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  • Adjoint method  (1)
  • Atlantic Ocean  (1)
  • 1
    Publication Date: 2024-01-26
    Description: Regional freshwater content (FWC) changes are studied over the period 1961–2018 using the GECCO3 ocean synthesis. In four dynamically distinct regions of the Atlantic, the study identifies causes for FWC variability with a focus on interannual and decadal time‐scale changes. Results show that in each region, it is a combination of the surface freshwater flux and the net freshwater transport across the region's boundaries that act jointly in changing the respective FWC. Surface flux mainly contributes to the FWC variability on multi‐decadal time scales. The impact of surface flux also increases toward the tropics. On shorter time scales, it is especially horizontal transport fluctuations, leading to FWC changes in mid and high latitudes. Going from north to the south, the transport across a single meridional boundary becomes less correlated with the FWC changes but the net transport across both boundaries plays an increasingly important role. Moreover, the subpolar box is mainly gyre driven, which differs from the other two, essentially overturning driven, North Atlantic boxes. In the tropical Atlantic, the shallow overturning cell and the deep overturning contribute about equal amounts to the freshwater variations.
    Description: Plain Language Summary: Causes for freshwater content (FWC) variability in the Atlantic Ocean are analyzed for four study areas over the period 1961–2018 based on a model simulation (GECCO3 ocean synthesis). Targeting relatively long time scales, interannual, decadal to multi‐decadal FWC changes are separated into the contributions from variations of the freshwater input/output through the ocean surface and from freshwater transport (FWT) variations related to the ocean circulation changes. Surface freshwater flux is more influential on multi‐decadal time scales, and its impact increases toward the tropics. On shorter time scales, the oceanic FWT across the boundaries of the region dominates the FWC changes in mid and high latitudes. The transport variability in the subpolar region is mainly driven by the horizontal circulation, while transports resulting from vertical salinity differences are more important at lower latitudes. Moreover, in the tropics transports related to shallow salinity differences are not negligible on interannual time scales.
    Description: Key Points: The net freshwater transport across the meridional boundaries dominates the freshwater content variations in mid and high latitudes. The importance of surface freshwater flux variations increases toward the tropics and on multi‐decadal time scales. Subpolar changes are mainly gyre driven, while overturning and especially the shallow overturning cells contribute more at lower latitudes.
    Description: Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659
    Description: https://icdc.cen.uni-hamburg.de/en/gecco3.html
    Description: http://www.metoffice.gov.uk/hadobs/en4/download-en4-2-2.html
    Description: https://www.cen.uni-hamburg.de/en/icdc/data/atmosphere/hoaps.html
    Keywords: ddc:551.46 ; Atlantic Ocean ; freshwater content (FWC) ; regional changes ; GECCO3
    Language: English
    Type: doc-type:article
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  • 2
    Publication Date: 2022-10-26
    Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Heimbach, P., Fukumori, I., Hills, C. N., Ponte, R. M., Stammer, D., Wunsch, C., Campin, J., Cornuelle, B., Fenty, I., Forget, G., Koehl, A., Mazloff, M., Menemenlis, D., Nguyen, A. T., Piecuch, C., Trossman, D., Verdy, A., Wang, O., & Zhang, H. Putting it all together: Adding value to the global ocean and climate observing systems with complete self-consistent ocean state and parameter estimates. Frontiers in Marine Science, 6 (2019):55, doi:10.3389/fmars.2019.00055.
    Description: In 1999, the consortium on Estimating the Circulation and Climate of the Ocean (ECCO) set out to synthesize the hydrographic data collected by the World Ocean Circulation Experiment (WOCE) and the satellite sea surface height measurements into a complete and coherent description of the ocean, afforded by an ocean general circulation model. Twenty years later, the versatility of ECCO's estimation framework enables the production of global and regional ocean and sea-ice state estimates, that incorporate not only the initial suite of data and its successors, but nearly all data streams available today. New observations include measurements from Argo floats, marine mammal-based hydrography, satellite retrievals of ocean bottom pressure and sea surface salinity, as well as ice-tethered profiled data in polar regions. The framework also produces improved estimates of uncertain inputs, including initial conditions, surface atmospheric state variables, and mixing parameters. The freely available state estimates and related efforts are property-conserving, allowing closed budget calculations that are a requisite to detect, quantify, and understand the evolution of climate-relevant signals, as mandated by the Coupled Model Intercomparison Project Phase 6 (CMIP6) protocol. The solutions can be reproduced by users through provision of the underlying modeling and assimilation machinery. Regional efforts have spun off that offer increased spatial resolution to better resolve relevant processes. Emerging foci of ECCO are on a global sea level changes, in particular contributions from polar ice sheets, and the increased use of biogeochemical and ecosystem data to constrain global cycles of carbon, nitrogen and oxygen. Challenges in the coming decade include provision of uncertainties, informing observing system design, globally increased resolution, and moving toward a coupled Earth system estimation with consistent momentum, heat and freshwater fluxes between the ocean, atmosphere, cryosphere and land.
    Description: Major support for ECCO is provided by NASA's Physical Oceanography program via a contract to JPL/Caltech, with additional support through NASA's Modeling, Analysis and Prediction program, the Cryosphere Science program, and the Computational Modeling and Cyberinfrastructure program. Supplemental funding was obtained throughout the years via standard grants to individual team members from NSF, NOAA, and ONR.
    Keywords: ECCO ; Global ocean inverse modeling ; Optimal state and parameter estimation ; Adjoint method ; Ocean observations ; Coupled Earth system data assimilation ; Ocean reanalysis ; Global ocean circulation
    Repository Name: Woods Hole Open Access Server
    Type: Article
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