27 September 2011

How Salty Is Your Ocean?

Posted by Dan Satterfield


From NASA-Goddard. A new image from the Aquarius satellite showing the salinity variations in the oceans.

The Aquarius satellite was recently launched to learn more about the oceans and answer some very nagging questions in a variety of fields (especially climate science). Notice how much saltier the Atlantic is than the Pacific, and if you have ever gotten a mouthful of ocean off of Miami Beach, you know it’s true. The Pacific is less salty and having swam in both, I can attest that the difference is noticeable!

Wikipedia has a nicely written article on the ITCZ. GOES image showing the ITCZ band of clouds.

You might ask why the area around the equator, (especially in the Pacific) is less saline, and the answer is the ITCZ. The Inter Tropical Convergence Zone is a belt of rather stormy weather caused by the overall global circulation pattern of the planet. High pressure belts at around 30 degrees north and south latitude cause the air to converge and heavy rainfall is the result (Google Hadley cells). The ITCZ moves with the sun, and this movement is responsible for the rainy/dry seasons that characterize the weather in tropical climates. All that rain makes the water fresher underneath the ITCZ, which is always more pronounced in the very wide Pacific. You can also see fresher water at the mouth of the Amazon River and at the outlet of the Ganges in the Bay of Bengal.

If you want to accurately forecast the weather and climate, you MUST understand the oceans, and we know far too little about them!

PS- I really should mention what is to me the most incredible fact of all about Aquarius, and that is just how does it measure the salinity of the oceans from orbit?? Why didn’t you ask!! 😉

The answer is that any object with a temperature emits electromagnetic radiation, and if you look at the oceans using a camera that sees light in the microwave region, it turns out the radiation changes if the sea water is more conductive. Salty water is more conductive than fresh water, and this is how salinity can be measured. It’s all in the light the oceans give off, but it’s light our eyes cannot see, and if you don’t find that cool, you’ve no imagination!