Changes in deep ocean temperature from a long time series in the Southern Ocean

What is it about?

We have used two decades of annual measurements of ocean temperature and salinity at all depths between Antarctica and South America to determine that in this location (statistically significant) cooling and compensating freshening of deep waters is added to by the northward migration of the Antarctic Polar Front. Year-to-year changes, almost entirely due to movements of the fronts, can be predicted by a simple relationship with surface velocity; however, the same relationship cannot be used for the trend.

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Why is it important?

How much excess heat is absorbed by the Southern Ocean and thereby sequestered in the deep ocean is one of the major factors for predicting future climate change. The Southern Ocean is both particularly energetic and particularly under-observed, making it difficult to constrain trends and to separate the effects of changes in water properties from the effects of moving water around. The twenty-one-year time series of annual full-depth measurements analysed here is unique, and allowed us to detect a significant trend in this region while accounting for temporal variability.