Flight over the glacier tongue

Forum Science Flight over the glacier tongue

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    Flight over the glacier tongue

    The icy tongue of the Ryder Glacier in North Greenland still extends far into the fjord, as this photo from aboard a helicopter shows. But even it already shows meltwater rivers on its surface. And not only that: Researchers have found that thicker sea ice at the entrance to the Greenland fjords can even accelerate the ice melt.

    The Arctic is particularly hard hit by climate change – this also applies to Greenland’s glaciers. Their defrosting rate has already quadrupled in some regions. More meltwater is already flowing into the sea through these glaciers than the climate models predict. In many places, the thawing ice forms real waterfalls, over which the water from meltwater pools and rivers plunges into the depths.

    The coastal glaciers of Greenland are particularly affected by the large melt. Because their icy tongues reach from the mainland far into the fjords and bays. As a result, the glacier tongues are exposed to the mostly significantly warmer sea water and thaw from above and below at the same time.

    A fjord glacier from above

    Even on the tongue of the Ryder Glacier in North Greenland, the summer ice melt does not pass, as this picture taken from the helicopter shows. The cracks and meltwater streams on the surface of the ice are clearly visible. But when a research team led by Christian Stranne from Stockholm University examined this and other coastal glaciers in northern Greenland more closely, they noticed something else:

    Paradoxically, the glacier tongues in many fjords thaw particularly quickly when the sea in front of the fjord entrance is still covered by thick sea ice. Although sea ice is actually a good insulator and protects the underlying water from warming from the sun and warm air, its presence in the fjords appears to be rather counterproductive, the researchers observed. Especially in summer 2019, which was particularly warm in Greenland, the glacier tongues in such fjords melted particularly strongly.

    Travel as Barriere

    But what is behind it? As Stranne and his team found out, this is due to the barrier effect of thick sea ice: when these meter-thick ice floes pile up in front of the entrance to a fjord, they impede the exchange of water between the fjord and the open ocean. As a result, warm water heated by the sun collects on the surface of the fjord.

    Because this upper water layer consists largely of the non-salty melt water of the glaciers, it cannot mix with the lower layers. This means that this water cannot flow under the sea ice barrier at the fjord entrance either – it accumulates in the fjord. “In the Sherard Osborn Fjord, which was sealed off from the open ocean by thick sea ice in the summer of 2019, the surface water temperature reached four degrees plus – that’s three degrees more than usual for this area in northern Greenland,” reports Stranne.

    For the glacier tongues in these sealed-off fjords, this means that instead of benefiting from the insulating effect of the sea ice, they are bathed in particularly warm water – and thaw correspondingly faster. (Communications Earth & Environment, 2021; doi: 10.1038 / s43247-021-00140-8)

    Source: Stockholm University

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Forum Science Flight over the glacier tongue