Dense Water Formation on the Icelandic Shelf and Its Contribution to the North Icelandic Jet. Issue 8 (16th August 2021)

• Record Type: Journal Article
• Authors: Garcia‐Quintana, Yarisbel; Grivault, Nathan; Hu, Xianmin; Myers, Paul G.
• Is Part Of: Journal of geophysical research. Volume 126:Issue 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-08-16
• Subjects: North Icelandic Jet -- shelf convection -- DSOW -- numerical modeling; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2020JC016951
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: The North Icelandic Jet (NIJ) is the densest component of the Denmark Strait Overflow Water, feeding the abyssal limb of the Atlantic Meridional Overturning Circulation. Here, by using observational and numerical model data, we explore the formation of overflow water on the Icelandic shelf, the mechanisms involved, and its potential contribution to the NIJ. The sparse observational data on the western Icelandic shelf for the month of February shows top‐to‐bottom mixing on the shelf, distinct and well separated from the dense water offshore, with densities larger than 27.8 kg/m 3 in some years. Using a 1‐D mixing model and winter heat flux reanalysis, we suggest that waters with densities exceeding 27.8 kg/m 3 are likely to be formed on the shelf in most years by the end of winter. High‐resolution numerical model data shows that the transformation of the Atlantic inflow along the northwest Icelandic shelf generates a dense plume whose waters feed into the NIJ. The bulk of the plume cascades down‐slope north of Iceland, funneled through deep cross‐shelf troughs, with some cascading occurring west of Iceland as well. During years of strong cascading events (2008, 2013, and 2016), the modeled dense plume potentially feeds up to 21% of the NIJ transport at the Siglunes and Kögur sections. Back‐tracked Lagrangian particle trajectories confirm that the western Icelandic shelf is a source of the NIJ. The dense plume transport and variability are found to be dependent on the total oceanic heat loss west of Iceland and along Denmark Strait. Plain Language Summary: Ocean currents distribute heat, nutrients, and gases. In the North Atlantic Ocean, through atmosphere‐ocean interaction, northward‐flowing surface warm waters lose heat as they approach sub‐polar latitudes. Consequently, they get heavier and sink to greater depths. During this sinking process, known as deep convection, the ocean's intermediate and deep waters are ventilated, providing them with nutrients and gases. Simultaneously, the heat released into the atmosphere directly moderates the local climate. Deep convection, which plays a crucial role in the Earth's climate, is known to occur in the Nordic Seas, where southward‐flowing currents carrying dense bottom waters are formed. The North Icelandic Jet (NIJ), suggested to be formed through deep convection, carries the heaviest waters formed in the Nordic Seas. In our study, by using model and observational data, we found that during the winters of 2008, 2013, and 2016 up to 21% of the lightest component of the NIJ comes from shelf convection occurring northwest of Iceland, where the continental shelf is not deeper than 250 m. These findings contribute to improving our understanding of the source waters of the NIJ. Key Points: Observations and model data show that overflow waters are formed on the northwest Icelandic shelf from the transformation of Atlantic inflow A dense plume is generated from this transformation through shelf convection linked to winter heat loss northwest of Iceland Waters from the modeled plume cascade north of Iceland feeding into the North Icelandic Jet contributing up to 21% of its lightest component