Book Description

This dissertation examines several aspects of the unique physical-biological system that controls biogeochemical cycling in the Ross Sea, the largest continental shelf sea along the Antarctic margin and the most biologically productive region in the Southern Ocean. The core component of the research involves interpretation of data from two oceanographic cruises to the region, one during Summer of 2005--2006 and another in Spring of 2006--2007. Four key research questions are addressed. (1) What physical mechanisms force spatial and temporal variability in mixing depths? (2) How does the dynamic physical environment characteristic of Antarctic continental shelf seas structure distributions of biomass and chemical tracers of production? (3) What key physical and physiological mechanisms control the 13C/12C ratio of organic and inorganic carbon in waters on the Ross Sea continental shelf? and (4) How do physiological variables interact with environmental variability to control phytoplankton taxonomic zonation? Chapter 1 presents an introduction to ocean carbon biogeochemistry and the oceanography of the Southern Ocean and the Ross Sea. Chapter 2 examines the mechanisms effecting early season stratification in the Ross Sea. Lateral advection in the region of upper ocean fronts is shown to be an important mechanism setting early season stratification. Chapter 3 examines several tracer-based methods for estimating upper ocean net community production in the Ross Sea, with explicit recognition of the complexities associated with control volume assumptions and high rates of temporal change. Chapter 4 considers the environmental controls on the distribution of 13C/12C ratios in the Ross Sea. It is shown quantitatively that the two dominant phytoplankton taxa in the Ross Sea have different intrinsic fractionation factors, likely as a result of differing carbon-acquisition physiologies. Air-sea exchange is shown to occur with very noisy fractionation. Finally, Chapter 5 examines the interaction of algal physiology with environmental variability, addressing the key physiological-environmental controls on the taxonomic distribution of phytoplankton in the Ross Sea. While it is difficult to draw concrete conclusions, the most compelling line of evidence suggests that differing photoprotective capacities is the most important physiological characteristic structuring taxonomic distributions. An appendix presents a design for an infrared absorbance-based instrument for the determination of total dissolved inorganic carbon in seawater.