‘Betty’ returns with info about eddies

In May, Betty (an ocean glider), spent 24 days travelling 610km through the Cook Strait’s turbulent waters continuously recording temperature, salinity, oxygen concentration, light, acoustic recordings, and more. This data is important for developing better models.

The results will take 6 months to analyse, but it’s already clear there’ll be some interesting insights as Betty spent 4 days stuck in an eddy (circled in white on the map above).

“We tried a few different things to get the glider out,” said Dr Joe O’Callaghan, a Coastal Physicist who leads NIWA’s ocean glider facility. “In the end we had to go around the outside, a bit like a swimmer escaping a rip current.”

What are eddies?

Eddies are ‘hot spots’ of intense biological and physical activity – there’s lots of energy and movement contained in a specific area, which affects nutrient mixing, temperature, salinity, and other environmental factors.

Eddies can now be observed in detail thanks to ocean gliders, which have only been around for 10 years.

“Satellites can provide information about conditions at the surface (such as temperature) but not what’s happening under the surface,” said Joe. “Eddies are an interesting type of ‘ocean weather’ – similar to a cloud front rolling in. They create strong ‘layers’ or boundaries, which can be difficult to cross so things can get trapped above or below.

“Now we have the technology, we can learn about their structure and behaviour, and exactly how conditions in the eddy differ from the surrounding water.”

In Tasman and Golden Bays eddies can last from several days up to a month.