17 November 2009

Climate change damaging the deep sea

Cosmos Online
Warming is affecting ecosystems 4,000 m down, a study has found, overturning the idea that deep sea abyssal plains are immune to surface changes.
Grenadier fish

A small grenadier fish swims over the seafloor at the research station off the coast of California. Between 1989 and 2004, the number of grenadier at here doubled, which the research say may be linked to the changing climate. Credit: MBARI

PORTLAND, OREGON: Climate change is affecting ecosystems over 4,000 m under the ocean, a study has found, overturning the idea that deep sea abyssal plains are immune to changes in surface waters.

The authors of the study found that activity in the atmosphere and surface waters determines the type and amount of biological material – such as algae and other microorganisms – that wind up on the abyssal plains.

Changes in surface waters result in changes far below, said co-author Ron Kauffman, a marine biologist at the University of San Diego, in California, USA. “Some of those changes include a reduced supply of nutrients to surface water communities,” he said. That, in turn, leads to reduced productivity and fewer of those organisms sinking to the deep ocean to feed deep sea ecosystems.

“All life interconnected”

Experts originally thought that the abyssal plains were stable ecosystems, isolated enough to be little affected by change elsewhere, but according to Ken Smith, a marine ecologist at the Monterey Bay Aquarium Research Institute (MBARI) and lead author of the study, published in the journal PNAS, deep-sea ecosystems are very much affected by climate change.

“More than ever, it is impossible to ignore the fact that all life on Earth is interconnected,” commented John Hocevar, oceans campaign director for Greenpeace USA. “The decisions President Obama and other world leaders make in the coming months will have far-reaching effects on all life on Earth, from human beings to the dark, cold deep sea,” he added.

The study covered nearly two decades worth of data gathered from two far flung research stations. One 200 km off the central coast of California and the second off the southwest coast of Ireland.

Far flung research stations

“We collected and evaluated a number of different measurements from those two sites,” said Kauffman. “We were able to see patterns that may reflect the underlying relationships between climate and various processes in the ocean, from the surface waters all the way down to the deep sea floor.”

The researchers also noted how the change in seasons affected the availability of food on the ocean floor, with summertime algal blooms on the surface dropping more crumbs for their neighbours up to 4,000 m below.

The scientists took samples from depths of 500 m and found that 20 to 50 % of material that rains down from the surface reaches those depths. Sediment traps at abyssal depths, however, revealed that less than 5 % of this material eventually reaches the bottom.

Because abyssal plains are involved in carbon cycling, the process by which carbon dioxide goes in and out of the atmosphere, the scientists think that deep-sea ecosystems will eventually be significantly affected by long-term climate change.

“Essentially, deep-sea communities are coupled to surface production,” said Smith. “Global change could alter the functioning of these ecosystems and the way carbon is cycled in the ocean.”

“I think that global warming will have a predominantly negative impact on deep-sea ecosystems if [it] leads to predicted changes in the dynamics of upper-ocean ecosystems,” agreed Kauffman.

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