anya-hess

Evolution of the Arabian Sea oxygen deficient zone following the Middle Miocene Climate Optimum: Global and regional drivers

Abstract

In the Arabian Sea, the South Asian Monsoon (SAM) causes intense upwelling, maintaining one of the world’s strongest oxygen deficient zones (ODZs). It is thought that SAM and associated upwelling initiated during the Miocene, but its timing and the timing of the strengthening of the associated ODZ remain controversial. My recent research on the eastern equatorial Pacific ODZ reveals that, contrary to expectations based on modern trends and our understanding of Miocene ocean circulation, the EEP ODZ was relatively weak during the Middle Miocene Climatic Optimum and strengthened during cooling at ~15 Ma. I invoke a strengthened biological pump in the Southern Ocean, which would have driven down oxygen concentrations in global deep waters. The proposed project expands this work to the Arabian Sea ODZ, addressing the question of whether the Miocene ODZs were driven by global changes or local changes such as SAM intensification in the Arabian Sea. To test this, I use the latest proxies for oxygenation (I/Ca) and denitrification (foraminifera-bound δ15N) to constrain the expansion of the Arabian Sea ODZ, and for upwelling (Mg/Ca in surface- and thermocline-dwelling foraminifera) to understand its relationship to SAM. By combining these proxies at sites proximal and distal to the ODZ, we can constrain the timing and rate of ODZ expansion and by comparing it to my EEP ODZ work we can understand it in a global context.

Biography

I have been passionate about the environment since childhood. In high school, I had the good fortune to take an Earth science class where I discovered how it uses all of the other sciences to understand the world around us. As an undergraduate at Bucknell University, I studied sedimentology and it was during my undergraduate thesis describing a section of organic-rich shale that I first became interested in low-oxygen environments, inhospitable and chemically unique. After completing a Master’s degree studying carbonate sedimentology at the University of Kansas, I went on to work as a geologist in the petroleum industry for five years. Ultimately, I decided to reorient my career and pursue a Ph.D. in paleoceanographic research, building on my background in marine sedimentology, with direct applications to understanding climate change. Now, as a Ph.D. candidate at Rutgers University working with Drs. Yair Rosenthal and Ken Miller, I study how oxygen deficient zones responded to past warm periods as a way to understand how they might respond to future climate change. I am fortunate to have had the support of several excellent mentors and have tried to continue that tradition by mentoring undergraduates, founding mentorship programs, and through the Association for Women Geoscientists serving on and chairing scholarship committees that support underrepresented groups in the geosciences.