Morphology of sea ice pressure ridges in the northwestern Weddell Sea in winter

To investigate the morphology and distR(i)bution of pressure R(i)dges in the northwestern Weddell Sea, ice surface elevation profiles were measured by a helicopter-borne laser altimeter duR(i)ng Winter Weddell Outflow Study with the German R/V Polarstern in 2006. An optimal cutoff height of 0.62 m, deR(i)ved from the best fits between the measured and theoretical R(i)dge height and spacing distR(i)butions, was first used to separate pressure R(i)dges from other sea ice surface undulations. It was found that the measured R(i)dge height distR(i)bution was well modeled by a negative exponential function, and the R(i)dge spacing distR(i)bution by a lognormal function. Next, based on the R(i)dging intensity R-i (the ratio of mean R(i)dge sail height to mean spacing), all profiles were clustered into three regimes by an improved k-means clusteR(i)ng algoR(i)thm: R-i <= 0.01, 0.01 < R-i <= 0.026, and R-i > 0.026 (denoted as C-1, C-2, and C-3 respectively). Mean (and standard deviation) of sail height was 0.99 (+/- 0.07) m in Regime C1, 1.12 (+/- 0.06) m in C-2, and 1.17 (+/- 0.04) m in C-3, respectively, while the mean spacings (and standard deviations) were 232 (+/- 240) m, 54 (+/- 20) m, and 31 (+/- 5.6) m. These three ice regimes coincided closely with distinct sea ice regions identified in a satellite radar image, where C-1 corresponded to the broken ice in the marginal ice zone and level ice formed in the Larsen Polynya, C-2 corresponded to the deformed first-and second-year ice formed by dynamic action in the center of the study region, and C-3 corresponded to heavily deformed ice in the outflowing branch of the Weddell Gyre. The results of our analysis showed that the relationship between the mean R(i)dge height and frequency was well modeled by a logaR(i)thmic function with a correlation coefficient of 0.8, although such correlation was weaker when consideR(i)ng each regime individually. The measured R(i)dge height and frequency were both greater than those reported by others for the Ross Sea. Compared with reported values for other parts of the Antarctic, the present R(i)dge heights were greater, but the R(i)dge frequencies and R(i)dging intensities were smaller than the most extreme of them. Meanwhile, average thickness of R(i)dged ice in our study region was significantly larger than that of the Coastal Ross Sea showing the importance of deformation and ice age for ice conditions in the northwestern Weddell Sea.