Global Warming

Marine Heatwaves

Heatwaves unfolding on the bottom of the ocean can be more intense and last longer than those on the sea surface, new research suggests, but such extremes in the deep ocean are often overlooked.

Bottom heatwaves ranged from 0.5 degrees Celisus to 3C warmer than normal temperatures and could last more than six months — much longer than heatwaves at the surface. Surface heatwaves can be picked up by satellites and can result in huge algal blooms. But, Amaya said, often no one knows a bottom marine heatwave is happening until the impacts show up in commercial bottom-dwelling species like lobsters and crabs.

The ocean has absorbed about 90% of the excess heat from global warming, with the ocean's average temperature increasing by about 0.9C over the last century. Marine heatwaves have become about 50% more frequent over the past decade. Past bottom marine heatwaves have decimated Pacific cod and snow crab populations which declined by 75% following the big marine heatwave in 2015. Warmer water, he said, can increase the energy needs of species at the same time that there's less prey available for them to eat, leading to more deaths and fewer births.