Projections for the way in which our planet will be affected by the current trend of rapid planetary warming are dire. Studies predict rapid fall-offs in crop production; the release of large amounts of carbon from soil; an increase in avalanches; and the loss of two-thirds of the animals on Earth by 2020. Now, a new report says that if we keep cooking the planet, there could be mass starvation on ocean floors.

"Abyssal ocean environments, which are over 3,000 m (1.9 mi) deep, are some of the most food-deprived regions on the planet," said Andrew Sweetman, a researcher at Heriot-Watt University in Edinburgh and lead author on the study. "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."

One reason for the dramatic dip in food is because the plankton that fall to the seabed to feed the creatures living there is itself facing a lack of nutrients due to ocean stratification brought about by rapidly warming temperatures.

To reach their conclusions, the researchers used the projections from 31 Earth-system models developed for the Intergovernmental Panel on Climate Change as part of its fifth assessment report, along with an analysis of a wide body of published ocean data. They analyzed such characteristics as temperature, acidity, oxygen levels and food supply to predict just how deep-sea-floor dynamics will change by the year 2100.

"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 on the study. "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."

This deep-sea-swelling sea cucumber known as a sea pig could be one of the casualties of climbing ocean temperatures(Credit: Ocean Networks Canada)

In the abyssal depths referenced by Sweetman above, temperatures are predicted to increase by one-half to one degree Celsius in the North Atlantic, Southern and Arctic Oceans, while at the more shallow "bathyal" depths in the Pacific, Atlantic and Arctic oceans, temperatures are predicted to rise by almost four degree Celsius. Bathyal ocean regions have depths between 200 and 3,000 m (656-9843 ft).

"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."

Not only will the increasing temperatures reduce biodiversity as well as the food supply reaching the animals that dwell in the depths of the oceans, but it will also rev the metabolic rates of those creatures, elevating their caloric requirements. This means that the marine animals will need more food at a time when less is available.

Less food for people too

Not only will elevated temperatures mean less food for deep-sea-dwellers, but the researchers say it could curtail the human food supply as well. That's because warming will change the way in which our oceans are stratified, and the way in which upwelling occurs, which is the process by which nutrients and oxygen are brought from sea depths up to the surface. If oxygen is not returned to the upper levels of the oceans, the fish that thrive there will die, affecting commercial fishing. Thurber points to a massive die-off of Dungeness crabs a decade ago due to low levels of oxygen in the water as one example.

"If we look back in Earth's history, we can see that small changes to the deep ocean caused massive shifts in biodiversity," Thurber said. "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."

The study from Thurber and his colleagues is available in the journal Elementa.

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