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Physical and biological processes that control the distributions of carbonate chemistry across the ACC domains and the marginal ice zone in the Southern Atlantic sector of the Southern Ocean
Author(s)
Jabulani, Christopher Nkosinathi
Date Issued
2024
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
The Southern Ocean plays an important role in global climate systems as a major sink of
atmospheric carbon dioxide through the biological and physical pumps that are responsible for
absorbing atmospheric carbon dioxide, storing heat, storing freshwater (sea ice) and
transporting carbon to the deep ocean. The Southern Ocean is the least sampled ocean
region, due to its remote location, cold, windy, and rough weather conditions. The number of
available in-situ carbonate chemistry observations are seasonally biased because they are
largely done in the summer season, and few have been reported for the winter to spring period.
This has hampered our understanding of the full seasonal biogeochemical cycle of carbonate
chemistry in this important ocean region. Furthermore, it is not well understood how models
respond to these gaps due to the lack of in-situ observations. To close these gaps and improve
our understanding of the spatial and temporal variability of the carbonate system in the
Southern Ocean, seawater samples for carbonate chemistry (Dissolved Inorganic Carbons
and Total Alkalinity) and macronutrients were collected along the GEOTRACES transect (GT)
and the marginal ice zone during the Southern oCean seAsonaL Experiment (SCALE) cruise
in October 2019.
In this thesis, the distributions of the carbonate system variables and the associated physical
and biological processes that control its distributions across the different Antarctic Circumpolar
Current domains (Subtropical, Subantarctic and Antarctic domains) are described and
presented. The dataset collected was grouped into two transects, namely the open ocean
GEOTRACES transect and the Marginal Ice Zones and used to characterise the distribution
of dissolved inorganic carbon and total alkalinity in the south Atlantic sector of the Southern
Ocean. The water column distributions of dissolved inorganic carbon and TA concentrations,
along both transects, showed low concentrations at the surface waters that increased with
depth. The northward decrease in DIC in the AAIW indicates the northward transport of
anthropogenic CO2 captured in the Southern Ocean. The Subtropical domain and the
Subantarctic domain had the lowest Dissolved Inorganic Carbon concentration with slightly
higher Total Alkalinity concentrations at the surface compared to the Antarctic domain. The
intermediate waters (Subtropical domain: 748 m to 1251 m; Subantarctic domain: 6 m to 748
m) had slightly higher Dissolved Inorganic Carbon concentrations and lower Total Alkalinity
concentrations while the deeper waters had high Dissolved Inorganic Carbon and Total
Alkalinity. The main processes that controlled the carbonate chemistry across these domains
were different. The dissolution of CaCO3 minerals dominated the Antarctic and Subantarctic domains whereas the processes of CO2 release by the ocean, photosynthesis and to a lesser
extent, the dissolution of CaCO3 dominated the Subtropical domain.
atmospheric carbon dioxide through the biological and physical pumps that are responsible for
absorbing atmospheric carbon dioxide, storing heat, storing freshwater (sea ice) and
transporting carbon to the deep ocean. The Southern Ocean is the least sampled ocean
region, due to its remote location, cold, windy, and rough weather conditions. The number of
available in-situ carbonate chemistry observations are seasonally biased because they are
largely done in the summer season, and few have been reported for the winter to spring period.
This has hampered our understanding of the full seasonal biogeochemical cycle of carbonate
chemistry in this important ocean region. Furthermore, it is not well understood how models
respond to these gaps due to the lack of in-situ observations. To close these gaps and improve
our understanding of the spatial and temporal variability of the carbonate system in the
Southern Ocean, seawater samples for carbonate chemistry (Dissolved Inorganic Carbons
and Total Alkalinity) and macronutrients were collected along the GEOTRACES transect (GT)
and the marginal ice zone during the Southern oCean seAsonaL Experiment (SCALE) cruise
in October 2019.
In this thesis, the distributions of the carbonate system variables and the associated physical
and biological processes that control its distributions across the different Antarctic Circumpolar
Current domains (Subtropical, Subantarctic and Antarctic domains) are described and
presented. The dataset collected was grouped into two transects, namely the open ocean
GEOTRACES transect and the Marginal Ice Zones and used to characterise the distribution
of dissolved inorganic carbon and total alkalinity in the south Atlantic sector of the Southern
Ocean. The water column distributions of dissolved inorganic carbon and TA concentrations,
along both transects, showed low concentrations at the surface waters that increased with
depth. The northward decrease in DIC in the AAIW indicates the northward transport of
anthropogenic CO2 captured in the Southern Ocean. The Subtropical domain and the
Subantarctic domain had the lowest Dissolved Inorganic Carbon concentration with slightly
higher Total Alkalinity concentrations at the surface compared to the Antarctic domain. The
intermediate waters (Subtropical domain: 748 m to 1251 m; Subantarctic domain: 6 m to 748
m) had slightly higher Dissolved Inorganic Carbon concentrations and lower Total Alkalinity
concentrations while the deeper waters had high Dissolved Inorganic Carbon and Total
Alkalinity. The main processes that controlled the carbonate chemistry across these domains
were different. The dissolution of CaCO3 minerals dominated the Antarctic and Subantarctic domains whereas the processes of CO2 release by the ocean, photosynthesis and to a lesser
extent, the dissolution of CaCO3 dominated the Subtropical domain.
Additional information
Thesis (Master of Marine Science)--Cape Peninsula University of Technology, 2024
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