Abstract
The Norwegian Sea gyre (NSG) is a large body of Arctic intermediate water and deep dense overflow waters, which circulate counterclockwise within the Norwegian Sea. Argo float trajectories presented in this study suggest that the NSG attains its strongest and most focused flow downstream of a confluence of subarctic waters from the Iceland Sea and the Jan Mayen Ridge at steep bathymetry north of the Faroe slope. Based on hydrographic data from a meridional standard section across this flow (1988 to present), the first baroclinic estimate of the NSG circulation strength is provided. We, furthermore, show that the NSG circulation regulates key aspects of both the poleward Atlantic Water (AW) currents and the equatorward near-bottom and mid-depth flows in the Norwegian Sea – the main arteries of the Meridional Overturning Circulation. More specifically, we demonstrate close links between the NSG circulation and (i) the observed Faroe Bank Channel Overflow (FBCO) transport, (ii) variable depth of the main thermocline separating AW from the underlying colder and denser subarctic water masses, and (iii) satellite-derived sea-surface heights (SSHs) in the southern Nordic Seas. In general, a strong NSG and weak FBCO transport are associated with an uplifted thermocline and depressed SSH. Along a narrow band near the Norwegian and Shetland slopes, a strong NSG – oppositely – links to a depressed interface. Daily records of the FBCO transport, and satellite altimetry in a sensitive region north of the Iceland-Faroe Ridge, complement our hydrographic monitoring of the NSG strength. Together these records constitute valuable indicators for aspects of the Norwegian Sea physical oceanography, which likely have an impact on regional climate, ecology and biological productivity.
Highlights
Total volume and heat transports from the North Atlantic to the Nordic Seas are estimated from observations along monitoring arrays at the Greenland-Scotland Ridge (Hansen and Østerhus, 2000; Hansen et al, 2015)
These results suggest a link between wind forcing, deep flow as well as the main interface between the overlying Atlantic Water (AW) and the underlying denser subarctic waters
While inflowing warm AW into the Nordic Seas toward the Arctic and returning dense overflow water at depth are typically studied separately, we here show that the variability in these key flows is intrinsically coupled
Summary
Total volume and heat transports from the North Atlantic to the Nordic Seas are estimated from observations along monitoring arrays at the Greenland-Scotland Ridge (Hansen and Østerhus, 2000; Hansen et al, 2015). Whether these heat anomalies reach the high Arctic is, strongly determined by the flow dynamics within the Nordic Seas – especially in the eastern part. AW flows cyclonically around the southeastern Norwegian Sea, wedged between the continental slopes [north of the IcelandFaroe Ridge (IFR), Faroe Plateau and west of Norway] and the body of the NSG
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