Scientists discover powerful heat waves at the bottom of the ocean

(ORDO NEWS) — In 2013, a monstrous offshore heatwave emerged off the coast of Alaska and soon spread as far south as Mexico along the Pacific coast of North America.

This went on far longer than anyone expected, destroying fisheries, causing toxic algae blooms, disturbing kelp forests and depriving seabirds of food.

At one point, a buoy bobbing on the surface of the ocean near Oregon detected frightening temperature spikes of up to seven degrees Celsius in less than an hour.

However, scientists, having focused on the temperature data coming from the surface of the ocean, had no idea what was happening in the depths.

New modeling by researchers at the US National Oceanic and Atmospheric Administration (NOAA) shows that marine heat waves can also propagate deep underwater, sometimes in tandem with heat waves that travel across the surface of the ocean, or when not. detectable warming signal upstairs.

The new analysis of the continental shelf waters surrounding North America also shows that these so-called bottom sea heat waves may be more intense and last longer than ocean surface heat waves, although they vary from coast to coast.

“Researchers have been investigating marine heat waves at the sea surface for more than a decade,” said lead author of the study, climate scientist Dillon Amaya of the NOAA Physical Sciences Laboratory.

But they were limited to data on extreme temperatures at the surface of the ocean, recorded by floating buoys or detected by ships or airborne satellites.

It is much more difficult to study ocean temperatures below the water column and along the continental shelves.

Some data exists, but the researchers behind this latest study have mostly had to extrapolate ocean surface observations, feeding that data into computer models to simulate ocean currents that rise from the depths, bringing essential nutrients into coastal waters.

“This is the first time we have been able to really dive deeper and appreciate how these extreme events unfold in the shallow waters of the seafloor,” says Amaya.

The analysis focused on the west and east coasts of North America, using data spanning three decades, from 1993 to 2019, to create simulations with a resolution of 8 kilometers.

Visualization of seabed features in the Western Atlantic Basin based on bathymetric data.

“Not only do seafloor heatwaves tend to persist longer than their surface counterparts, the researchers write in their paper, but there are many regions where seafloor heatwave intensity tends to exceed surface heatwave intensity. sea ​​in the same place.

The analysis showed that these two types of marine heat waves tend to occur simultaneously in shallow water areas where surface and bottom waters mix.

According to the simulations, temperature spikes along the seafloor ranged from half a degree Celsius to 5 degrees Celsius.

But in deeper parts of the continental shelf, sea heat waves at the bottom can develop without any sign of surface warming.

“That means it can happen without the knowledge of [fisheries] leaders until the effects start to show,” says Amaya.

The researchers say their results highlight the importance of maintaining long-term ocean monitoring systems, especially as scientists are only just beginning to understand the impact of heatwaves on the seafloor.

Developing new surveillance capabilities to alert marine resource managers to bottom warming conditions can also help us better understand what has happened in the past and be prepared for what will happen in the future.

Unusually high temperatures in the subsurface ocean have been linked to invasive winged fish entering new coastal areas in the southeastern United States and have led to the near collapse of the million-dollar lobster fishery as lobsters’ weakened immune systems are threatened by parasites.

“Obviously we need to pay closer attention to the ocean floor, where some of the most valuable species live, which can experience completely different heatwaves from those on the surface,” says study co-author NOAA oceanographer Michael Jacox.

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