Deep oceans at risk from climate change

Close-up of a tripod fish at 1960 meters depth in the Northeast Providence Channel near Eleuthera Island. Photo courtesy NOAA.

‘It is the equivalent of having summer for the first time in thousands to millions of years’

Staff Report

Deep sea ecosystems that have barely been explored are at risk from global warming, as low-oxygen zones spread and ocean acidification increaseses. By 2100, organisms deep on the  ocean floor may face starvation and sweeping ecological changes, according to scientists from 20 of the world’s leading oceanographic research warned last week.

“Biodiversity in many of these areas is defined by the meager amount of food reaching the seafloor and over the next 80-plus years – in certain parts of the world – that amount of food will be cut in half,” said Andrew Thurber, an Oregon State University marine ecologist and co-author of the study, published in the journal Elementa.

“We likely will see a shift in dominance to smaller organisms. Some species will thrive, some will migrate to other areas, and many will die. Parts of the world will likely have more jellyfish and squid, for example, and fewer fish and cold water corals,” he said.

The study used projections of ocean warming to project how  the temperature, amount of oxygen, acidity (pH) and food supply to the deep-sea floor will change by the year 2100. Even in some of the deepest ocean zones, temperatures could increase betwen 0.5 and 1 degree Celsius. In other areas between 200 and 3,000 meters depth, the increase could be as great as 4 degrees Celsius.

“While four degrees doesn’t seem like much on land, that is a massive temperature change in these environments,” Thurber said. “It is the equivalent of having summer for the first time in thousands to millions of years.”

If the organisms can survive the increased temperatures, they may have a hard time finding enough food as their metabolism increases, said Andrew Sweetman, a researcher at Heriot-Watt University in Edinburgh and lead author on the study.

“Abyssal ocean environments, which are over 3,000 meters deep, are some of the most food-deprived regions on the planet,” Sweetman said. “These habitats currently rely on less carbon per meter-squared each year than is present in a single sugar cube. Large areas of the abyss will have this tiny amount of food halved and for a habitat that covers half the Earth, the impacts of this will be enormous.”

Warming ocean temperatures are also increasing stratification in some areas, while boosting upwelling in others. This can change the amount of nutrients and oxygen in the water that is brought back to the surface from the deep sea. This low-oxygen water can affect coastal communities, including commercial fishing industries, which harvest groundfish from the deep sea globally and especially in areas like the Pacific Coast of North America, Thurber said.

“A decade ago, we even saw low-oxygen water come shallow enough to kill vast numbers of Dungeness crabs,” Thurber pointed out. “The die-off was massive.”

Areas most likely to be affected by the decline in food are the North and South Pacific, North and South Atlantic, and North and South Indian oceans.

“The North Atlantic in particular will be affected by warmer temperatures, acidification, a lack of food and lower oxygen,” Thurber said. “Water in the region is soaking up the carbon from the atmosphere and then sending it on its path around the globe, so it likely will be the first to feel the brunt of the changes.”

The researchers warned that small changes in the deep ocean in past eras have triggered massive shifts in biodiversity.

“These shifts were driven by those same impacts that our model predict are coming in the near future. We think of the deep ocean as incredibly stable and too vast to impact, but it doesn’t take much of a deviation to create a radically altered environment,” Thurber concluded.

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