Andrey Novikhin

Near-bottom water warming in the Laptev Sea in response to atmospheric and sea-ice conditions in 2007

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 shelfs submarine permafrost.

Changes in distribution of brine waters on the Laptev Sea shelf in 2007

Combined salinity and δ18O data from summer 2007 reveal a significant change in brine production in the Laptev Sea relative to summer 1994. The distribution of river water and brine enriched waters on the Laptev Sea shelf is derived based on mass balance calculations using salinity and δ18O data. While in 1994 maximal influence of brines is seen within bottom waters [Bauch et al., 2009a], in 2007 the influence of brines is highest within the surface layer and only a moderate influence of brines is observed in the bottom layer. In contrast to 2007, salinity and δ18O data from summer 1994 clearly identify a locally formed brine enriched bottom water mass as mixing endmember between surface layer and inner shelf waters on one side and with higher salinity water from the outer Laptev Sea on the other side. In 2007 the brine enriched waters are predominantly part of the surface regime and the mixing endmember between surface layer and outer shelf waters is replaced by a relatively salty bottom water mass. This relatively salty bottom water probably originates from the western Laptev Sea. The inverted distribution of brines in the water column in 2007 relative to 1994 suggests a less effective winter sea-ice formation in winter 2006/2007 combined with advection of more saline waters from the western Laptev Sea or the outer shelf precedent to 1 the climatically extreme summer 2007. The observed changes result in an altered export of waters from the Laptev Sea to the Arctic Ocean halocline.