Study on Extreme Parameters of Drift Ice in the Northern Barents Sea

This paper attempts to characterize the long-time extreme behaviors of drift ice in the northern Barents Sea from 1987 to 2016 using ice motion dataset from NSIDC and ice thickness datasets from NECP-CFSR and CFSv2. Three typical locations from west to east have been chosen for statistical analysis. Results show that the annual ice velocity extrema primarily ranges between 15 and 50 cms⁻¹, with the simultaneous directions predominantly from W to SE. For first-year ice thickness, the annual thickness maxima approximately range from 90 to 170 cm, but with an obvious decreasing trend. Regarding the extreme parameters estimation, four fundamental extreme value distribution functions, namely, Gumbel, Weibull, generalized extreme value and Pearson type III distributions are selected to obtain different return values of ice velocity and thickness. All functions have passed the K-S test but with different goodness of fit at the three sites. In particular, Gumbel distribution possesses higher extreme values at longer return periods. Furthermore, the patterns of co-occurrence distribution for concurrent ice velocity and ice thickness are calculated and analyzed.

Drift ice is often driven by winds and sea currents; consequently it can potentially pose hazardous threats for ocean engineering, marine structures and offshore activities. However, in the Barents Sea the available literatures mostly concern about sea ice concentration and its interactions with thermodynamic-dynamic factors, such as atmospheric anomalies and inflowing Atlantic warm waters. By contrast, little studies have focused on peculiarities of extreme ice velocity and thickness conditions for offshore drift ice in the Barents Sea.

At present, measuring and tracking the ice drift has been a hot spot in the northern Barents Sea. Vinje and Kvambekk (1991) presented that drift ice near the Svalbard was about 20 cms⁻¹. Løset and Carstens (1996) initially described the iceberg observation program in the western Barents Sea in 1987. In May 2003, in the northern Barents Sea some icebergs motioned towards a direction of 228° with average speed 14 cms⁻¹ (Zubakin et al., 2005) and maximum was 24 cms⁻¹ (Dmitriyev et al., 2005). In spring 2004, the largest speeds near the Novaya Zemlya were between 39.7 and 48.9 cms⁻¹ (Dmitriyev et al., 2005). Nesterov et al. (2009) found that the average observed ice drift speed was 17 cms⁻¹ and the maximum was 50 cms⁻¹ in the northeastern Barents Sea. Further in western Barents Sea, the drift ice characteristics such as velocities and directions are compared with winds and tidal currents (Marchenko et al., 2011; Marchenko and Marchenko, 2015). Specially, their observable drift ice data is from ice trackers with short measuring intervals. Duan et al. (2018) estimated 100-year winds can reach 28 ms^{− 1} in the northern zone. Regarding the drift ice thickness, Forsström et al. (2011) collected the some discrete 44-points thickness measurements using drillings in the marginal ice zone during 1999-2008. King et al. (2017) presented two raw helicopter-brome-electromagnetic thickness data in March 2003 and 2004 in the northwestern part, indicating the modal thickness varying regionally from 60 to 140 cm. Besides, many researches have been focusing on developing new algorithms to quantify drift ice features using the scattered observations and satellite data (e.g. Kaleschke et al., 2016; Marchenko, 2018).