Seawater is a lot more complex than a simple solution of water and sodium chloride. As researchers have been discovering for the past century, it is a highly variable cocktail, and its particular makeup can have a substantial impact everything from coral to currents.

To make sure monitoring and modeling of the globe's biggest bodies of water stay accurate, UNESCO's Intergovernmental Oceanographic Commission (IOC) has adopted a new official definition for seawater. A report [pdf], published earlier this year, details the updated methods for keeping tabs on the changing seas.

Historically, oceanographers have defined seawater based on its salinity, which they inferred by taking measurements of the water's electrical conductivity. The measurements, tracked on the PSS (practical salinity scale), helped provide standardized data sets for the world over, making possible a more nuanced level of mapping.

But in the 1970s researchers Peter Brewer and Al Bradshaw noticed that deep-sea waters (which have a higher concentration of salt) did not quite behave the same as did samples from standard North Atlantic surface waters (a 35 to 1,000 salt to water ratio).

So they enlisted the help of Frank Millero, a professor of marine and physical chemistry at the University of Miami's Rosenstiel School of Marine & Atmospheric Science, to find a better way to gauge the world's seawater. Millero and others, including the mathematician and physicist Rainer Feistel and Trevor McDougall at the Center for Australian Weather and Climate Research, set to work developing standard guidelines that would allow for more accurate assessment of salinity.

Samples will still be measured using conductivity (via carefully calibrated instruments) to maintain data consistency, says Gary Lagerloef, a senior scientist at the nonprofit Earth & Space Research (ERS). Only after the measurements are recorded will they be corrected using the new calculations, he explains.

And the new definition doesn't stop at corrected salinity levels. It also takes into account other crucial properties, such as heat capacity and enthalpy (a system's energy determined by its temperature, pressure and composition). Millero calls this new seawater equation a "black box," into which researchers can input salinity values, collection location and depth, and come out with more accurate information about the properties of the water in that area. "This is much more useful to modelers because everything is built into one equation," Millero says. It will allow them to paint a clearer picture of where ocean mixing happens and thus permit more accurate ocean current—and climate—models.

"It's going to be important in the long run," says Lagerloef, who is leading NASA's Aquarius satellite mission to measure ocean salinity from space. "It's a small correction," he says, but "the ocean responds to very subtle changes in density" triggered by its heat content and chemistry.

The new calculations have even proved to hold fast at high temperatures, and they have already been put to work in the industrial sector. The new guidelines are slated to take effect in the research world next year.

5 Comments

1. 1. JamesDavis 08:07 AM 7/28/09

   That article certainly left you wanting more information and left a lot of unanswered questions. They have been studying the ocean for a hundred years and still don't know anything about it. I bet those oceanographers and their numerous teams can't answer these simple questions: Where does the salt come from that makes the ocean so dangerously salty to humans if they dring the water and why is ocean salt so healthy for us when we sprinkle it on our foods? If the salt comes from land, why isn't it concertrated in rivers, lakes, streams, and rivers? Where does the salt go to when a hurricane picks up the salty water and rains fresh water when it gets over land? Are there any scientist who can answer these questions? I have wondered about this all my life and no one seems able to answer them.

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2. 2. Jokunen 09:50 AM 7/28/09

   JamesDavis:
   
   Ancient animals developed in ocean when there was 0.9% of salt. That is the salt content of land animals, including humans. If water we consume has more than that, like ocean water with 3.5%, it has to be flushed out with fresh water. If we consume only fresh produce, we may need more salt to stay at 0.9%, therefore additional salt may be healthy. But typically Western food itself contains more salt than we need per day.
   
   Salt is weathered from rocks and is transported by rivers to ocean. So there is some salt in fresh waters, but it has accumulated to oceans, because they can not transport it anywhere. This accumulation has been gradual, over hundreds of millions of years, so even tiny salt amounts per year have had time to make a change.
   
   When water leaves the ocean by evaporation, it leaves the salt behind it. One good example is dead sea at Israel. Another is Mediterranean sea that would dry out, if there would not be replacement water coming from Atlantic ocean through Gibraltar. Both are more salty than the water flowing into them.
   
   There is nothing mystic about those processes. Obviously you have not asked your questions in right places.

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3. 3. frgough 10:01 AM 7/29/09

   Your first sentence is a fine example of circular reasoning. Land animals have 0.9% salt concentration because they developed in an ocean with 0.9% salt concentration. How do we know the oceans has 0.9% salt concentration? Well, because humans and other land animals have 0.9% salt concentration, of course.

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4. 4. Diogmatic in reply to Jokunen 10:21 AM 7/29/09

   Jokunen,
   
   You made two statements which were unsubstantiated:
   
   1. "Ancient animals developed in ocean when there was 0.9% of salt"
   
   Evidence for this would be what? The standard uniformitarian/junior-school rate equation, y =mx + c, perhaps?
   
   I'm not disputing that oceans had less salinity in the past, I would however suggest that no one knows what the original salinty was, or indeed *when* that was. They could guess, but then, so could a 7 year old.
   
   2. "This accumulation has been gradual, over hundreds of millions of years, so even tiny salt amounts per year have had time to make a change."
   
   This is an evolutionary assumption, though not quite the "uniformitarian" one mentioned above. Good Scientists should NOT assume 4.5 billion years (ocean ~3.8 By) then measure the salinity of the ocean and thus calculate the rate of salt accumulation from continental erosion to be so and so.
   
   The correct method would be to measure the rate of erosion (continent) and deposition (ocean) . Then, upon measuring the salinity of the ocean, calculate the remaining unknown variable, its age. I think the number comes out at a few millions of years - not billions. And that assumes, "uniformitarian" deposition. If rates were higher at any point in the past the millions would quickly become thousands.
   
   And yes, I agree: "There is nothing mystic about those processes" . They have been observed to happen rapidly.
   

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5. 5. ShyGuy in reply to JamesDavis 10:29 PM 8/25/09

   you are a very clever person, this is almost exactly what i thought when i read this.

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