The American Geophysical Unions science magazine EOS has shared the news that melting ice from enormous glaciers such as Thwaites and Pine Island in the Amundsen Sea Embayment, located in the vulnerable West Antarctic, is responsible for the slowing down of deep-sea conveyor belt currents according to new scientific reporting published in Nature.
The ice shelf waters around the Ross Sea are being freshened by downstream melting of the Amundson Sea glaciers, where meltwater from the Swiss Cheesification of the underbelly of marine extensions of Thwaites and Pine Island glaciers are being softened by a consistent influx of warm ocean water that tunnels miles upward through the ice from the sea bed.
Gunn and Matthew England used continuous data from research vessels and moorings to track temperature, salinity, oxygen, and flow in the Weddell and Ross Seas and the Adélie Land coast. The data shows that the flows are now "become fresher, lighter, and smaller in volume since the 1990s, and the abyssal circulation has slowed by almost a third. The largest changes occurred in flows from the Ross Sea."
“We’re in an area downstream of a lot of meltwater,” Gunn said. This meltwater from glaciers makes the ocean surface less salty, and when it freezes, the waters below are less dense than normal, falling into the deep more slowly.
“Given that we expect the ice to continue melting, the most likely outcome is a continuation in the slowdown,” Gunn said.
Meanwhile, a recent study led by oceanographer Shenjie Zhou, a postdoc at the British Antarctic Survey, showed a 20% slowdown in the Atlantic sector off Antarctica’s Weddell Sea. Zhou and his colleagues suggested that weakening of offshore winds, as part of a natural cycle, is shrinking ice-producing areas.
Both the Weddell Sea and Australian Antarctic Basin observations are early warning signs of a slowing overturning circulation, Zhou said. The main driver may differ between the two areas, but “the overall pattern will be determined by the weakest points of the system.”
The observations are consistent with ocean–atmosphere–sea ice model projections published earlier this year showing that Antarctic overturning circulation could slow 40% by 2050 if greenhouse gas emissions continue unabated.
The projected changes are already well underway, said University of New South Wales oceanographer and modeler Matthew England, a coauthor on the modeling work and the new study on the Australian Antarctic Basin. The consequences of an ongoing slowing or collapse would be profound and likely irreversible, he said.
The slowing down of the deep sea current portends a significant shift of "the equilibrium of the ocean and its role as a climate regulator."
A slower circulation could mean less carbon dioxide and heat are absorbed into the oceans.Fears of unknown impacts on marine ecosystems as the deep water circulation is critical to ventilate the ocean deep with oxygen and thinned stratification. According to Kathy Gunn, "a physical oceanographer at the Commonwealth Scientific and Industrial Research Organisation in Hobart, Tasmania, "Ocean stagnation will mean nutrients from the deep may not make it to the surface."
If the research is believed, it is a significant blow to Earth's climate system.
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