The North Icelandic Jet is fed by transformation of Atlantic Waters on the Icelandic shelf

Yarisbel Garcia Quintana1, Nathan Grivault2, Xianmin Hu3 and Paul G. Myers1,4, (1)University of Alberta, Earth and Atmospheric Sciences, Edmonton, AB, Canada, (2)University of Alberta, Edmonton, AB, Canada, (3)Bedford Institute of Oceanography, Dartmouth, NS, Canada, (4)University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada
Abstract:
Exchange flows between the sub-polar North Atlantic and the Arctic Ocean via the Nordic Seas are key

components of the global climate system. The northward heat transport by the Atlantic Water affects Arctic sea
ice and land ice cover, ecosystems, European weather and global climate, while the southward deep overflows
feed the abyssal limb of the Atlantic Meridional Overturning Circulation (AMOC), affecting global climate. 
Here we explore a potential source for the North Icelandic Jet, which feeds the Denmark Strait Overflow,
the densest component of the
AMOC. To do so, we use an eddy-permitting, 1/12 regional configuration
of the Nucleus for European Modelling of the Ocean
. We examine the transformation of the North Icelandic
Irminger Current (NIIC) in a region of the northwest Icelandic shelf and the large-scale circulation response,
over the period 2002 to 2018. We propose an overturning loop where the upper limb is the transformation of the
NIIC on the Icelandic shelf, and the NIJ being the lower limb. Strong winter heat lost on the northwest Icelandic
shelf increases the density of the
NIIC waters, allowing them to sink to the shelf bottom. A dense
(denser than 27.8
kg/m3) plume is generated as a result and travels anticyclonically on the Icelandic
shelf from the formation region, cascading down slope north of Iceland forced by
bathymetric irregularities.
As a response to the dense plume a depression in the sea surface height propagates also
anticyclonically from
the formation region which in turns generates an offshore cyclonic flow that carries the dense waters back
towards Denmark Strait, as they cascade. The transport of dense waters (denser than 27.8
kg/m3) crossing
the 500 m
isobath towards deeper layers, north of Iceland, was found to be in the range 0.25 - 1.25 Sv
(seasonally changing), which is sufficient to feed the observed transport of the
NIJ. The dense water
formation process has its maximum generally from December to March. The dense water formation timing
points out for it to be the source of the strong regime of the
NIJ. The identified loop can be dynamically
explained by previous modelling work exploring the large-scale circulation response to dense water formation
near an island. Observational data from 1929 to present confirms the presence of waters denser than
28
kg/m3 in the study region on the Iceland Shelf.