Assessment of variability of the thermohaline structure and transport of Atlantic water in the Arctic Ocean based on NABOS CTD data

Abstract

Abstract. Data of CTD transects across continental slope of the Eurasian Basin and the St. Anna Trough performed during NABOS (Nansen and Amundsen Basins Observing System) project in 2003–2015 are used to assess transport and propagation features of the Atlantic Water (AW) in the Arctic Ocean. Estimates of θ-S indices and volume flow rate of the current carrying the AW in the Eurasian Basin were obtained. The assessments were based on the analysis of CTD data including 33 sections in the Eurasian Basin, 4 transects in the St. Anna Trough and 2 transects in the Makarov Basin; additionally a CTD transect of the PolarStern-1996 expedition (PS-96) was considered. Using spatial distributions of temperature, salinity, and density on the transects and applying θ-S analysis, the variability of thermohaline pattern on the AW pathway along the slope of Eurasian Basin was investigated. The Fram Strait branch of the Atlantic Water (FSBW) was satisfactorily identified on all transects, including two transects in the Makarov Basin (along 159° E), while the сold waters, which can be associated with the influence of the Barents Sea branch of the Atlantic water (BSBW), on the transects along 126° E, 142° E and 159° E, were observed in the depth range below 800 m and had a negligible effect on the spatial structure of isopycnic surfaces. Special attention was paid to the variability of the volume flow rate of the AW propagating along the continental slope of the Eurasian Basin. The geostrophic volume flow rate was calculated using the dynamic method. An interpretation of the spatial and temporal variability of hydrological parameters characterizing the flow of the AW in the Eurasian Basin is presented. The geostrophic volume flow rate decreases significantly farther away from the areas of the AW inflow to the Eurasian Basin. Thus, the geostrophic estimate of the volume rate for the AW flow in the Makarov Basin at 159° E was found to be more than an order of magnitude smaller than the estimates of the volume flow rate in the Eurasian Basin, implying that the major part of the AW entering the Arctic Ocean circulates cyclonically within the Nansen and Amundsen Basins. There is an absolute maximum of θmax (AW core temperature) in 2006–2008 time series and a maximum in 2013, but only at 103° E. Salinity S(θmax) (AW core salinity) time series display an increase of the AW salinity in 2006–2008 and 2013 (at 103° E) that can be referred to as a AW salinization in the early 2000-ies. The maxima of θmax and S(θmax) in 2006–2008 and 2013 were accompanied by the volume flow rate highs. Additionally the time average volume rates were calculated for the FSBW flow (in the longitude range 31–92° E), for the BSBW flow in the St. Anna Trough and for a combined FSBW and BSBW flow in longitude range 94–107° E. A detailed discussion of the results is presented.