Gyres Affect Sea Life, Climate
Giant Ocean Eddies Influence Local Climate and Marine Organisms
Oct 2, 2008
Gyres are enormous swirling oceanic eddies, which can be thousands of kilometres across. Rotating clockwise, the water in these eddies doesn’t mix with the rest of the ocean, and can trap heat, pollutants and organisms.
The most famous gyre is associated with the Gulf Stream in the North Atlantic, bringing warmer water that gives that European region a milder climate than at similar latitudes on the other side of the globe.
In the Southern Ocean, scientists from University of New South Wales have been studying the East Australian Current, which performs a similar warming effect on Eastern Australia, as well as mixing heat across the Antarctic Circumpolar Current.
Professor Matt England from the UNSW's Climate Change Research Centre, used the Gulf Stream to explain the important role gyres play in heat transfer around the planet.
"After releasing heat to the atmosphere, the waters re-circulate toward the equator, where they regain heat and rejoin the flow into the Gulf Stream.
“In this way the ocean's gyres play a fundamental role in pumping heat poleward, and cooler waters back to the tropics. This moderates the planet's extremes in climate in a profound way, reducing the equator-to-pole temperature gradients that would otherwise persist on an ocean-free planet."
Computer Modelling Detects Likely Gyres
Working with German colleagues at the University of Paderborn and the Technical University of Dresden, the UNSW team discovered that, although gyres can be enormous, they can escape detection by observation of the average water flow or sea surface height.
Gyres have a seasonal movement and their depth is not easily discernible from satellite observations. which can only record surface phenomena.
Team leader, UNSW Mathematician Dr Gary Froyland, said that instead of more observations at sea, they applied a mathematical technique known as Lagrangian analysis, allowing them to take into account all possible current movements simultaneously and pick out the least intensive mixing regions.
“The Southern Ocean is very expensive to sample experimentally with buoys, thus there are few observations at depth,” he said.
“The water in the gyres does not mix well with the rest of the ocean, so for long periods these gyres can trap pollutants, nutrients, drifting plants and animals, and become physical barriers that divert even major ocean currents.
“Using computer simulations, we were able to clearly identify where gyres and eddies trap drifting surface material in the seas near Antarctica.”
Gyres Distribute or Trap Marine Life
Not only do gyres affect water temperature and climate conditions around the planet, they can influence the distribution of marine organisms, by trapping them, or pushing them around.
“Marine life that relies on currents for transportation is particularly influenced,” Dr Froyland said.
“If outside the gyre, it is likely they will be transported around it; however, once entering the gyre, they are unlikely to leave it.”
The Southern Ocean Connects All Oceans
The Southern Ocean was the best place to investigate gyres, he said. “It has arguably the greatest impact on the world's oceans as it connects all major oceanic basins.”
Thanks to the computer modelling Dr Froyland was able to complete his share of the research, “entirely in my office”, avoiding the chilly depths of the ocean towards Antarctica.
The researchers will go on to investigate how the three-dimensional flow in the gyres extends deep down into the ocean, further revealing their potential to influence climate and marine life.
See also: New Hope for Coral Reefs from Map
