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

Abstract

The Atlantic Water (AW) enters the Arctic through the Fram Strait and the Barents Sea, and propagates with the Arctic Boundary Current (ABC) cyclonically along the Arctic continental margins (Rudels et al., 2012; Schauer et al., 1997). In the Barents Sea and north of Svalbard, the AW is warmer than the near-freezing polar waters and occupies the near-surface layer of the water column, delaying sea ice formation and melting ice that is advected into the region (Meyer et al., 2017; Smedsrud et al., 2013). This sea ice melt leads to a gradual cooling and freshening of surface waters, and subsequently to subduction of the eastward propagating AW. The Barents Sea branch of the AW exits the shelf regions mainly through St. Anna Trough and joins the eastward propagating Fram Strait branch. A

A Steady Regime of Volume and Heat Transports in the Eastern Arctic Ocean in the Early 21st Century

“…These vertical (lateral) heat losses are equivalent to 3.1 (1770) W/m 2 of annual vertical (horizontal) AW heat flux along the 1900-km path from Fram Strait to the central Laptev Sea through a 300-km wide (700-m tall) cross-slope section. This estimate of summer vertical heat flux agrees well with doublediffusive heat fluxes of 3-4 W/m 2 derived from microstructure observations made in 2007 and 2008 (Polyakov et al, 2019) and 2018 (Schulz et al, 2021) in the eastern EB. Since we compare the heat transports made in different periods and considering the positive AW temperature trend in Fram Strait (0.06 • C/year; Beszczynska-Möller et al, 2012), uncertainties of our estimates are high and the actual vertical AW heat loss may be greater.…”

Turbulent Mixing and the Formation of an Intermediate Nepheloid Layer Above the Siberian Continental Shelf Break

“…The acoustic backscatter data of the ADCP was not suited to describe PM concentration, we suspect that the majority of suspended particles were too small to reflect the 75 kHz acoustic signal. Details on the instrumentation, data processing and sampling procedures can be found in Schulz et al (2021) (MSS and CTD) and Polyakov, Rippeth, Fer, Alkire, et al (2020); 2020) (ADCP).…”

Increasing Nutrient Fluxes and Mixing Regime Changes in the Eastern Arctic Ocean

“…Nitrate concentrations were highest below the AW temperature maximum at 10.5–12.3 mmol m −3 . Above the continental slope, where nutrient‐rich AW is mixed with nutrient‐poor shelf water (Schulz, Janout, et al., 2021), the nitrate concentrations were generally lower compared to profiles measured further offshore (e.g., Figure 1b). The discrete sample nitrate concentrations from both 2007 and 2008 exhibit the same vertical pattern as the measured profiles in 2018, but nitrate concentrations in the AW layer were slightly higher (10.8–14.8 mmol m −3 , data not shown) than in 2018.…”

“…In summer 2018, vertical conductivity, temperature, depth (CTD, SBE9+, Seabird Scientific) and Submersible Ultraviolet Nitrate Profiler (SUNA) nitrate concentration profile measurements were performed in the Laptev and East Siberian Seas (Figure 1a). At 22 of 85 stations, additional measurements with a microstructure profiler (MSS, MSS90L, Sea and Sun Technology, Germany) were carried out after the CTD casts, to obtain vertical profiles of turbulent dissipation rates (see Schulz, Janout, et al., 2021, for details on instrumentation and post‐processing). Both CTD and MSS were equipped with fluorescence sensors (WETLabs ECO‐FLNTU and Turner Designs Cyclops 7, respectively).…”

“…Energy conversion mechanisms to generate enhanced mixing from larger scale flow anomalies have just recently been described (Schulz, Büttner, et al., 2021). In addition, over the past decade and a half, warming (Barton et al., 2018) and shoaling of the AW (Polyakov et al., 2017, 2020) together with a weakening of the overlying halocline have led to significantly increased ventilation of the AW (Polyakov et al., 2020; Schulz, Janout, et al., 2021). Hence, the largely unresolved nutrient dynamics in the Siberian sector might be in transition, along with the ongoing oceanographic regime shift.…”