Global ocean across shelf currents at the shelf break

Product information Product name Global ocean across shelf currents at the shelf break Product version v2-0 Coverage January 1993 – December 2016 Covers different shelf break definitions from 300 to 800 m depth Resolution Monthly 0.25° x 0.25° Contact Daniel J. [e-mail] Jamie D. [e-mail] Product description Ocean surface wind, currents and waves and their interactions play a major role in governing the exchange of heat, energy and carbon between the atmosphere and the ocean, and their onward transport. These global ocean currents are a combination of geostrophic currents (CG) due to dynamic pressure gradients and the Coriolis effect (resulting in mesoscale and submesoscale dynamics), Ekman currents (CE) due to wind stress on the surface water, and other ageostrophic components including tides, and the radial motion of surface waves and swell systems (called Stokes drift). These currents span across multiple depths within the mixed layer and together characterize the net transport of water across the shelf break and into, or out of, shelf seas at the surface. Using a globally resolved observation-based ocean current re-analysis data set that includes geostrophic, and wind driven Ekman currents at two depths (Rio et al., 2014, 2016) and a wave model re-analysis of Stokes drift data (Rascle & Ardhuin, 2013) allows characterisation of the across shelf flows of each component. As described in Shutler et al. (2025), these datasets are used with a on-to shelf vector at the shelf break to assess the magnitude of the on-to shelf (and along shelf) currents at each shelf break location. We refer the user to Shutler et al. for an extensive description of the processing steps. The data used within Shutler et al. (2025) was the 500m version (i.e where the shelf break is defined at the 500m contour) is used but supplementary versions are provided at 300 to 800m (at 100m intervals). The temporal period used in Shutler et al. (2025) was 1995 to 2015 to align to the ocean carbon observations, however the underlying data were generated between 1993 and 2016 and then subset. Version 2 (v2-0) introduced an uncertainty analysis that propagated the underlying current uncertainties following the Guide to the Expression of Uncertainty in Measurement (GUM) framework (BIPM, 2008). The uncertainties arose from the Globcurrent datasets (CMEMS, 2023) representing a Type A uncertainty, along with a fixed uncertainty (20 %) for the Stokes drift representing a Type B uncertainty. These were propagated through the on-shelf current analysis with a 1000 ensemble Monte Carlo approach that perturbed the u and v current components independently. The on-to shelf vector was assumed to have no uncertainty. Variables All variables are provided in a single netCDF file, that has been zipped to reduce file sizes with a filename: Shutler_et_al_XXXm_total_current_data_CMEMS_1993_2016_vY-Y.nc. XXX refers to the depth definition of the shallow contour for assigning the on-to shelf vector, and Y-Y indicates the version number. All files are provided within a single zip (Shutler_et_al_global_across_shelf_currents_vY-Y.zip) containing 6 netCDF files reflecting the different shelf break definition. Variable Units Description ekman_current m s-1 Ekman surface across-shelf break current ekman_current_along m s-1 Ekman surface along-shelf break current geostrophic_current m s-1 Geostrophic surface across-shelf break current geostrophic_current_along m s-1 Geostrophic surface along-shelf break current stokes_current m s-1 Stokes surface across-shelf break current stokes_current_along m s-1 Stokes surface along-shelf break current total_current m s-1 Total surface across-shelf break current total_current_along m s-1 Total surface along-shelf break current Each variable contains an uncertainty estimate (append ‘_err’ to the netCDF variable name) that follows the BIPM (2008) principles. These are expressed at a 2 sigma confidence level (or 95% confidence). How to cite these data Please cite the DOI of this dataset (with the version), the manuscript that describes the analysis to retrieve the across shelf currents (Shutler et al., 2025) and the underlying Globcurrent record (CMEMS, 2023). Known Issues v2-0 (15-09-2025): We are aware of an issue with the along-shelf currents where the currents ‘randomly’ flip between positive and negative moving along the shelf break. This is due to the definition of along-shelf not being “defined” within the analysis. We are working to fix this. Therefore along-shelf currents should be interpreted as a magnitude and not “direction” currently. This does not affect the generation of the across shelf currents. Acknowledgements and Funding The authors acknowledge funding through the European Space Agency (ESA) Sea surface KInematics Multiscale monitoring (SKIM) Mission Science study (contract 4000124734/18/NL/CT/gp), the ESA SKIM Scientific Performance Evaluation study (contract 4000124521/18/NL/CT/gp), and from the Convex Seascape Survey (https://convexseascapesurvey.com/). Changelog Version Changes since previous version v2-0 Updated to include propagated uncertainty estimates on the across and along shelf currents. This uncertainty is solely due to the uncertainty in the ocean surface currents and assumes the on-to shelf vector has no uncertainty. Prior versions Initial versions of the dataset with the submission of Shutler et al. (2025) Updated to use CMEMS Globcurrent analysis instead of legacy GlobCurrent versions (previously used in initial analysis) Updated to output the along shelf current as well as the across shelf currents References BIPM. (2008). Evaluation of measurement data—Guide to the expression of uncertainty in measurement. CMEMS. (2023). Global Total (COPERNICUS-GLOBCURRENT), Ekman and Geostrophic currents at the Surface and 15m [Data set]. Mercator Ocean International. https://doi.org/10.48670/MDS-00327 Rascle, N., & Ardhuin, F. (2013). A global wave parameter database for geophysical applications. Part 2: Model validation with improved source term parameterization. Ocean Modelling, 70, 174–188. https://doi.org/10.1016/j.ocemod.2012.12.001 Rio, M.-H., Mulet, S., & Picot, N. (2014). Beyond GOCE for the ocean circulation estimate: Synergetic use of altimetry, gravimetry, and in situ data provides new insight into geostrophic and Ekman currents: Ocean circulation beyond GOCE. Geophysical Research Letters, 41(24), 8918–8925. https://doi.org/10.1002/2014GL061773 Rio, M.-H., Johannessen, J., & Donlon, C. (2016). Product data handbook: The combined geostropy+ekman currents (v2). Retrieved from eftp.ifremer.fr/data/globcurrent/documentation/older_version Shutler, J. D., Ford, D. J., Holding, T., Ubelmann, C., Gaultier, L., Collard, F., et al. (2025). Wind‐Driven Control of Shelf‐Sea CO2 Sinks. Global Biogeochemical Cycles, 39(9), e2024GB008461. https://doi.org/10.1029/2024GB008461