PhD Title: Global climate impacts from changes in Antarctic Intermediate Water
Supervisors: Karen Heywood, David Stevens, Zhaomin Wang (formerly at BAS).
The IPCC AR4 report stated that "the major mid-depth water mass in the SH, Antarctic Intermediate Water (AAIW), has ... been freshening since the 1960s". The aim of this project was to investigate how changes in this water mass could feed back in to the climate system in the future. This involved the use of the coupled climate model, HadCM3, within which I made perturbations of temperature and salinity at depth in each of the three major ocean basins.
Results from the initial Atlantic AAIW experiments have been published in Climate Dynamics (Graham et al. 2011). More recently, results from each of the ocean basins have been compared in Graham et al. (2013, J Clim). Some key results presented in this paper:
Whilst my PhD project was model-based, I also had the chance to try out some practical oceanography on board the SOFINE cruise in Nov-Dec 2008.
- Perturbed AAIW can reach the sea surface within 10 years.
- Sea surface temperature anomalies occur when AAIW surfaces at higher latitudes (>30 deg).
- The response to cooler, fresher AAIW is both greater and more significant than that for warmer, saltier AAIW.
- The North Atlantic is particularly sensitive to cool, fresh perturbations.
- Changes in AAIW can cause basinwide changes in the surface ocean and overlying atmosphere on multidecadal timescales.