Productive detours – Atlantic water inflow and acoustic backscatter in the major troughs along the Svalbard shelf

Harald Gjøsæter,Randi B. Ingvaldsen,Anna Nikolopoulos,Jon Albretsen,Tore Hattermann,Sebastian Menze

doi:10.1016/j.pocean.2020.102447

Abstract

Atlantic Water (AW) flowing along the western and northern Svalbard shelf-break extends the Atlantic domain into the Arctic and is the region’s major source of heat, nutrients and advected plankton. We investigated the inflow and recirculation of AW into four major troughs that cut into the Svalbard shelf, the Isfjorden, Kongsfjorden, Hinlopen and Kvitøya Troughs, and related the circulation patterns to acoustic backscatter observed with echosounders and Acoustic Doppler Current Profilers. The acoustic observations showed higher levels of backscatter from fish in the Hinlopen Trough compared to the shelf and shelf-break north of Svalbard. This coincides with a steady inflow of nutrients, biomass and heat into the trough with the AW. Trough circulation was characterized using output from a high-resolution regional ocean model and particle tracking simulations. All four troughs experience topographically steered recirculation (in-and-outflow) of AW, but the troughs on the western Svalbard shelf showed a stronger seasonality than the troughs on the northern shelf. The Hinlopen Trough receives the strongest AW inflow and the most direct inflow from the shelf-break boundary current. The troughs form hybrid habitats between the shelf and shelf-break that extend the Atlantic advective domain closer to the Svalbard coastline.

Highlights

The Svalbard shelf forms a transition zone between boreal, arctic and coastal ecosystems, whose boundaries are changing with global warm ing (Fossheim et al, 2015; Haug et al, 2017)
Outside Isfjorden Trough (IT), Atlantic Water (AW) is centered at the shelf-break and stretches into the trough and fjord
Previous modeling studies (Hattermann et al, 2016; Wekerle et al, 2017), Acoustic Doppler Current Profilers (ADCPs) observations (Menze et al, 2019) and the Conductivity-Temperature-Depth pro filer (CTD) sections from this study indicate that AW frequently recirculates within Hinlopen trough and strait

Summary

Introduction

The Svalbard shelf forms a transition zone between boreal, arctic and coastal ecosystems, whose boundaries are changing with global warm ing (Fossheim et al, 2015; Haug et al, 2017). The warm and saline AW flows along the Svalbard shelf as a boundary current, termed the West Spitsbergen Current (WSC) and Arctic Circumpolar Boundary Current north-east of Svalbard. This current is the major heat, carbon and plankton supply to the Arctic Ocean and is an important feature of the earth’s climate system (Wassmann et al, 2015; Bluhm et al, 2015). AW is known to spread onto the Svalbard shelf and into the troughs This has been best studied in Isfjorden and Kongsfjorden (Nilsen et al, 2016). In this paper we investigate how topographically steered currents transport AW into the four major troughs and discuss how this renders the troughs special habitats along the shelf

Methods

Results

Discussion

Conclusion