Marine heat waves don't just hit coral reefs. They can cause chaos on the seafloor
Most of us know what a heat wave feels like on land—sweltering heat for days. But oceans get heat waves too. When water temperature goes over a seasonal threshold for five days or more, that's a marine heat wave. They do ...
Over 90% of the heat trapped by greenhouse gases has gone into our oceans. So it's no surprise marine heat waves are getting much more intense and more frequent. This year has been off the charts. From April this year, the world's average ocean temperature has been the highest ever recorded.
Since the 1980s, satellites have revolutionized ocean science by making it possible to take daily measurements of ocean temperatures. But satellites watch from above. They can't see what's happening below the surface.
Our new research published in Communications Earth & Environment explores what's happening in deeper waters. It turns out, marine heat waves aren't just on the surface. In the most devastating marine heat waves, heat can penetrate right down to the sea bed. Remarkably, some heat waves only affect the seafloor.
Why do deep marine heat waves matter?
While we usually only see sea creatures at the surface of the ocean, there's life all the way down. In the shallower seafloors of the continental shelf—the sunken parts of our continents—live fish, kelp beds, sponges, cold water corals, shellfish and crustaceans.
We usually think of marine heat waves as extreme heat at the surface which can cause bleaching and coral death as in this photo of 2022 bleaching at Western Australia’s Ningaloo reef. Credit: Joel Johnsson
In addition to coastal moorings, this oceanographic instrument also measures temperature and salinity of the ocean. Credit: Amandine Schaeffer, CC BY-ND
This figure shows the different types of marine heat waves affecting coastal waters (shown by the anomalous heat in red). Credit: Author provided, CC BY-ND