Life cycle of antarctic intermediate water in a changing climate
File(s)
Author(s)
Meuriot, Ophélie
Type
Thesis
Abstract
Antarctic Intermediate Water (AAIW) is a water mass formed in the Southern Ocean and characterised by a mid-depth salinity minimum. It spreads northward in the Atlantic, Indian and Pacific basins. Although it is thought to play a key role in the global water cycle and overturning circulation, predicting future changes in the water mass is hampered by the large uncertainties in its model representation. The aim of the thesis is to assess how CMIP6 models represent the life cycle (formation, circulation and fate) of AAIW as well as to investigate the response of AAIW to future climate change.
The spatial variability of AAIW in the Southern Hemisphere is investigated by looking at the depth and properties (temperature, salinity and density) of the vertical salinity minimum. In UKESM1-0-LL, a light, shallow, warm and fresh bias of the vertical salinity minimum is identified compared to observations. In future scenarios, the vertical salinity minimum lightens and warms although the position where the salinity minimum outcrops remains stable irrespective of radiative forcing.
In 39 CMIP6 models, the intermediate depths in the Atlantic, Pacific and Indian basins are shown to be connected via a supergyre. The supergyre is found to homogenise AAIW core properties. The homogenisation of AAIW core properties is maintained in the future, although the supergyre tends to intensify and shift poleward.
The role of eddies in the northward salt transport in the Atlantic is assessed in the HadGEM3-GC31 HighResMIP model family. Eddies are found to contribute to the salt transport at intermediate depths between 35°S and 20°S as well as between the equator and 20°N. The results show that an increase in model resolution improves the representation of the northward extent of AAIW.
The spatial variability of AAIW in the Southern Hemisphere is investigated by looking at the depth and properties (temperature, salinity and density) of the vertical salinity minimum. In UKESM1-0-LL, a light, shallow, warm and fresh bias of the vertical salinity minimum is identified compared to observations. In future scenarios, the vertical salinity minimum lightens and warms although the position where the salinity minimum outcrops remains stable irrespective of radiative forcing.
In 39 CMIP6 models, the intermediate depths in the Atlantic, Pacific and Indian basins are shown to be connected via a supergyre. The supergyre is found to homogenise AAIW core properties. The homogenisation of AAIW core properties is maintained in the future, although the supergyre tends to intensify and shift poleward.
The role of eddies in the northward salt transport in the Atlantic is assessed in the HadGEM3-GC31 HighResMIP model family. Eddies are found to contribute to the salt transport at intermediate depths between 35°S and 20°S as well as between the equator and 20°N. The results show that an increase in model resolution improves the representation of the northward extent of AAIW.
Version
Open Access
Date Issued
2024-02-12
Date Awarded
01/05/2024
License URL
Advisor
Plancherel, Yves
Lique, Camille
Publisher Department
Earth Science & Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)