Bad Astronomy

Saline the ocean blue

In June, NASA launched the Earth-observing satellite Aquarius, designed to observe and measure the salinity content of the ocean surface. This turns out to be important because salty water flows differently than pure water, and how the currents interact drives a lot of the way heat is transferred across the Earth’s oceans. And that drives a lot of climate behavior, including climate change.

Scientists just released the first global map of ocean surface salinity, showing surprising (to me) variations across the planet:


Neat! [Click to verucafy.]

In the map, blue/purple is lower salinity, and red/orange is higher concentrations. The average value is about 35 grams of salt per kilo of water (about 0.6 ounces of salt to one pint of water), but it varies a lot. And it’s not just latitude dependent, which would’ve been my first guess. The Pacific equatorial waters are low in salt, but the levels in the Atlantic are higher. North Pacific is low, north Atlantic higher. The western Indian ocean is high, the eastern part low.


Apparently these measurements are tough to make. Aquarius has an instrument which measures the emission of the ocean surface in the infrared. Salty water doesn’t emit IR as efficiently, so the salinity can be measured exploiting this. However, waves on the surface mess this up, so the spacecraft has a way to measure how strong the waves are (using what’s called a radar scatterometer, which is totally cool name for an instrument) so they can account for that as well.

Observations like this are crucial for us to understand just how our fiendishly complex planet works. Especially now, when our climate is changing, and those changes are evident even year by year.

Image credit: NASA/GSFC/JPL-Caltech

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