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1. Mechanisms of Offshore Solid and Liquid Freshwater Flux from the East Greenland Current

   https://doi.org/10.1175/JPO-D-23-0120.1  

   Spall, Michael A. ; Semper, Stefanie ; Våge, Kjetil ( February 2024 , Journal of Physical Oceanography)

   The mechanisms that control the export of freshwater from the East Greenland Current, in both liquid and solid form, are explored using an idealized numerical model and scaling theory. A regional, coupled ocean–sea ice model is applied to a series of calculations in which key parameters are varied and the scaling theory is used to interpret the model results. The offshore ice flux, occurring in late winter, is driven primarily by internal stresses and is most sensitive to the thickness of sea ice on the shelf coming out of Fram Strait and the strength of alongshore winds over the shelf. The offshore liquid freshwater flux is achieved by eddy fluxes in late summer while there is an onshore liquid freshwater flux in winter due to the ice–ocean stress, resulting in only weak annual mean flux. The scaling theory identifies the key nondimensional parameters that control the behavior and reproduces the general parameter dependence found in the numerical model. Climate models predict that winds will increase and ice export from the Arctic will decrease in the future, both of which will lead to a decrease in the offshore flux of sea ice, while the influence on liquid freshwater may increase or decrease, depending on the relative changes in the onshore Ekman transport and offshore eddy fluxes. Additional processes that have not been considered here, such as more complex topography and synoptic wind events, may also contribute to cross-shelf exchange.

   The purpose of this study is to provide a basic understanding of what controls the flux of sea ice and low-salinity water from the East Greenland shelf into the interior of the Greenland and Iceland Seas. This is a potentially important process since it has been shown that sufficient freshening of the surface waters in the interior of the Nordic seas can inhibit deep convection and the associated air–sea heat flux and water mass transformation. A combination of idealized computer models and basic theory indicates that the fluxes of liquid and solid freshwater are controlled by different mechanisms and occur at different times of the year. Accurate representation in climate models will require representation of small-scale processes such as mesoscale eddies and gradients of ice thickness across the shelf.

    

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2. Evolution and Transformation of the North Icelandic Irminger Current Along the North Iceland Shelf

   https://doi.org/10.1029/2021JC017700  

   Semper, Stefanie ; Våge, Kjetil ; Pickart, Robert S. ; Jónsson, Steingrímur ; Valdimarsson, Héðinn ( March 2022 , Journal of Geophysical Research: Oceans)

   The North Icelandic Irminger Current (NIIC) flowing northward through Denmark Strait is the main source of salt and heat to the north Iceland shelf. We quantify its along‐stream evolution using the first high‐resolution hydrographic/velocity survey north of Iceland that spans the entire shelf along with historical hydrographic measurements as well as data from satellites and surface drifters. The NIIC generally follows the shelf break. Portions of the flow recirculate near Denmark Strait and the Kolbeinsey Ridge. The current's volume transport diminishes northeast of Iceland before it merges with the Atlantic Water inflow east of Iceland. The hydrographic properties of the current are modified along its entire pathway, predominantly because of lateral mixing with cold, fresh offshore waters rather than air‐sea interaction. Progressing eastward, the NIIC cools and freshens by approximately 0.3°C and 0.02–0.03 g kg⁻¹per 100 km, respectively, in both summer and winter. Dense‐water formation on the shelf is limited, occurring only sporadically in the historical record. The hydrographic properties of this locally formed water match the lighter portion of the North Icelandic Jet (NIJ), which emerges northeast of Iceland and transports dense water toward Denmark Strait. In the region northeast of Iceland, the NIIC is prone to baroclinic instability. Enhanced eddy kinetic energy over the steep slope there suggests a dynamical link between eddies shed by the NIIC and the formation of the NIJ as previously hypothesized. Thus, while the NIIC rarely supplies the NIJ directly, it may be dynamically important for the overturning circulation in the Nordic Seas.

    

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3. The Iceland Greenland Seas Project

   https://doi.org/10.1175/BAMS-D-18-0217.1  

   Renfrew, I. A. ; Pickart, R. S. ; Våge, K. ; Moore, G. W. ; Bracegirdle, T. J. ; Elvidge, A. D. ; Jeansson, E. ; Lachlan-Cope, T. ; McRaven, L. T. ; Papritz, L. ; et al ( September 2019 , Bulletin of the American Meteorological Society)

   null (Ed.)

   Abstract The Iceland Greenland Seas Project (IGP) is a coordinated atmosphere–ocean research program investigating climate processes in the source region of the densest waters of the Atlantic meridional overturning circulation. During February and March 2018, a field campaign was executed over the Iceland and southern Greenland Seas that utilized a range of observing platforms to investigate critical processes in the region, including a research vessel, a research aircraft, moorings, sea gliders, floats, and a meteorological buoy. A remarkable feature of the field campaign was the highly coordinated deployment of the observing platforms, whereby the research vessel and aircraft tracks were planned in concert to allow simultaneous sampling of the atmosphere, the ocean, and their interactions. This joint planning was supported by tailor-made convection-permitting weather forecasts and novel diagnostics from an ensemble prediction system. The scientific aims of the IGP are to characterize the atmospheric forcing and the ocean response of coupled processes; in particular, cold-air outbreaks in the vicinity of the marginal ice zone and their triggering of oceanic heat loss, and the role of freshwater in the generation of dense water masses. The campaign observed the life cycle of a long-lasting cold-air outbreak over the Iceland Sea and the development of a cold-air outbreak over the Greenland Sea. Repeated profiling revealed the immediate impact on the ocean, while a comprehensive hydrographic survey provided a rare picture of these subpolar seas in winter. A joint atmosphere–ocean approach is also being used in the analysis phase, with coupled observational analysis and coordinated numerical modeling activities underway. 

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4. Lagrangian Perspective on the Origins of Denmark Strait Overflow

   https://doi.org/10.1175/JPO-D-19-0210.1  

   Saberi, Atousa ; Haine, Thomas W. ; Gelderloos, Renske ; Femke de Jong, M. ; Furey, Heather ; Bower, Amy ( August 2020 , Journal of Physical Oceanography)

   null (Ed.)

   Abstract The Denmark Strait Overflow (DSO) is an important contributor to the lower limb of the Atlantic meridional overturning circulation (AMOC). Determining DSO formation and its pathways is not only important for local oceanography but also critical to estimating the state and variability of the AMOC. Despite prior attempts to understand the DSO sources, its upstream pathways and circulation remain uncertain due to short-term (3–5 days) variability. This makes it challenging to study the DSO from observations. Given this complexity, this study maps the upstream pathways and along-pathway changes in its water properties, using Lagrangian backtracking of the DSO sources in a realistic numerical ocean simulation. The Lagrangian pathways confirm that several branches contribute to the DSO from the north such as the East Greenland Current (EGC), the separated EGC (sEGC), and the North Icelandic Jet (NIJ). Moreover, the model results reveal additional pathways from south of Iceland, which supplied over 16% of the DSO annually and over 25% of the DSO during winter of 2008, when the NAO index was positive. The southern contribution is about 34% by the end of March. The southern pathways mark a more direct route from the near-surface subpolar North Atlantic to the North Atlantic Deep Water (NADW), and needs to be explored further, with in situ observations. 

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5. Mean Conditions and Seasonality of the West Greenland Boundary Current System near Cape Farewell

   https://doi.org/10.1175/JPO-D-20-0086.1  

   Pacini, Astrid ; Pickart, Robert S. ; Bahr, Frank ; Torres, Daniel J. ; Ramsey, Andrée L. ; Holte, James ; Karstensen, Johannes ; Oltmanns, Marilena ; Straneo, Fiammetta ; Le Bras, Isabela Astiz ; et al ( October 2020 , Journal of Physical Oceanography)

   null (Ed.)

   Abstract The structure, transport, and seasonal variability of the West Greenland boundary current system near Cape Farewell are investigated using a high-resolution mooring array deployed from 2014 to 2018. The boundary current system is comprised of three components: the West Greenland Coastal Current, which advects cold and fresh Upper Polar Water (UPW); the West Greenland Current, which transports warm and salty Irminger Water (IW) along the upper slope and UPW at the surface; and the Deep Western Boundary Current, which advects dense overflow waters. Labrador Sea Water (LSW) is prevalent at the seaward side of the array within an offshore recirculation gyre and at the base of the West Greenland Current. The 4-yr mean transport of the full boundary current system is 31.1 ± 7.4 Sv (1 Sv ≡ 10 6 m 3 s −1 ), with no clear seasonal signal. However, the individual water mass components exhibit seasonal cycles in hydrographic properties and transport. LSW penetrates the boundary current locally, through entrainment/mixing from the adjacent recirculation gyre, and also enters the current upstream in the Irminger Sea. IW is modified through air–sea interaction during winter along the length of its trajectory around the Irminger Sea, which converts some of the water to LSW. This, together with the seasonal increase in LSW entering the current, results in an anticorrelation in transport between these two water masses. The seasonality in UPW transport can be explained by remote wind forcing and subsequent adjustment via coastal trapped waves. Our results provide the first quantitatively robust observational description of the boundary current in the eastern Labrador Sea. 

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