Downward particle fluxes at south-eastern Fram Strait (Svalbard)

Water masses in the eastern Fram Strait are strongly influenced by the interaction between Atlantic and Arctic waters, and by atmospheric forcing, thus contributing to drive the global thermohaline circulation. There is considerable variability in the system due to different forcing (e.g., atmospheric, internal, tidal, shelf dynamics) that play an important role especially in the uppermost layer of the ocean. On the contrary, it is not entirely clear which processes are responsible for the inter-annual and seasonal variability of the deep flow in the western Spitsbergen region.

The oceanographic deep-sea mooring S1 has been deployed since 2014 on the continental slope offshore Storfjorden at a water depth of approx. 1000 m. In 2014-2016 and 2017-2018, a twin mooring (ID2) was also placed 140 km north of S1 at approximately the same depth in order to monitor spatial differences of the properties and dynamics of the water along continental slope.

Short-term fluctuations of thermohaline properties and currents at 1000 m depth were repeatedly measured both at S1 and ID2 in different years. Such oscillations were related to the passage of internal waves and/or eddies by the passage of intense atmospheric storms, which in turn trigger intrusions of AW into the deep layer, with tricky effects on ecosystem functioning.

Similarly to thermohaline properties, spatial and temporal fluctuations in total mass fluxes were also recorded. Annual particle fluxes ranged between 67 and 198 g m^-2 y^-1 at site S1, while  ID2 had approximatively twice the values of S1. Here, we discuss the drivers influencing the particle sources and the downward fluxes in the eastern Fram strait.

Peak values of particle fluxes occurred in late winter-early summer, in the same season of maximum variability of thermohaline properties. But, they were not perfectly synchronous with turbidity peaks. A time lag of a couple of months was detected between max turbidity and particle deposition in the sediment trap, when the currents slowdown. Actually, turbidity does not appear to be related to current speed, but to current direction (SE-NW). We suggest that upslope currents (E-ward), which occur during warm water intrusions, are able to resuspend bottom sediment at the shelf edge. From our dataset it is apparent that often (but not always) the water turbidity increases during the current rotation from eastward to the following NW direction.