Abstract
Abstract. Variability of surface water masses of the Laptev and the East Siberian seas in August–September 2018 is studied using in situ and satellite data. In situ data were collected during the ARKTIKA-2018 expedition and then complemented with satellite-derived sea surface temperature (SST), salinity (SSS), sea surface height, wind speed, and sea ice concentration. The estimation of SSS fields is challenging in high-latitude regions, and the precision of soil moisture and ocean salinity (SMOS) SSS retrieval is improved by applying a threshold on SSS weekly error. For the first time in this region, the validity of DMI (Danish Meteorological Institute) SST and SMOS SSS products is thoroughly studied using ARKTIKA-2018 expedition continuous thermosalinograph measurements and conductivity–temperature–depth (CTD) casts. They are found to be adequate to describe large surface gradients in this region. Surface gradients and mixing of the river and the sea water in the ice-free and ice-covered areas are described with a special attention to the marginal ice zone at a synoptic scale. We suggest that the freshwater is pushed northward, close to the marginal ice zone (MIZ) and under the sea ice, which is confirmed by the oxygen isotope analysis. The SST-SSS diagram based on satellite estimates shows the possibility of investigating the surface water mass transformation at a synoptic scale and reveals the presence of river water on the shelf of the East Siberian Sea. The Ekman transport is calculated to better understand the pathway of surface water displacement on the shelf and beyond.
Highlights
The eastern part of the Eurasian Arctic remains one of the less studied areas of the Arctic Ocean
We suggest that the active displacement started in the ice-covered conditions after the maximum of river discharge in June–July, with progressive opening, part of the river water was mixed within the upper sea layer and exchanged heat with the atmosphere
Satellite DMI sea surface temperature (SST) and soil moisture and ocean salinity (SMOS) sea surface salinity (SSS) “A” estimates are cross-validated with conductivity– temperature–depth (CTD) data and continuous TSG measurements rarely done in this region
Summary
The direction of the surface freshwater circulation is supposed to correspond to a general displacement of the intermediate Atlantic Water: mainly eastward following the coastline (Carmack et al, 2016) This eastward transport brings the water masses of the Laptev Sea over the shelf of the East Siberian Sea where they meet Pacific-origin waters (Lenn et al, 2009; Semiletov et al, 2005). In the Arctic, the reported mixed layer depth (MLD) varies between 5 and 50 m depending on region, time, and whether it is measured in open water or under ice (10 m in the Laptev and the East Siberian seas and 5 m in the central Arctic Ocean and northern Barents Sea in summer, Timokhov and Chernyavskaya, 2009; 10–15 m in the Beaufort Sea close to the marginal ice zone (MIZ) in summer, Castro et al, 2017; 20 m in the Barents Sea in late summer, Pfirman et al, 1994; 40–50 m under the ice close to the North Pole in winter, Vivier et al, 2016). We propose following the upper ocean water displacement and discuss what causes it on a daily basis
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