The temperature of seawater around Antarctica is rising, according to research using detailed records going back half a century.
The research, published in the journal Science, shows how shallow shelf seas of West Antarctica have warmed over the decades.
This has accelerated the melting and sliding of glaciers in the area.
It also reveals that other Antarctic areas, which have not yet started to melt, could experience melting for the first time with consequences for sea-level rise.
Scientists looked at data from oceanographic records dating back to 1960 and found that temperatures in the West Antarctic Amundsen Sea and the Bellingshausen Sea have been rising.
Karen Heywood, from the Centre for Ocean and Atmospheric Sciences at the University of East Anglia, said the Antarctic ice sheet is a giant water reservoir.
The ice cap on the southern continent is on average 2,100 metres thick and contains about 70% of the world’s fresh water.
“If this ice mass were to melt completely, it could raise the global sea level by 60 metres,” Professor Heywood says. “That not going to happen, but it gives you an idea of how much water is stored there.”
The temperatures of the warmest waters near the sea bed in the Bellingshausen sea have warmed from about 0.8 degrees celcius in the 1970s to about 1.2 in the 2010s.
“This might not sound like much,” says the lead author of the study, Sunke Schmidtko from GEOMAR in Germany. “But it is a large amount of extra heat available to melt the ice.”
The water around Antarctica is also shown to be getting less salty, which is consistent with more ice melting from the Antarctic continent.
The research reveals that more warm water is being transported towards the ice. This accelerates the melting of glaciers from below and triggers the sliding of big glaciers towards the sea.
The southwestern Weddell Sea is a colder area where a large-scale melting of ice has not yet happened – and is one of the areas where this warm deep water is getting closer.
Professor Heywood says: “Although many of the large ice shelves buttressing the Antarctic ice sheet are not yet melting, the source of warm water seems to be getting closer, so these ice shelves could begin to melt in future which is worrying in terms of global sea level rise.”
The exact reasons for the increase of the heating and the rising of warm water masses has not yet been completely resolved.
It could be related big variations in wind systems over the southern hemisphere.
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