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44069-GB2
The Role of Reactive Phosphorus Regeneration in Cretaceous Oceanic Anoxic Events

Kristina L. Faul, Mills College

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).  The goal of this project is to test whether phosphorus is preferentially regenerated from Cretaceous OAE sediments, and to elucidate the role that 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 (ODP) 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.

During year one of my ACS-PRF grant, I generated preliminary data from 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.

During year two of my ACS-PRF grant, my undergraduate research assistant, Margaret Scampavia, and I accomplished many of our data generation goals.  We ordered and received samples from the Integrated ODP for deep sea sediment sites in the eastern North Atlantic, on Blake Nose in the western North Atlantic, on Shatsky Rise in the western North Pacific, and on Demerera Rise in the equatorial Atlantic.  After making solutions and preparing equipment, Margaret practiced and refined her P extraction and measurement skills.  We tested the extraction procedure on high organic C sediments deposited in the modern ocean (Bodega and Tomales Bay, California) in order to ground-truth our expectations for phosphorus content of high organic C sediments deposited during Cretaceous OAEs.  We found that most of the bioreactive P in these sediments was in the form of organic P, which has implications for what we expect in our Cretaceous samples.  Margaret began to process samples from Site 1258, Demerara Rise, which has multiple extensive tracts of high organic-C laminated black shales, thought to be formed under anoxic conditions.  Margaret is now working on developing a methodology for using the spectrophotometer at Mills College, so that we do not have to travel to other research institutions to use instrumentation.  Samples from additional sites have also been prepared and are ready for extraction as soon as the Demerara Rise samples have been completed.  We are confident that data generation for the project will be finished over the next several months.

This research has had an enormous positive impact on my career and on Margaret, the student participating in the project.  Through this research, Margaret has had the opportunity to participate in every aspect of the project, including data acquisition and interpretation, and to visit and use instrumentation at various research institutions such the University of California Santa Cruz (UCSC) and Bodega Marine Laboratory.  In her own words, Margaret “has found this project to be an excellent opportunity to develop [her] research and problem solving skills in a field of interest.”  As a faculty member at a small liberal arts college for women, this research has enabled me to continue to participate actively in my field, to mentor students in a research setting, and, in combination with other accomplishments, to earn tenure at Mills College.

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