• Balaguru, K., , P. Chang, , R. Saravanan, , L. R. Leung, , Z. Xu, , M. K. Li, , and J.-S. Hsieh, 2012: Ocean barrier layers’ effect on tropical cyclone intensification. Proc. Natl. Acad. Sci. USA, 109, 14 34314 347, doi:10.1073/pnas.1201364109.

    • Search Google Scholar
    • Export Citation
  • Bingham, F. M., , G. R. Foltz, , and M. J. McPhaden, 2012: Characteristics of the seasonal cycle of surface layer salinity in the global ocean. Ocean Sci., 8, 915929, doi:10.5194/os-8-915-2012.

    • Search Google Scholar
    • Export Citation
  • Bourlès, B., and et al. , 2008: The PIRATA program: History, accomplishments, and future directions. Bull. Amer. Meteor. Soc., 89, 11111125, doi:10.1175/2008BAMS2462.1.

    • Search Google Scholar
    • Export Citation
  • Coles, V. J., , M. T. Brooks, , J. Hopkins, , M. R. Stukel, , P. L. Yager, , and R. R. Hood, 2013: The pathways and properties of the Amazon River plume in the tropical North Atlantic Ocean. J. Geophys. Res., 118, 68946913, doi:10.1002/2013JC008981.

    • Search Google Scholar
    • Export Citation
  • Cravatte, S., , T. Delcroix, , D. X. Zhang, , M. J. McPhaden, , and J. Leloup, 2009: Observed freshening and warming of the western Pacific warm pool. Climate Dyn., 33, 565589, doi:10.1007/s00382-009-0526-7.

    • Search Google Scholar
    • Export Citation
  • Curry, R., , B. Dickson, , and I. Yashayaev, 2003: A change in the freshwater balance of the Atlantic Ocean over the past four decades. Nature, 426, 826829, doi:10.1038/nature02206.

    • Search Google Scholar
    • Export Citation
  • Da-Allada, C. Y., , G. Alory, , Y. du Penhoat, , E. Kestenare, , F. Durand, , and N. M. Hounkonnou, 2013: Seasonal mixed-layer salinity balance in the tropical Atlantic Ocean: Mean state and seasonal cycle. J. Geophys. Res., 118, 332345, doi:10.1029/2012JC008357.

    • Search Google Scholar
    • Export Citation
  • Dessier, A., , and J. R. Donguy, 1994: The sea surface salinity in the tropical Atlantic between 10°S and 30°N—Seasonal and interannual variations (1977–1989). Deep-Sea Res., 41, 81100, doi:10.1016/0967-0637(94)90027-2.

    • Search Google Scholar
    • Export Citation
  • Durack, P. J., , S. E. Wijffels, , and R. J. Matear, 2012: Ocean salinities reveal strong global water cycle intensification during 1950 to 2000. Science, 336, 455458, doi:10.1126/science.1212222.

    • Search Google Scholar
    • Export Citation
  • Fairall, C. W., , E. F. Bradley, , J. E. Hare, , A. A. Grachev, , and J. B. Edson, 2003: Bulk parameterization of air–sea fluxes: Updates and verification for the COARE algorithm. J. Climate, 16, 571591, doi:10.1175/1520-0442(2003)016<0571:BPOASF>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Ferry, N., , and G. Reverdin, 2004: Sea surface salinity interannual variability in the western tropical Atlantic: An ocean general circulation model study. J. Geophys. Res., 109, C05026, doi:10.1029/2003JC002122.

    • Search Google Scholar
    • Export Citation
  • Ffield, A., 2007: Amazon and Orinoco River plumes and NBC rings: Bystanders or participants in hurricane events? J. Climate, 20, 316333, doi:10.1175/JCLI3985.1.

    • Search Google Scholar
    • Export Citation
  • Foltz, G. R., , and M. J. McPhaden, 2008: Seasonal mixed layer salinity balance of the tropical North Atlantic Ocean. J. Geophys. Res., 113, C02013, doi:10.1029/2007JC004178.

    • Search Google Scholar
    • Export Citation
  • Foltz, G. R., , and M. J. McPhaden, 2009: Impact of barrier layer thickness on SST in the central tropical North Atlantic. J. Climate, 22, 285299, doi:10.1175/2008JCLI2308.1.

    • Search Google Scholar
    • Export Citation
  • Foltz, G. R., , S. A. Grodsky, , J. A. Carton, , and M. J. McPhaden, 2004: Seasonal salt budget of the northwestern tropical Atlantic Ocean along 38°W. J. Geophys. Res., 109, C03052, doi:10.1029/2003JC002111.

    • Search Google Scholar
    • Export Citation
  • Foltz, G. R., , C. Schmid, , and R. Lumpkin, 2013: Seasonal cycle of the mixed layer heat budget in the northeastern tropical Atlantic Ocean. J. Climate, 26, 81698188, doi:10.1175/JCLI-D-13-00037.1.

    • Search Google Scholar
    • Export Citation
  • Grodsky, S. A., , J. A. Carton, , and F. O. Bryan, 2014a: A curious local surface salinity maximum in the northwestern tropical Atlantic. J. Geophys. Res., 119, 484495, doi:10.1002/2013JC009450.

    • Search Google Scholar
    • Export Citation
  • Grodsky, S. A., , G. Reverdin, , J. A. Carton, , and V. J. Coles, 2014b: Year-to-year salinity changes in the Amazon plume: Contrasting 2011 and 2012 Aquarius/SACD and SMOS satellite data. Remote Sens. Environ., 140, 1422, doi:10.1016/j.rse.2013.08.033.

    • Search Google Scholar
    • Export Citation
  • Held, I. M., , and B. J. Soden, 2006: Robust responses of the hydrological cycle to global warming. J. Climate, 19, 56865699, doi:10.1175/JCLI3990.1.

    • Search Google Scholar
    • Export Citation
  • Hu, C., , E. T. Montgomery, , R. W. Schmitt, , and F. E. Muller-Karger, 2004: The dispersal of the Amazon and Orinoco River water in the tropical Atlantic and Caribbean Sea: Observation from space and S-PALACE floats. Deep-Sea Res., 51, 11511171, doi:10.1016/j.dsr2.2004.04.001.

    • Search Google Scholar
    • Export Citation
  • Johns, W. E., , T. N. Lee, , F. A. Schott, , R. J. Zantopp, , and R. H. Evans, 1990: The North Brazil Current retroflection: Seasonal structure and eddy variability. J. Geophys. Res., 95, 22 10322 120, doi:10.1029/JC095iC12p22103.

    • Search Google Scholar
    • Export Citation
  • Johnson, E. S., , G. S. E. Lagerloef, , J. T. Gunn, , and F. Bonjean, 2002: Surface salinity advection in the tropical oceans compared with atmospheric freshwater forcing: A trial balance. J. Geophys. Res., 107, 8014, doi:10.1029/2001JC001122.

    • Search Google Scholar
    • Export Citation
  • Kraus, E. B., , and J. S. Turner, 1967: A one-dimensional model of the seasonal thermocline. Tellus, 19, 98105, doi:10.1111/j.2153-3490.1967.tb01462.x.

    • Search Google Scholar
    • Export Citation
  • Lee, T., , G. Lagerloef, , M. M. Gierach, , H.-Y. Kao, , S. Yueh, , and K. Dohan, 2012: Aquarius reveals salinity structure of tropical instability waves. Geophys. Res. Lett., 39, L12610, doi:10.1029/2012GL052232.

    • Search Google Scholar
    • Export Citation
  • Lumpkin, R., , and S. L. Garzoli, 2005: Near-surface circulation in the tropical Atlantic Ocean. Deep-Sea Res. I, 52, 495518, doi:10.1016/j.dsr.2004.09.001.

    • Search Google Scholar
    • Export Citation
  • Lumpkin, R., , and S. L. Garzoli, 2011: Interannual to decadal variability in the southwestern Atlantic’s surface circulation. J. Geophys. Res., 116, C01014, doi:10.1029/2010JC006285.

    • Search Google Scholar
    • Export Citation
  • Lumpkin, R., , and G. C. Johnson, 2013: Global ocean surface velocities from drifters: Mean, variance, El Niño–Southern Oscillation response, and seasonal cycle. J. Geophys. Res. Oceans, 118, 29923006, doi:10.1002/jgrc.20210.

    • Search Google Scholar
    • Export Citation
  • Maes, C., , J. Picaut, , and S. Belamari, 2002: Salinity barrier layer and onset of El Niño in a Pacific coupled model. Geophys. Res. Lett., 29, 2206, doi:10.1029/2002GL016029.

    • Search Google Scholar
    • Export Citation
  • McPhaden, M. J., , and G. R. Foltz, 2013: Intraseasonal variations in the surface layer heat balance of the central equatorial Indian Ocean: The importance of zonal advection and vertical mixing. Geophys. Res. Lett., 40, 2737–2741, doi:10.1002/grl.50536.

    • Search Google Scholar
    • Export Citation
  • Mignot, J., , C. de Boyer Montégut, , A. Lazar, , and S. Cravatte, 2007: Control of salinity on the mixed layer depth in the world ocean: 2. Tropical areas. J. Geophys. Res., 112, C10010, doi:10.1029/2006JC003954.

    • Search Google Scholar
    • Export Citation
  • Mignot, J., , A. Lazar, , and M. Lacarra, 2012: On the formation of barrier layers and associated vertical temperature inversions: A focus on the northwestern tropical Atlantic. J. Geophys. Res., 117, C02010, doi:10.1029/2011JC00743.

    • Search Google Scholar
    • Export Citation
  • Muller-Karger, F. E., , C. R. McClain, , and P. L. Richardson, 1988: The dispersal of the Amazon’s water. Nature, 333, 5658, doi:10.1038/333056a0.

    • Search Google Scholar
    • Export Citation
  • Niiler, P. P., , and E. B. Kraus, 1977: One-dimensional models of the upper ocean. Modelling and Prediction of the Upper Layers of the Ocean, E. B. Kraus, Ed., Pergamon, 143–172.

  • Pailler, K., , B. Bourles, , and Y. Gouriou, 1999: The barrier layer in the western tropical Atlantic Ocean. Geophys. Res. Lett., 26, 20692072, doi:10.1029/1999GL900492.

    • Search Google Scholar
    • Export Citation
  • Park, S., , C. Deser, , and M. A. Alexander, 2005: Estimation of the surface heat flux response to sea surface temperature anomalies over the global oceans. J. Climate, 18, 45824599, doi:10.1175/JCLI3521.1.

    • Search Google Scholar
    • Export Citation
  • Qu, T. D., , S. Gao, , and I. Fukumori, 2011: What governs the North Atlantic salinity maximum in a global GCM? Geophys. Res. Lett., 38, L07602, doi:10.1029/2011GL046757.

    • Search Google Scholar
    • Export Citation
  • Reverdin, G., , E. Kestenare, , C. Frankignoul, , and T. Delcroix, 2007: Surface salinity in the Atlantic Ocean (30°S–50°N). Prog. Oceanogr., 73, 311340, doi:10.1016/j.pocean.2006.11.004.

    • Search Google Scholar
    • Export Citation
  • Sato, K., , T. Suga, , and K. Hanawa, 2006: Barrier layers in the subtropical gyres of the world’s oceans. Geophys. Res. Lett., 33, L08603, doi:10.1029/2005GL025631.

    • Search Google Scholar
    • Export Citation
  • Sprintall, J., , and M. Tomczak, 1992: Evidence of the barrier layer in the surface layer of the tropics. J. Geophys. Res., 97, 73057316, doi:10.1029/92JC00407.

    • Search Google Scholar
    • Export Citation
  • Terray, L., , L. Corre, , S. Cravatte, , T. Delcroix, , G. Reverdin, , and A. Ribes, 2012: Near-surface salinity as nature’s rain gauge to detect human influence on the tropical water cycle. J. Climate, 25, 958977, doi:10.1175/JCLI-D-10-05025.1.

    • Search Google Scholar
    • Export Citation
  • Tzortzi, E., , S. A. Josey, , M. Srokosz, , and C. Gommenginger, 2013: Tropical Atlantic salinity variability: New insights from SMOS. Geophys. Res. Lett., 40, 21432147, doi:10.1002/grl.50225.

    • Search Google Scholar
    • Export Citation
  • Vellinga, M., , and P. Wu, 2004: Low-latitude freshwater influence on centennial variability of the Atlantic thermohaline circulation. J. Climate, 17, 44984511, doi:10.1175/3219.1.

    • Search Google Scholar
    • Export Citation
  • Vialard, J., , and P. Delecluse, 1998: An OGCM study for the TOGA decade. Part II: Barrier layer formation and variability. J. Phys. Oceanogr., 28, 10891106, doi:10.1175/1520-0485(1998)028<1089:AOSFTT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Wang, C. Z., , S. F. Dong, , and E. Muñoz, 2010: Seawater density variations in the North Atlantic and the Atlantic meridional overturning circulation. Climate Dyn., 34, 953968, doi:10.1007/s00382-009-0560-5.

    • Search Google Scholar
    • Export Citation
  • Wentz, F. J., , L. Ricciardulli, , K. Hilburn, , and C. Mears, 2007: How much more rain will global warming bring? Science, 317, 233235, doi:10.1126/science.1140746.

    • Search Google Scholar
    • Export Citation
  • Yu, L. S., 2011: A global relationship between the ocean water cycle and near-surface salinity. J. Geophys. Res., 116, C10025, doi:10.1029/2010JC006937.

    • Search Google Scholar
    • Export Citation
  • Yu, L. S., , and R. A. Weller, 2007: Objectively analyzed air–sea heat fluxes for the global ice-free oceans (1981–2005). Bull. Amer. Meteor. Soc., 88, 527539, doi:10.1175/BAMS-88-4-527.

    • Search Google Scholar
    • Export Citation
  • Zhou, Y. P., , K.-M. Xu, , Y. C. Sud, , and A. K. Betts, 2011: Recent trends of the tropical hydrological cycle inferred from Global Precipitation Climatology Project and International Satellite Cloud Climatology Project data. J. Geophys. Res., 116, D09101, doi:10.1029/2010JD015197.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 58 58 15
PDF Downloads 37 37 8

Transport of Surface Freshwater from the Equatorial to the Subtropical North Atlantic Ocean

View More View Less
  • 1 NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida
© Get Permissions
Restricted access

Abstract

The transport of low-salinity water northward in the tropical and subtropical North Atlantic Ocean influences upper-ocean stratification, vertical mixing, and sea surface temperature (SST). In this study, satellite and in situ observations are used to trace low-salinity water northward from its source in the equatorial Atlantic and to examine its modification through air–sea fluxes and vertical mixing. In contrast to gridded climatologies, which depict a gradual northward dispersal of surface freshwater from the equatorial Atlantic, satellite observations and direct measurements from four moorings in the central tropical North Atlantic show a distinct band of surface freshwater moving northward from the equatorial Atlantic during boreal fall through spring, with drops in sea surface salinity (SSS) of 0.5–2.5 psu in the span of one to two weeks as the low SSS front passes. The ultimate low-latitude source of the low SSS water is found to be primarily Amazon River discharge west of 40°W and rainfall to the east. As the low-salinity water moves northward between 8° and 20°N during October–April, 70% of its freshwater in the upper 20 m is lost to the combination of evaporation, horizontal eddy diffusion, and vertical turbulent mixing, with an implied rate of SSS damping that is half of that for SST. During 1998–2012, interannual variations in SSS along 38°W are found to be negatively correlated with the strength of northward surface currents. The importance of ocean circulation for interannual variations of SSS and the small damping time scale for SSS emphasize the need to consider meridional freshwater advection when interpreting SSS variability in the tropical–subtropical North Atlantic.

Corresponding author address: Gregory R. Foltz, NOAA/Atlantic Oceanographic and Meteorological Laboratory, 4301 Rickenbacker Cswy., Miami, FL 33149. E-mail: gregory.foltz@noaa.gov

Abstract

The transport of low-salinity water northward in the tropical and subtropical North Atlantic Ocean influences upper-ocean stratification, vertical mixing, and sea surface temperature (SST). In this study, satellite and in situ observations are used to trace low-salinity water northward from its source in the equatorial Atlantic and to examine its modification through air–sea fluxes and vertical mixing. In contrast to gridded climatologies, which depict a gradual northward dispersal of surface freshwater from the equatorial Atlantic, satellite observations and direct measurements from four moorings in the central tropical North Atlantic show a distinct band of surface freshwater moving northward from the equatorial Atlantic during boreal fall through spring, with drops in sea surface salinity (SSS) of 0.5–2.5 psu in the span of one to two weeks as the low SSS front passes. The ultimate low-latitude source of the low SSS water is found to be primarily Amazon River discharge west of 40°W and rainfall to the east. As the low-salinity water moves northward between 8° and 20°N during October–April, 70% of its freshwater in the upper 20 m is lost to the combination of evaporation, horizontal eddy diffusion, and vertical turbulent mixing, with an implied rate of SSS damping that is half of that for SST. During 1998–2012, interannual variations in SSS along 38°W are found to be negatively correlated with the strength of northward surface currents. The importance of ocean circulation for interannual variations of SSS and the small damping time scale for SSS emphasize the need to consider meridional freshwater advection when interpreting SSS variability in the tropical–subtropical North Atlantic.

Corresponding author address: Gregory R. Foltz, NOAA/Atlantic Oceanographic and Meteorological Laboratory, 4301 Rickenbacker Cswy., Miami, FL 33149. E-mail: gregory.foltz@noaa.gov
Save