IMOS eXpendable Bathythermograph (XBT) profiles contribute to the study of long term temperature trends in the Southern Ocean.
The waters south of Australia have seen rapid change over the past quarter century with global consequences for climate and the risks from impacts like sea level rise. The Southern Ocean has stored an exceptionally large amount of the heat associated with climate change, transferred from the atmosphere and locked away in subsurface water-masses. But without decades of consistent global oceanographic effort in the eXpendable Bathythermograph (XBT) program, supported by many individual sources like Integrated Marine Observing System, we’d be blind to this significant transformation on our doorstep.
Since 1992 scientists from Australia, France, and the United States have collaborated to maintain a regular, long-term XBT oceanographic time-series between Hobart, Tasmania, and the French Antarctic base at Dumont d’Urville as part of the SURVOSTRAL program.
Hitching a ride on the regular resupply voyages conducted by the French Institut Polaire aboard the vessel l’Astrolabe, scientists have been able to collect thousands of valuable XBT temperature profiles down to 800m depth, as well as using the ship’s thermosalinograph to take high resolution measurements of the sea surface temperature.
Usually occurring five times per year between October and March, this effort has yielded a unique, long-term climate-quality dataset in a traditionally data-sparse region, allowing scientists to monitor the pace of climate change in the remote high latitude Southern Ocean.
The recent Nature Communications publication by Auger et al (2021): Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability, assessed this valuable XBT data collection. This study unlocks long-term trends and how they compare to the natural variability in stored ocean heat, showing significant, robust warming in the upper 800 m of the Southern Ocean. These results have implications for the global climate and sea level rise as the warmer ocean waters flows eastward, into regions where enhanced ice sheet melt has been previously identified.
The results from these prized long-term, continuous observations of the Southern Ocean are critical for assessing models of circulation, ice-sheet and glacier melt in Antarctica and estimates of future sea-level rise across the globe. Such future projections will help communities prepare for climate change impacts on their local area.
It is vital we maintain our commitment to long-term ocean observations globally and specifically around Australia as we move into a period of increasing risk from a warming world.
Auger, M., Morrow, R., Kestenare, E. et al. Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability. Nat Commun 12, 514 (2021). https://doi.org/10.1038/s41467-020-20781-1
This news item was written by Rebecca Cowley, Chris Chapman, & Thomas Moore, CSIRO.