Fifty-Year Trends in Global Ocean Salinities and Their Relationship to Broad-Scale Warming

Abstract

Using over 1.6 million profiles of salinity, potential temperature, and neutral density from historical archives and the international Argo Program, this study develops the three-dimensional field of multidecadal linear change for ocean-state properties. The period of analysis extends from 1950 to 2008, taking care to minimize the aliasing associated with the seasonal and major global El Niñ o-Southern Oscillation modes. Large, robust, and spatially coherent multidecadal linear trends in salinity to 2000-dbar depth are found. Salinity increases at the sea surface are found in evaporation-dominated regions and freshening in precipitationdominated regions, with the spatial pattern of change strongly resembling that of the mean salinity field, consistent with an amplification of the global hydrological cycle. Subsurface salinity changes on pressure surfaces are attributable to both isopycnal heave and real water-mass modification of the temperaturesalinity relationship. Subduction and circulation by the ocean's mean flow of surface salinity and temperature anomalies appear to account for most regional subsurface salinity changes on isopycnals. Broad-scale surface warming and the associated poleward migration of isopycnal outcrops drive a clear and repeating pattern of subsurface isopycnal salinity change in each independent ocean basin. Qualitatively, the observed global multidecadal salinity changes are thus consonant with both broad-scale surface warming and the amplification of the global hydrological cycle.

Formation and variability of the South Pacific Sea Surface Salinity maximum in recent decades

“…The ratio between the three processes is consistent with what was found by Qu et al [2011] in the North Atlantic Salinity Maximum. The modeled salinity maximum waters have their 20 year average salinity increasing by 0.02 pss/yr which is qualitatively consistent with the ''dry get dryer'' paradigm although stronger than the estimated from different observation data sets and time periods by Terray et al [2012] and Durack and Wijffels [2010]. The observations and the models both show high-salinity waters variability at the seasonal and longer time scales.…”

“…These, in turn, are thought to influence the mean background temperature distribution in the equatorial band and hence could modulate low-frequency tropical variability [Schneider et al, 1999;McPhaden and Zhang, 2004;Laurian et al, 2009]. At the multidecadal time scale, the observations of positive salinity trends in these cores have been interpreted as the likely signature of global change [Cravatte et al, 2009;Durack and Wijffels, 2010;Terray et al, 2012]. To the first order, these trends result from the EÀP forcing increase in positive EÀP regions as expected by the Clausius Clapeyron relationship in a warming world [Held and Soden, 2006;Seager et al, 2010].…”

Multidecadal-scale adjustment of the ocean mixed layer heat budget in the tropics: examining ocean reanalyses

“…1), and fresh water flux values from atmospheric reanalyses. We neglect fresh water fluxes here because of their uncertainty in reanalyses and because halosteric trends in density are smaller than thermosteric trends (Durack and Wijffels 2010;Levitus et al 2012) and examine the momentum and heat fluxes that are applied to the ocean reanalyses. , and e density with a variable threshold criterion equivalent to a 0.2 °C decrease (DReqDTm02).…”

Baseline biogeochemical data from Australia's continental margin links seabed sediments to water column characteristics

“…The Indonesian Throughflow (ITF), which flows through the Indonesian Seas towards northern Australia, allows for the interoceanic exchange between the Pacific and Indian oceans (Wijffels et al 2002). This is a region of intense summer rainfall, significant terrestrial run-off and some of the lightest (warm and fresh ¼ low density) seawater on the planet (Durack and Wijffels 2010). Two tropical water sources, one from the equatorial Indian Ocean, via the South Java Current, and the other from the equatorial Pacific Ocean, via the ITF, join the westward flow of the South Equatorial Current in the top 100 m of the Indo-Australian Basin (Domingues et al 2007).…”