In the last decades, the Arctic region has gained a large interest because of climate changes and relevant effects on ice melting and global warming. Abrupt changes in the atmosphere are responsible for significant changes in ocean water masses and large-scale circulation patterns, which in turn affect the global climate. Studying ocean circulation and related processes along the west Svalbard slope and within the Storfjorden (south Svalbard Archipelago) is essential to describe the thermohaline circulation and the dense water formation (DWF) in the Arctic, and the way they contribute to the global thermohaline circulation.
DWF processes in this region depend on the rate of cooling and homogenisation of the Atlantic water along its northwards pathway, brine rejection phenomena, boundary convection on the Arctic Ocean shelves and slopes, and deep open-ocean convection in the central gyres of the Greenland and Iceland Seas. This study focuses on brine rejection, shelf convection and entrainment processes, which occur on the west Svalbard margin and in the Storfjorden during the winter season.
Two short (~140m) moorings (named S1 and ID2, figure 1) were deployed ~1000m deep along the slope in 2014, to collect multiannual time-series in an area of potential interaction between the West Spitsbergen Current and the descending dense shelf plumes. Four oceanographic cruises were carried out between 2014 and 2017 to integrate time-series with CTD (conductivity-temperature-depth) casts in the area.
One purpose of this research activity was to study the role played by bottom currents in the formation of two sediment drifts (Isfjorden and Bellsund). At S1 and ID2, time-series revealed a large thermohaline and current variability during the winter period, from October to April. Our data highlight the presence of a stable signal of Norwegian Sea Deep Water (θ = -0.90°C, S = 34.90, σθ = 28.07 kg m-3) at 1000m depth, influenced by occasional intrusions of warmer (up to +2°C), saltier (up to ~35), and less dense (down to 27.98 kg m-3) water during fall-winter periods. Interestingly, such intrusions occur simultaneously at both sites, despite their distance (~170km), suggesting also that winter meteorological perturbations play an important role in triggering dense shelf plumes. In this paper, the origin, timing, and role of shelf turbidity plumes (denser than TS plumes), which descend along the slope and undergo a strong entrainment process that modify their properties will be discussed. The role of possible mesoscale processes and land-sea atmosphere interactions will also be investigated.
EPIC Alfred Wegener Institut