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OSNAP: Overturning in the Subpolar North Atlantic


OSNAP is an international program designed to provide a continuous record of the full-water column, trans-basin fluxes of heat, mass and freshwater in the subpolar North Atlantic. The OSNAP observing system consists of two legs: one extending from southern Labrador to the southwestern tip of Greenland across the mouth of the Labrador Sea (OSNAP West), and the second from the southeastern tip of Greenland to Scotland (OSNAP East).

The observing system also includes subsurface floats (OSNAP Floats) in order to trace the pathways of overflow waters in the basin and to assess the connectivity of currents crossing the OSNAP line.

OSNAP: Floats

Deep RAFOS floats were used to track the pathways of the lower limb of the overturning circulation through the subpolar North Atlantic.  These passive drifters were ballasted to drift at depths ranging from 1800 to 2800 meters, and deployed in the deep boundary currents: along the western side of the Reykjanes Ridge in the Iceland Basin, Read More

in the Charlie-Gibbs Fracture Zone which is a deep channel connecting the east and west North Atlantic Basins just south of the Rekjanes Ridge, along the eastern side of the Reykjanes Ridge, and, finally, along the eastern side of Greenland in the Irminger Sea.  The floats seeded the components of the deep AMOC limb: the Iceland-Scotland Overflow Water (ISOW) in the Iceland Basin, through the CGFZ, and along the east side of the Irminger Sea, and the combination of ISOW and Denmark Strait Overflow Water (DSOW) that makes up the deep limb on the west side of the Irminger Sea (east of Greenland).  Using this tool allowed us to connect the deep limb of the AMOC between and beyond the mooring arrays.

OSNAP: Moorings

The Bower Lab is responsible for the Greenland Deep Boundary Current mooring array located offshore of the shelf break east of Greenland, bracketing the OOI Irminger Node.

OSNAP: Gliders

EKE across supolar norht atlantic w/ glider track loc

A WHOI-OUC collaboration took place from 2014-2016 where TWR gliders were deployed and maintained west of the Rockall Plateau along the OSNAP line.  The glider array was used to measure the highly variable branch of the NAC which travels over the Charlie-Gibbs Fracture Zone and continues into the Iceland Basin, meandering northward towards the Iceland-Scotland sill.

Data access

Greenland Deep Western Boundary Current Mooring data are available at OSNAP Data.

Dataset: Bower, A., Straneo, F. Furey, H., Biló, T., Bahr, F. "Overturning in the Subpolar North Atlantic Program (OSNAP) moored current meter, temperature, conductivity, salinity and pressure data collected on subsurface moorings M1, M2, M3 and M4 between June 2018 and August 2020." 2023-06. DOI:10.26025/1912/66314

Dataset: Houk, A., Bower, A. "Greenland Deep Western Boundary Current (GDWBC) Mooring Data 2020-2022." 2024-05. DOI: 10.26025/1912/69370


Koman, G., A. Bower, P. Holiday, H. Furey, Y. Fu, and T. Bilo, 2023. Decreasing transport of the Deep Western Boundary Current in the subpolar Atlantic.  Nature Geosciences, submitted.

Furey, H., Bower, A., Ramsey, A., Houk, A., & Meunier, T. (2024). Variability of Iceland Scotland Overflow Water Across the Reykjanes Ridge: 2‐Years of Moored Observations in the Bight Fracture Zone. Journal of Geophysical Research: Oceans, 129(6), e2023JC020463. doi:10.1029/2023JC020463

Furey, H., N. Foukal, A. Anderson, and A. Bower, 2023. Investigation of the source of Iceland Basin freshening: virtual particle tracking with satellite-derived geostrophic surface velocities. Remote Sensing,

Bower, A., J. Vazquez-Cuervo, and E. Comstock, 2024. Navigating a sea of obstacles: Ocean science for people with disabilitiesOceanography, 36(4),

Koman, G., M.C. Curran, A.L. Ramsey, A.S. Bower, and H.H. Furey, 2023. Listening to the ocean: using data sonification to teach students about the role of ocean circulation in climate change. Science Activities,

Fu, Y., M.S. Lozier, T.C. Bilo, A.S. Bower, S.A. Cunningham, F. Cyr, M.F. de Jong, B. deYoung, L. Drysdale, N. Fraser, N. Fried, H.H. Furey, G. Han, P. Handmann, N.P. Holliday, J. Holte, M.E. Inall, W.E. Johns, S. Jones, J. Karstensen, F. Li, A. Pacini, R.S. Pickart, D. Rayner, F. Straneo, and I. Yashayaev, 2023. Seasonality of the meridional overturning circulation in the subpolar North Atlantic. Communications Earth & Environment,

Zou, S., A. Bower, S. Lozier, and H. Furey, 2023. Deep ocean circulation in the subpolar North Atlantic observed by acoustically-tracked floats. Progress in Oceanography, (2023): 102975.

Furey, H., E. Park, and A. Houk, 2022.  AR6901_Cruise Report_OSNAP_GDWBC_2022 WHOI Cruise Report, 160 pp.

Lozier, M. Susan, A.S. Bower, H.H. Furey, K.L. Drouin, X. Xu, and S. Zou, 2022. Overflow water pathways in the North Atlantic.  Progress in Oceanography, V208,

Zou, S., Bower, A.S., Furey, H., Pickart, R.S., Houpert, L. and Holliday, N.P., 2021. Observed Deep Cyclonic Eddies around Southern Greenland. Journal of Physical Oceanography, 51(10), pp.3235-3252.

Valdes, J., and H. Furey, 2021. WHOI 260Hz Sound Source - Tuning and Assembly. Woods Hole Oceanographic Institution Technical Report, WHOI-2021-02, 65 pp. doi: 10.1575/1912/27173

Ramsey, A., H. Furey, and A. Bower, 2020. Overturning of the Subpolar North Atlantic Program (OSNAP): RAFOS Float Data Report, June 2014 - January 2019.Woods Hole Oceanographic Institution Technical Report, WHOI-2020-06; doi:10.1575/1912/26515.

Zou, S., A. Bower, H. Furey, S. Lozier, and X. Xu, 2020.  Redrawing the Iceland-Scotland Overflow Water Pathways in the North Atlantic. Nature Communications, 11(1), pp.1-8.

Curran, C., A. Ramsey, and A. Bower, 2020. Learning about ocean currents one track at a time. Science Activities. doi: 10.1080/00368121.2021.1885333.

Bower, A., Lozier, S., Biastoch, A., Drouin, K., Foukal, N., Furey, H., Lankhorst, M., Rühs, S. and Zou, S., 2019. Lagrangian views of the pathways of the Atlantic Meridional Overturning Circulation. Journal of Geophysical Research: Oceans, 124(8), pp.5313-5335.

Lozier, M.S., F. Li, S. Bacon, F. Bahr, A. Bower, S. Cunningham, F. de Jong, L. de Steur, B. DeYoung, J. Fischer, S. Gary, B. Greenan, N.P. Holliday, A. Houk, L. Hupert, M. Inall, W. Johns, H. Johnson, J. Karsetensen, G. Koman, I. LeBras, X. Lin, N. Mcackay, D. Marshall, H. Mercier, M. Oltmanns, R.S. Pickart, A. Ramsey, D. Rayner, F. Straneo, V. Tierry, D.J. Torres, R. Williams, C. Wilson, J. Yang, I. Yashayaev, J. Zhao, 2018. A sea change in our view of overturning in the subpolar North Atlantic. Science, 363(6426), 516-521, doi:10.1126/science.aau6592.

Ramsey, A., H. Furey, and A. Bower, 2018. Deep floats reveal ocean circulation patterns. Eos, 99,

Xu, X., A. Bower, H. Furey, and E. Chassignet, 2018. Variability of the Iceland-Scotland overflow water transport through the Charlie-Gibbs Fracture Zone: Results from an eddying simulation and observations. Journal of Geophysical Research – Oceans, 123, 5808-5823,

Zhao, J., A. Bower, J. Yang, and X. Lin, 2018.  Meridional heat transport variability induced by mesoscale processes in the subpolar North Atlantic.  Nature Communications, 9(1), 1124, doi:10.1038/s41467-018-03134-x.

Zou, S., M. S. Lozier, W. Zenk, A. Bower, and W. Johns, 2017.  Observed and modeled pathways of the Iceland Scotland Overflow Water in the eastern North Atlantic.  Progress in  Oceanography, 159, 211-222,

Bower, A., and H. Furey, 2017. Iceland-Scotland overflow water transport variability through the Charlie-Gibbs Fracture Zone and the impact of the North Atlantic CurrentJournal of Geophysical Research – Oceans,  doi:10.1002/2017JC012698.

Lozier, M.S., S. Bacon, A.S. Bower, S.A. Cunningham, M.F. de Jong, L. de Steur, B. deYoung, J. Fischer, S.F. Gary, B.J.W. Greenan, P. Heimbach, N.P. Holliday, L. Houpert, M.E. Inall, W.E. Johns, H.L. Johnson, J. Karstensen, F. Li, X. Lin, N. Mackay, D. P. Marshall, H. Mercier, P.G. Myers, R. S. Pickart, H.R. Pillar, F. Straneo, V. Thierry, R.A. Weller, R.G. Williams, C. Wilson, J. Yang, J. Zhao, and J.D. Zika, 2017. Overturning in the Subpolar North Atlantic Program: a new international ocean observing systemBulletin of the American Meteorological Society, 98, 737-752, doi:


This project is generously funded by the National Science Foundation.

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