Climate change is causing rapid, deeper and more extensive acidification in the Arctic Ocean

Photo credit: I. Quaile

Photo credit: I. Quaile

A new study reported in Nature Climate Change this week says ocean acidification is spreading rapidly in the western Arctic Ocean in both area and depth. That means a much wider, deeper area than before is becoming so acidic that many marine organisms of key importance to the food chain will no longer be able to survive there.

The study by an international team including scientists from the USA, China and Sweden, is based on data collected between the 1990s and 2010. Presumably, things have got worse rather than better since then. Unfortunately, it takes a long time for scientific research to be evaluated, reviewed and published, so current developments can easily overtake assessments which are already alarming enough in themselves. So yes, I would say this should make us sit up and listen, and lend even more urgency to the need for reducing emissions and combating climate change.

Acid bath for shellfish

Ocean acidification is a process that happens when carbon dioxide out of the air dissolves in the sea, lowering the pH of the water. This reduces the concentration of aragonite in the water, a form of calcium carbonate which shellfish and other marine organisms use to build their shells or skeletons. If the water becomes too acidic, this cannot be formed to the same extent, leaving the animals without their protective shells.

The latest published research shows that acidification is not only affecting much wider areas of the Arctic Ocean, but also that it is happening down to a much greater depth than before.

Between the 1990s and 2010, acidified waters expanded northward around 300 nautical miles from the Chukchi slope off the coast of northwestern Alaska, to just below the North Pole, the scientists write. At the same time the depth of acidified waters has increased from approximately 325 feet to over 800 feet, or from 100 to 250  metres.

“The Arctic Ocean is the first ocean where we see such a rapid and large-scale increase in acidification, at least twice as fast as that observed in the Pacific or Atlantic oceans”, said Professor Wei-Jun Cai from the University of Delaware and Mary A.S. Lighthipe, Professor of Earth, Ocean and Environment at the same University. Cai is the US lead principal investigator on the project.

“The rapid spread of ocean acidification in the western Arctic has implications for marine life, particularly clams, mussels and tiny sea snails that may have difficulty building or maintaining their shells in increasingly acidified waters”, said Richard Feely, senior scientist with NOAA and a co-author.

Tiny sea snails called pteropods are part of the Arctic food web and important to the diet of salmon and herring. Their decline could affect the larger marine ecosystem.

Among the Arctic species potentially at risk from ocean acidification are subsistence fisheries of shrimp and varieties of salmon and crab.

The polar regions are suffering more than others, because cold water absorbs CO2 faster.

Less ice to hold back warm water 

The acidification study published this week used water samples taken during cruises by the Chinese ice breaker XueLong (snow dragon) in the summer 2008 and 2010 from the upper ocean of the Arctic’s marginal seas, right up to the North Pole, as well as data from three other cruises going back to 1994. The data, along with model simulations, suggest that increased Pacific Winter Water, driven by circulation patterns and retreating sea ice in the summer season, is primarily responsible for the expansion of ocean acidification, according to Di Qi, the lead author of the paper.

This water from the Pacific comes through the Bering Strait and shelf of the Chukchi Sea into the Arctic basin. Melting sea ice is one factor which allows more of the Pacific water to flow into the Arctic Ocean. The Pacific Ocean water is already high in carbon dioxide and has higher acidity. As it moves north, its acidity increases further for various reasons.

The melting and retreating of Arctic sea ice in the summer months also lets Pacific water move further north than in the past.

The scientists have observed that Arctic ocean ice melt in summer used to occur only in shallow waters with depths of less than 650 feet or 200 meters. But now, it spreads further into the Arctic Ocean.

“It’s like a melting pond floating on the Arctic Ocean. It’s a thin water mass that exchanges carbon dioxide rapidly with the atmosphere above, causing carbon dioxide and acidity to increase in the meltwater on top of the seawater”, said Cai. “When the ice forms in winter, acidified waters below the ice become dense and sink down into the water column, spreading into deeper waters.”

Climate chaos – not just for polar bears 

In 2010, I spent some time with scientists conducting the world’s first experiments in nature, off the coast of Svalbard, to establish exactly how increasing acidification affects the flora and fauna in the Arctic Ocean.

Mesocosms, or giant test-tubes, were lowered into the sea to capture a water column with living organisms inside it. Different amounts of CO2 were added to simulate the effects of different emissions scenarios in the coming decades.

Similar experiments are still being conducted in different ocean areas. Results so far have been scary to say the least.

Mussels, snails, sea urchins, starfish, coral, fish, “some of these species will simply not be able to compete with others in the ocean of the future”, Ulf Riebesell from the Helmholtz Institute for Ocean Research in Kiel, GEOMAR, told me in an interview back in 2013, when he was a lead author of a report by the International Programme on the State of the Oceans (IPSO). He was also one of the scientists in charge of that first Arctic acidification in situ experiment I witnessed back in 2010. He is currently coordinator of the German national project Biological Impacts of Ocean ACIDification (BIOACID).

Riebesell says the sea water in the Arctic could become corrosive within a few decades. “The shells and skeletons of some sea creatures would simply dissolve”, he told me.

Deutsche Welle, 2 March 2017. Article.

 

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Ocean acidification in the IPCC AR5 WG II

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