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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