From the University of Southampton
A new study of satellite data from the last 19 years reveals that fresh water from melting glaciers has caused the sea-level around the coast of Antarctica to rise by 2cm more than the global average of 6cm.
Researchers at the University of Southampton detected the rapid rise in sea-level by studying satellite scans of a region that spans more than a million square kilometres.
The melting of the Antarctic ice sheet and the thinning of floating ice shelves has contributed an excess of around 350 gigatonnes of freshwater to the surrounding ocean. This has led to a reduction in the salinity of the surrounding oceans that has been corroborated by ship-based studies of the water.
“Freshwater is less dense than salt water and so in regions where an excess of freshwater has accumulated we expect a localised rise in sea level,” says Craig Rye, lead author of the paper that has been published in the journal Nature Geoscience.
In addition to satellite observations, the researchers also conducted computer simulations of the effect of melting glaciers on the Antarctic Ocean. The results of the simulation closely mirrored the real-world picture presented by the satellite data.
“The computer model supports our theory that the sea-level rise we see in our satellite data is almost entirely caused by freshening (a reduction in the salinity of the water) from the melting of the ice sheet and its fringing ice shelves,” says Craig.
“The interaction between air, sea and ice in these seas is central to the stability of the Antarctic Ice Sheet and global sea levels, as well as other environmental processes, such as the generation of Antarctic bottom water, which cools and ventilates much of the global ocean abyss.”
The research was carried out in close collaboration with researchers at the National Oceanography Centre and the British Antarctic Survey.
The full paper Rapid sea-level rise along the Antarctic margins in response to increased glacial discharge is published in Nature Geoscience.
Rapid sea-level rise along the Antarctic margins in response to increased glacial discharge
- Nature Geoscience (2014) doi:10.1038/ngeo2230
The Antarctic shelf seas are a climatically and ecologically important region, and are at present receiving increasing amounts of freshwater from the melting of the Antarctic Ice Sheet and its fringing ice shelves1, 2, primarily around the Antarctic Peninsula and the Amudsen Sea. In response, the surface ocean salinity in this region has declined in past decades3, 4, 5, 6, 7, 8, 9. Here, we assess the effects of the freshwater input on regional sea level using satellite measurements of sea surface height (for months with no sea-ice cover) and a global ocean circulation model. We find that from 1992 to 2011, sea-level rise along the Antarctic coast is at least 2 ± 0.8 mm yr−1 greater than the regional mean for the Southern Ocean south of 50° S. On the basis of the model simulations, we conclude that this sea-level rise is almost entirely related to steric adjustment, rather than changes in local ocean mass, with a halosteric rise in the upper ocean and thermosteric contributions at depth. We estimate that an excess freshwater input of 430 ± 230 Gt yr−1 is required to explain the observed sea-level rise. We conclude that accelerating discharge from the Antarctic Ice Sheet has had a pronounced and widespread impact on the adjacent subpolar seas over the past two decades.
Fortunately, they provide an SI file, seen here: http://www.nature.com/ngeo/journal/vaop/ncurrent/extref/ngeo2230-s1.pdf
Figure S4 is telling:
It seems there is a “pause” that has developed in SLR around Antarctica starting around 2005 continuing through 2012.
For reference, this map from NOAA/NESDIS shows that there is in fact about 2 cm of SLR around some parts of Antractica, but the main SLR is a big red patch in the Western Pacific:
While the Rye et al. paper says ice melt from the continent is the cause, it may also be simply a matter of winds. Note that the red spotch of SLR on the map above is mainly an issue of winds and ENSO. Around Antarctica, we have a strong circumpolar wind pattern, as is seen in the video below about ozone over Antarctica:
That circumpolar wind pattern around Antarctica can act as a sea level rise enhancer, as described in this paper:
Rapid subsurface warming and circulation changes of Antarctic coastal waters by poleward shifting winds
Spence et al. 2014
The southern hemisphere westerly winds have been strengthening and shifting poleward since the 1950s. This wind trend is projected to persist under continued anthropogenic forcing, but the impact of the changing winds on Antarctic coastal heat distribution remains poorly understood. Here we show that a poleward wind shift at the latitudes of the Antarctic Peninsula can produce an intense warming of subsurface coastal waters that exceeds 2 °C at 200-700 m depth. The model simulated warming results from a rapid advective heat flux induced by weakened near-shore Ekman pumping, and is associated with weakened coastal currents. This analysis shows that anthropogenically induced wind changes can dramatically increase the temperature of ocean water at ice sheet grounding lines and at the base of floating ice shelves around Antarctica, with potentially significant ramifications for global sea level rise.
Bottom line: I’m not much worried about the claims made about SLR in Antarctica being due to ice melt. There may be some enhancement, but to say it is the sole reason, when other fcators are clearly at play is just your typical climate alarmism at work.
UPDATE: Having written this piece late in the evening, my fatigue must have caused me to forget this graphic. Temperature over Antarctica seems to to be ever so slightly negative trending.