Petra Dekens, PhD , San Francisco State University
To characterize upwelling conditions during the early Pliocene we must determine the relative abundance of the dominant types of phytoplankton present in the surface ocean. This will be achieved using two productivity indicators: lithostratigraphy using grain size analysis, and organic biomarkers. The use of these two proxies will not only characterize changes in productivity and water column stratification, it will also allow us to differentiate between changes in primary productivity and preservation within the sedimentary environment.
The organic biomarker and grain size analyses will be done at two sites along the California margin: ODP site 1014 is (32.8˚N, 120.0˚W) and ODP site 1022 (40.0˚N, 125.5˚W). Although I was not able to recruit a graduate student to begin working on this project in the fall of 2010 as I had hoped, I have now recruited both an undergraduate and graduate student to work on this project. Jenny Miles is an undergraduate geology student who was working in my lab and has decided to do a senior thesis project with me. Because ODP site 1022 samples were already available in my lab, our initial work is focusing on this site. Jenny has now been to Moss Landing Marine Labs several times, and in collaboration with Ivano Aiello, has begun work with the laser particle size analyzer. The optimization of the technique is almost complete. Jenny has also begun examining smear slides of the sediment using a petrographic microscope to verify the grain types and calibrate that to the laser particle size analyzer data. The grain size analysis work for ODP site 1022 will be completed by January of 2012 and a second undergraduate student will generate the grain size analysis work for ODP site 1014.
Biomarkers have been used to reconstruct SSTs and the relative abundances of different phytoplankton on many time scales. Biomarkers make it possible to reconstruct the relative abundances of diatoms, coccolithophorids, and dinoflagelates, and given the preferred habitats of these different phytoplankton groups in the modern ocean, a change of a system with more coccolithophorids and fewer diatoms to a system with fewer coccolithophorids and more diatoms would indicate an increase in upwelling (and therefore a decrease in stratification of the water column). Valarie Schwartz is a graduate student who began her work with me in the fall of 2011. Valerie received a BS in Geology and a minor in chemistry at Skidmore college, and her strong chemistry background makes her an ideal student for this project. Valerie’s project will focus on the biomarker analysis at both sites. In the spring of 2012 we will be working with colleagues at the University of Miami, the Virginia Institute of Marine Science, and UC Santa Cruz, to optimize the lab protocol for organic extractions and biomarker identification. The biomarker records will be generated in the summer and fall of 2011.