New research shows ocean acidification is spreading rapidly in the Arctic
The new researchoffsite link shows that between the 1990s and 2010, acidified waters expanded northward approximately 300 nautical miles from the Chukchi Sea slope off the coast of northwestern Alaska to just below the North Pole. Also, the depth of acidified waters increased from approximately 325 feet below the surface to more than 800 feet.
Ocean acidification is occurring because the ocean is absorbing carbon dioxide from the atmosphere. When seawater absorbs carbon dioxide, its acidity is increased, which decreases the building blocks used by shellfish to grow their shells.
“Acidification 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, NOAA senior scientist and a co-author of the research.
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, he said, and communities that depend on these popular food fish.
“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 study co-author Wei-Jun Cai of the University of Delawareoffsite link.
Pacific winter water is changing Arctic chemistry
Analysis of Arctic ocean data and model simulations showed that increased flow of water from the Pacific into the Arctic during winter, called Pacific winter water, driven by circulation patterns and retreating sea ice in the summer, is primarily responsible for the expansion of ocean acidification in the Arctic, according to Di Qi, the paper’s lead author.
In recent years, melting sea ice has allowed more Pacific water to flow into the Arctic Ocean and build up there. Pacific Ocean water is already high in carbon dioxide. As the ocean mass moves, it absorbs additional carbon dioxide from decomposing organic matter in the water and sediments, increasing the water’s overall acidity.
The melting and retreating of Arctic sea ice in the summer months has allowed Pacific winter water to move further north.
“The melting sea ice is like a pond floating on the Arctic Ocean,” said Cai. “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. When the ice forms in winter, acidified waters below the ice become dense and sink down into the water column, spreading into deeper waters.”