• Craig, P. M., D. Ferreira, and J. Methven, 2017: The contrast between Atlantic and Pacific surface water fluxes. Tellus A, 69, 1330454, https://doi.org/10.1080/16000870.2017.1330454.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Durack, P. J., and S. E. Wijffels, 2010: Fifty-year trends in global ocean salinities and their relationship to broad-scale warming. J. Climate, 23, 43424362, https://doi.org/10.1175/2010JCLI3377.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ferrari, R., and D. Ferreira, 2011: What processes drive the ocean heat transport? Ocean Modell., 38, 171186, https://doi.org/10.1016/j.ocemod.2011.02.013.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ferreira, D., and J. Marshall, 2015: Freshwater transport in the coupled ocean-atmosphere system: A passive ocean. Ocean Dyn., 65, 10291036, https://doi.org/10.1007/s10236-015-0846-6.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ferreira, D., J. Marshall, and J.-M. Campin, 2010: Localization of deep water formation: Role of atmospheric moisture transport and geometrical constraints on ocean circulation. J. Climate, 23, 14561476, https://doi.org/10.1175/2009JCLI3197.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ferreira, D., and et al. , 2018: Atlantic-Pacific asymmetry in deep water formation. Annu. Rev. Earth Planet. Sci., 46, 327352, https://doi.org/10.1146/annurev-earth-082517-010045.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Fox-Kemper, B., R. Ferrari, and R. Hallberg, 2008: Parameterization of mixed layer eddies. Part I: Theory and diagnosis. J. Phys. Oceanogr., 38, 11451165, https://doi.org/10.1175/2007JPO3792.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Gent, P. R., and J. C. McWilliams, 1990: Isopycnal mixing in ocean circulation models. J. Phys. Oceanogr., 20, 150155, https://doi.org/10.1175/1520-0485(1990)020<0150:IMIOCM>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Griffies, S. M., 1998: The Gent–McWilliams skew flux. J. Phys. Oceanogr., 28, 831841, https://doi.org/10.1175/1520-0485(1998)028<0831:TGMSF>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Griffies, S. M., 2004: Fundamentals of Ocean Climate Models. Princeton University Press, 518 pp.

    • Crossref
    • Export Citation
  • Griffies, S. M., 2012: Elements of the Modular Ocean Model (MOM). GFDL Ocean Group Tech. Rep. 7, 645 pp., https://mom-ocean.github.io/assets/pdfs/MOM5_manual.pdf.

  • Grist, J. P., S. A. Josey, J. D. Zika, D. G. Evans, and N. Skliris, 2016: Assessing recent air-sea freshwater flux changes using a surface temperature-salinity space framework. J. Geophys. Res. Oceans, 121, 87878806, https://doi.org/10.1002/2016JC012091.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Groeskamp, S., S. M. Griffies, D. Iudicone, R. Marsh, A. G. Nurser, and J. D. Zika, 2019: The water mass transformation framework for ocean physics and biogeochemistry. Annu. Rev. Mar. Sci., 11, 271305, https://doi.org/10.1146/annurev-marine-010318-095421.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Helm, K. P., N. L. Bindoff, and J. A. Church, 2010: Changes in the global hydrological-cycle inferred from ocean salinity. Geophys. Res. Lett., 37, L18701, https://doi.org/10.1029/2010GL044222.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hieronymus, M., J. Nilsson, and J. Nycander, 2014: Water mass transformation in salinity–temperature space. J. Phys. Oceanogr., 44, 25472568, https://doi.org/10.1175/JPO-D-13-0257.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Holmes, R. M., J. D. Zika, and M. H. England, 2019a: Diathermal heat transport in a global ocean model. J. Phys. Oceanogr., 49, 141161, https://doi.org/10.1175/JPO-D-18-0098.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Holmes, R. M., J. D. Zika, R. Ferrari, A. F. Thompson, E. R. Newsom, and M. H. England, 2019b: Atlantic Ocean heat transport enabled by Indo-Pacific heat uptake and mixing. Geophys. Res. Lett., 46, 13 93913 949, https://doi.org/10.1029/2019GL085160.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Jochum, M., 2009: Impact of latitudinal variations in vertical diffusivity on climate simulations. J. Geophys. Res., 114, C01010, https://doi.org/10.1029/2008JC005030.

    • Search Google Scholar
    • Export Citation
  • Kiss, A. E., and et al. , 2020: ACCESS-OM2 v1. 0: A global ocean-sea ice model at three resolutions. Geosci. Model Dev., 13, 401442, https://doi.org/10.5194/gmd-13-401-2020.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Large, W. G., J. C. McWilliams, and S. C. Doney, 1994: Oceanic vertical mixing: A review and a model with a nonlocal boundary layer parameterization. Rev. Geophys., 32, 363403, https://doi.org/10.1029/94RG01872.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Liu, X., A. Köhl, and D. Stammer, 2017: Dynamical ocean response to projected changes of the global water cycle. J. Geophys. Res. Oceans, 122, 65126532, https://doi.org/10.1002/2017JC013061.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Redi, M. H., 1982: Oceanic isopycnal mixing by coordinate rotation. J. Phys. Oceanogr., 12, 11541158, https://doi.org/10.1175/1520-0485(1982)012<1154:OIMBCR>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schauer, U., and M. Losch, 2019: “Freshwater” in the ocean is not a useful parameter in climate research. J. Phys. Oceanogr., 49, 23092321, https://doi.org/10.1175/JPO-D-19-0102.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Schmitt, R. W., 2008: Salinity and the global water cycle. Oceanography, 21, 1219, https://doi.org/10.5670/oceanog.2008.63.

  • Sijp, W. P., M. H. England, and J. M. Gregory, 2012: Precise calculations of the existence of multiple AMOC equilibria in coupled climate models. Part I: Equilibrium states. J. Climate, 25, 282298, https://doi.org/10.1175/2011JCLI4245.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Simmons, H. L., S. R. Jayne, L. C. S. Laurent, and A. J. Weaver, 2004: Tidally driven mixing in a numerical model of the ocean general circulation. Ocean Modell., 6, 245263, https://doi.org/10.1016/S1463-5003(03)00011-8.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Skliris, N., R. Marsh, S. A. Josey, S. A. Good, C. Liu, and R. P. Allan, 2014: Salinity changes in the world ocean since 1950 in relation to changing surface freshwater fluxes. Climate Dyn., 43, 709736, https://doi.org/10.1007/s00382-014-2131-7.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Skliris, N., J. D. Zika, G. Nurser, S. A. Josey, and R. Marsh, 2016: Global water cycle amplifying at less than the Clausius-Clapeyron rate. Sci. Rep., 6, 38752, https://doi.org/10.1038/srep38752.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Stewart, K., and et al. , 2020: JRA55-do-based repeat year forcing datasets for driving ocean–sea-ice models. Ocean Modell., 147, 101557, https://doi.org/10.1016/J.OCEMOD.2019.101557.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Talley, L. D., 2008: Freshwater transport estimates and the global overturning circulation: Shallow, deep and throughflow components. Prog. Oceanogr., 78, 257303, https://doi.org/10.1016/j.pocean.2008.05.001.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Tréguier, A.-M., and et al. , 2014: Meridional transport of salt in the global ocean from an eddy-resolving model. Ocean Sci., 10, 243255, https://doi.org/10.5194/os-10-243-2014.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Tsubouchi, T., and et al. , 2012: The Arctic Ocean in summer: A quasi-synoptic inverse estimate of boundary fluxes and water mass transformation. J. Geophys. Res., 117, C01024, https://doi.org/10.1029/2011JC007174.

    • Search Google Scholar
    • Export Citation
  • Tsujino, H., and et al. , 2018: JRA-55 based surface dataset for driving ocean–sea-ice models (JRA55-do). Ocean Modell., 130, 79139, https://doi.org/10.1016/j.ocemod.2018.07.002.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Walin, G., 1977: A theoretical framework for the description of estuaries. Tellus, 29, 128136, https://doi.org/10.3402/tellusa.v29i2.11337.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wijffels, S. E., 2001: Ocean transport of fresh water. Ocean Circulation and Climate, International Geophysics, Vol. 77, Elsevier, 475–488.

    • Crossref
    • Export Citation
  • Wijffels, S. E., R. W. Schmitt, H. L. Bryden, and A. Stigebrandt, 1992: Transport of freshwater by the oceans. J. Phys. Oceanogr., 22, 155162, https://doi.org/10.1175/1520-0485(1992)022<0155:TOFBTO>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wills, R. C., and T. Schneider, 2015: Stationary eddies and the zonal asymmetry of net precipitation and ocean freshwater forcing. J. Climate, 28, 51155133, https://doi.org/10.1175/JCLI-D-14-00573.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wunsch, C., and P. Heimbach, 2013: Two decades of the Atlantic meridional overturning circulation: Anatomy, variations, extremes, prediction, and overcoming its limitations. J. Climate, 26, 71677186, https://doi.org/10.1175/JCLI-D-12-00478.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wüst, G., 1936: Surface salinity, evaporation and precipitation in the oceans. Länderkundliche Forschung, Festschrift Norbert Krebs zur Vollendung des 60. Lebensjahres dargebracht, Engelhorn, 347–359.

  • Zika, J. D., M. H. England, and W. P. Sijp, 2012: The ocean circulation in thermohaline coordinates. J. Phys. Oceanogr., 42, 708724, https://doi.org/10.1175/JPO-D-11-0139.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zika, J. D., W. P. Sijp, and M. H. England, 2013: Vertical heat transport by ocean circulation and the role of mechanical and haline forcing. J. Phys. Oceanogr., 43, 20952112, https://doi.org/10.1175/JPO-D-12-0179.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zika, J. D., N. Skliris, A. G. Nurser, S. A. Josey, L. Mudryk, F. Laliberté, and R. Marsh, 2015: Maintenance and broadening of the ocean’s salinity distribution by the water cycle. J. Climate, 28, 95509560, https://doi.org/10.1175/JCLI-D-15-0273.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Zika, J. D., N. Skliris, A. T. Blaker, R. Marsh, A. G. Nurser, and S. A. Josey, 2018: Improved estimates of water cycle change from ocean salinity: The key role of ocean warming. Environ. Res. Lett., 13, 074036, https://doi.org/10.1088/1748-9326/AACE42.

    • Crossref
    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 241 241 20
Full Text Views 53 53 4
PDF Downloads 69 69 6

Internal Salt Content: A Useful Framework for Understanding the Oceanic Branch of the Water Cycle

View More View Less
  • 1 a School of Mathematics and Statistics, University of New South Wales, Sydney, New South Wales, Australia
  • | 2 b Climate Change Research Centre, ARC Centre of Excellence for Climate Extremes, Sydney, New South Wales, Australia
© Get Permissions Rent on DeepDyve
Restricted access

Abstract

The global water cycle is dominated by an atmospheric branch that transfers freshwater away from subtropical regions and an oceanic branch that returns that freshwater from subpolar and tropical regions. Salt content is commonly used to understand the oceanic branch because surface freshwater fluxes leave an imprint on ocean salinity. However, freshwater fluxes do not actually change the amount of salt in the ocean and—in the mean—no salt is transported meridionally by ocean circulation. To study the processes that determine ocean salinity, we introduce a new variable “internal salt” along with its counterpart “internal fresh water.” Precise budgets for internal salt in salinity coordinates relate meridional and diahaline transport to surface freshwater forcing, ocean circulation, and mixing and reveal the pathway of freshwater in the ocean. We apply this framework to a 1° global ocean model. We find that for freshwater to be exported from the ocean’s tropical and subpolar regions to the subtropics, salt must be mixed across the salinity surfaces that bound those regions. In the tropics, this mixing is achieved by parameterized vertical mixing, along-isopycnal mixing, and numerical mixing associated with truncation errors in the model’s advection scheme, whereas along-isopycnal mixing dominates at high latitudes. We analyze the internal freshwater budgets of the Indo-Pacific and Atlantic Ocean basins and identify the transport pathways between them that redistribute freshwater added through precipitation, balancing asymmetries in freshwater forcing between the basins.

Significance Statement

Recent efforts to measure changing rainfall patterns have focused on sea surface salinity. This presents a number of challenges because salinity is determined by surface freshwater fluxes as well as circulation and mixing within the ocean, which depend on salinity gradients. We introduce the concepts of “internal salt” and “internal fresh water,” which measure the salt and freshwater content associated with variations in salinity within water masses in the ocean. We present precise budgets of internal salt and freshwater that we use to identify the oceanic pathways through which precipitation added in the subpolar and tropical regions is redistributed to balance evaporation in the subtropics. Future studies will investigate the response of circulation and mixing to long-term water cycle change.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Christopher Bladwell, c.bladwell@unsw.edu.au

Abstract

The global water cycle is dominated by an atmospheric branch that transfers freshwater away from subtropical regions and an oceanic branch that returns that freshwater from subpolar and tropical regions. Salt content is commonly used to understand the oceanic branch because surface freshwater fluxes leave an imprint on ocean salinity. However, freshwater fluxes do not actually change the amount of salt in the ocean and—in the mean—no salt is transported meridionally by ocean circulation. To study the processes that determine ocean salinity, we introduce a new variable “internal salt” along with its counterpart “internal fresh water.” Precise budgets for internal salt in salinity coordinates relate meridional and diahaline transport to surface freshwater forcing, ocean circulation, and mixing and reveal the pathway of freshwater in the ocean. We apply this framework to a 1° global ocean model. We find that for freshwater to be exported from the ocean’s tropical and subpolar regions to the subtropics, salt must be mixed across the salinity surfaces that bound those regions. In the tropics, this mixing is achieved by parameterized vertical mixing, along-isopycnal mixing, and numerical mixing associated with truncation errors in the model’s advection scheme, whereas along-isopycnal mixing dominates at high latitudes. We analyze the internal freshwater budgets of the Indo-Pacific and Atlantic Ocean basins and identify the transport pathways between them that redistribute freshwater added through precipitation, balancing asymmetries in freshwater forcing between the basins.

Significance Statement

Recent efforts to measure changing rainfall patterns have focused on sea surface salinity. This presents a number of challenges because salinity is determined by surface freshwater fluxes as well as circulation and mixing within the ocean, which depend on salinity gradients. We introduce the concepts of “internal salt” and “internal fresh water,” which measure the salt and freshwater content associated with variations in salinity within water masses in the ocean. We present precise budgets of internal salt and freshwater that we use to identify the oceanic pathways through which precipitation added in the subpolar and tropical regions is redistributed to balance evaporation in the subtropics. Future studies will investigate the response of circulation and mixing to long-term water cycle change.

© 2021 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Christopher Bladwell, c.bladwell@unsw.edu.au
Save