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October 4, 2011 / Dave Gorham

It’s the Salt’s Fault: Our Ever-Circulating Oceans

The age of Aquarius, as told in 2011, is about an orbiting Earth science satellite that is able to measure the salinity content of the Earth’s oceans. This is not trivial. For the first time, thanks to the Aquarius instrument aboard an Argentinean satellite, a global perspective of the distribution of salt across the oceans is now available for analysis. With this data, a better understanding of ocean circulation patterns will lead to a better understanding of changing global climates. Prior to Aquarius, like using an axe to chisel a chess piece, scientists had only a basic understanding of varying oceanic salt distributions and its impact on global climate. In fact, much of the oceans’ salinity was uncharted, especially south of the equator. With enough precision to measure a pinch of salt in a gallon of water, Aquarius has provided more data in two weeks than the previous 100 years of measurements.

This composite of the first two and a half weeks' of data since the instrument became operational on August 25. Yellow and red colors represent areas of higher salinity, with blues and purples indicating areas of lower salinity. Image: NASA

ImpactWeather Sr. Meteorologist Chris Hebert explains: “It’s salinity that drives the thermohaline circulation in the world’s oceans. In the North Atlantic, it’s the main current that carries warm tropical water northward toward Greenland.  Water with a higher saline content is more dense, so it sinks faster in northern latitudes, driving the current. Over time, it melts northern ice and salinity decreases due to the increase of fresh water, resulting in a cold phase of the Atlantic Multidecadal Oscillation. During the cold phase, ice builds up and salinity slowly increases.  Eventually, the salinity gets high enough that the current picks up speed, leading to another warm phase that might last 30-40 years.”

Stripped to its core, salt moves heat around and ocean current is driven by the density of the water. Typically cooler, denser water sinks and moves south, while warmer, less dense water rises and moves north in a never-ending cycle. It’s the temperature of sea water, which covers 70% of the Earth’s surface, that drives synoptic scale climates and has a pronounced effect on tropical cyclone development (or non-development). With a better understanding of ocean currents, climatologists and meteorologists will gain a better handle on both short- and long-range forecasts and climate patterns.

Global thermohaline circulation. Image: Wikipedia

There is concern among some scientists that, given global climate change, a dramatic slowing or termination of the Thermohaline Circulation is possible. In theory, a warmer Earth would melt more glacial and polar ice while initiating more large-scale rain events. The result would be  a greater influx of fresh meltwater and rainwater into the oceans of the world. With a higher content of fresh (less dense) water, the circulation could be slowed, interrupted or even terminated. Countries that would most clearly see this effect would be northern countries near a warm current such as Iceland, Norway, Sweden, Ireland and Great Britain that would begin to cool without the warming ocean current. It’s exactly this situation which has advanced the paradox of global warming instigating global cooling. Scientists point to the Little Ice Age as an example of changes to the ocean circulation patterns.

Launched in June of this year, the satellite carries an international payload of seven additional instruments and will scan the entire globe once every seven days from 408 miles about the Earth’s surface. Combined, these instruments will measure such things as cosmic radiation, aurorae, sea surface temperature, atmospheric humidity, electromagnetic radiation and a demonstration of new technology involving GPS and inertial navigation in addition to the primary instrument, Aquarius. Aquarius is expected to be a 5-year mission.

This artist's impression shows the SAC-D satellite that houses the Aquarius instrument over South America. Image: Wikipedia.

Learn more of NASA’s Aquarius satellite here. Even better, watch this nicely done and succinct video from NASA and the Goddard Space Flight Center.

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