ALBERT

Description: We present two time series of bottom current and temperature collected 8 m above the seabed on either side of a large sediment drift located on the continental rise of the Pacific margin of the Antarctic Peninsula. The mean current speed is comparable (6.2 cm s−1 and 6.1 cm s−1 respectively), but the mean direction differs by about 121°. The direction of mean flow follows the bathymetric contour, and the maximum speed never exceeds 20 cm s−1 (below the typical benthic storm threshold). The potential temperature is remarkably stable (0.11 ± 0.01°C and 0.13 ± 0.02°C at the two sites). The cross-covariance indicates a significant peak at 20.2 days lag, slightly longer than the travel time of 18.7 days calculated between the two stations following the isobaths (98.4 km) and thus providing evidence for the topographic control on bottom water flow. The observed bottom water flow is consistent with deposition of Holocene hemipelagic sediments of the ‘drift maintenance’ stage. Indicators for palaeoceanographic conditions during glacial periods of the ‘drift maintenance’ stage and the older ‘drift growth’ stage are at present too scarce to understand fully how the past oceanographic conditions influenced the evolution of the drifts.

Description: 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.

Description: The large-scale circulation and dense water formation (DWF) in the Svalbard archipelago influence the thermohaline circulation in the whole Arctic. In particular, DWF depends on the rate of cooling and homogenisation of the Atlantic water along its northward pathway, brine rejection, boundary convection on shelves and slopes, and open-ocean convection. This study focuses on brine rejection, shelf convection and entrainment processes, which occur in the SW Spitsbergen area. Two short (~140m) moorings (named S1 and ID2), deployed at a depth of ~1040 m over the slope, collected multiannual (2014-2017) time-series in an area of interaction between the West Spitsbergen Current and the descending dense shelf plumes. Time-series revealed a large thermohaline and current variability between October and April. Data highlight the presence of Norwegian Sea Deep Water (θ = -0.90°C, S = 34.90, σθ = 28.07 kg m-3) 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 (~170 km), suggesting that winter meteorological perturbations play an important role in triggering dense shelf plumes, which collect particulate matter during their descent. Here we discuss the origin, timing, and role of such turbidity plumes in a period characterized by a general warming and ice reduction of the Arctic.

Description: The Arctic region has gained a large interest because of climate changes and its effects on ice melting and global warming. Abrupt changes in the atmosphere are responsible for significant changes in the ocean water masses and large-scale circulation, which in turn affect again the global climate. The knowledge of the circulation and related processes along the southwest (SW) offshore Svalbard area and within Storfjorden (southern Svalbard Archipelago) is essential to describe the thermohaline circulation and the dense water formation (DWF) in the Arctic, and how 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, the brine rejection, boundary convection on the Arctic Ocean shelves and slopes, and the deep open-ocean convection in the central gyres of the Greenland and Iceland Seas. Here, we focus on the brine rejection, shelf convection and entrainment processes, which happen on the west shelf/slope of Svalbard and in the Storfjorden during the winter season. Two short (130m) moorings (S1 and I2) were deployed in 2014 in the SW offshore Svalbard at ~1000m depth, with the purpose of collecting multiannual time-series in an area of potential interaction between the Western Spitsbergen Current and the dense shelf plumes. Three oceanographic cruises were carried out to integrate time-series with CTD casts in the area. One purpose of this research activity was to combine geophysical and oceanographic data to study the interaction of bottom currents and sediment drifts (contourites) formations. At S1 and I2, 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 influenced by occasional intrusions of warmer, saltier, and less dense water during fall-winter periods. Interestingly, such intrusions occur simultaneously at both sites, despite their distance (~170km). We discuss the origin, timing, and role of shelf turbidity plumes (denser than TS plumes), which descend along slope and undergo a strong entrainment process that modify their properties. The role of possible mesoscale processes is also investigated.

Description: 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.