25 Apr 2022
25 Apr 2022
Status: this preprint is open for discussion.

Deep through-flow in the Bight Fracture Zone and its imprint in the Irminger Sea

Tillys Petit1,a, Virginie Thierry1, and Herlé Mercier1 Tillys Petit et al.
  • 1Univ Brest, CNRS, Ifremer, IRD, Laboratoire d'Océanographie Physique et Spatiale (LOPS), IUEM, F29280, Plouzané, France
  • apresent address: National Centre for Atmospheric Science, Department of Meteorology, University of Reading, Reading, UK

Abstract. Iceland-Scotland Overflow Water (ISOW) is exported from the Nordic Seas into the Iceland Basin to feed the lower limb of the Meridional Overturning Circulation. The Bight Fracture Zone (BFZ) is known to be a major route for ISOW toward the Irminger Sea, but the role of this gateway in the evolution of ISOW properties over the subpolar gyre is unclear. A combination of ship-based and Deep-Argo data gathered between 2015 and 2018 allows us to investigate the pathways and hydrological evolution of ISOW as it flows through the BFZ, as well as its influence on the ISOW properties in the Irminger Sea. The ISOW flow through the BFZ amounts to 0.76 ± 0.2 Sv and is mainly fed by the lighter part of the ISOW layer flowing west of 29–30° W as part of the East Reykjanes Ridge Current in the Iceland Basin. In the rift valley of the BFZ, between an eastern and a western sill, the bathymetry of the BFZ shapes a cyclonic circulation along which the ISOW layer is homogenised. The largest changes in ISOW properties are however observed downstream of the western sill, at the exit of the BFZ. There, ISOW is mixed isopycnally with comparatively fresher ISOW from the Irminger Sea and lies over denser ISOW that entered the Irminger Sea south of the BFZ. These fresher ISOW result from the erosion of the ISOW core by mixing with inflows from the interior of the Irminger Sea as ISOW flows northward from the Charlie-Gibbs Fracture Zone. Hence, our analysis reveals the key role of the BFZ through-flow in compensating these inputs of fresh inflows along the northward Irminger Current.

Tillys Petit et al.

Status: open (until 20 Jun 2022)

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  • RC1: 'Comment on egusphere-2022-248', Anonymous Referee #1, 04 May 2022 reply

Tillys Petit et al.

Tillys Petit et al.


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Short summary
The hydrological evolution of deep water carried within the lower limb of the Atlantic Meridional Overturning Circulation (AMOC) is analysed from a combination of ship-based and Deep-Argo data gathered between 2015 and 2018. In our study, we show that its evolution through a main fracture zone of the Reykjanes Ridge have a large impact on the lower limb of the AMOC in compensating fresh inputs of dense water from the interior of the Irminger Sea.