Drivers of variability in Southern Ocean water mass formation regions
Subantarctic Mode Water (SAMW) forms on the northern side of the Subantarctic Front, in regions of deep winter mixed layers. The water mass is responsible for absorbing a significant proportion of the anthropogenic CO2 and heat that is taken up by the global ocean. Two modes of SAMW are present in t...
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| Format: | Thesis |
| Language: | English |
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University of Southampton
2021
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| Online Access: | https://eprints.soton.ac.uk/452918/ https://eprints.soton.ac.uk/452918/1/Sanders_Rachel_PhD_Thesis_Dec_2021.pdf https://eprints.soton.ac.uk/452918/2/Sanders_Rachel_Permission_to_deposit.pdf |
| Summary: | Subantarctic Mode Water (SAMW) forms on the northern side of the Subantarctic Front, in regions of deep winter mixed layers. The water mass is responsible for absorbing a significant proportion of the anthropogenic CO2 and heat that is taken up by the global ocean. Two modes of SAMW are present in the Pacific, a lighter central Pacific mode (CPSAMW), and a denser Southeast Pacific mode (SEPSAMW). Antarctic Intermediate Water (AAIW), characterised by a salinity minimum, forms to the south of SAMW, via the subduction of northward flowing Antarctic Surface Water. Each water mass has experienced significant interannual variability in recent years. In this study, mixed layer temperature and salinity budgets are computed in the SAMW formation regions, to determine the processes responsible for variability in the properties of the mixed layers that ultimately subduct as SAMW. The results of the budgets are used to determine the drivers of interannual variability in the Southern Ocean water mass formation regions. The dominant drivers in the variability of both temperature and salinity of the SAMW formation region mixed layers are shown to be surface buoyancy fluxes, horizontal advection and entrainment. Salinity advection in each water mass formation region is found to be strongly correlated with sea ice area in the northern Ross Sea, with the strongest impact occurring at lags of up to two years. Correlation is also found between meridional salinity advection in the southeast Pacific water mass formation regions, and sea ice area in the northern Amundsen/Bellingshausen Sea, suggesting freshwater fluxes due to sea ice melt reach the SEPSAMW formation region over six months. Patterns in Ross Sea sea ice appear to be related to those in the El Nino Southern Oscillation (ENSO), which drives a 10-15 ˜year cycle that is also seen in salinity advection, with the strongest signal in the AAIW formation regions. In 2016, the winter mixed layer in the southeast Pacific SAMW formation region was anomalously shallow, warm and ... |
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