Structure and Transport of Atlantic Water North of Svalbard From Observations in Summer and Fall 2018

Abstract

The transport of warm Atlantic Waters north of Svalbard is one of the major heat and salt sources to the Arctic Ocean. The circulation pathways and the associated heat transport influence the variability in the Arctic sea ice extent, the onset of freezing, and marine ecosystems. We present observations obtained from research cruises and an autonomous underwater glider mission in summer and fall 2018, to describe the hydrographic structure, volume transport, and circulation patterns of the warm Atlantic Water Boundary Current between 12°E and 24°E north of Svalbard. The Atlantic Water volume transport reaches a maximum of 3.0 ± 0.2 Sv in October, with an intraseasonal variability of 1 Sv (1 Sv = 106 m3 s−1). During summer and late fall, we observed an Atlantic Water recirculation flowing westward (0.1–0.2 Sv) in the outer part of the section away from the shelf break. This counter current appears to be a part of an anticyclonic circulation in the Sofia Deep. The strength of the Atlantic Water recirculation and the Atlantic Water boundary current is very sensitive to the wind stress curl: The boundary current volume transport doubled in less than a week, corresponding to a transition from strongly negative (−10−6 N m−3) to strongly positive (10−6 N m−3) wind stress curl over the Sofia Deep. A previously unknown, deep bottom‐intensified current is observed to flow parallel to the boundary current, between the 1,500 and 2,000 m isobaths. Historical data in the region support the presence of the bottom‐intensified current.

Atlantic Water Properties, Transport and Heat Loss From Mooring Observations North of Svalbard

“…This short term response is in agreement with the hypothesis developed in Kolås et al. (2020), who suggested a short‐term adjustment of isopycnals in response to wind forcing.…”

“…This bottom-intensified current consists either of Arctic Intermediate Water (AIW, −0.8 < Θ < 0°C and 35.06 < S A < 35.09 g kg −1 ), a common water mass in the Arctic Ocean created by ocean convection in the Greenland Sea (Rudels et al, 2005), or of Eurasian Basin Deep Water (EBDW, −1.1 < Θ < 0°C and S A > 35.06 g kg −1 ) (Sundfjord et al, 2020). The counter current on the lower slope has already been documented along the slope north of Svalbard in previous studies using ship sections (Kolås et al, 2020;Pérez-Hernández et al, 2017). The other notable pattern is the countercurrent on the upper slope in spring, with averaged westward velocities of about 0.1 m s −1 (Figures 5c and 5g).…”

“…The bottom-intensified current observed in both arrays at the outer moorings has earlier been detected from a fall cruise in Pérez-Hernández et al (2017). In the first detailed Kolås et al (2020) documented this current feature in hydrographic sections performed in both July and September 2018. They found a bottom-intensified current of 1.5 Sv, representing 35% of the observed flow entering the Arctic Ocean.…”

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

“…Pérez-Hernández et al (2017) using synoptic-scale cross-slope CTD sections between 21 and 33 • E reported along-slope AW volume transport of 2.31 ± 0.29 Sv. Kolås et al (2020) utilizing CTD data from ship-based surveys and an autonomous underwater glider mission in summer and fall 2018 reported AW volume transport of 3.0 ± 0.2 Sv, with an intraseasonal variability of 1 Sv. The plausible reasons for that wide range of AW volume transport estimates are different time scales of observations used for transport calculations (i.e., synoptic scale at Svalbard and annual scale at the Laptev Sea slopes) concurrent by the strong annual variability of those transports.…”

Planktic Foraminiferal and Pteropod Contributions to Carbon Dynamics in the Arctic Ocean (North Svalbard Margin)

“…The presence of the subpolar pteropod L. retroversa at slope stations 3, 4 and 6 could be interpreted as a stronger influence of the warmer Atlantic waters on the northern Svalbard margin. An increase in the Atlantic water inflow was observed in this area between summer and late fall of 2018 (Kolås et al, 2020).…”