Carbon chemistry during the late summer in the Ross Sea, Antarctica [electronic resource]

The Ross Sea is the most biologically productive region in the Southern Ocean and is a large atmospheric CO2 sink. In addition, the Ross Sea is vulnerable to anthropogenic ocean acidication. This dissertation focuses on carbon data from the first biogeochemical process cruise to the Ross Sea during the late summer. Chapter 1 presents around 1700 surface water total alkalinity (TA) measurements from the Ross Sea and Southern Ocean. In addition, I use a TA-salinity relationship and historical pCO2 measurements to estimate the carbonate saturation state of surface waters in the Ross Sea during the winter. Results from this analysis suggest that the Ross Sea is not likely to become undersaturated with respect to aragonite from anthropogenic ocean acidication until the year 2070. Chapter 2 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 associated with green frazil ice from algal accumulation. It is hypothesized that strong katabatic winds in Terra Nova Bay prevents the formation of more opaque ice and results in circulation patterns that concentrate algae and frazil ice into wind-rows. The buoyant properties of the frazil ice may keep the algae near the surface for longer periods of time where light is more abundant while deepening mixed layers may supply growth limiting micronutrients from below. This late season NCP was rapidly exported to below 200 m and kept surface pCO2 low even though the mixed layer deepened and entrained CO2-enriched water from below. In Chapter 3, I examine the impact of late season NCP on air-to-sea CO2 flux rates. I calculate CO2 flux rates between the atmosphere and ocean using pCO2 and wind speed data from 20 cruises in the Ross Sea (2003-2013), including from the late summer cruise. In addition, annual flux rates are estimated from nutrient budgets from the late summer cruise. 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). Chapter 4 builds on the previous chapters by using daily 500-m resolution satellite imagery (February/March, 2003-2017) to identify green frazil ice hot spots and examine interannual variability in green frazil ice extent. I find that green frazil ice is concentrated in 11 of the 13 major sea ice production polynyas, with the greenest frazil ice in Terra Nova Bay and Cape Darnley polynyas. The results suggest that although there is substantial unexplained interannual variability, green frazil ice on average covers over 300,000 square kilometers during March. Together these chapters provide important insights into carbon cycling on Antarctic continental shelves.

Keywords: Earth System Science.
Advisor: Dunbar Robert B.
Arrigo Kevin R. advisor. Thesis advisor
Casciotti Karen Lynn