“This retreat has had a huge impact on inland glaciers, because releasing them from the sea bed removes friction, causing them to speed up and contribute to global sea level rise.” Hannes Konrad Centre for Polar Observation and Modelling, University of Leeds, Leeds, UK and the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
The great ice sheet on the continent of Antarctica is rapidly losing ground because it is being eroded by warm ocean water circulating beneath its floating edge a new study has found. The study, published March 27, 2018 in Nature Geoscience, provides evidence that the Southern Ocean melted “1,463 km2 of Antarctica’s underwater ice between 2010 and 2016 – an area the size of Greater London”.
The first complete map ever prepared for this region (embedded below), on how the ice sheet’s submarine edge illustrates that the “grounding line”, is shifting. Antarctica’s 3 mile thick ice sheet flows straight into the ocean due to gravity pulling the ice along deep submarine troughs, “the grounding line is the place where their base leaves the sea floor and begins to float”.
x xYouTube VideoCentre for Polar Observation and Modelling writes:
Dr Konrad said: “Our study provides clear evidence that retreat is happening across the ice sheet due to ocean melting at its base, and not just at the few spots that have been mapped before now. This retreat has had a huge impact on inland glaciers, because releasing them from the sea bed removes friction, causing them to speed up and contribute to global sea level rise.”
The researchers also found some unexpected behaviour. Although retreat of the Thwaites Glacier grounding line in West Antarctica has sped up, at the neighbouring Pine Island Glacier – until recently one of the fastest retreating on the continent – it has halted. This suggests that the ocean melting at its base may have paused.
The team, led by Dr Hannes Konrad, found that grounding line retreat has been extreme at eight of the ice sheet’s 65 biggest glaciers. The pace of deglaciation since the last ice age is roughly 25 metres per year. The retreat of the grounding line at these glaciers is more than five times that rate.
The biggest changes were seen in West Antarctica, where more than a fifth of the ice sheet has retreated across the sea floor faster than the pace of deglaciation.
.The main driver of sea level rise 10 years ago was Greenland. “More recently, the Antarctic’s estimated contribution has been raised by the Intergovernmental Panel on Climate Change. But its forecasts were based on measurements from the two main west Antarctic glaciers – Thwaites and Pine Island – a sample that provides an overly narrow and conservative view of what is happening when compared with the new research”.
Antarctica's glaciers carry ice from the interior of the continent to the ocean. This NASA illustration shows where the ice is moving fastest; areas in red have the fastest flow, followed by those in pink and purple.Bob Berwyn of InsideClimate News writes.
The grounding line retreat reinforces concerns about a worst-case Antarctic meltdown scenario, with global sea level rising 10 feet by 2100. Along with the melting from below caused by warm ocean water, a 2015 study showed how global warming is melting ice shelves from above by causing more surface melting. That lets water penetrate deep down into the ice sheets and shelves. When it refreezes, it fractures the ice sheet from within.
Climate models suggest that the current rate of retreat could lead to "centennial-scale collapse of the inland catchment areas," the study says. That suggests that huge areas of ice far from the ocean could collapse within 100 years, leading to unexpected pulses of sea level rise.
The land-based ice can also speed up in response to ice shelf thinning more than 500 miles away, according to a new study by British and German climate scientists who showed that the effects of localized ice shelf thinning can reach across the entire shelf. Konrad said those findings help show where Antarctica is most vulnerable to future ocean warming, including the large Ross and Filchner-Ronne ice shelves.
Oceanographers have detected a trend of decreasing salinity in Antarctic waters fed by ice sheet melt. That affects the density of the deep, very cold waters that drive key ocean currents that affect climate at the surface. The additional freshwater flow into the Southern Ocean could address the timing of key biological cycles, particularly phytoplankton which forms the base of the food web.
x xYouTube Video