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ESS Ph.D. Dissertation Defense - Hans DeJong
This talk comprises the public portion of the PhD dissertation defense from approximately 2:00-3:00 PM.
Department: Earth System Science
Graduate Student: Hans DeJong
Advisor: Rob Dunbar
Title: Carbon chemistry during the late summer in the Ross Sea, Antarctica
Abstract: The Ross Sea is the most biologically productive region in the Southern Ocean, is a large atmospheric CO2 sink, and is vulnerable to ocean acidification. This dissertation focuses on carbon data from the first biogeochemical process cruise to the Ross Sea during the late summer. Chapter One utilizes surface carbon system measurements to estimate when the Ross Sea will become corrosive to carbonate minerals from ocean acidification. Chapter Two provides evidence for substantial net community production (NCP) during the late summer in Terra Nova Bay in the western Ross Sea. This is the first study to document substantial late season NCP in Antarctic shelf waters, which is attributed to algae in frazil ice. In Chapter Three I examine the impact of late season NCP on air-to-sea CO2 flux rates. The results suggest that the Ross Sea as a whole is a lesser atmospheric CO2 sink than previously reported. Terra Nova Bay is the exception, with extraordinary air-to-sea CO2 flux rates there during the late summer caused by the unique coupling of strong katabatic winds and low surface pCO2 values (from late season NCP). In Chapter Four I utilize daily 500-m resolution satellite imagery (February/March, 2003-2017) to identify green frazil ice hot spots, which are associated with late season NCP. I find that green frazil ice is concentrated in 11 of the 13 major sea ice production polynyas and covers over 300,000 square kilometers during March. Together these chapters provide important insights into carbon cycling on Antarctic continental shelves.