The biogeochemistry of Southern Ocean intermediate and mode waters

This dissertation is dedicated to the investigation of the role of intermediate and mode waters formed in the Southern Ocean in the transport of biogeochemically important chemical species, like oxygen, carbon and certain nutrients. The three main investigations discussed employ the use of standard hydrographic measurements of temperature, salinity, and pressure as well as bottle measurements of dissolved oxygen, nitrate, phosphate, alkalinity and pH. These measurements were made during cruises carried out during the World Ocean Circulation Experiment in the South Pacific, on a cruise in the Southeast Pacific of the R/V SONNE sponsored by the University of Copenhagen, and on a cruise in the Southeast Indian sponsored by Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO).; Chapter 1 outlines the circulation scenarios currently used to determine the global oceanic ventilation of subthermocline waters and, as a result, the total oceanic sink for anthropogenic carbon dioxide due to the solubility of the gas in sea water. Chapter 2 describes the formation process of Southeast Indian Subantarctic Mode Water documented during a January, 1998, cruise on the R/V Franklin. Measurements made of alkalinity and pH on this cruise are used to demonstrate the role of the formation of Subantarctic Mode Water in determining the distribution of alkalinity, nutrients and dissolved inorganic carbon in the Great Australian Bight. Chapter 3 uses data gathered during an expedition on the R/V SONNE in the Southeast Pacific to compare the effect of the formation of Antarctic Intermediate Water on the transport of carbon in the shallow-overturning circulation with that of Southeast Indian Subantarctic Mode Water. A simple mass balance is used to demonstrate the importance of mode and intermediate waters formed in the Southern Ocean to the global oceanic uptake and transport of atmospheric CO₂. Chapter 4 uses three north-south hydrographic transects completed during the World Ocean Circulation Experiment to document the potential variability in the uptake and transport of oxygen in Antarctic Intermediate Water.