A first estimate of global Antarctic Bottom Water transport variability from GRACE satellite data

Date

2022

Authors

Jeffree, Jemma

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Abstract

Antarctic Bottom Water (AABW) is a key component of global ocean circulation. Observations of AABW temperature and salinity suggest that AABW volumes and transport may be decreasing, which would impact global warming. There are no direct observations of AABW transport to corroborate this hypothesis. I develop a new method of reconstructing AABW transport variability using observations from the Gravity Recovery and Climate Experiment (GRACE) mission. Using two common physical approximations: hydrostatic and geostrophic balance, I theoretically relate GRACE satellite data linearly to ocean transport. I further investigate the utility of GRACE data to reconstruct AABW with an ocean general circulation model. I calculate both of these quantities in the model, and link them using a linear regression. I tweak aspects of the linear regression to optimise the reconstruction of AABW. My reconstruction from model-simulated GRACE data can capture almost all (87%) of AABW transport variance in the model. When realistic uncertainty is added to the GRACE data, the reconstruction can still capture 77% of AABW transport variance. The reconstruction error is only marginally worse in another general circulation model with different physics, so I conclude that this reconstruction method is not unique to the model it was developed in and it can be applied to observational GRACE data. These advances allow me to create the first global reconstruction of AABW transport variability over twenty years. This reconstruction shows significant interannual variability, which has not previously been observed, but no significant trends. My reconstruction provides new information on the interannual variability of AABW transport, but more accurate GRACE data or better ways of using this data are needed to discern AABW transport trends.

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Keywords

AABW, GRACE, interannual variability

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Thesis (Honours)

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