Predicting the future of the sea ice

Chances that the 2008 ice extent will fall below last year's record minimum is about 8 percent, researchers forecast after having run a number of different models predicting the fate of the Arctic sea ice this summer.

But there is still reason for concern; the scientists are almost certain the ice extent will fall below the minimum of 2005, which was the second lowest year on record. With a probability of 80% the minimum ice extent in 2008 will be in the range between 4.16 and 4.70 million km2.

This fall IPY-project DAMOCLES will dispatch eleven research missions into the Arctic to better understand the future of the sea ice.

Ensamble simulation
The researchers have employed a technique named ‘ensemble simulation' where atmospheric conditions from the years 1988 through 2007 have been prescribed to force an ocean-sea model.

The ocean-sea ice model calculates oceanic circulation, temperature, and salinity as well as sea ice drift, thickness, and concentration among other variables. The model incorporates the basic dynamical and thermodynamic equations that govern ocean and sea ice. Thus, it is able to reconstruct, starting from given initial conditions, the history of ocean and sea development through time.

Input to the model are several atmospheric quantities that are necessary to calculate the heat, water and momentum exchanges between the different media. One can say that the model is "forced" by these atmospheric data.

DAMOCLES researchers Frank Kauker, Ruediger Gerdes and Michael Karcher have written an article abut it.

Read the whole article here.

Foto: Eric Brossier/Vagabond/DAMOCLES
The Polar Yacht “Vagabond” participates in the DAMOCLES project from 2005 to 2008.

Sound calculations
"After the strong decrease of the Arctic ice during the last summer, climate scientists all around the world are constantly asked: how will the ice develop in the next years?" described Prof. Dr. Rüdiger Gerdes from the Alfred Wegener Institute his motivation. "To answer this question, we did not want to guess, but to rely on sound calculations."

Scenarios of the long-term development of sea ice clearly indicate a de-creased ice cover - exact prognoses for the following summer, however, are not yet possible. This is mainly due to the fact that the short-term development of sea ice depends strongly on the actual atmospheric conditions, namely the weather and in particular wind, cloud cover and air temperatures.

Because the exact atmospheric conditions which determine the weather patterns in the Arctic Ocean during the coming months are not predictable, Rüdiger Gerdes and his team have entered atmospheric data of the last twenty years into an ocean sea ice model.

"Through this, we are still not able to make a definitive statement on sea ice cover in September. This 'trick' enables us to compute the bandwidth of possible ice covers, and to quantify the probability of extreme events", said Gerdes.

Reality check
Apart from the variability of atmospheric quantities during the melting season, ice thickness at the beginning of the season determines the new ice minimum. Accordingly, computations of ice thickness enter the models of the researchers. Start conditions from June 27th 2008 were used for their current prognosis.

Different from long-term prognoses, the researchers' forecasts can quickly be checked by reality.

"It is a first test, and all participating researchers are eager to know how their prognosis has fared at the end of the summer. In the end, this small competition serves the optimisation of our models, so that we are able to improve our predictions concerning short-term seasonal fluctuations. It has to be added, however, that even perfect models would not be able to rule out a component of chance regarding the atmosphere. These forecasts will always be about probability, and not exact prognoses", Rüdiger Gerdes concluded.

Cruises this fall
Eleven research cruises will be carried through as part of the DAMOCLES programme (Developing Arctic Modelling and Observing Capabilities for Long-term Environment Studies) during the summer and autumn 2008, see detailed list below. On some of the cruises it is possible for journalists or media to join.

Cruise:Oceania cruise
Vessel: R/V Oceania
Dates: June 19 ¬- July 23, 2008
Location: Norwegian, Barents & Greenland Seas and Fram Strait
Purpose: Atlantic Water transport (volume, heat and salt) into the Arctic Ocean and its variabilities
Contact: Jan Piechura: piechura@iopan.gda.pl
http://www.iopan.gda.pl/oceania/oceania.html

Cruise:ARKXXIII-2
Vessel: R/V Polarstern
Dates: July 04 - August 10, 2008
Location: Section across Fram Strait at 79°N:
Purpose: CTD section, exchange of mooring array and deployment of glider
Contact: Ursula Schauer: Ursula.Schauer@awi.de
Gerhardt Kattner: Gerhard.Kattner@awi.de
http://www.awi.de/en/infrastructure/ships/polarstern/

Cruise:ASCOS
Vessel: R/V Oden
Dates: July 23 - September 22, 2008
Location: North East Passage
Purpose: Study low level clouds
Contact: Michael Tjernstrom: michaelt@misu.su.se
Caroline Leck: lina@misu.su.se
URL: http://www.ascos.se/

Cruise:TBA
Vessel: R/V XueLong
Dates: July 31 - September 13, 2008
Location: High Arctic
Purpose: TBA
Contact: Jari Haapala: Jari.Haapala@fimr.fi

Cruise:TBA
Vessel: RV Håkon Mosby
Dates: August 4 - August 18, 2008
Location: Along 78 45 N (Fram strait)
Purpose: Deploy three moorings; two tomography moorings and a MMP
Contact: Hanne Sagen: hanne.sagen@nersc.no

Cruise:Nordic LSBI
Vessel: R/V Yakov Smirnitskii
Dates: August 12 - September 24, 2008
Location: North East passage
Purpose: Investigate the fluxes and transformation of carbon, from the
terrestrial organic carbon input by river runoff and by coastal erosion
Contact: Leif Anderson: leifand@chem.gu.se
Göran Björk: gobj@gvc.gu.se

Cruise:ARKXXIII-3
Vessel: R/V Polarstrern
Dates: August 15 - October 19, 2008
Location: Central Arctic and East Siberian Sea
Purpose: Cross-basin CTD section and deployment of ice-tethered platforms
Contact: Ursula Schauer: Ursula.Schauer@awi.de
Dr. Wilfried Jokat: Wilfried.Jokat@awi.de
http://www.awi.de/en/infrastructure/ships/polarstern/

Cruise:TBA
Vessel: R/V Lance
Dates:August 30 - September 19, 2008
Location: Fram strait
Purpose: TBA
Contact: Edmond Hansen: edmond.hansen@npolar.no

Cruise:TBA
Vessel: Jan Mayen
Dates: September 05 - September 18, 2008
Location: Barents sea
Purpose: Recovering and redeploying the moorings
Contact: Cecilie Mauritzen: cecilie.mauritzen@met.no

Cruise:TBA
Vessel: RV Håkon Mosby
Dates: September 18 - October 1, 2008
Location: Storfjorden, Svalbard
Purpose: i) Service bottom-mounted current profilers monitoring the dense overflow water from Storfjorden, ii) conduct turbulence profiles to study mixing of the overflow, iii) conduct measurements off Bear Island to study internal wave induced mixing near the critical latitude for the semi-diurnal period.
Contact: Ilker Fer: Ilker.Fer@bjerknes.uib.no

Cruise:TBA
Vessel: K/V Svalbard
Dates: September 19 - September 29, 2008
Location: Along 78 45 N (Fram strait)
Purpose: Positioning of transponders, download of first data set using acoustic modems, record bathymetry data, listen to acoustic source and to acoustic ambient noise using a hydrophone from the ship.
Contact: Hanne Sagen: hanne.sagen@nersc.no

Read More about DAMOCLES here

(Top picture: Eric Brossier/Vagabond/DAMOCLES)