EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Iceland-Scotland Overflow Water Transport Variability through the Deep Bight Fracture Zone

Heather Furey1, Amy Bower1, Bill Johns2, Andree Ramsey1, and Adam Houk2
Heather Furey et al.
  • 1Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA (
  • 2Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, Florida, USA

Iceland Scotland Overflow Water (ISOW), a component of the deep limb of the Atlantic Meridional Overturning Circulation (AMOC), is the equilibrated product of dense overflow into the eastern North Atlantic basin.  Modeling results and recent observations have suggested that a significant westward transport of ISOW (~1x106 m3s-1) may occur through the Bight Fracture Zone (BFZ) near 57°N, the first major channel through the Reykjanes Ridge where ISOW can cross into the Irminger Sea.  The remaining denser (and deeper) ISOW has been shown to leave the Iceland Basin westward via the Charlie-Gibbs Fracture Zone near 53°N, or southward into the West European Basin. Until now, there have been no measured time series in the BFZ to validate model results. Single moorings placed in the north and south channels of the BFZ from summer 2015 to summer 2017 were used to estimate a mean combined transport across the fracture zone of 0.8 ± 0.4 x106 m3s-1 westward, with each channel contributing about half of the mean transport. Variability between the two channels on shorter (month-long) times scales can be extreme: in March of 2016, for example, north channel transport was ~0.4 x106 m3s-1 eastward, while south channel transport was ~0.8 x106 m3s-1 westward.  For this 2-year period, transport is stronger in the summer (0.9-1.2 x106 m3s-1) than in winter (0.5-0.7 x106 m3s-1), where large fluctuations including complete reversals suggest transport variability may be affected by winter storms.  This mooring record also shows a fresh anomaly in ISOW beginning in early 2017, which has been shown by others to originate from the surface waters near the Grand Banks region of the western north Atlantic.  Transport variability in this two-year record is examined in the context of the transport variability of the OSNAP mooring arrays on the east and west flanks of the Reykjanes Ridge just north of BFZ during the same time period.  An observationally-based understanding of how the Iceland and Irminger basins communicate with each other via the deep limb of the AMOC through the BFZ will provide fundamental insight into the pathways and processes that define the subpolar AMOC system.

How to cite: Furey, H., Bower, A., Johns, B., Ramsey, A., and Houk, A.: Iceland-Scotland Overflow Water Transport Variability through the Deep Bight Fracture Zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7999,, 2021.


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