Decadal-Scale Temperature Trends in the Southern Hemisphere

Sarah Gille

Scripps Institution of Oceanography
UCSD
9500 Gilman Drive
La Jolla
CA 92014
USA

Fewer ocean temperature observations have been collected in the Southern Hemisphere than in the Northern Hemisphere during the last 50 years, which has made long-term temperature trends difficult to evaluate. For the Southern Hemisphere in particular, temperature profiles collected by Argo and profiling ALACE floats provide an important benchmark against which temperature trends in the upper 1000 m of the ocean can be assessed. In this analysis, temperature observations collected from bottle data, CTD observations, XBTs, profiling ALACE floats, and Argo floats are intercompared using 1990s observations as a reference. Each observation is compared with all other observations collected within a specified geographic radius, and regions with no observations are assumed to have trends similar to well-sampled regions. Different temperature measurement methods are largely in agreement in the 1990s, though XBTs tend to appear slightly warm and profiling ALACE floats slightly cold; these differences may reflect biases in spatial and temporal sampling patterns. Overall, results show that the upper 1000 m of the Southern Ocean have warmed substantially since the 1930s period at all depths. Warming signals are pronounced within the Antarctic Circumpolar Current, which may indicate that the ACC has migrated southward or that heat has been input to the system.