The data the researchers used to study the oceans was collected from missions like Aquarius, an early sea surface salinity measuring satellite launched in 2011. It uses instruments called radiometers to see how the ocean’s microwave radiation changes, indicating changes in salinity.
Since the launch of that mission, technology has improved to allow more high-resolution data from new missions like the European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) mission and NASA’s Soil Moisture Active Passive (SMAP) mission.
When taken together, these three missions provide data on ocean salinity on a global level stretching back for a full decade. The researchers were particularly interested in coastal waters, which are the parts of the ocean closest to land. These are not only most important to humans, given how concentrated settlements are to coastlines, but are also thought to be regions where changes to the planet’s water cycle would be seen most.
The research found that the ocean salinity in these coastal waters peaked in March and fell to its lowest in September, following a regular yearly pattern. That’s different from the rest of the ocean, open waters, where it peaks in February to April and drops in July to October. The effects were bigger in the coastal waters than on the open ocean, and the yearly variations in salinity at the coastlines were strongly correlated with the El Niño system.
“Given the sensitivity to rainfall and runoff, coastal salinity could serve as a kind of bellwether, indicating other changes unfolding in the water cycle,” Fournier said.
