Discovering Seismic Heat Waves Deep in the Ocean

In 2013, a violent offshore heat wave known as “The Blob” originated off the coast of Alaska and quickly spread as far south as Mexico and along the Pacific coast of North America.

It lasted much longer than anyone expected, devastating fisheries, causing toxic algae blooms and starving seabirds.

At one point, a buoy bobbing over the ocean near Oregon recorded frightening spikes in temperature as high as seven degrees Celsius in less than an hour. The ocean was very hot.

But scientists who focused their attention on temperature data coming from the surface of the ocean had no idea what was happening at depth.

Now, new modeling by researchers at the US National Oceanic and Atmospheric Administration (NOAA) shows that marine heat waves can propagate into the deep sea as well — sometimes along with heat waves surging across the surface of the ocean, or when there are no detectable signs of warming. .

A new analysis of the continental shelf waters surrounding North America has also shown that these hypothesized lower 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 studying marine heat waves at the sea surface for more than a decade,” says lead author Dillon Amaya, a climatologist at NOAA’s Physical Science Laboratory.

But it was limited by a cache of data on extreme ocean surface temperatures recorded by buoys floating on the surface of the water, or detected by ships or satellites overhead. It is very difficult to study ocean temperatures below the water column and along the continental shelf.

There is some data, but the researchers behind this latest study mostly had to extrapolate ocean surface observations and feed that data into computer models to simulate ocean currents rising from the depths to deliver essential nutrients to coastal waters.

“For the first time, we were able to dive deeper and appreciate how these extreme events develop in the shallow waters of the seafloor,” says Amaya.

The analysis focused on the west and east coasts of North America, using data from three decades, from 1993 to 2019, to model with an accuracy of 8 kilometers, or about 5 miles, which is enough to show how hotspots overlap with seafloor features.

“Not only do marine benthic heatwaves tend to last longer than their surface counterparts, but there are many regions where the intensity of marine benthic heatwaves tends to exceed that of surface marine heatwaves at the same location,” the researchers write. his research. their paper.

The analysis showed that these two types of marine heat waves, as a rule, occur simultaneously in shallow water, where surface and bottom waters mix. Modeling also shows that the rise in temperature along the seafloor ranged from half a degree Celsius to 5 degrees Celsius.

But in the deep parts of the continental shelf, seafloor waves can develop without any sign of surface warming. “This means it can happen without the knowledge of the fishery leaders until the effects start to show,” says Amaya.

The researchers say their findings highlight the importance of maintaining long-term ocean monitoring systems, especially as scientists are just beginning to assess the impact of marine benthic heatwaves. Developing new monitoring capabilities to alert marine resource managers to bottom warming conditions can also help us better understand what has happened in the past and prepare for what will happen in the future.

“Obviously we need to pay more attention to the ocean floor, where some of the most valuable species live, and heatwaves can be very different from surface heatwaves,” says NOAA oceanographer Michael Jacox, who participated in the study. “You need to understand that burning fossil fuels is pushing ocean ecosystems to their limits. Since the Earth’s water oceans currently absorb about 90% of excess heat from global warming, heat waves in sea droplets are 20 times more likely to occur.”

The study is published in the journal Nature Communications.

Source: Science Alert