SAMS sea ice research has just been highlighted by Nature in their online news.
The RECARO consortium wrote a recent article for the American Geophysical Union paper Eos regarding an EU project coordinated by Dr Jeremy Wilkinson. Nature has written a feature about this key paper, which describes experiments carried out at the Hamburg Ship Model Basin (www.hsva.de), in the Arctic Environmental Test Basin (AETB). By simulating waves of different frequencies and amplitude, the researchers were able gain valuable insight into Arctic sea ice formation.
Ice tank experiments highlight changes in sea ice types
With the ongoing and probably continuing reduction of summer sea-ice extent in the Arctic, the predominant mechanism of sea-ice formation in the Arctic Ocean is likely to change in the future. While in the past, substantial new-ice formation occurred under pre-existing ice, the fraction of sea-ice formation in open water will increase significantly. There, sea ice formation starts with the development of small ice crystals suspended in the water, called frazil ice (WMO, 1985). Under quiescent conditions, these crystals accumulate at the surface to form an unbroken ice sheet, or nilas. Under turbulent conditions, caused by wind and waves, frazil ice continues to grow and forms into a thick, soupy mixture called grease ice. Eventually the frazil ice will coalesce into small, rounded ice pieces known as pancake ice, which finally consolidate into an ice sheet with the return of calm conditions. This so-called frazil-pancake-ice sheet cycle is today frequently observed in the Antarctic (Lange, 1989). It is favoured by oceanic conditions with significant stretches of open water, since these allow larger waves and hence increased turbulence to develop. Given the increase of such open water in the Arctic Ocean caused by the retreating summer sea ice, the frazil-pancake-ice sheet cycle may also become the dominant ice formation process during freeze-up in the Arctic.
We here report on a new series of laboratory experiments that specifically aims at increasing our understanding of the processes underlying such new-ice formation, both under turbulent and under quiescent conditions. In separate tanks, starting from open water, we simultaneously grew ice under both conditions. During this time the associated atmospheric, cryospheric and oceanographic variables were constantly monitored. These experiments built on results from previous studies, most notably Haas et al., 1999, Shen et al., 2001 and Doble et al., 2003.
Our project ‘Understanding the impact of a REduced ice Cover in the ARctic Ocean’ (RECARO), involved over 20 partners from 10 European countries, Japan and the USA. It consisted of two experimental phases, a two-week experiment in November 2007 and a one-week experiment in March 2008. RECARO studies complement the comprehensive basin-wide evaluation of sea-ice processes performed under the EU-funded DAMOCLES project.
The experimental layout
The experiments took place at the Hamburg Ship Model Basin (www.hsva.de), in the
Arctic Environmental Test Basin (AETB) which is 30 m in length, 6m in width and filled with salt-water to a depth of 1.2 m. To provide for the two scenarios of ice growth under quiescent and under turbulent wave-dominated conditions, the AETB was subdivided into 3 separate tanks. The first tank, Tank 1, was a turbulence-free zone, while the other two tanks, Tank 2 and 3 were used to study ice formation under a wave-dominated environment. Tank 2 and 3 were identical in size, but each had a separate wave maker and ended in a raised beach to limit the wave reflections. All tanks were isolated from each other by sealed wooden barriers. A schematic of the tanks can be seen in figure 1. Within each tank, a number of different sensors were placed, including
• oceanographic sensors: temperature, salinity, turbulence and wave field;
• meteorological sensors: air temperature, humidity and air pressure;
• cryospheric sensors: ice thickness, concentration, crystal structure, salinity and brine content, optical properties and ice strength.
The experiments described here will improve our understanding of the processes behind the two different ice formation regimes as well as their respective influences on the ocean and atmosphere. This should allow for a better characterization of the development of sea ice in the Arctic Ocean during freeze-up, especially the optical and physical properties of new ice types, the associated brine drainage, and sea ice wave dynamics. This could guide the incorporation of these ice regimes into future coupled sea-ice models.
Doble, M. J., M. D. Coon, and P. Wadhams (2003), Pancake ice formation in the Weddell Sea, J. Geophys. Res., 108(C7), 3209, doi:10.1029/2002JC001373.
Haas, C., + ten. 1999 Multidisciplinary ice tank study shedding new light on sea ice growth processes. Eos, 80. 507-513.
Lange, M.A., S.F. Ackley, P. Wadhams, G.S. Dieckmann, H. Eicken (1989) Development of sea ice in the Weddell Sea Antarctica, Ann. Glaciol., 12:92-96
Shen, H.H., S.F. Ackley and M. Hopkins (2001) A conceptual model for pancake-ice formation in a wave field, Ann. Glaciol., 33(1), 361-367.
WMO (1985). World Meteorological Organization: WMO sea-ice nomenclature, terminology, codes and illustrated glossary, WMO/DMM/BMO 259-TP-145, Secretariat of the WMO, Geneva.
The work was supported by the European Community's Integrated Infrastructure Initiative HYDRALAB III, Contract no. 022441(RII3). Further support was given through the EU project “DAMOCLES” and the home institutes of the participating scientists. The authors would like to thank the HSVA for their hospitality, technical and scientific support as well as Jamie Morison (APL-UW) and Frank Nilsen (UNIS) for the use of their equipment.