs). My goal for this project is to test whether phosphorus is preferentially regenerated from Cretaceous OAE sediments, and the role phosphorus generation might play in continuing to fuel these high productivity events. I am doing this by determining reactive phosphorus and organic C burial during four different OAEs at several recently drilled Ocean Drilling Program sites. Lower than modern ocean (Redfield) C to P ratios in these sediments could imply that preferential P regeneration occurred. This available phosphorus could have repleted the surface ocean with nutrients and fueled sustained high productivity during OAEs. This process, if it occurred, would have profound implications for understanding oceanic organic C burial.
To carry out this project, I first had to set up protocols for the phosphorus extraction to be carried out at Mills College. I also needed to set up my new research laboratory space in our brand new Natural Sciences Building, which my department moved into during Spring 2007. Two undergraduate students, Jennifer Black, an Environmental Science major, and Kelly Stewart, an Environmental Studies major, worked with me during Spring and Summer 2007 setting up my lab and developing the phosphorus extraction procedure. Although these tasks were necessary for the project to proceed, they were not specifically carried out on samples for this project, so I did not pay these students from the ACS-PRF grant. However, in the first year I did use the grant to purchase equipment (a muffle furnace) and other laboratory supplies necessary for the project.
I have generated some preliminary data from Ocean Drilling Program (ODP) sites on Blake Nose, located in the western tropical North Atlantic. Preliminary reactive phosphorus concentration and mass accumulation rate data from ODP Sites 1049, 1050, and 1052 indicate that indicate P deposition could be elevated during OAEs. I have also found that these sites have Cretaceous age organic C to reactive P ratios that are lower than modern ocean (Redfield) organic C to reactive P ratios, possibly indicating preferential regeneration of reactive P during Cretaceous anoxic events. However, organic C to organic P ratios are very similar to or higher than modern ocean ratios, indicating that further analysis is needed regarding the relationship between reactive and organic P and how each reflects oceanic and sedimentary processes.
Currently, Margaret Scampavia, a Mills undergraduate senior in Biology, is working with me to test the extraction procedure on high organic C sediments deposited in the modern ocean in order to ground-truth our expectations for phosphorus content of high organic C sediments deposited during Cretaceous OAEs. During Summer 2008 she will receive a summer stipend to begin to analyze the full suite of Cretaceous Black Shale samples from Blake Nose and other ODP sites. Thus, I hope to complete most of our data collection during Summer 2008.
