Study eyes warm water incursions from the Pacific
In the past 20 years, acidified waters have expanded in the Arctic ocean, spreading northward from Alaska’s Chukchi Sea coastline to just below the North Pole. The pool of acidified water is also getting deeper, from 100 to 250 meters, according to a new study in the journal Nature Climate Change.
In a press release, the researchers said it’s the first time they’ve documented such a rapid and large-scale increase in acidification, “at least twice as fast as that observed in the Pacific or Atlantic oceans,” according to University of Delaware professor Wei-Jun Cai.
The changes will impact different types of ocean life, including tiny marine snails known to be susceptible to ocean acidification, said NOAA scientist Richard Feely. Other Arctic species potentially at risk from ocean acidification are fisheries of shrimp and varieties of salmon and crab — all important food sources for indigenous communities.
The data was gathered by a Chinese ice breaker during the summers of 2008 and 2010 from the upper ocean of the Arctic’s marginal seas to the basins as far north as 88 degrees latitude, just below the North Pole, as well as data from three other cruises. The researchers measured the saturation state for aragonite, a carbonate mineral that marine organisms need to build their shells, to calculate the pH.
The results suggest the increasing acidification is being caused by warmer water from the Pacific intruding into the Arctic, driven by circulation patterns and retreating sea ice in the summer season, according to Di Qi, the paper’s lead author and a doctoral student of Chen.
The warm water surges into the Arctic through the Bering Strait and the off the shelf of the Chukchi Sea. In recent years, melting sea ice has allowed more of the Pacific water to flow through the Bering Strait into the Arctic Ocean. Pacific Ocean water is already high in carbon dioxide and has higher acidity. As the ocean mass moves north, it absorbs additional carbon dioxide from decomposing organic matter in the water and sediments, increasing acidity.
The melting and retreating of Arctic sea ice in the summer months also has allowed warmer Pacific waters to move further north than in the past when currents pushed it westward toward the Canadian archipelago.
Arctic ocean ice melt in the summer, once found only in shallow waters of depths less than 650 feet or 200 meters, now 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.”