Data from three satellite missions has been merged to produce a global time-series showing sea-surface salinity measurements between 2010 and 2018 (related: Mapping the Salinity of the Ocean). A product of the European Space Agency’s Climate Change Initiative (CCI), these datasets mark the most complete global coverage of sea-surface salinity.
Monitoring trends in sea-surface salinity has important applications. Extreme climatic events such as El Niño can be indicated by changes in salinity levels. Sea salinity levels are also used to study the water cycle, ocean–atmosphere exchanges, and ocean circulation. All of these processes are part of the Earth’s climate system, transporting heat, nutrients, and carbon around the globe.
CCI is a research initiative that aims to develop accurate and longterm datasets for each of the 21 Essential Climate Variables, as mandated by the United Nations Framework Convention on Climate Change and the Intergovernmental Panel on Climate Change. Researchers from the team have generated weekly and monthly views of sea-surface salinity during the nine-year time period at a spatial resolution of 50 km. Using microwave sensors onboard the SMOS, Aquarius, and Soil Moisture Active Passive satellite missions, sea salinity was calculated based on observations of brightness temperature.
Since the 1950s, sea salinity measurements have been taken in situ onboard ships, leading to a coarse dataset. At the beginning of the 21st century, ocean floats called Argo were launched, taking measurements every 300 km every ten days. One of the CCI team leads, Jacqueline Boutin of LOCEAN notes, “By combining and comparing measurements between the different sensors, the team has been able to improve the precision of maps of sea-surface salinity by roughly 30%. Monitoring salinity from space helps to resolve spatial and temporal scales that are poorly sampled by in situ platforms that make direct observations, and fills gaps in the observing system.”
The dataset is freely available for download from the CCI Open Data Portal.