Two years ago, former NASA climate scientist James Hansen and a number of colleagues devised a terrifying scenario in which giant freshwater pulses from melting glaciers could topple the circulation of the oceans into a world of fast-rising seas and even superstorm. Hansen's scenario was based on a computer simulation, not hard data from the real world, and met with skepticism from a number of other climate researchers. Now, a new oceanographic study seems to have confirmed one aspect of this picture – at least at an early stage.
The new investigation, which is based on measurements off the coast of the eastern Antarctic, shows that Antarctic glaciers actually melt the ocean around them. And this in turn blocks a process in which cold and salty seawater sinks below the sea surface in winter, forming "the densest water on earth," as study author Alessandro Silvano, University researcher, formulated by Tasmania in Hobart, Australia
This so-called Antarctic groundwater has not formed in two key regions of the Antarctic, as research shows ̵
These are two of the fastest melting regions of the Antarctic, and no wonder: when cold surface water does not sink any more, a deeper layer of warm ocean water can travel across the continental shelf and reach the base of glaciers cold water stays up. This warmer water then quickly melts the glaciers and the associated large floating ice floes.
In other words, the melting of the Antarctic glaciers seems to trigger a "feedback loop" in which this melting, triggered by its effect on the oceans, triggers even more. The melting water stratifies the ocean column, with cold fresh water on the surface and warmer water below. Then the lower layer melts glaciers and creates even more meltwater – not to mention rising seas when glaciers lose mass.
"What, we found out that this is not just a modeling study, but something we've seen in the real ocean," said Silvano, who researched Science Advances with colleagues from various other institutions in Australia and Japan performed. "Our study shows, for the first time, real evidence of this mechanism, and our study shows it has already happened."  Hansen said that "this study provides a nice little example of the processes we talk about in our work."
"In the large-scale question, it is still too early to say how these feedback Processes will be impacted by empirical evidence, "Hansen said by e-mail. "If we stick to the usual emission rates for global warming to continue to increase, I expect the freshwater injection rate to increase (mainly through rapid ice breakup and meltdown). This experiment will take place over the next few years and decades."
According to Matthew Long, a marine scientist at the National Center for Atmospheric Research, the study is "consistent with a large amount of existing literature that suggests warming and refreshing the deep ocean in the southern hemisphere"
"The fact that we see constant warming and refreshment that the processes we expect in the next century are already underway, "said Long. "In fact, this study is part of a growing body of evidence that suggests that the oceans are changing – and that the pace of change is accelerating."
If the process of bottomwater formation in Antarctica is at least compromised in some regions, it would then be analogous to a process in the Southern Hemisphere that has already caused great concern and significantly greater attention – a possible slowdown in circulation circulation North Atlantic, thanks to the ocean's renewal before the melting of the ocean Greenland
"Of these two key areas of deepwater formation, the North Atlantic has been widely considered more vulnerable to global warming," said Stefan Rahmstorf, a scientist at the Potsdam Institute for Climate Impact Research Changes in Education of dense deep water in the North Atlantic. "It is therefore of some concern that we now see increasing signs that the deepwater formation around the Antarctic is already affected."
Rahmstorf pointed to additional studies, which also indicate that groundwater formation in the Antarctic is changing. In one case, a 2017 study based on measurements from the Southern Indian Ocean, where Antarctic bottom water travels after leaving the Southern Ocean found that this deep water became fresher over time, especially in the last decade.
One caveat However, with the current study, the researchers found that deep water does not form in two key Antarctic regions, but they can not really tell when a change took place in those regions. Measurements do not go far enough for that, study author Silvano said. So it is possible that the deep water formation in these regions was interrupted long before the modern period of intense global warming. That would make it harder to record current events about man-made climate change.
The mechanism discovered by the study, in which the refreshing water from glaciers inhibits the descent of colder surface waters, would presumably continue to apply.
Silvano said his main concern was that in addition to ocean melting, Antarctica could also melt more of the surface as the climate continues to warm – causing much more meltwater to form in the ocean. Unlike Greenland, this is usually not done in the Antarctic. But it could.
Silvano also said that if the formation of Antarctic bottom water slows down, the global consequences could be massive. The process buries heat and carbon dioxide deep below the sea surface – without this process, heat and CO2 could remain in the atmosphere.
And then there is the problem of rising sea-level, if the feedback between the ocean and the
"The idea is that this mechanism of rapid ocean warming and warming has triggered sea-level rise at other times, like the last one Glacier maximum, if we know a rapid sea-level rise of five meters per century, "said Silvano. "And we think that this mechanism was the cause of a rapid sea-level rise"
In the future, he said, "it is possible that with global warming, some other Antarctic areas will see complete inhibition of bottomwater formation This feedback begins. "
(This story was not edited by NDTV staff and is automatically generated from a syndicated feed.)