Hi, thank you for the opportunity to “Ask a scientist”…I am going round and round about the latest publication of the Western Antarctic ice melt by Eric Rignot. I have seen the latest on the NSIDC site and it shows the extent of the Antarctic to be larger than last year and is considered a record. Is there any conflict between these two seemingly disparate data? I was thinking that the extent does not take into consideration the thickness of the ice but I cant find any hard data to back me up…any help in this regard? Thanks a lot.
I’m not sure I understand your question, but I’ll try. Firstly, I think you’re talking about sea ice extent. It’s important to note the difference between grounded land ice, sea ice, ice shelves and icebergs. It’s not easy! I wrote this to help: Ice shelves, icebergs and sea ice.
These different types of icey things are all doing different things. Glaciers around the Antarctic Peninsula and in West Antarctica are generally receding. East Antarctica is generally considered fairly stable, but glaciers are retreating there too1, and there is evidence that it may have potential for instability2. Ice shelves around the Antarctic Peninsula are thinning and some have fragmented and disappeared3. Glaciers that used to flow into these now absent ice shelves are accelerating and receding, and it can take decades for them to regain equilibrium. The two papers in the news this week showed that Pine Island Glacier and Thwaites Glacier are accelerating and ice discharge is increasing, which suggests that rapid, irreversible recession may be imminent.
In contrast to these changes, which directly result in increased rates of sea level rise, sea ice extent is increasing around some parts of Antarctica4. It isn’t uniform; sea ice is decreasing around the western Antarctic Peninsula, for example5. Sea ice extent is increasing most north of the Ross Ice Shelf6. It seems to be associated with decreased sea surface temperatures.
There are several theories for this increase in sea ice. The first is that warm ocean currents are penetrating onto the continental shelf. They are driven by changes in atmospheric circulation. The incursion of relatively warm Circumpolar Deep Water onto the continental shelf and beneath ice shelves drives basal melting of ice shelves and marine-terminating glaciers and ice streams7. This results in a layer of cool, fresh water on the surface of the ocean that easily freezes, resulting in increased sea-ice extent6. Salinity, density and temperature stratification contribute to this water freezing more easily.
Others have argued that sea ice extent is increasing as a result of changed atmospheric circulation8. This may be related to the present positive phase of the Southern Annular Mode, which involves an intensification and southward migration of Southern Ocean westerlies, which results in atmospheric cooling of some parts of Antarctica.
This is an active area of research and scientists are very interested in investigating the reasons behind this trend. I expect several exciting papers will be published soon.
1. Miles BWJ, Stokes CR, Vieli A, Cox NJ. Rapid, climate-driven changes in outlet glaciers on the Pacific coast of East Antarctica. Nature 2013, 500(7464): 563-566.
2. Mengel M, Levermann A. Ice plug prevents irreversible discharge from East Antarctica. Nature Clim Change 2014, advance online publication.
3. Cook AJ, Vaughan DG. Overview of areal changes of the ice shelves on the Antarctic Peninsula over the past 50 years. The Cryosphere 2010, 4(1): 77-98.
4. Turner J, Overland J. Contrasting climate change in the two polar regions. Polar Research 2009, 28(2): 146-164.
5. Harangozo S. Atmospheric circulation impacts on winter maximum sea ice extent in the west Antarctic Peninsula region (1979–2001). Geophysical Research Letters 2006, 33(2).
6. Bintanja R, van Oldenborgh GJ, Drijfhout SS, Wouters B, Katsman CA. Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion. Nature Geosci 2013, advance online publication.
7. Pritchard HD, Ligtenberg SRM, Fricker HA, Vaughan DG, van den Broeke MR, Padman L. Antarctic ice-sheet loss driven by basal melting of ice shelves. Nature 2012, 484(7395): 502-505.
8. Thompson DW, Solomon S. Interpretation of recent Southern Hemisphere climate change. Science 2002, 296(5569): 895-899.