Marine heat waves also affect the seabed and can be even more intense and lasting than those affecting the more superficial waters: this is demonstrated by the first complete analysis of marine heat waves, conducted on the waters covering the continental shelf of North America and which represent a crucial habitat for many valuable species on the market such as lobsters and cod.
The study is published in Nature Communications by a team of researchers led by the US Agency for the study of oceans and atmosphere (Noaa) which was also attended by the Italian Antonietta Capotondi, physical oceanographer at Noaa and the University of Colorado to Boulder.
"Researchers have been studying marine heat waves at the sea surface for more than a decade," says first author of the study, Dillon Amaya of NOAA.
"This is the first time we've been able to really dive deeper and assess how these extreme events play out along shallow seabeds."
Graphical representation of the depth of the western Atlantic as seen by satellites (source: NOAA, National Environmental Satellite and Information Service)
To make up for the lack of data, the researchers started from the observations made on the sea surface (thanks to satellites, ships and buoys) and inserted them into some predictive models that allow to simulate ocean currents and the influence of the atmosphere, in order to reconstruct the seabed temperatures.
The analysis focused on the east and west coasts of North America, based on data collected between 1993 and 2019, and produced simulations with a resolution of 8 kilometers.
The results indicate that seabed heat waves tend to persist longer (even months) and are sometimes more intense than those observed on the surface in the same location, with temperature increases ranging between 0.5 and 3 degrees.
Shallow and deep heat waves tend to be synchronous in regions where the waters are shallower and mix better, while where the waters are deeper, heat waves on the seabed can occur even without there being obvious signs in surface.
Fishermen therefore risk perceiving the phenomenon only when the effects on the marine ecosystem become visible and for this, the researchers conclude, a long-term monitoring system would be necessary.