(ORDO NEWS) — The expected weakening of the Atlantic ocean currents as part of the global AMOC circulation could exacerbate the already catastrophic effects of global climate change and lead to the rapid disappearance of Arctic glaciers.
This connection was revealed by scientists from the University of Bremen (Germany), the Helmholtz Center for Ocean Research (Germany), the University of São Paulo (Brazil) and the Institute of Geology and Mineralogy of the University of Cologne (Germany). The results of the study are published in the journal Nature Communications.
The Atlantic Meridional Circulation (AMOC) is a system of ocean currents that carry warm, salty waters in the upper ocean, including the Gulf Stream, northward and cold deep waters southward.
It is a fundamental mechanism of climate regulation, combining atmospheric and thermohaline, that is, associated with temperature and salinity, factors.
The AMOC is expected to weaken significantly in the 21st century due to climate change, with the consequence that the risk of extreme weather events will increase.
It is assumed that AMOC collapses occurred during the last ice age. According to one of the widely discussed hypotheses, the cause was a massive release of fresh water as a result of the melting of icebergs during one of the Heinrich events, when, due to the instability of the Laurentian ice sheet, the rate of glacier descent into the sea increased sharply.
However, circumstantial evidence suggests that the deep-sea circulation of the ocean weakened even before the Heinrich event and itself became the cause of the destabilization of the ice sheet.
The researchers analyzed the ratio of magnesium and calcium in the shells of the ancient foraminifera Neogloboquadrina pachyderma, recovered from the sediments of the western subpolar part of the North Atlantic.
It is known that the ratio of magnesium and calcium depends on the sea water temperature: the higher the temperature, the more magnesium will be included in the shell calcite.
In addition, the ratio of oxygen-18 and oxygen-16 isotopes was determined, from which the regional salinity indices of the Atlantic were derived. The studied samples covered the last 35 thousand years.
It turned out that over the past 27 thousand years, each Heinrich event, the cyclicity of which was 5-10 thousand years, was preceded by a significant and sharp increase in the temperature of subsurface waters in the Atlantic.
According to the authors of the work, this is the first convincing evidence that the accumulation of heat in the ocean provoked the melting of the marine margins of the Laurentian ice sheet around the Labrador Sea, which entailed the Heinrich event – the sliding of glaciers into the sea and breaking off a huge number of icebergs.
Recurring warming of subsurface waters in the subpolar Atlantic corresponds to periods of weakening of AMOC.
According to the researchers’ conclusions, the weakening of AMOC, which humanity expects in the near future, can lead to an acceleration of the warming of the North Atlantic, a deterioration in the stability of modern Arctic glaciers and the balance of fresh water in the North Atlantic.
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