Abstract
AbstractThe Lofoten Basin in the eastern Nordic Seas plays a central role in modifying the warm Atlantic Water inflow toward the Arctic Ocean. Here, the Atlantic Water experiences increased residence times, cooling, and substantial transformation. In this study, we investigate the Atlantic Water inflow pathways to the Lofoten Basin and their vertical and seasonal variations using 2‐D and 3‐D Lagrangian simulations forced by a high‐resolution ocean model. Atlantic Water enters the basin from all directions, but we find two main inflow pathways at all vertical levels, one close to the Lofoten Escarpment in the southeast, associated with the Slope Current, and another close to the Helgeland Ridge in the southwest, associated with the Front Current. The surface inflow exhibits a stronger seasonal forcing than the inflow at depth as well as a stronger heat loss that is dominated by water masses entering the basin from the south. At deeper levels, the warm inflow from the east cools, while the relatively colder inflow from the west warms. The 2‐D and 3‐D synthetic trajectories show similar pathways. However, they are affected differently by the seasonal signal, giving different heat exchange patterns. Our results have implications for how results from Lagrangian observations in the region should be interpreted.
Highlights
The Lofoten Basin (LB) in the Norwegian Sea is recognized as a region for the retention and modification of the warm and saline Atlantic Water (AW) carried by the Norwegian Atlantic Current (NwAC) northward toward the Arctic Ocean (Koszalka et al, 2011; Mauritzen, 1996; Rossby et al, 2009)
We first focus on the general circulation at 200 m, which is representative for the AW inflow in the eastern Nordic Seas, as the flows in this region are relatively weakly stratified and to a large extent steered by topography
There are drifters entering the LB from all sides, but two major inflow regions stand out: the “Lofoten Slope Inflow” (LSI) to the southeast, close to the continental slope, and the “Helgeland Inflow” (HI) to the southwest, approximately where the 3,000-m contour does not close
Summary
The Lofoten Basin (LB) in the Norwegian Sea is recognized as a region for the retention and modification of the warm and saline Atlantic Water (AW) carried by the Norwegian Atlantic Current (NwAC) northward toward the Arctic Ocean (Koszalka et al, 2011; Mauritzen, 1996; Rossby et al, 2009). Large surface heat and buoyancy loss in winter result in cooling (Isachsen, 2015; Rossby et al, 2009; Richards & Straneo, 2015), and the modified water masses sink and form a warm anomaly at depth, compensated by their high salinity (Bosse et al, 2018; Segtnan et al, 2011). Quantifying and understanding processes that modify the AW en route to the Arctic are important with implications for the regional climate and marine ecosystems (Årthun et al, 2018; Kovacs et al, 2011; Ogawa et al, 2018), as well as impacts on the Arctic sea ice cover (Årthun et al, 2019)
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