[1] This paper examines a hydrographic response to the wind-driven coastal polynya activity over the southeastern Laptev Sea shelf for April-May 2008, using a combination of Environmental Satellite (Envisat) advanced synthetic aperture radar (ASAR) and TerraSAR-X satellite imagery, aerial photography, meteorological data, and SBE-37 salinity-temperature-depth and acoustic Doppler current profiler land-fast ice edgemoored instruments. When ASAR observed the strongest end-of-April polynya event with frazil ice formation, the moored instruments showed maximal acoustical scattering within the surface mixed layer, and the seawater temperatures were either at or 0.02°C below freezing. We also find evidence of the persistent horizontal temperature and salinity gradients across the fast ice edge to have the signature of geostrophic flow adjustment as predicted by polynya models.

In this paper we present new data from ship-based measurements and two-year observations from moorings in the Laptev Sea along with Russian historical data. The observations from the Laptev Sea in 2007 indicate that the bottom water temperatures on the mid-shelf increased by more than 3°C compared to the long-term mean as a consequence of the unusually high summertime surface water temperatures. Such a distinct increase in near-bottom temperatures has not been observed before. Remnants of the relatively warm bottom water occupied the mid-shelf from September 2007 until April 2008. Strong polynya activity during March to May 2007 caused more summertime open water and therefore warmer sea surface temperatures in the Laptev Sea. During the ice-free period in August and September 2007, the prevailing cyclonic atmospheric circulation deflected the freshwater plume of the River Lena to the east, which increased the salinity on the mid-shelf north of the Lena Delta. The resulting weaker density stratification allowed more vertical mixing of the water column during storms in late September and early October, leading to the observed warming of the near-bottom layer in the still ice-free Laptev Sea. In summer and autumn 2008, when the density stratification was stronger and sea surface temperatures were close to the long-term mean, no near-bottom water warming was observed. Warmer water temperatures near the seabed may also impact the stability of the shelf's submarine permafrost

For offshore constructions the knowledge on sediment transport dynamics is essential and the quantification of suspended particulate matter (SPM) is of major importance. The Laptev Sea shelf is one of the largest Siberian shelf seas and ice-covered for about nine months a year. In order to use indirect measuring devices for the quantification of SPM concentration on the Laptev Sea shelf, optical (turbidity meter) and acoustic (ADCP; Acoustic Doppler Current Profiler) backscatter sensors were compared to assess their potential for the investigation of SPM dynamics in an arctic environment. To estimate SPM concentrations from optical backscatter signals, these were converted using the linear relation between the backscatter signals and SPM concentrations derived from water samples. Applying the theoretical interaction of sound in the water with SPM the acoustic backscatter signals were transformed adapting a previously established approach. SPM concentrations estimated from the backscattered signals of both sensors showed a close similarity to SPM concentrations obtained from filtered water samples. While the ADCP offers distinct advantages over the turbidity meter in that it allows measurement of the complete concentration profile, bottom location, and currents, co-deployment of both sensors are recommended for improved SPM measurements.

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