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Overturning in the Subpolar North Atlantic Program : a new international ocean observing system (2017)

Lozier, M. Susan ; Bacon, Sheldon ; Bower, Amy S. ; [et al.]

American Meteorological Society

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Publication Date: 2022-05-25

Description: Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 98 (2017): 737-752, doi:10.1175/BAMS-D-16-0057.1.

Description: For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change–Meridional Overturning Circulation and Heatflux Array (RAPID–MOCHA) at 26°N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.

Description: The authors gratefully acknowledge financial support from the U.S. National Science Foundation (NSF; OCE-1259102, OCE-1259103, OCE-1259618, OCE-1258823, OCE-1259210, OCE-1259398, OCE-0136215, and OCE-1005697); the U.S. National Aeronautics and Space Administration (NASA); the U.S. National Oceanic and Atmospheric Administration (NOAA); the WHOI Ocean and Climate Change Institute (OCCI), the WHOI Independent Research and Development (IRD) Program, and the WHOI Postdoctoral Scholar Program; the U.K. Natural Environment Research Council (NERC; NE/K010875/1, NE/K010700/1, R8-H12-85, FASTNEt NE/I030224/1, NE/K010972/1, NE/K012932/1, and NE/M018024/1); the European Union Seventh Framework Programme (NACLIM project, 308299 and 610055); the German Federal Ministry and Education German Research RACE Program; the Natural Sciences and Engineering Research Council of Canada (NSERC; RGPIN 227438-09, RGPIN 04357, and RG-PCC 433898); Fisheries and Oceans Canada; the National Natural Science Foundation of China (NSFC; 41521091, U1406401); the Fundamental Research Funds for the Central Universities of China; the French Research Institute for Exploitation of the Sea (IFREMER); the French National Center for Scientific Research (CNRS); the French National Institute for Earth Sciences and Astronomy (INSU); the French national program LEFE; and the French Oceanographic Fleet (TGIR FOF).

Description: 2017-10-24

Repository Name: Woods Hole Open Access Server

Type: Article

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Observation-based estimates of heat and freshwater exchanges from the subtropical North Atlantic to the Arctic (2022)

Li, Feili ; Lozier, M. Susan ; Holliday, Naomi Penny ; [et al.]

Elsevier

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Publication Date: 2022-05-27

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Li, F., Lozier, M. S., Holliday, N. P., Johns, W. E., Le Bras, I. A., Moat, B. I., Cunningham, S. A., & de Jong, M. F. Observation-based estimates of heat and freshwater exchanges from the subtropical North Atlantic to the Arctic. Progress in Oceanography, 197, (2021): 102640, https://doi.org/10.1016/j.pocean.2021.102640.

Description: Continuous measurements from the OSNAP (Overturning in the Subpolar North Atlantic Program) array yield the first estimates of trans-basin heat and salinity transports in the subpolar latitudes. For the period from August 2014 to May 2018, there is a poleward heat transport of 0.50 ± 0.05 PW and a poleward salinity transport of 12.5 ± 1.0 Sv across the OSNAP section. Based on the mass and salt budget analyses, we estimate that a surface freshwater input of 0.36 ± 0.05 Sv over the broad subpolar-Arctic region is needed to balance the ocean salinity change created by the OSNAP transports. The overturning circulation is largely responsible for setting these heat and salinity transports (and the derived surface freshwater input) derived from the OSNAP array, while the gyre (isopycnal) circulation contributes to a lesser, but still significant, extent. Despite its relatively weak overturning and heat transport, the Labrador Sea is a strong contributor to salinity and freshwater changes in the subpolar region. Combined with trans-basin transport estimates at other locations, we provide new estimates for the time-mean surface heat and freshwater divergences over a wide domain of the Arctic-North Atlantic region to the north and south of the OSNAP line. Furthermore, we estimate the total heat and freshwater exchanges across the surface area of the extratropical North Atlantic between the OSNAP and the RAPID-MOCHA (RAPID Meridional Overturning Circulation and Heat-flux Array) arrays, by combining the cross-sectional transports with vertically-integrated ocean heat and salinity content. Comparisons with the air-sea heat and freshwater fluxes from atmospheric reanalysis products show an overall consistency, yet with notable differences in the magnitudes during the observation time period.

Description: F.L. and M.S.L. were supported by the National Science Foundation (OCE-1948335). W.E.J. was supported by the National Science Foundation grants RAPID (OCE-1332978 and OCE-1926008) and OSNAP (OCE-1756231 and OCE-1948198). I.A.L.B. was supported by the National Science Foundation (OCE-1756272 and OCE-2038481). B.M. was supported by the UK Natural Environment Research Council for the RAPID-AMOC program and the ACSIS program (NE/N018044/1). S.A.C. and N.P.H. were supported by UK NERC National Capability programmes the Extended Ellett Line and CLASS (NE/R015953/1), NERC grants UK OSNAP (NE/K010875/1, NE/K010875/2, NE/K010700/1), UK OSNAP Decade (NE/T00858X/1, NE/T008938/1). S.A.C. received additional supports from the Blue-Action project (European Union’s Horizon 2020 research and innovation program, grant 727852) and the iAtlantic project (European Union’s Horizon 2020 research and innovation program, grant 210522255).

Keywords: Oceanic heat and salinity transports ; Surface heat and freshwater exchange ; Overturning and gyre circulation

Repository Name: Woods Hole Open Access Server

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How much Arctic fresh water participates in the subpolar overturning circulation? (2021)

Le Bras, Isabela A. ; Straneo, Fiamma ; Muilwijk, Morven ; [et al.]

American Meteorological Society

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Publication Date: 2022-05-27

Description: Author Posting. © American Meteorological Society, 2021. 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 51(3), (2021): 955–973, https://doi.org/10.1175/JPO-D-20-0240.1.

Description: Fresh Arctic waters flowing into the Atlantic are thought to have two primary fates. They may be mixed into the deep ocean as part of the overturning circulation, or flow alongside regions of deep water formation without impacting overturning. Climate models suggest that as increasing amounts of freshwater enter the Atlantic, the overturning circulation will be disrupted, yet we lack an understanding of how much freshwater is mixed into the overturning circulation’s deep limb in the present day. To constrain these freshwater pathways, we build steady-state volume, salt, and heat budgets east of Greenland that are initialized with observations and closed using inverse methods. Freshwater sources are split into oceanic Polar Waters from the Arctic and surface freshwater fluxes, which include net precipitation, runoff, and ice melt, to examine how they imprint the circulation differently. We find that 65 mSv (1 Sv ≡ 106 m3 s−1) of the total 110 mSv of surface freshwater fluxes that enter our domain participate in the overturning circulation, as do 0.6 Sv of the total 1.2 Sv of Polar Waters that flow through Fram Strait. Based on these results, we hypothesize that the overturning circulation is more sensitive to future changes in Arctic freshwater outflow and precipitation, while Greenland runoff and iceberg melt are more likely to stay along the coast of Greenland.

Description: We gratefully acknowledge the U.S. National Science Foundation: this work was supported by Grants OCE-1258823, OCE-1756272, OCE-1948335, and OCE-2038481. L.H.S. thanks the U.S. Norway Fulbright Foundation for the Norwegian Arctic Chair Grant 2019-20 that made the visit to Scripps Institution of Oceanography possible. N.P.H. acknowledges support by the U.K. Natural Environment Research Council (NERC) National Capability program CLASS (NE/R015953/1), and Grants U.K.-OSNAP (NE/K010875/1, NE/K010875/2) and U.K.-OSNAP Decade (NE/T00858X/1). We acknowledge the World Climate Research Programme, which, through its Working Group on Coupled Modelling, coordinated and promoted CMIP6.

Keywords: Arctic ; North Atlantic Ocean ; Conservation equations ; Meridional overturning circulation ; Ocean circulation ; Inverse methods

Repository Name: Woods Hole Open Access Server

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Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation (2021)

Li, Feili ; Lozier, M. Susan ; Bacon, Sheldon ; [et al.]

Nature Research

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Publication Date: 2022-05-27

Description: © The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Li, F., Lozier, M. S., Bacon, S., Bower, A. S., Cunningham, S. A., de Jong, M. F., DeYoung, B., Fraser, N., Fried, N., Han, G., Holliday, N. P., Holte, J., Houpert, L., Inall, M. E., Johns, W. E., Jones, S., Johnson, C., Karstensen, J., Le Bras, I. A., P. Lherminier, X. Lin, H. Mercier, M. Oltmanns, A. Pacini, T. Petit, R. S. Pickart, D. Rayner, F. Straneo, V. Thierry, M. Visbeck, I. Yashayaev & Zhou, C. Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation. Nature Communications, 12(1), (2021): 3002, https://doi.org/10.1038/s41467-021-23350-2.

Description: Changes in the Atlantic Meridional Overturning Circulation, which have the potential to drive societally-important climate impacts, have traditionally been linked to the strength of deep water formation in the subpolar North Atlantic. Yet there is neither clear observational evidence nor agreement among models about how changes in deep water formation influence overturning. Here, we use data from a trans-basin mooring array (OSNAP—Overturning in the Subpolar North Atlantic Program) to show that winter convection during 2014–2018 in the interior basin had minimal impact on density changes in the deep western boundary currents in the subpolar basins. Contrary to previous modeling studies, we find no discernable relationship between western boundary changes and subpolar overturning variability over the observational time scales. Our results require a reconsideration of the notion of deep western boundary changes representing overturning characteristics, with implications for constraining the source of overturning variability within and downstream of the subpolar region.

Description: We acknowledge funding from the Physical Oceanography Program of the U.S. National Science Foundation (OCE-1259398, OCE-1756231, OCE-1948335); the U.K. Natural Environment Research Council (NERC) National Capability programs the Extended Ellett Line and CLASS (NE/R015953/1), and NERC grants UK-OSNAP (NE/K010875/1, NE/K010875/2, NE/K010700/1) and U.K. OSNAP Decade (NE/T00858X/1, NE/T008938/1). Additional support was received from the European Union 7th Framework Program (FP7 2007-2013) under grant 308299 (NACLIM), the Horizon 2020 research and innovation program under grants 727852 (Blue-Action), 862626 (EuroSea). We also acknowledge support from the Royal Netherlands Institute for Sea Research, the Surface Water and Ocean Topography-Canada (SWOT-C), Canadian Space Agency, the Aquatic Climate Change Adaptation Services Program (ACCASP), Fisheries and Oceans Canada, an Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant, and from the China’s national key research and development projects (2016YFA0601803), the National Natural Science Foundation of China (41925025) and the Fundamental Research Funds for the Central Universities (201424001). Support for the 53°N array by the RACE program of the German Ministry BMBF is acknowledged, as is the contribution from Fisheries and Oceans Canada’s Atlantic Zone Monitoring Program.

Repository Name: Woods Hole Open Access Server

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Local and downstream relationships between Labrador Sea Water volume and North Atlantic meridional overturning circulation variability (2019)

Li, Feili ; Lozier, M. Susan ; Danabasoglu, Gokhan ; [et al.]

American Meteorological Society

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Publication Date: 2022-05-26

Description: Author Posting. © American Meteorological Society, 2019. 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 Climate 32(13), (2019): 3883-3898, doi:10.1175/JCLI-D-18-0735.1.

Description: While it has generally been understood that the production of Labrador Sea Water (LSW) impacts the Atlantic meridional overturning circulation (MOC), this relationship has not been explored extensively or validated against observations. To explore this relationship, a suite of global ocean–sea ice models forced by the same interannually varying atmospheric dataset, varying in resolution from non-eddy-permitting to eddy-permitting (1°–1/4°), is analyzed to investigate the local and downstream relationships between LSW formation and the MOC on interannual to decadal time scales. While all models display a strong relationship between changes in the LSW volume and the MOC in the Labrador Sea, this relationship degrades considerably downstream of the Labrador Sea. In particular, there is no consistent pattern among the models in the North Atlantic subtropical basin over interannual to decadal time scales. Furthermore, the strong response of the MOC in the Labrador Sea to LSW volume changes in that basin may be biased by the overproduction of LSW in many models compared to observations. This analysis shows that changes in LSW volume in the Labrador Sea cannot be clearly and consistently linked to a coherent MOC response across latitudes over interannual to decadal time scales in ocean hindcast simulations of the last half century. Similarly, no coherent relationships are identified between the MOC and the Labrador Sea mixed layer depth or the density of newly formed LSW across latitudes or across models over interannual to decadal time scales.

Description: FL and MSL are thankful for the financial support from the National Science Foundation (NSF) Physical Oceanography Program (NSF-OCE-12-59102, NSF-OCE-12-59103). The NCAR contribution was supported by the National Oceanic and Atmospheric Administration (NOAA) Climate Program Office (CPO) under Climate Variability and Predictability Program (CVP) Grant NA13OAR4310138 and by the NSF Collaborative Research EaSM2 Grant OCE-1243015. NCAR is sponsored by the NSF. NPH is supported by NERC programs U.K. OSNAP (NE/K010875) and ACSIS (National Capability, NE/N018044/1). Y-OK is supported by NOAA CPO CVP (NA17OAR4310111) and NSF EaSM2 grant (OCE-1242989). AR is supported by NASA-ROSES Modeling, Analysis and Prediction 2016 NNX16AC93G-MAP. RZ is supported by NOAA/OAR. Argo data were collected and made freely available by the International Argo Program and the national programs that contribute to it (http://www.argo.ucsd.edu, http://argo.jcommops.org). The Argo Program is part of the Global Ocean Observing System (http://doi.org/10.17882/42182). Data from the RAPID-MOCHA-WBTS array funded by NERC, NSF and NOAA are freely available from www.rapid.ac.uk/rapidmoc. We thank Stephen Griffies for providing access to the GFDL-MOM025 COREII simulation output and Matthew Harrison and Xiaoqin Yan for their comments on the manuscript. We also thank the anonymous reviewers for their valuable comments.

Description: 2020-06-11

Keywords: North Atlantic Ocean ; Deep convection ; Meridional overturning circulation ; Model comparison

Repository Name: Woods Hole Open Access Server

Type: Article

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