A team of Australian researchers has found that climate change has made ocean eddies, which are drivers of ocean currents and weather, increase in activity over the past few decades.
Ocean eddies are large whirlpools of water, that can range from ten to hundreds of kilometres in diameter.
Much like cyclones in the atmosphere, they have a dramatic effect on other ocean currents by shifting warm and cold water around, which can then affect weather in complicated ways. They also redistribute salts, minerals and nutrients in the seas.
“A really good example is the Gulf Stream. The reason why Europe is warmer than it should be is mostly because all these eddies and meanders [are] moving towards the UK,” says Josué Martínez Moreno, a researcher at the ARC Centre of Excellence for Climate Extremes at ANU, and lead author on a paper describing the research, published in Nature Climate Change.
Martínez Moreno was part of a team of researchers based at the Australian National University and the University of New South Wales who examined satellite records from 1993 through to 2020 to trace strength in the eddies around the globe. They used databases of sea surface temperature and sea surface height to deduce how the eddies were behaving.
“The changes we found suggest that regions that were already rich in eddies are becoming even richer. This includes the eddy-rich Southern Ocean around Antarctica, as well as some of the world’s major boundary currents like the East Australian Current” says Martínez Moreno.
He says this finding is consistent with other large-scale climate monitoring research. “It goes right to this idea that has become really popular, that dry gets drier and wet gets wetter.”
It’s difficult to examine these currents at a large scale from sea level. Researchers rely on satellite data, which, according to Martínez Moreno, has only been detailed enough to examine ocean eddies since the early 1990s, meaning that it’s only recently been possible to spot decades-long changes.
In 1993, the first satellite that could measure ocean height in detail was launched. “Although these satellites are thousands of kilometres above the surface of the ocean, they can measure changes of a few centimetres,” says Martínez Moreno.
While eddy variability increased overall, it decreased in tropical oceans. Predicting the specific consequences from this in complicated, but the authors believe it will affect the exchange of heat and carbon between the ocean and the atmosphere, which would then change weather patterns and currents.
“What we found is a global-scale reorganisation of the ocean’s energy over the past three decades. These changes are often not taken into account in our projections of a warmer world, because typically present-day climate models do not resolve ocean eddies” says Martínez Moreno.
“Ocean eddies play a profound role in both climate and ecosystems, regulating the mixing and transport of heat, carbon, biota, and nutrients. Thus, our findings have far-reaching implications for climate and fisheries,” says Martínez Moreno.
“Our research emphasises how crucial it is to incorporate ocean eddies into future climate projections. Without resolving this component of ocean flow, we could be missing something critical to climate.”
Good luck with the submission of your thesis, Josué! From the team at Cosmos Magazine.
Ellen Phiddian is a science journalist at The Royal Institution of Australia.
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