The 2013-2016 marine heat wave known as “The Blob” warmed a vast area of surface waters across the northeastern Pacific, disrupting West Coast marine ecosystems, distressing salmon returns and damaging commercial fisheries.
But now, new research from the National Oceanic and Atmospheric Administration (NOAA) shows that marine heat waves also happen deep underwater. They used a combination of observations and computer models to generate the first broad assessment of bottom marine heat waves in the productive continental shelf surrounding North America.
Marine heat waves drastically impact the health of ocean ecosystems around the globe, disrupting the productivity and distribution of organisms as small as plankton and as large as whales. Because of this, there has been significant effort to study, track and predict the timing, intensity, duration and physical drivers of these events.
Most of that research has focused on temperature extremes of the ocean’s surface. Sea surface temperatures are also good indicators for many physical and biochemical ocean characteristics of sensitive marine ecosystems.
About 90% of the excess heat due to global warming has been absorbed by the ocean, which has warmed by about 1.5C over the past century. Marine heatwaves have become about 50% more prevalent over the past decade.
The research team found that on the continental shelves around North America, bottom marine heat waves tend to persist longer than their surface counterparts, and can have larger warming signals than the surface waters above. Surface and bottom marine heat waves can occur at the same time in the same location, especially in shallower regions where surface and bottom waters mix.
But bottom marine heat waves can also occur with little or no indication of warming at the surface, which has important implications for the management of commercially important fisheries. “That means it can be happening without managers realizing it until the impacts start to show,” said lead author Dillon Amaya.
“We know that early recognition of marine heat waves is needed for proactive management of the coastal ocean,” said co-author Michael Jacox. “Now it’s clear that we need to pay closer attention to the ocean bottom, where some of the most valuable species live and can experience heat waves quite different from those on the surface.”
www.scitechdaily.com/deep-impact-heat-waves-happen-at-the-bottom-of-the-ocean-too