Thursday, September 22, 2011

First Aquarius Map

The first map of ocean salinity as measured by the Aquarius satellite was released today. (NASA link.) I like that I can look at this and know what I'm seeing. Usually oceanographers specify salinity as a ratio to a standard KCL solution (potassium chloride.) This is called the Practical Salinity Scale. It is used for any measurement based on conductivity and has no units. I think they are making the assumption here that grams per kilogram is the same as PSU, for practical salinity units, which is of course a silly name, because it's unit-less. g/kg is a compromise I'm willing to accept.

Anyway, 35 is what oceanographers consider nominal for PSU. Green is normal sea water. That blue band across the Pacific? That's an equatorial counter current moving towards South America. When it's blue like that it's called La Niña. You can equate lower salinity with lower temperature in this case. If it was an El Niño year there would be a red band across the Pacific indicating hotter, saltier water from increased evaporation. The side effect of that low evaporation in the Pacific is Texas is very dry. Dry earth heats up more than wet earth, and I am here to testify to it. The lowest high temperature in September in Austin so far is 90°F. There might be two more of those days and this is not one of them. It's going to be 101°F this weekend.

I'm not sure what the Gulf of Mexico salinity looks like in a normal summer (No La Niña or El Niño.) Looks to me like the lack of fresh water from Texas and Mexico is making it pretty salty on the West. I'm glad my Georgia home is producing lots of water. That blue and purple area in the aptly named Florida Big Bend is from fresh water input from the Appalachicola and Mississippi Rivers. That's what makes it oyster friendly.

The other big purple and blue blotch off the Venezuela part of South America is the Orinoco and the Amazon comes out of that notch farther south. You can see it runs north and heads across towards Africa in the Equatorial Counter Current. I love that I can see features in an up-to-date salinity map that I had to memorize off lines and arrows on maps.

I'm not sure what to make of all that detail of differences down around Antartica. That's kind of fascinating.

And you can tell a lot of sea ice is melting up in the Arctic adding all that fresh water to the surface.

Thanks Aquarius! Fun times!


  1. Hiya Barbara, it's an interesting map. I wonder, is the increased salinity in the Atlantic due to increased heat evaporation? Would that be due to the Atlantic being a smaller body of water than the Pacific? There are other streams and currents than the Gulf Stream and they don't appear to be associated with areas of such notable salinity.

    Forgive me if it's a daft question...I've just woken up.

  2. Yes, it's evaporation in the Atlantic. The map of ocean currents would be more useful if it also showed prevailing winds. Every year as much water as two Amazon rivers evaporates from the surface of the Atlantic and the trade winds carry it across Central America where it rains in the tropical Pacific. The reason it doesn't just go like that until the Pacific is fresh and the Atlantic is brine is because of that deep water current pattern I explained in the ocean circulation primer I wrote back in June. That works on time scales of 1000 years though, where surface salinity can be relevant to weather on an annual basis, as we're seeing in Texas this year.

    Here's a nice thorough explanation of why the surface of the Atlantic is so salty.