We know oceans are rapidly warming and that sea level is rising, but now researchers have discovered evidence that ocean eddies are becoming more energetic over large regions of the ocean.
Ocean eddies are whirlpools with sizes between 10 and 100 kilometres across, somewhat like cyclones in the atmosphere. They are responsible for the “weather” in the ocean, moving warm and cold water from one location to another. In this way, eddies move and mix heat, carbon, salt, and nutrients and affect everything, from regional processes right up to the global ocean circulation.
The discovery of changing eddy energy was made by a team of ANU and UNSW researchers from the ARC Centre of Excellence for Climate Extremes. Their work, published today in Nature Climate Change, shows clear changes to the distribution and strength of these eddies, which had not been previously detected.
“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” said lead author, Josué Martínez Moreno.
This research was only possible now because of the length of the satellite record. Despite satellites being thousands of kilometres above the Earth’s surface, amazingly, they can detect variations of the sea-surface elevation of just a few centimetres.
Up to recently, our understanding on how ocean eddies were changing was limited by the sparse ocean measurements and the short duration of the satellite record.
While satellites did have the capacity to detect eddy changes by looking at sea-surface elevation and ocean temperatures, the record has only just become long enough to draw robust conclusions about longer-term trends over time.
Using available data from 1993 until 2020, the researchers analysed changes in the strength of the eddies over the whole globe. They found a significant increase in eddy strength over the Southern Ocean, as well as significant changes in eddy activity over the boundary currents – the intense flows of water along the boundaries of the major ocean basins, like the Gulf Stream and the East Australian Current.
“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” said 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”.
“Our research emphasizes 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.”
- Paper: Global changes in oceanic mesoscale currents over the satellite altimetry record. Nature Climate Change.