Variability of the thermohaline structure and transport of Atlantic water in the Arctic Ocean based on NABOS (Nansen and Amundsen Basins Observing System) hydrography data

Abstract

Abstract. Conductivity–temperature–depth (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 2002–2015 and a transect from the 1996 Polarstern expedition are used to describe the temperature and salinity characteristics and volume flow rates (volume transports) of the current carrying the Atlantic water (AW) in the Arctic Ocean. The variability of the AW on its pathway along the slope of the Eurasian Basin is investigated. A dynamic Fram Strait branch of the Atlantic water (FSBW) is identified in all transects, including two transects in the Makarov Basin (along 159∘ E), while the cold waters on the eastern transects along 126, 142, and 159∘ E, which can be associated with the influence of the Barents Sea branch of the Atlantic water (BSBW), were observed in the depth range below 800 m and had a negligible effect on the spatial structure of isopycnic surfaces. The geostrophic volume transport of AW decreases farther away from the areas of the AW inflow to the Eurasian Basin, decreasing by 1 order of magnitude in the Makarov Basin at 159∘ E, 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 a trend of an increase in AW salinity over time, which can be referred to as an AW salinization in the early 2000s. The maxima of θmax and S(θmax) in 2006 and 2013 are accompanied by the volume transport maxima. The time average geostrophic volume transports of AW are 0.5 Sv in the longitude range 31–92∘ E, 0.8 Sv in the St. Anna Trough, and 1.1 Sv in the longitude range 94–107∘ E.

On the Along‐Slope Heat Loss of the Boundary Current in the Eastern Arctic Ocean

“…Zhurbas and Kuzmina (2020) further report a typical cooling of the AW core temperature by 1–2°C per 1,000 km travel distance along the slope, in the area between 31°E and 159°E, which is stronger than the cooling of 1.2°C over approximately 2,500 km travel distance observed in this study. This bias might be due to the further upstream extent of the study area investigated in Zhurbas and Kuzmina (2020), where the cooling is generally stronger (Zhurbas & Kuzmina, 2020). The relatively small temperature anomalies compared to the observed cooling, together with the consistent heat content decrease observed along the AW pathway (Figure 7) give confidence that the estimated heat loss is mainly caused by progressive cooling along the ABC travel pathway rather than upstream variability, in agreement with Lenn et al.…”

“…As the core of the AW (i.e. the largest mid‐water temperature anomalies) is typically found at positions deeper than the 1,000 m isobath (this study, Polyakov et al., 2020a; Zhurbas & Kuzmina, 2020), it is questionable how representative the high current velocities at the upper slope are for the propagation speed of the AW.…”

“…We thus consider the impact on heat loss estimates further downstream to be much smaller. Multiyear hydrographic surveys conducted in the Laptev Sea between 2002 and 2015 show that the core temperature of the AW layer differs by up to 0.9°C during this 13 year time period, and by up to 0.5°C in consecutive years (Zhurbas & Kuzmina, 2020). Zhurbas and Kuzmina (2020) further report a typical cooling of the AW core temperature by 1–2°C per 1,000 km travel distance along the slope, in the area between 31°E and 159°E, which is stronger than the cooling of 1.2°C over approximately 2,500 km travel distance observed in this study.…”

“…Multiyear hydrographic surveys conducted in the Laptev Sea between 2002 and 2015 show that the core temperature of the AW layer differs by up to 0.9°C during this 13 year time period, and by up to 0.5°C in consecutive years (Zhurbas & Kuzmina, 2020). Zhurbas and Kuzmina (2020) further report a typical cooling of the AW core temperature by 1–2°C per 1,000 km travel distance along the slope, in the area between 31°E and 159°E, which is stronger than the cooling of 1.2°C over approximately 2,500 km travel distance observed in this study. This bias might be due to the further upstream extent of the study area investigated in Zhurbas and Kuzmina (2020), where the cooling is generally stronger (Zhurbas & Kuzmina, 2020).…”

“…Γ = 1 was applied in the calculation of the heat flux within the AW thermocline. et al, 2020a;Zhurbas & Kuzmina, 2020), it is questionable how representative the high current velocities at the upper slope are for the propagation speed of the AW.…”