Da it is again, the catastrophe scenario that was conjured up so impressively in gloomy, apocalyptic scenes in Roland Emmerich’s Hollywood shocker “The Day After Tomorrow”: The global marine circulation – the global conveyor belt – in the world’s oceans, driven by different temperatures and salinity levels, collapses . The transport of warm surface water to Europe and the American east coast, which has been so stable for millennia, is drying up, temperatures are literally plummeting – ice age-like cold snaps are threatening life.
Since then, an Australian-American research group in Nature reported on her studies on developments around Antarctica, this specter is haunting the climate scene again. The starting point were the observations that have been made again and again since the 1990s that the Antarctic bottom water and the currents running around the southern continent are changing noticeably. Added to this is the unprecedented data collection on accelerated ice melt at the South Pole, particularly on the Antarctic Peninsula and in West Antarctica, where huge expanses of ice shelf jut out into the sea and are apparently melting at an accelerating rate.
Many polar researchers fear that the enormous meltwater masses could massively disrupt the deep currents around Antarctica. Because the area below a depth of 4000 meters, where the bottom water consists of particularly dense, because salty and cold water, forms a kind of pump for the global conveyor belt. As in the north on the edge of the Greenland Sea in the North Atlantic, where the North Atlantic Meridional Overturning Circulation (AMOC) pump millions of cubic meters of dense surface water per second sink and drive the global conveyor belt, the deep-flowing water body off Antarctica is also a crucial driver for the upheaval of the oceans. The cold water feeds four out of five oceans. If this pump dried up, the heat exchange and the weather around the world would be changed almost overnight.
Disturbing findings
However, a lot has to happen for this global conveyor belt, the “thermohaline circulation”, to actually collapse. This became clear time and again in the quite cautious reports and warnings of the Intergovernmental Panel on Climate Change (IPCC). Evidence for a collapse is thin, but evidence for potentially critical changes accelerating climate change is mounting.
Now, meltwater analysis by Qian Li of the Massachusetts Institute of Technology and Matthew England of the University of New South Wales are certainly among those disturbing findings. What they have found is that deep currents off Antarctica could slow — and continue to warm — by as much as forty percent by mid-century. The whole thing is driven by the melting of the huge ice sheets. The freshwater runoff from the melting glaciers dilutes the saltwater. In addition, the surface water is heated and less and less ice forms. However, the cold surface water, which cools down particularly under the so-called polynyas and increases the salt concentration because the salt does not crystallize, is urgently needed.
Normally this water sinks down along the coasts and in a way feeds the bottom water. In the meantime, however, according to the measurements of the last few years, warm water masses have spread in the depths. The cold deep water is visibly displaced. “Particularly worrying,” says Matthew England, is the warming in the Amundsen Sea and Bellingshausen Sea off the West Antarctic coast, where the water on the ice shelf coast is warming particularly quickly and the meltwater inflows are particularly large.
A feedback could quickly occur here: the warmer water allows the ice masses to melt even faster. In fact, that was the strongest impression that this year’s Polarstern expedition to the Bellinghausen Sea left on the Bremerhaven team at the Alfred Wegener Institute: “Where has all the ice gone?” wondered the polar researchers. Never before had they observed so little sea ice in the region. In fact, since systematic measurements began, there has never been as little sea ice around Antarctica as there was this southern summer.
The eternal ice as a tragic myth
It is not yet possible to say how meaningful these observations and the new model calculations from the ice front really are for the future of the climate. But that this monstrous ice melt at the poles – also around the North Pole and on Greenland – can get things rolling quickly is also shown by the findings that a British team has just made off the coast of Norway in Nature has reported.
The seabed off the coast was surveyed from ships to document the retreat of the ice sheets after the end of the ice age more than 15,000 years ago. Wave-like furrows on the sea floor, which formed at the grounding lines of the ice margins marked by the tides, bear witness to the disappearance of the glaciers. What the researchers found seemed unthinkable for a long time: that the massive ice sheets sometimes retreated by up to 600 meters in a single day with warming. The historical record off the Antarctic Peninsula was a good 50 meters per day. That’s roughly the rate at which the fast-flowing Pope Glacier in West Antarctica is currently shrinking. The so-called eternal ice is thus proving to be more and more clearly a tragic myth, a mere wishful thinking.
#Temperature #chaos #ice #pole #spectacle