Monitoring the flow of Atlantic water through the Faroe-Shetland Channel

This report presents results from an experiment, carried out in 2011-2012 within the EU-THOR project to investigate whether future monitoring of the Atlantic water transport through the Faroe-Shetland Channel might be more efficiently achieved on another section than the traditional Munken-Fair Isle section. The new section is less affected by meso-scale activity and narrower, allowing better horizontal resolution of the mooring array, but the experiment revealed that moving to the new section involved other drawbacks. The experiment also confirmed an earlier conjecture that data from satellite altimetry might provide better estimates of transport variations than estimates based on in situ measurements, solely. Previous efforts to determine the average volume transport of Atlantic water through the channel and its variations have been hampered by lack of information on the thickness variations of the Atlantic layer. Re-evaluating the historical data set, we find that the transport estimates are not significantly affected by assuming that the lower boundary of the Atlantic layer is fixed, equal to the average 5°C-isotherm. Based on the conclusions of this report, we recommend that future in situ monitoring in the channel is re-focused

The Iceland-Faroe slope jet: a conduit for dense water toward the Faroe Bank Channel overflow

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Semper, S., Pickart, R. S., Vage, K., Larsen, K. M. H., Hatun, H., & Hansen, B. The Iceland-Faroe slope jet: a conduit for dense water toward the Faroe Bank Channel overflow. Nature Communications, 11(1), (2020): 5390, doi:10.1038/s41467-020-19049-5.Dense water from the Nordic Seas passes through the Faroe Bank Channel and supplies the lower limb of the Atlantic Meridional Overturning Circulation, a critical component of the climate system. Yet, the upstream pathways of this water are not fully known. Here we present evidence of a previously unrecognised deep current following the slope from Iceland toward the Faroe Bank Channel using high-resolution, synoptic shipboard observations and long-term measurements north of the Faroe Islands. The bulk of the volume transport of the current, named the Iceland-Faroe Slope Jet (IFSJ), is relatively uniform in hydrographic properties, very similar to the North Icelandic Jet flowing westward along the slope north of Iceland toward Denmark Strait. This suggests a common source for the two major overflows across the Greenland-Scotland Ridge. The IFSJ can account for approximately half of the total overflow transport through the Faroe Bank Channel, thus constituting a significant component of the overturning circulation in the Nordic Seas.Support for this work was provided by the Bergen Research Foundation Grant BFS2016REK01 (S.S. and K.V.), the U.S. National Science Foundation Grants OCE-1558742 and OCE-1259618 (R.S.P.), the Danish Ministry of Climate, Energy and Utilities (K.M.H.L., H.H., and B.H.) and the European Union’s Horizon 2020 research and innovation programme under grant agreement 727852 (Blue-Action) (K.M.H.L., H.H., and B.H.)

Discovery of an unrecognized pathway carrying overflow waters toward the Faroe Bank Channel

The dense overflow waters of the Nordic Seas are an integral link and important diagnostic for the stability of the Atlantic Meridional Overturning Circulation (AMOC). The pathways feeding the overflow remain, however, poorly resolved. Here we use multiple observational platforms and an eddy-resolving ocean model to identify an unrecognized deep flow toward the Faroe Bank Channel. We demonstrate that anticyclonic wind forcing in the Nordic Seas via its regulation of the basin circulation plays a key role in activating an unrecognized overflow path from the Norwegian slope – at which times the overflow is anomalously strong. We further establish that, regardless of upstream pathways, the overflows are mostly carried by a deep jet banked against the eastern slope of the Faroe-Shetland Channel, contrary to previous thinking. This deep flow is thus the primary conduit of overflow water feeding the lower branch of the AMOC via the Faroe Bank Channel

Eddy formation near the west coast of Greenland

Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 1992-2002, doi:10.1175/2008JPO3669.1.This paper extends A. Bracco and J. Pedlosky’s investigation of the eddy-formation mechanism in the eastern Labrador Sea by including a more realistic depiction of the boundary current. The quasigeostrophic model consists of a meridional, coastally trapped current with three vertical layers. The current configuration and topographic domain are chosen to match, as closely as possible, the observations of the boundary current and the varying topographic slope along the West Greenland coast. The role played by the bottom-intensified component of the boundary current on the formation of the Labrador Sea Irminger Rings is explored. Consistent with the earlier study, a short, localized bottom-trapped wave is responsible for most of the perturbation energy growth. However, for the instability to occur in the three-layer model, the deepest component of the boundary current must be sufficiently strong, highlighting the importance of the near-bottom flow. The model is able to reproduce important features of the observed vortices in the eastern Labrador Sea, including the polarity, radius, rate of formation, and vertical structure. At the time of formation, the eddies have a surface signature as well as a strong circulation at depth, possibly allowing for the transport of both surface and near-bottom water from the boundary current into the interior basin. This work also supports the idea that changes in the current structure could be responsible for the observed interannual variability in the number of Irminger Rings formed.AB is supported by WHOI unrestricted funds, JP by the National Science Foundation OCE 85108600, and RP by 0450658

The North Atlantic subpolar gyre regulates the spawning distribution of blue whiting (Micromesistius poutassou Risso)

The spawning stock of blue whiting (Micromesistius poutassou), an economically important pelagic gadoid in the North Atlantic Ocean, increased threefold after 1995. The reproductive success of the stock is largely determined during the very early stages of life, but little is known about the spawning dynamics of this species. Here we show that the spawning distribution of blue whiting is variable, regulated by the hydrography west of the British Isles. When the North Atlantic subpolar gyre is strong and spreads its cold, fresh water masses east over Rockall Plateau, the spawning is constrained along the European continental slope and in a southerly position near Porcupine Bank. When the gyre is weak and conditions are relatively saline and warm, the spawning distribution moves northwards along the slope and especially westwards covering Rockall Plateau. The apparent link between the spawning distribution and the subpolar gyre is the first step towards understanding the reproduction variability, which currently is the main challenge for appropriate management of the blue whiting stock

The subpolar gyre regulates silicate concentrations in the North Atlantic

publishedVersio

The ICES Working Group on Oceanic Hydrography:A bridge from in-situ sampling to the remote autonomous observation era

The ICES (International Council for the Exploration of the Sea) Working Group on Oceanic Hydrography (WGOH) was established in the late 1970's with the aim of gathering experts in physical oceanography to provide regular science-based assessments of the North Atlantic hydrographical condition (basically termohaline fields). From the beginning, the WGOH has relied on repeated long-term in-situ sampling at key sites around the North Atlantic, the Nordic Seas and adjacent shelf seas. An annual Report on Ocean Climate (IROC), produced by the WGOH since the late 1990's, summarizes trends in regional hydrography and identifies patterns linking these changes across the North Atlantic. Regional analyses are prepared by local experts who are directly involved in the monitoring programs responsible for collecting data presented in the report. An interactive webpage created in 2013 allows users to browse and download data that inform the IROC. Within the last two decades the physical oceanography community has evolved quickly incorporating technological advances such as autonomous devices into classical in-situ sampling programs. The WGOH has embraced such technological developments without diverting focus from ongoing in-situ long-term monitoring programs. Having longstanding experience synthesizing data and expertise from a large number of operational programs spanning an extensive international footprint, the WGOH has a unique perspective to offer the global ocean observing community. Here we discuss how we might foster connections with ICES to benefit the GOOS (Global Ocean Observing System) community