Abstract
AbstractThe North Icelandic Jet (NIJ) is an important source of dense water to the overflow plume passing through Denmark Strait. The properties, structure, and transport of the NIJ are investigated for the first time along its entire pathway following the continental slope north of Iceland, using 13 hydrographic/velocity surveys of high spatial resolution conducted between 2004 and 2018. The comprehensive dataset reveals that the current originates northeast of Iceland and increases in volume transport by roughly 0.4 Sv (1 Sv ≡ 106 m3 s−1) per 100 km until 300 km upstream of Denmark Strait, at which point the highest transport is reached. The bulk of the NIJ transport is confined to a small area in Θ–S space centered near −0.29° ± 0.16°C in Conservative Temperature and 35.075 ± 0.006 g kg−1 in Absolute Salinity. While the hydrographic properties of this transport mode are not significantly modified along the NIJ’s pathway, the transport estimates vary considerably between and within the surveys. Neither a clear seasonal signal nor a consistent link to atmospheric forcing was found, but barotropic and/or baroclinic instability is likely active in the current. The NIJ displays a double-core structure in roughly 50% of the occupations, with the two cores centered at the 600- and 800-m isobaths, respectively. The transport of overflow water 300 km upstream of Denmark Strait exceeds 1.8 ± 0.3 Sv, which is substantially larger than estimates from a year-long mooring array and hydrographic/velocity surveys closer to the strait, where the NIJ merges with the separated East Greenland Current. This implies a more substantial contribution of the NIJ to the Denmark Strait overflow plume than previously envisaged.
Highlights
Plumes of cold, dense overflow water spill across gaps in the Greenland–Scotland Ridge from the Nordic Seas to the North Atlantic
As such, determining the formation processes and pathways of the Denmark Strait Overflow Water (DSOW) is necessary to further our understanding of the overturning in the Nordic Seas, and the Atlantic Meridional Overturning Circulation (AMOC)
Studies based on quasi-synoptic measurements (Rudels et al 2002), historical data (Eldevik et al 2009), chemical tracers (Tanhua et al 2005), and high-resolution numerical simulations (Köhl et al 2007) corroborated the notion that the East Greenland Current (EGC) is the main source of overflow water to Denmark Strait
Summary
Dense overflow water spill across gaps in the Greenland–Scotland Ridge from the Nordic Seas to the North Atlantic. Using data from multiple shipboard surveys, Våge et al (2011, 2013) demonstrated that the current is a distinct source of dense water to the Denmark Strait overflow plume This was further verified by Harden et al (2016) using measurements from a year-long mooring array approximately 200 km north of the sill. Behrens et al (2017) found little variability in the volume transport of the current on seasonal to interannual time scales in their model study, while Huang et al (2019) determined that month-to-month variation of the NIJ strength is significantly correlated with air–sea buoyancy forcing north of Iceland They explained this connection via the mechanism presented by Spall et al (2017), in which convection on the continental slope of an island leads to cyclonic flow around the island. We consider the data from the grid point closest to the mooring as well as one grid point directly north of Denmark Strait (at the same latitude farther west)
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