4.5 Impact of Floe-Size Dependent Processes on Sea Ice Evolution

Tuesday, 24 January 2017: 11:30 AM
Conference Center: Skagit 3 (Washington State Convention Center )
Lettie A. Roach, National Institute of Water and Atmosphere, Wellington, New Zealand; and C. M. Bitz, S. M. Dean, and C. H. Horvat

The region of sea ice between the open ocean and start of continuous sea ice cover can be extensive. In the summer, over 50% of observed Antarctic sea ice extent can be classified as belonging to this marginal ice zone (Stroeve et al., 2016). In this region of heterogeneous sea ice cover, floes vary in size from centimetres to kilometres and significant heat flux exchanges can occur between ice, ocean and atmosphere. Variation in floe size determines the importance of lateral melt (Steele, 1992), which is significant for floes up to 50km in size (Horvat et al., 2016), as well as the response of ice to mechanical stresses (Feltham, 2005). It also determines the attenuation of ocean surface waves (Doble & Bidlot, 2013) which can fracture sea ice hundreds of kilometres away from the ice edge during storms (Kohout et al., 2013) and accelerate ice retreat (Thomson & Rogers, 2014). We therefore hypothesize that floe-size dependent processes are a key factor in determining sea ice evolution during the melt season and the location of the ice edge.

The sea ice components of global climate models are currently unable to represent lateral floe sizes, describing only the distribution of ice into thickness categories (Thorndike et al., 1975, Hunke et al., 2010). As a result they represent the marginal ice zone primarily as decreasing concentration due to thermodynamic effects. Thus, to test our hypothesis, we have developed a framework to model the distribution of sea ice in lateral floe size categories for a global-scale sea model.

We adapt the mathematical formulation of a fully prognostic joint floe size and thickness distribution presented in Horvat & Tziperman (2015) for the Los Alamos sea ice model, CICE. New floe-size dependent melt and growth are integrated with the existing numerical scheme. We include a parametrization for ocean surface waves that are attenuated according to sea ice properties and determine floe break-up. Unlike previous studies (Williams et al., 2013; Tsamados et al., 2015; Dumont et al., 2011), we make no assumptions as to the shape of the floe size distribution; it is an emergent property arising from thermodynamics and wave fracture only. Preliminary results suggest that inclusion of floe-size dependent processes accelerates the rate of melt, in support of our hypothesis.

References

Doble, M. J. and J.-R. Bidlot (2013). "Wave buoy measurements at the Antarctic sea ice edge compared with an enhanced ECMWF WAM: Progress towards global waves-in-ice modelling." Ocean Modelling 70: 166-173.

Dumont, D., A. Kohout and L. Bertino (2011). "A wave-based model for the marginal ice zone including a floe breaking parameterization." Journal of Geophysical Research-Oceans 116: 12.

Feltham, D. L. (2005). "Granular flow in the marginal ice zone." Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 363(1832): 1677-1700.

Herman, A. (2010). "Sea-ice floe-size distribution in the context of spontaneous scaling emergence in stochastic systems." Physical Review E 81(6): 066123.

Horvat, C. and E. Tziperman (2015). "A prognostic model of the sea-ice floe size and thickness distribution." The Cryosphere 9(6): 2119-2134.

Horvat, C., E. Tziperman and J.-M. Campin (2016). "Interaction of sea ice floe size, ocean eddies and sea ice melting." Geophysical Research Letters: n/a-n/a.

Hunke, E. C., W. H. Lipscomb and A. K. Turner (2010). "Sea-ice models for climate study: retrospective and new directions." Journal of Glaciology 56(200): 1162-1172.

Kohout, A. L., M. J. M. Williams, S. M. Dean and M. H. Meylan (2014). "Storm-induced sea-ice breakup and the implications for ice extent." Nature 509(7502): 604-+.

Steele, M. (1992). "Sea ice melting and floe geometry in a simple ice‐ocean model." Journal of Geophysical Research: Oceans 97(C11): 17729-17738.

Stroeve, J. C., S. Jenouvrier, G. G. Campbell, C. Barbraud and K. Delord (2016). "Mapping and Assessing Variability in the Antarctic Marginal Ice Zone, the Pack Ice and Coastal Polynyas." The Cryosphere Discuss. 2016: 1-40.

Thomson, J. and W. E. Rogers (2014). "Swell and sea in the emerging Arctic Ocean." Geophysical Research Letters 41(9): 3136-3140.

Thorndike, A. S., D. A. Rothrock, G. A. Maykut and R. Colony (1975). "Thickness distribution of sea ice." Journal of Geophysical Research-Oceans and Atmospheres 80(33): 4501-4513.

Tsamados, M., D. Feltham, A. Petty, D. Schroeder and D. Flocco (2015). "Processes controlling surface, bottom and lateral melt of Arctic sea ice in a state of the art sea ice model." Philosophical Transactions of the Royal Society A: Mathematical Physical and Engineering Sciences 373(2052): 30.

Williams, T. D., L. G. Bennetts, V. A. Squire, D. Dumont and L. Bertino (2013). "Wave–ice interactions in the marginal ice zone. Part 1: Theoretical foundations." Ocean Modelling 71: 81-91.

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