Understanding influences on the marine phosphorus budget during Quaternary glacial- interglacial cycles: Insights from Hawaiian fossil corals

Abstract

All organisms require phosphorus, and its distribution and abundance in the ocean limits primary production over short- and long-term timescales. As the marine sources and sinks of P are intimately controlled by climatic processes, anthropogenic climate and environmental change has and will continue to cause perturbations to the marine phosphorus cycle. It is critical that we understand the history of marine phosphorus cycling and its response(s) to climate fluctuations in a variety of environmental and oceanographic settings. I propose to investigate phosphorus cycle dynamics in a shallow water, oceanographically isolated tropical reef environment during Quaternary glacial-interglacial cycles. I will analyze past seawater phosphate concentrations through the penultimate glacial-interglacial transition using the novel proxy carbonate-associated phosphate (CAP). As a result of combined global and local processes, I anticipate observing low phosphate levels during warm intervals and elevated phosphate during cooler intervals, reaching a peak at maximum glaciation that persists into early stages of warming. I predict that this glacial increase in phosphate concentrations was driven by global fall in sea level, reducing burial of P on continental shelves, and enhanced local weathering and P runoff from the Hawaiian Islands. These hypotheses will be further investigated by comparing P trends with those of coral skeleton nitrogen isotopes from the same samples, providing an additional constraint on nutrient budgets. Findings from this study will contribute to a better understanding of historical phosphorus cycling and enhance our ability to anticipate future warming-forced changes. Further, use of CAP in this study will aid in its development as a geochemical proxy.

Biography

My interest in geology stemmed from childhood experiences collecting Miocene fossils along the Chesapeake Bay in southern Maryland, where I grew up. It wasn’t until my time at Smith College, though, that I fully embraced this interest and became hooked on sedimentary geochemistry research as a tool to understand the history of life and environments on Earth. After graduating with a BA in Geoscience in 2021, I started my PhD at Virginia Tech working with Dr. Benjamin Gill. My research thus far has focused on using stable isotope geochemistry and redox proxies to evaluate environmental instability as a driver of extinctions during the Cambrian. In 2022, I took a step outside my comfort zone and applied to participate in IODP Expedition 389, Hawaiian Drowned Reefs. As part of Exp. 389, I am applying similar geochemical tools in much younger systems, studying how climate-forced nitrogen fluctuations affected coral reef health in the Pleistocene. My Schlanger Fellowship project will add phosphorus analyses as well, providing unique insights into nutrient fluxes and weathering that nitrogen alone cannot provide.