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This is chapter 11 of the State of Environmental Science in Svalbard (SESS) report 2019 (https://sios-svalbard.org/SESS_Issue2). Off the Svalbard archipelago, in the eastern Fram Strait, at 1000 m depth along the continental slope, we observed temperature and salinity fluctuations that were more prominent between October and April. Data were acquired employing an oceanographic mooring deployed at 76°N 013°E from June 2014. Since then, the most noteworthy episode lasted more than 15 days in December 2016/January 2017 when the temperature rose from the typical value of -0.9°C to over 2°C. At the same time, bottom currents increased significantly, to 85 cm/s. Normally, these bottom currents flow around 10-15 cm/s. This region is characterized by the passage of Atlantic Water flowing northward in the upper layer, bringing relatively warm water to the Arctic Ocean. Below 800 m depth, the Norwegian Deep Sea Water, colder and less salty, also flows northward. Thanks to the scientific community that carries out measurements both in the ocean and in the atmosphere, we know that the Arctic is progressively warming up; we see this in the gradual melting of sea ice and ice on land. However, it is not clear how much of this warming is caused by human activities and what consequence it will have. In order to record and to study environmental changes and anomalies, we need time series. To provide robust climate data, such series must span decades. Achieving this goal requires great effort in terms of international collaborations, both economic and scientific.

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&ndash, 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.

This is chapter 6 of the State of Environmental Science in Svalbard (SESS) report 2018 (https://sios-svalbard.org/SESS_Issue1). In the Fram Strait, a remarkable increase in the temperature and salinity of inflowing Atlantic Water has been observed since the 1990s. This is in part a natural trend, but recent temperature anomalies, ~1°C relative to the 1970s are related to anthropogenic causes. Air temperature increased by about 3°C in the 20th century and meteorological stations at Svalbard confirm this positive trend. At the West Spitsbergen margin, Atlantic and Arctic waters converge, mix and exchange, while air–sea interactions and shelf–slope dynamics trigger vertical mixing and formation of cold and salty water. This water is sufficiently dense to sink to greater depths and contribute to the global thermohaline circulation. The circulation process permits exchange of heat (i.e., energy) between low and high latitudes. Since the formation of dense water and its spreading at greater depths are strongly influenced by the properties of Atlantic Water, which have been changing in the last decades, we cannot exclude the possibility that the global thermohaline circulation may change in the near future. We analysed oceanographic data (obtained from shelf and deep-sea oceanographic moorings and hydrographic cruises) and meteorological data from the west Svalbard margin, comparing temperature and salinity variability in the deep ocean flow and the wind regime. Time-series revealed occasional intrusions of warm and salty waters at 1000 m depth, mainly during the period October – April, quasi-simultaneously at several locations more than 150 apart, along the continental slope west of Svalbard. The fact that the most energetic events, both in the deep flow and in the wind speed, occurred with similar periodicities (10-20 days) suggests atmospheric storms as the likely forcing mechanism underlying the observed deep sea variability. Others energetic events with periodicity of 12 and 24 hours, instead, could be related to internal tidal oscillations. The fact that the most energetic events, both in the deep flow and in the wind speed, had similar periodicities (10-20 days) suggests atmospheric storms as the likely forcing mechanism underlying the observed deep-sea variability. Other energetic events with periodicity of 12 and 24 hours could instead be related to tidal oscillations.