Ships and Satellites Together Modelling World Ocean Salinity and Temperature

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After a mix of snow, headwinds, and fog we made it to Robertson Fjord. I saw my first fogbow! Over the past few days we collected our first deep trough and near glacial casts. It was thrilling. We will be at our furthest North in a few days, planning to get some great never before acquired data. You cannot get much further North than Cape Alexander as the sea becomes ices floes threatening to lock you in.

Enjoy the guest blog below from NASA scientists that we are providing surface salinity data to. We ran a special instrument from Chesapeake Bay (latitude 38° N) and now up towards Dodge Glacier (78° N). This data will serve as a comparison to what the NASA satellite, Aquarius and other international satellites are measuring from space. The device working 24/7 on our vessel is RBR ltd.’s  thermosalinograph (TSG) and is in a test and evaluation phase. It is similar to the conductivity-temperature depth profiler (or CTD) that we drop to the seafloor for vertical profiles.

The TSG was installed so that a through-hull port below the waterline and a pump supply sea water constantly via hose into small water tank where an internal CTD like device analyzes the sample before it is pumped overboard. Specifically, as with a CTD, the water properties measured by a TSG are the temperature (T) and electrical conductivity (C). Conductivity is measured as a proxy for the water salinity which is a function of the amount (i.e. mass and chemical composition) of dissolved salts. Using the measured values of temperature and salinity (and pressure when the unit measures at depth), a mathematic formula is used to calculate the salinity. The TSG is installed under our guest scientist’s berth (bunk), a cozy nook in the main saloon.

Why do we study the water around Greenland?

Guest Blog: NASA Scientists Ludovic Brucker, Guillaume Vernieres, and Emmanuel Dinatt

Waters around Greenland and in the Arctic are very dynamic and play a great role in ocean circulation around the entire planet. The circulation of the oceans controlled by ocean salinity and temperature, is named thermocline circulation.

Variations in ocean salinity and temperature can result from complicated physical processes. To understand them, we need in-situ measurements (giving us reference data, they are often associated with ship cruises like the Greenland Climate Project), satellite observations to study a larger area, frequently) and models, (to test out understanding and to create forecasts).

In spite of the importance of polar waters for ocean and environmental sciences, they suffer from a lack of in situ salinity measurements. The polar regions are not easily accessible and offer challenging environments (with icebergs for example).

Therefore, these regions are under sampled compared to other regions on the planet, making it challenging to study the physical processes taking place at high latitudes.

Around Greenland, especially in the Baffin Bay, the Greenland ice sheet melts and releases freshwater into the ocean. This water changes the salinity and temperature of the oceans and seas, and in turn influences the ocean circulation of the planet.

For the last 5 years, satellite data allows us to study salinity almost everywhere and continuously. These satellite observations of salinity are reliable over the tropical and mid-latitude warm oceans, but satellite salinity observations in the polar oceans are challenging. To mention only two examples of the challenges: (1) polar ocean water are cold and satellite measurements are less sensitive to salinity in polar waters; (2) the presence of sea ice and ice bergs adds complexity to the retrieval of accurate salinity.

 

Very low salinities are observed at high latitudes, but some of the freshest waters are found in narrow coastal currents such as the East Greenland current, making it challenging to be observed using satellite remote sensing because of their proximity to the coast. While the direct impact of runoff on the coastal currents may be difficult to detect from space, model results have shown that large melt water runoffs from the Greenland ice sheet change the salinity of the seas surrounding Greenland, especially in Baffin Bay.

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