Asked by Richard
In short, yes, they are melting! East Antarctica gains some snow, but for more is lost each year by the West Antarctic and Antarctic Peninsula ice sheets.
In more detail, the story of melting glaciers in Antarctica is a complex one. Overall, the Greenland and Antarctic ice sheets are melting and contributing to sea level rise at a rate of 0.59 ± 0.20 mm per year, but the rate at which individual glaciers are melting varies by region1. A brand new publication by Sasgen et al. (The Cyrosphere, open access), shows that, overall, the mass balance of the entire Antarctic Ice Sheet was negative (-114 ± 23 Gigatonnes per year [Gt yr-1]) from January 2003 to September 20122. This new estimate lies within the range of previous estimates1, but takes into account improved calculations of glacioisostatic uplift. That means that the Antarctic Ice Sheet loses 114,000,000,000 tonnes of ice every year. In 2010, there were about 1,000,000,000 cars in the world, and the average weight of a car is about 1 tonne. So every year, the Antarctic Ice Sheet loses more mass than 100 times the mass of all the cars in the world. Every year.
The Antarctic Peninsula
Of all the ice in Antarctica, the Antarctic Peninsula Ice Sheet is changing most rapidly. This spine of mountains extends further north than other regions, and the smaller mountain glaciers have shorter response times. In this region, warmer ocean currents are penetrating onto the continental shelf (driven by changing wind patterns, caused by rapidly warming air temperatures here)3,4. These warmer oceanic currents are melting ice shelves from below5. The increased summer melt season6 and warmer summer air temperatures7 lead to more meltwater ponding on ice shelves, which melt downwards and cause the ice shelves to disintegrate rapidly8-10. This has led to glaciers on the Antarctic Peninsula accelerating, thinning and receding in response to their changed boundary conditions, directly contributing to sea level rise, even 10+ years after ice-shelf collapse11. In addition to the changes in ice shelves, glaciers on the Antarctic Peninsula are thinning12, accelerating13 and receding9,14,15. Small mountain glaciers are particularly important contributors to current sea level rise16,17.
The West Antarctic Ice sheet
The West Antarctic Ice Sheet had a mass balance of -116 ± 15 Gt yr-1 from 2003-20122. Glaciers around the West Antarctic Ice Sheet are currently thinning5,18, have a strongly negative mass balance19, and are accelerating19. Pine Island Glacier, one of the largest ice streams in Antarctica, drains a large proportion of the West Antarctic Ice Sheet and is showing dramatic dynamic behaviour, including ice-shelf thinning and recession. Mass loss is accelerating overall across the West Antarctic Ice Sheet.
The East Antarctic Ice Sheet
The East Antarctic Ice Sheet is the largest of the Antarctic ice sheets, and is generally considered to be more stable. It’s positive mass balance partially, but not completely, offsets ice-loss in the Antarctic Peninsula and in West Antarctica. It has a positive mass balance of 26 ± 13 Gt yr-1 2. The pattern of mass increase is bimodal, with mass loss acceleration in Wilkes Land and decreasing mass loss in Dronning Land and Enderby Land. The mass loss acceleration in West Antarctica is counterbalanced by this deceleration of mass loss in East Antarctica2. Mass balance anomalies and the observed positive mass balance is because snow fall has been increasing in the interior of the East Antarctic Ice Sheet20, resulting in ice-sheet thickening. This is because precipitation in the interior increases under a warmer global climate21. Some models predict that increased snow fall over the East Antarctic Ice Sheet will continue to offset mass balance losses elsewhere in Antarctica22. However, this may be offset by increased ice discharge, meaning that it will have little effect in mitigating global sea level rise. In addition, the layer of cold, fresh water around Antarctica caused by the release of large quantities of icebergs during glacier recession and ice-shelf collapse freezes more easily, resulting in more sea ice around Antarctica23. This may have the effect of reducing the amount of snowfall in East Antarctica in the future.
A recent analysis of outlet glaciers along the Pacific coast of East Antarctica showed that glaciers respond quickly and coherently to air temperature and sea ice trends, linked through the Southern Annular Mode. This suggests that parts of this ice sheet may be more vulnerable to external forcing than previously thought24. Some glaciers, such as Totten Glacier, the largest discharger of ice within the ice sheet, are thinning and receding21.
To summarise: yes, glaciers in Antarctica are continuing to melt. And ever more rapidly as well.
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2. Sasgen, I. et al. Antarctic ice-mass balance 2003 to 2012: regional reanalysis of GRACE satellite gravimetry measurements with improved estimate of glacial-isostatic adjustment based on GPS uplift rates. The Cryosphere 7, 1499-1512 (2013).
3. van Lipzig, N.P.M., King, J.C., Lachlan-Cope, T.A. & van den Broeke, M.R. Precipitation, sublimation and snow drift in the Antarctic Peninsula region from a regional atmospheric model. Journal of Geophysical Research 109, D24106 (2004).
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