Ocean salinity – the key to the global water cycle?

21 October 2015, by CEN Universität Hamburg

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Dynamics in the sea: Salinity offers an important parameter for explaining the complex processes involved in the global water cycle

Last week, about 80 oceanographers from around the globe gathered at Hamburg’s Museum für Völkerkunde to discuss the latest findings ...

Last week, about 80 oceanographers from around the globe gathered at Hamburg’s Museum für Völkerkunde to discuss the latest findings on “salinity and freshwater changes in the ocean.” The four-day conference was organized by DFG Research Group 1740 “Atlantic Freshwater Cycle,” which is coordinated by Prof. Detlef Stammer at Universität Hamburg’s Center for Earth System Research and Sustainability (CEN).

The salinity of our oceans can offer valuable insights into trends in the global water cycle. The measurement data presented at the conference examined different aspects, e.g. precipitation and evaporation in the oceans, or melting ice in polar and subpolar regions. But the level of salt in the oceans isn’t simply an indicator; it is also an important climate motor: even small changes in salinity can accelerate or slow global currents, with palpable consequences for the climate.

Determining salinity may sound easy, but measuring it precisely and comprehensively poses considerable technical and practical challenges for researchers. For many years, the only equipment at their disposal consisted of probes, ships, and remote-controlled measuring devices (gliders). Eventually, satellite measuring systems were also introduced.

“Satellites offer a unique opportunity to better monitor processes, both spatially and chronologically,” says Julia Köhler, a doctoral candidate at Hamburg’s Institute of Oceanography and a member of the CEN. To date, important data was primarily provided by the NASA/Argentinian satellite Aquarius/SAC-D, which stopped taking measurements this June, and by the ESA satellite SMOS. SMOS can comprehensively measure salinity across the entire planet in just three days, explains the young researcher. Köhler compared the data from Aquarius and SMOS with the results of conventional methods, and presented her findings at the conference. Satellite systems still have difficulties measuring in the higher latitudes, as the low temperatures distort the data. Her conclusion: “Generally speaking, there is still room for improvement when it comes to the quality of satellite data.”

Further sessions at the conference focused on the modeling and comparability of data, as well as the role of salt in dynamic processes, e.g. in the Arctic Ocean, at the mouth of the Amazon, and in the Indian Ocean. In the conference’s opening address, the oceanographer Ray Schmitt from Massachusetts claimed that the salinity of the oceans holds the key to a better understanding of the global water cycle – and promptly furnished an example of why global programs for measuring ocean salinity should be continued and intensified: in some cases, salinity can be used to provide more accurate forecasts of precipitation on land than conventional temperature-based approaches. This advantage is of great importance, he argued, as the availability of water is already one of the greatest social problems our planet faces.

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