SNAP-DRAGON: Subpolar North Atlantic Processes - Dynamics and pRedictability of vAriability in Gyre and OverturNing

Lead Research Organisation: University of Oxford
Department Name: Earth Sciences

Abstract

SNAP-DRAGON will produce a step change in our understanding of the processes that link atmospheric changes to subpolar ocean variability, their implications for ocean and climate predictability in this region, and the degree to which we can trust their representation in climate models.

The subpolar North Atlantic Ocean, stretching between the UK, Greenland and Canada, plays a crucial role in local and global climate. This is the critical region where much of the warm water flowing northward in the upper North Atlantic releases its heat to the atmosphere and is converted to cold, dense water, before flowing southward again at depth in what is known as the Atlantic overturning circulation. The huge amount of heat this circulation carries northward and releases to the atmosphere impacts the storm track that determines the weather over western Europe. The overturning circulation also has profound implications for African rainfall and hurricane statistics via its effect on sea surface temperatures at lower latitudes. In addition, the sinking of water in the subpolar region ventilates the deep ocean, transferring heat and carbon away from the surface and moderating the impact of anthropogenic greenhouse gases on surface temperature. Any warm water which does not sink in the subpolar region recirculates or carries its heat further north towards the Arctic, influencing sea-ice conditions and polar marine ecosystems before it too sinks and flows south.

Recently, the first ever observations of the overturning circulation in the subpolar North Atlantic have been made by the Overturning in the Subpolar North Atlantic Programme (OSNAP, www.o-snap.org). These have revealed large amplitude variations in the overturning, but raised questions about the locations and processes that give rise to this variability, and its likely impact on surface ocean conditions and climate.

Representing this region properly in climate models is essential if we are to make useful climate predictions on seasonal, interannual, decadal and longer timescales. However, the current generation of models struggle to represent the processes we know to be important here, and disagree with the observations on the locations in which warm water is transformed into dense water. The disagreements limit our confidence in model predictions. We cannot assess model performance properly because we do not understand all the links between atmospheric conditions and ocean circulation variability.

In SNAP-DRAGON we will combine OSNAP and other observations with numerical models that can represent small-scale processes to work out what causes variations in subpolar ocean circulation. Once we know which processes are most important and how they work, we will be able to establish what climate models are getting wrong, and suggest improvements. This will improve predictions of ocean and climate variability in the subpolar North Atlantic and beyond.

We will investigate how cold, dense waters find their way into the boundary currents that export them to the south. We will establish the role that winds play, which is likely more complicated than we have assumed in the past. And we will determine the impact on overturning variability of changes in freshwater export from the Arctic and Greenland. To characterize and quantify these key processes, in addition to using ocean observations, we will perform "What if?" experiments in ocean models, asking questions such as: what happens to the subpolar ocean circulation if the atmospheric jet stream over the Atlantic shifts or strengthens? We will use statistical methods more common in weather forecasting to figure out how subpolar ocean properties and overturning connect to potentially predictable larger-scale atmospheric circulation patterns. And we will employ innovative ways of combining models with observations to determine a best estimate of the evolution of the subpolar North Atlantic over the OSNAP observation period.

Planned Impact

We target two broad communities and one specific community as beneficiaries of SNAP-DRAGON. The broad communities are (i) those who require seasonal to decadal and longer-term climate forecasts for risk management and planning purposes, and (ii) those who are interested in knowing more about the North Atlantic Ocean and about climate research. The specific community is DSTL and the Royal Navy.

Seasonal, decadal and longer-term climate forecasts provide information to planners and policymakers to assess the risk of hazards and to understand the level of vulnerability of people and infrastructure. They are part of the suite of information needed to plan how to respond to risk and reduce exposure to hazards. Planners and policy-makers need to have an understanding of the skill of predictions in order to decide how to respond: uncertainty is a key challenge for decision-making. These stakeholders will directly benefit in the long-term from SNAP-DRAGON through improved skill in seasonal, decadal and longer-term climate predictions which will come about as we identify processes in models that work well, and those that require improvement.

There is growing interest in ocean literacy as people are increasingly aware of climate change, species extinctions and plastic and other pollution, through the efforts of popular figures such as David Attenborough and Greta Thurnberg. Politicians are responding to that interest too, and attendees at OceanObs19 heard that political staffers and researchers predominantly rely on google for instantaneous information about latest research. Thus, a growing audience is looking for easily-digestible information in a range of formats delivered online in a timely manner. This broad community will benefit by having access to our background knowledge and new information presented and made available in a range of easily accessible ways. The information will contribute to the UN Decade of Ocean Science for Sustainable Development (2021-2030) through a focus on providing material to promote ocean literacy.

The Defence Science and Technology Laboratory (DSTL) and the Royal Navy are also looking for information on the latest research about the North Atlantic. They will benefit from having close interaction with SNAP-DRAGON researchers throughout the project, and thereby having access to research as it is developing.

Publications

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Loose N (2021) Leveraging Uncertainty Quantification to Design Ocean Climate Observing Systems in Journal of Advances in Modeling Earth Systems

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Le Bras I (2022) Slantwise Convection in the Irminger Sea in Journal of Geophysical Research: Oceans

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Roussenov V (2022) Historical Reconstruction of Subpolar North Atlantic Overturning and Its Relationship to Density in Journal of Geophysical Research: Oceans

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Chassignet E (2023) Impact of the New England Seamount Chain on Gulf Stream Pathway and Variability in Journal of Physical Oceanography

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Storer BA (2022) Global energy spectrum of the general oceanic circulation. in Nature communications

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Årthun M (2023) Future strengthening of the Nordic Seas overturning circulation. in Nature communications

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Jackson L (2022) The evolution of the North Atlantic Meridional Overturning Circulation since 1980 in Nature Reviews Earth & Environment

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Robson J (2023) Contrasting internally and externally generated Atlantic Multidecadal Variability and the role for AMOC in CMIP6 historical simulations. in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences

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Le Bras IA (2023) Labrador sea water spreading and the Atlantic meridional overturning circulation. in Philosophical transactions. Series A, Mathematical, physical, and engineering sciences

 
Description In this award we have improved our understanding of the processes by and locations in which water is made dense in the subpolar North Atlantic, a critical part of the Atlantic meridional overturning circulation. We have identified key processes and explored how well-represented they are in ocean and climate models. We have learned, for example, that water mass densification in the east and west is connected through a range of mechanisms, and that much of the variability in the rate of dense water formation arises due to changes in the position of density outcrops.
Exploitation Route Results will inform ocean and climate model development, as well as future observing system design.
Sectors Aerospace

Defence and Marine

Agriculture

Food and Drink

Environment

Government

Democracy and Justice

 
Description Diapycnal watermass transformation in alpha versus beta regimes
Amount £79,410 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 09/2022 
End 06/2023
 
Description Lagrangian views of the subpolar North Atlantic Ocean
Amount £80,000 (GBP)
Funding ID 2440395 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 09/2020 
End 09/2024
 
Description MEZCAL - Methods for Extending the horiZontal Coverage of the Amoc Latitudinally and retrospectively
Amount £1,000,000 (GBP)
Funding ID NE/Y004272/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 11/2023 
End 03/2026
 
Title Data for "Saturation of destratifying and restratifying instabilities during down front wind events: a case study in the Irminger Sea" 
Description This archive contains processed data used in the study "Saturation of destratifying and restratifying instabilities during down front wind events: a case study in the Irminger Sea". We are grateful for the financial support of the Natural Environment Research Council (grants NE/L002612/1 and NE/T013494/1). This work used the ARCHER2 UK National Supercomputing Service (https://www.archer2.ac.uk). We would also like to thank Andrew Coward for providing computational support. The results contain modified Copernicus Climate Change Service information 2020. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains. The results contain modified GEBCO data produced by the GEBCO Compilation Group (2023) GEBCO 2023 Grid (doi:10.5285/f98b053b-0cbc-6c23-e053-6c86abc0af7b) 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
Impact Collaborative paper 
URL https://zenodo.org/record/8232681
 
Title Lagrangian Decomposition of the Meridional Heat Transport at 26.5N - Water Parcel Crossings of the RAPID 26.5N Array 
Description This dataset contains the initial and final positions and properties of Lagrangian trajectories evaluated using 5-day mean velocity and tracer fields output from the ORCA0083-N06 ocean sea-ice model hindcast (1958-2015). Numerical water parcels are initialised to sample the full-depth southward transport across the RAPID 26.5N array every month during 2004-2015. Water parcels are advected backwards-in-time using a bespoke version of TRACMASS v7.1 Lagrangian particle tracking tool which enables users to specify a custom domain using a mask netCDF file. Particles are initialised on the first-available day of each month (based on the centre of the model 5-day mean field windows) between 2004 and 2015 (inclusive) before being advected backwards-in-time within the North Atlantic Ocean until any one of four termination conditions are met: (1) water parcels reach the RAPID 26.5N array, (2) water parcels reach the OSNAP (West or East) arrays in the subpolar North Atlantic, (3) water parcels reach either the English Channel or Gibraltar Strait, or (4) particles reach the maximum advection time of 25-years. The 25-year maximum advection time ensures that we adequately resolve the subtropical gyre circulation north to the RAPID 26.5N array. The pathway transporting dense North Atlantic Deep Water from the OSNAP arrays to RAPID at 26.5N is not fully resolved in this Lagrangian experiment since these water parcels transit on multi-decadal timescales. The number of water parcels initialised in each model-grid cell scales with the total northward transport through that cell, such that the maximum possible transport conveyed by any single particle is 5.0 mSv (mSv == 10-3 Sv), enabling the calculation of robust Lagrangian statistics. In reality, the average. water parcel has an associated volume transport of 3.3 mSv which is conserved throughout its circulation. Water parcel locations (converted to geographical coordinates) and properties (conservative temperature, absolute salinity, potential density [TEOS-10]) are output on every model-grid cell crossing. TRACMASS determines particle properties on grid-cell crossings by taking the average of the properties stored at the nearest two T-grid points. Here, we provide the initial and final locations and properties of all water parcels initialised from RAPID 26.5N. All Lagrangian experiments were completed using the JASMIN High-Performance Computing facility (https://jasmin.ac.uk). For a complete description of the ORCA0083-N06 hindcast configuration see: Moat et al. (2016). For a complete description of TRACMASS v7.1 see: https://www.tracmass.org 
Type Of Material Database/Collection of data 
Year Produced 2023 
Provided To Others? Yes  
Impact Collaborative paper 
URL https://zenodo.org/doi/10.5281/zenodo.10069799
 
Title Lagrangian overturning in the eastern subpolar North Atlantic Ocean - ORCA025-GJM189 Particle Trajectory Dataset 
Description This dataset contains the output of Lagrangian particle tracking experiments using 5-day mean velocity and hydrographic fields from the ORCA025-GJM189 ocean sea-ice model hindcast configured during the Drakkar project in which numerical particles are initialised along the northward inflows across the Overturning in the Subpolar North Atlantic Program (OSNAP) East section. Particles are advected using a bespoke version of TRACMASS v7.1 Lagrangian particle tracking tool using the regular step-wise stationary advection scheme and an adapted implementation of the vertical turbulent mixing parameterisation created by Paris et al. (2013) for the Connectivity Modelling System Lagrangian particle tracking tool. This vertical turbulent mixing scheme only acts on particles found within the surface mixed layer (as evaluated along particle trajectories) and randomly reshuffles them according to a maximum vertical velocity of 10 cm/s - characteristic of vertical convective plumes. Note, particles cannot be artificially subducted across the base of the mixed layer into the ocean interior using this scheme. Particles are initialised on the first-available day of each month (based on the centre of the model fields 5-day mean windows) between 1976 and 2008 (inclusive) before being advected within the Iceland and Irminger Basins until any one of three termination conditions are met: 1) particles return southward across OSNAP East, 2) particles flow northward across the Greenland-Scotland Ridge, or 3) particles reach the maximum advection time of 7-years. The 7-year maximum advection time ensures >99.1% of all initialised particles meet one of conditions 1) or 2), hence only 0.9% of all particles are terminated between OSNAP East and the Greenland-Scotland Ridge. The number of particles initialised in each model-grid cell scales with the total northward transport through that cell, such that the maximum possible transport conveyed by any single particle is 2.5 mSv (mSv == 1E-3 Sv), enabling the calculation of robust Lagrangian statistics. Particle locations (referenced to the original ORCA025 model grid) and properties (potential temperature, salinity, potential density and local mixed layer depth) are stored in the output files on every model-grid cell crossing. TRACMASS determines particle properties on grid-cell crossings by taking the average of the properties stored at the nearest two T-grid points. In total, four Lagrangian experiments were conducted at the Department of Earth Sciences, University of Oxford. Please see README.md for a full description of all Lagrangian experiments and the accompanying output files. For a complete description of the ORCA025-GJM189 hindcast configuration see: https://github.com/meom-configurations/ORCA025.L75-GJM189. For a complete description of TRACMASS v7.1 see: https://github.com/TRACMASS/tracmass 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
Impact Paper 
URL https://zenodo.org/record/6573899
 
Title Subpolar ocean variability analysis using DePreSys4 hindcast output 
Description The dataset contains python scripts and pre-processed data, which was generated using DePreSys4 Met Office ensemble hindcast output. These scripts were used to create a subset of ensemble members based on seasonal NAO indices. The approach could be used to perform an ensemble-composite analysis to examine the impacts of NAO forcing on the ocean circulation in the subpolar North Atlantic ocean. 
Type Of Material Database/Collection of data 
Year Produced 2022 
Provided To Others? Yes  
Impact Papers 
URL https://zenodo.org/record/7096230
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation Florida State University
Country United States 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation Georgia Institute of Technology
Country United States 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation Meteorological Office UK
Country United Kingdom 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation NCAR National Center for Atmospheric Research
Country United States 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation National Centre for Atmospheric Science (NCAS)
Country United Kingdom 
Sector Charity/Non Profit 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation National Oceanography Centre
Country United Kingdom 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation Scottish Association For Marine Science
Country United Kingdom 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation University of Liverpool
Country United Kingdom 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation University of Reading
Department Department of Meteorology
Country United Kingdom 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation University of Texas at Austin
Country United States 
Sector Academic/University 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Description SNAP-DRAGON NSF-NERC project team 
Organisation Woods Hole Oceanographic Institution
Country United States 
Sector Charity/Non Profit 
PI Contribution I wrote the proposal that funded this FIC collaborative call, and lead the project. I also supervise one of the 9 early career scientists employed on the grant.
Collaborator Contribution This project involves 5 US and 5 UK institutions as well as the UK Met Office. Researchers at each institution are using different but complementary approaches to determine the link between atmospheric forcing and variations in ocean circulation and properties in the sub polar North Atlantic.
Impact SNAP informal seminar series for researchers interested in the sub polar North Atlantic. A growing list of publications.
Start Year 2020
 
Title fraserwg/irminger-proj: v1.1 
Description Code from the submitted version of the manuscript. 
Type Of Technology Software 
Year Produced 2023 
Impact Paper 
URL https://zenodo.org/record/7145224