How salty are the world’s oceans? Ocean salinity is a key variable of Earth’s water cycle and a key driver of ocean dynamics. The Global Climate Observing System and the Global Ocean Observing System have identified ocean salinity as an essential climate variable: a “must-include” variable in climate models. Recently, through the advent of new observing technologies, research based on salinity measurements has gained prominence within the scientific and operational communities.
To review recent research progress and discuss future plans, 115 scientists and representatives of operational services met at Sorbonne University in Paris for the fifth Ocean Salinity Science Conference.
Since the fourth Ocean Salinity Science Conference in 2017, groundbreaking studies have taken advantage of the improved quality and longer time series (50-kilometer resolution, 9 years) of satellite sea surface salinity (SSS) measurements. These studies have also taken advantage of SSS data’s complementarity with in situ and other satellite observations, process studies, and ocean modeling.
Participants at November’s meeting presented results on observations of the spatiotemporal variability of fresh SSS structures in the Arctic Ocean, the tropical ocean basins, the Bay of Bengal, and the Indonesian Throughflow. Climate events such as the El Niño–Southern Oscillation and Indian Ocean Dipole influence both freshwater sources (river plumes and intense precipitation) and freshwater transport in the ocean. Presenters showed how newly observed salinity variability was used to assess earlier model simulations in the Bay of Bengal and to revisit the major freshwater sources governing the water transport through the Indonesian Throughflow.
Other research presented at the meeting demonstrated the large contribution of eddies to salinity transport, evident in the tropical Pacific Ocean near 10°N and in the Gulf of Maine. Satellite and recent in situ campaigns (Salinity Processes in the Upper-Ocean Regional Study 2) allowed researchers to further quantify the wind’s influence on tropical rainfall penetration into the ocean, suggesting that rainfall, and the ocean water freshening that it causes, is distributed very unevenly within the 50-kilometer pixels in the satellite data.
Presenters illustrated the potential of satellite SSS assimilation into operational models. In one example, the simulated SSS for 2014–2015 in the northern tropical Pacific improved by as much as 10%. In another study, significant correlation of Niño 3.4 region sea surface temperature anomaly forecasts extended from 4 to 7 months. Other presenters summarized work on long-term trends in such phenomena as water mass and subduction processes, which were further elaborated by new in situ data and modeling studies and related to changes in air-sea fluxes.
Meeting discussions stressed the need for extended time series of global SSS observations and for pursuing collaborative efforts between the Soil Moisture and Ocean Salinity (SMOS), Soil Moisture Active Passive (SMAP), and Aquarius satellite science teams to advance radiative transfer models at the L band frequency range and reduce uncertainties in satellite SSS measurements. They also emphasized collaborations between satellite, in situ, and modeling teams to fully benefit from model assimilation experiments and extend these experiments into operational applications.
International collaborative efforts between satellite science teams are organized through projects such as the SMOS Pilot Mission Exploitation Platform and the SSS Climate Change Initiative from the European Space Agency and the Salinity Continuity Processing and the Ocean Salinity Science Team from NASA.
The 60 talks and 46 posters from this meeting are available at the meeting website.
—Jacqueline Boutin ([email protected]) and Gilles Reverdin, Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques, Sorbonne Université, Paris, France; and Susanne Mecklenburg, European Space Research Institute, European Space Agency, Frascati, Italy