Reports: ND256964-ND2: Establishing the Temperature Sensitivity of Amino Acid Racemization Rates in Planktonic Foraminifera

Katharina Billups, PhD, University of Delaware

In this project I am exploring the use of amino acid racemization (D/L ratios) in paleothermometry. We are focusing on three planktic foraminiferal species from a number of sites located along two Atlantic Ocean depth transects (2000-4800 m water depth). Well-dated samples from the late Holocene (~6 Ka) will determine the sensitivity of the forward racemization rate in the temperature range of ~4-1°C, from which the corresponding rate constants will be calculated. One of the sites will then provide preliminary depositional temperature data for the glacial period, ~ 20 Ka. This data set will serve as proof-of-concept for a research project aiming at assembling a map of glacial paleotemperatures for the deep ocean. This project is allowing the PI, whose analytical expertise has been solely with the stable isotopic composition of marine carbonates, to expand paleoceanographic research questions anchored in organic biochemistry. Samples will be analyzed at the state-of-the art Amino Acid Geochronology Laboratory at Northern Arizona University ensuring that optimum pretreatment procedures will be followed and highest quality data will be generated. Results from this study are important to the Petroleum Research Fund because they will quantify the temperature sensitivity of amino acid racemization, which, at the fine scale, is a lingering uncertainty in aminostratigraphy, a method commonly used to correlate marine terraces and to date sea level high stands. There has been a one year delay in getting the project started. The graduate student who originally worked on this project had a change of heart and left our program after one semester. Thus, after the start of the grant, only deep sea sediments from one of the regions, the depth transect in the North Atlantic Ocean, were processed (a total of 12 core intervals). A new graduate student matriculated this fall semester, and she has already completed picking of all foraminifera from these samples. We have made arrangements for the student to visit the Geochronology Laboratory at Northern Arizona University in January 2018 to learn the various cleaning methods and to help analyze her samples. We are planning for her to visit the core repository in Bremen during the summer 2018 where she will be picking already processed samples from the second depth transect, the one in the South Atlantic. She will then apply what she has learned in Arizona to set up the cleaning methods in my lab in Delaware. This project is ideally suited for the new student who has an Honors B.S. in Chemistry. Thus, this project offers her an opportunity to expand her knowledge of chemistry to environmental applications and to gain hands-on training in an analytical geochemistry lab. And, because the AAR methodology is outside my area of expertise, the project offers her an opportunity to demonstrate intellectual and practical independence from her advisor (me).