DOI: 10.25381/cput.27241830.v1
title: 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.

description: 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 cycLe Experiment 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) were 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 CO<sub>2</sub> captured in the Southern Ocean. The Subtropical domain and the Subantarctic domain had the lowest Dissolved Inorganic Carbon concentration with slightly high Total Alkalinity concentrations at the surface as 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 CaCO<sub>3</sub> minerals dominated the Antarctic and Subantarctic domains whereas the processes of CO<sub>2</sub> release by the ocean, photosynthesis and to a lesser extent, the dissolution of CaCO<sub>3</sub> dominated the Subtropical domain. <br>