Deep Flow Variability Offshore South-West Svalbard (Fram Strait)

Abstract

Water mass generation and mixing in the eastern Fram Strait are strongly influenced by the interaction between Atlantic and Arctic waters and by the local atmospheric forcing, which produce dense water that substantially contributes to maintaining the global thermohaline circulation. The West Spitsbergen margin is an ideal area to study such processes. Hence, in order to investigate the deep flow variability on short-term, seasonal, and multiannual timescales, two moorings were deployed at ~1040 m depth on the southwest Spitsbergen continental slope. We present and discuss time series data collected between June 2014 and June 2016. They reveal thermohaline and current fluctuations that were largest from October to April, when the deep layer, typically occupied by Norwegian Sea Deep Water, was perturbed by sporadic intrusions of warmer, saltier, and less dense water. Surprisingly, the observed anomalies occurred quasi-simultaneously at both sites, despite their distance (~170 km). We argue that these anomalies may arise mainly by the effect of topographically trapped waves excited and modulated by atmospheric forcing. Propagation of internal waves causes a change in the vertical distribution of the Atlantic water, which can reach deep layers. During such events, strong currents typically precede thermohaline variations without significant changes in turbidity. However, turbidity increases during April–June in concomitance with enhanced downslope currents. Since prolonged injections of warm water within the deep layer could lead to a progressive reduction of the density of the abyssal water moving toward the Arctic Ocean, understanding the interplay between shelf, slope, and deep waters along the west Spitsbergen margin could be crucial for making projections on future changes in the global thermohaline circulation.

The International Bathymetric Chart of the Arctic Ocean Version 4.0

“… Alaska Fisheries Science Center of the US National Oceanic and Atmospheric Administration’s National Marine Fisheries Service (NOAA Alaskan Fisheries) Bathymetry data from the Alaska bathymetry compilations for the Aleutian Islands, central and western Gulf of Alaska and Norton Sound: https://www.afsc.noaa.gov/RACE/groundfish/Bathymetry/default.htm Digitized chart soundings, Alaska: Proofed digitized historical chart soundings from “smooth sheets” covering Alaskan waters 44 – 47 Alfred Wegener Institute (AWI) 81 Cruises of Multibeam data in the Atlantic and Indian Ocean region . 11 Cruises of multibeam data in the South and West Pacific: https://www.pangaea.de/ https://www.pangaea.de/expeditions/cr.php/Polarstern https://webapp-srv1a.awi.de/eBathy/datasets2.php National Institute of Oceanography and Applied Geophysics (OGS), Infrastructures Division; Barcelona University (UB), Department of Stratigraphy, Paleontology and Marine Geosciences (now Department of Earth and Ocean Dynamics); University of Bremen, MARUM – Center for Marine Environmental Sciences; University of Tromsø (UiT), The Arctic University of Norway, CAGE, Centre for Arctic Gas Hydrate; Italian Navy, Italian Hydrographic Institute OGS provided a combined grid of the following datasets Multibeam bathymetry from EGLACOM cruise with RV OGS-Explora in 2008 to the western Barents Sea margin 48 Multibeam bathymetry from SVAIS cruise with RV Hesperides 2007 to the western Barents Sea margin 49 Multibeam bathymetry from DEGLABAR cruise with RV OGS-Explora in 2015 to the western Barents Sea margin 50 Multibeam bathymetry from EDIPO cruise with RV OGS-Explora in 2015 to the western Barents Sea margin 51 Multibeam bathymetry by MARUM from MSM30 (CORIBAR) cruise with RV M.S. Merian in 2013 to the western Barents Sea margin 52 Multibeam bathymetry by University of Tromsø from Glacibar cruise with RV Jan Mayen in 2009 to the western Barents Sea margin 53 , 54 Multibeam bathymetry by Italian Hydrographic Institute from High North 17 and 18 cruise with RV Alliance in 2017 and 2018 to the western Barents Sea margin 55 , 56 British Antarctic Survey (BAS), UK NERC Polar Data Centre ...…”

“…Multibeam bathymetry from EDIPO cruise with RV OGS-Explora in 2015 to the western Barents Sea margin 51 …”

Ocean Exchange and Circulation

“…Furthermore, the deep flow variability and the dynamics related to internal waves are analyzed in the paper published by Bensi et al [18], where the authors take into account the bottom current flows and thermohaline variability in the eastern part of the Fram Strait, which is a crossroad of waters between the North Atlantic and the Arctic Ocean. Starting from a detailed analysis of time series data collected through deep-sea oceanographic moorings, the authors discuss the ocean-atmosphere interactions in a region where they are particularly intense, and where they lead to multiple oceanographic processes, like shelf-slope dynamics, deep water variability through the mixing of Polar and Atlantic waters, as well as sea ice and dense water formation.…”

New Approaches for the Observation of Transient Phenomena in Critical Marine Environment

“…The two main water masses originating outside the study areas are the Atlantic water (AW) element of the West Spitsbergen Current (WSC) and Arctic water (ArW) of the coastal current. Both these currents flow northward along the west Spitsbergen margin, steered by the slope edge topography [18,19]. Recent years have been characterised by an increase in the temperature and frequency of warm AW incursions into west Spitsbergen fjords, alongside an increase in the temperature of the WSC [12].…”