Abstract
Scattering structures, including deep (>200 m) scattering layers are common in most oceans, but have not previously been properly documented in the Arctic Ocean. In this work, we combine acoustic data for distribution and abundance estimation of zooplankton and fish with biological sampling from the region west and north of Svalbard, to examine high latitude meso- and epipelagic scattering layers and their biological constituents. Our results show that typically, there was strong patchy scattering in the upper part of the epipelagic zone (440 m) in the Arctic habitat north of Svalbard compared to those south in the Fram Strait west of Svalbard (WMD ~400 m). The surface integrated backscatter (Nautical Area-Scattering Coefficient, NASC, sA [m2∙nmi-2]) was considerably lower in the waters around Svalbard compared to the more southern regions (62-69oN). Also, the mesopelagic nautical area scattering coefficient was a factor of approximately 6-10 lower around Svalbard compared to the areas in the south-eastern part of the Norwegian Sea ~62o30’N. The documented patterns and structures, particularly the DSL and its constituents, will be key reference points for understanding and quantifying future changes in the pelagic ecosystem at the entrance to the Arctic Ocean.
Highlights
Deep scattering layers (DSL) are a near universal feature throughout the worlds oceanic regions at depths of about 200–1,000 m (Irigoien et al, 2014)
The objectives of this paper are to (1) describe the bioacoustic patterns and relate them to the distribution and abundance of plankton and fish caught by various types of gear throughout the water column, (2) to relate these findings to the processes that might contribute to the creation and maintenance of the observed patterns, (3) to compare the DSL found around Svalbard, with the DSL’s observed in other regions of the Northern Atlantic, along the Norwegian coast and to some observations from the western Atlantic Ocean, and (4) to propose techniques for monitoring further changes in the Arctic deep-water pelagic community
In the current work we present the environmental situation from one transect on the west side of Spitsbergen (Transect 2— Fram Strait North), quite similar to the transect further south (Transect 6—Fram Strait South), and one transect north of Svalbard (Transect 4—Hinlopen)
Summary
Deep scattering layers (DSL) are a near universal feature throughout the worlds oceanic regions at depths of about 200–1,000 m (Irigoien et al, 2014). The focus of this study is on large-scale epipelagic and mesopelagic scattering structures in the Fram strait and north of Svalbard archipelago from the shelf waters into the deep adjacent basins and their relation to the distribution and abundance of plankton and fish caught by various types of gear throughout the water column. The eastern Fram Strait is characterized by the West Spitsbergen Current carrying warm Atlantic Water northwards along the shelf-break (Fahrbach et al, 2001; Schauer and BeszczynskaMöller, 2009; Beszczynska-Möller et al, 2012), continuing eastwards on the northern side of Svalbard (Figure 1). Warm Atlantic Water fills most of the upper water column in eastern Fram Strait Reaching these high latitudes, the Atlantic flow meets the sea ice and waters of polar origin making the region a transition zone between Atlantic and Arctic conditions (Rudels et al, 2000; Rudels, 2009). In addition to bringing heat, the Atlantic flow supplies the region with nutrients and drifting organisms like zooplankton (Kosobokova and Hirche, 2009) and most certainly fish larvae
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