Thin-ice dynamics and ice production in the Storfjorden polynya for winter seasons 2002/2003–2013/2014 using MODIS thermal infrared imagery
Abstract. Spatial and temporal characteristics of the Storfjorden polynya, which forms regularly in the proximity of the islands Spitsbergen, Barentsøya and Edgeøya in the Svalbard archipelago under the influence of strong northeasterly winds, have been investigated for the period of 2002/2003 to 2013/2014 using thermal infrared satellite imagery. Thin-ice thicknesses were calculated from MODIS ice-surface temperatures combined with ECMWF ERA-Interim atmospheric reanalysis data in an energy-balance model. Associated quantities like polynya area and total ice production were derived and compared to previous remote sensing and modeling studies. A basic coverage-correction scheme was applied to account for cloud gaps in the daily composites. On average, both polynya area and ice production are thereby increased by about 30%. The sea ice in the Storfjorden area experiences a late fall freeze-up in several years over the 12-winter period, which becomes most apparent through an increasing frequency of large thin-ice areas until the end of December. In the course of an average winter season, ice thicknesses below 10 cm are dominating within the Storfjorden basin. During the regarded period, the mean polynya area is 4555.7 ± 1542.9 km2. Maximum daily ice production rates can reach as high as 26 cm d−1, while the average ice production is estimated at 28.3 ± 8.5 km3 per winter and therefore lower than in previous studies. Despite this comparatively short record of 12 winter seasons, a significant positive trend of 20.2 km3 per decade could be detected, which originates primarily from a delayed freeze-up in November and December in recent winter seasons. This contrasts earlier reports of a slightly negative trend in accumulated ice production prior to 2002. Although featuring more pronounced interannual variations between 2004/2005 and 2011/2012, our estimates underline the importance of this relatively small coastal polynya system considering its contribution to the cold halocline layer through salt release during ice-formation processes. In addition, calculated quasi-daily thin-ice thickness charts represent a valuable data set for atmosphere and ocean modeling applications.