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Rate of North Atlantic acidification doubled in last decade

 

The North Atlantic is gulping down twice as much human-caused carbon and becoming increasingly acidic, intensifying alarm for marine creatures

Climate News Network, Feb. 12, 2016

The North Atlantic Ocean is responding rapidly to climate change: it has absorbed 50% more carbon from human activities in the last 10 years, than in the previous decade, a new study shows.

In effect, it has become both a sink for the byproduct of the fossil fuel combustion that is driving global warming, and at the same time an index of the impact humans are now having on the ocean and atmosphere.

Scientists from the University of Miami’s school of marine and atmospheric science established the Atlantic’s hunger for carbon dioxide by simply looking at data samples taken a decade apart.

They report in the journal Global Biogeochemical Cycles that the data were collected in two international ship-based studies. One was CLIVAR, short for Climate Variability CO2 Repeat Hydrography, the other GO-SHIP, or the Global Ocean Ship-based Hydrographic Investigations Program.

Unprecedented rate

The extra CO2 absorbed means a change in ocean chemistry: the oceans are becoming increasingly acidic at an unprecedented rate, with unknown consequences for corals, shellfish and juvenile fish.

“This study shows the impact all of us are having on the environment and that our use of fossil fuels isn’t only causing climate to change, but also affects the oceans by decreasing the pH,” said Ryan Woolsey, of the University of Miami, one of the authors.

But that is not the only change in the region. Jon Hawkings, of the University of Bristol, UK, and colleagues report in the same journal that they spent three months in 2012 and 2013 sampling the flow of water from two glaciers in Greenland and calculated that the overall melt from the northern hemisphere’s biggest ice sheet is now delivering the nutrient phosphorus into the Arctic at about the same level as the Mississippi, or the Amazon.

Since, once again, the Greenland ice sheet is melting as a response to global warming, humans are as a consequence altering ocean productivity. By how much is less certain: the researchers still have to establish how much of the nutrient crushed from the rocks by the moving glaciers is getting to the open ocean.

“It could stimulate growth of plankton at the base of the food web, which could impact birds, fish and marine mammals higher up the food chain,” said Dr Hawkings. “The research also suggests ice sheet-derived phosphorus could eventually reach the northern Pacific and Atlantic Oceans, which are connected to the Arctic Ocean.”

Underestimated consequences

Both studies indicate a warming ocean. And research by German scientists now suggests that humans have underestimated one important consequence of this rate of warming; the rise in global sea levels.

They report in the Proceedings of the National Academy of Sciences that the expansion of the oceans as a consequence of raised temperature could lift sea levels by an average of 1.4mm a year. Until now, oceanographers have assumed that the calculated expansion would add up to perhaps 0.7mm a year. The new study doubles that estimate.

“This height difference corresponds to roughly twice the volume from the melting ice sheets of Greenland,” said one of the authors, Roelof Rietbroek of the University of Bonn. 

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