The Filchner-Ronne Ice Shelf fringing the Weddell Sea, Antarctica,may start to melt rapidly in this century and no longer act as abarrier for ice streams draining the Antarctic Ice Sheet. Thesepredictions are made by climate researchers of the Alfred WegenerInstitute for Polar and Marine Research in the HelmholtzAssociation in the coming issue of the British science magazine"Nature". They refute the widespread assumption that ice shelves in theWeddell Sea would not be affected by the direct influences ofglobal warming due to the peripheral location of the Sea. The results of the climate modelers from the Alfred WegenerInstitute will come as a surprise to the professional world withthe majority of experts assuming that the consequences of globalwarming for Antarctica would be noticeable primarily in theAmundsen Sea and therefore in the western part of Antarctica. |
"The Weddell Sea was not really on the screen because we allthought that unlike the Amundsen Sea its warm waters would not beable to reach the ice shelves. But we found a mechanism whichdrives warm water towards the coast with an enormous impact on theFichner-Ronne Ice Shelf in the coming decades", says Dr. HartmutHellmer, oceanographer at the Alfred Wegener Institute and leadauthor of the study. Using different model calculations, he and his colleagues Dr. FrankKauker, Dr.
Ralph Timmermann and Dr. Jurgen Determann as well asDr. Jamie Rae from Met Office Hadley Centre, U.K., demonstrate thatas a result of a chain reaction large ice masses could presumablyslide into the ocean within the next six decades. This chain reaction is triggered by rising air temperatures abovethe southeastern Weddell Sea.
"Our models show that the warmer airwill lead to the currently solid sea ice in the southern WeddellSea becoming thinner and therefore more fragile and mobile in a fewdecades", says Frank Kauker. If this happens, fundamental transportprocesses will change. "This will mean that a hydrographic front in the southern WeddellSea will disappear which has so far prevented warm water fromgetting under the ice shelf. According to our calculations, thisprotective barrier will disintegrate by the end of this century",explains Hartmut Hellmer.
An inflow of warmer water beneath the Filchner-Ronne Ice Shelf willmelt the ice from below. "We expect the greatest melting rates nearthe so-called grounding line, the zone in which the ice shelfsettles on the sea floor at the transition to the glacier. At thispoint the Filchner-Ronne Ice Shelf is melting today at a rate ofaround 5 metres per year. By the turn of the next century the meltrates will rise to up to 50 metres per year", says Hellmer'scolleague Jurgen Determann. How the ice streams behind will react in the event of a melt ofsuch enormous proportions is currently being investigated by JurgenDetermann.
One thing is obvious, however: "Ice shelves are likecorks in the bottles for the ice streams behind them. They reducethe ice flow because they lodge in bays everywhere and rest onislands. If, however, the ice shelves melt from below, they becomeso thin that the dragging surfaces become smaller and the icebehind them starts to move", explains Hartmut Hellmer. "If the high melting rates are completely compensated by inland iceflow, this loss in mass would correspond to an additional rise inglobal sea level of 4.4 millimetres per year", adds JurgenDetermann. According to the latest estimates based on remotesensing data, global sea level rose for the period 2003-2010 at arate of 1.5 millimetres per year due to melting of glaciers and iceshelves.
This occurs in addition to the 1.7 millimetres per yeardue to thermal expansion of the oceans. The forecasts of the current study are based on independentcalculations of the ocean models BRIOS (Bremerhaven Regional IceOcean Simulations) and FESOM (Finite Element Sea Ice Ocean Model). The scientists used the atmospheric projections of the British MetOffice Hadley Centre in Exeter as forcing data. These included, forexample, information on the future development of the wind and ofthe temperature in Antarctica.
Hartmut Hellmer and his colleagues have thoroughly checked themodel results for being realistic: "We started the BRIOS model in1860 to see whether its results also represent the currentsituation. We found that this condition was satisfied. For example,the water temperatures for the Weddell Sea predicted by BRIOS areclose to those we have actually measured in the recent past", saysRalph Timmermann. Adding, "The BRIOS model has been verified on many occasions in thepast. It correctly predicts sea ice thickness, concentration, anddrift as well as circulation patterns.
And FESOM is well on the wayto attaining BRIOS status. However, it has a far higher resolution,which is why we have to wait a long time until the computer hascalculated several decades and more. BRIOS only needs less than aweek for a century." The study was conducted as part of the EU-funded research programme"Ice2sea". This project brings together scientists from 24 leadingresearch institutions of the European Union and from Chile, Norwayand Iceland.
Together, the scientists aim for decoding theinteractions between ice and climate and in this way facilitatemore precise predictions about the effects of melting ice on sealevel. More information on the Ice2sea project is available here .
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