Elephant seals refuel at mid-ocean eddies

Eddies the size of Eastern states spin like smoke rings in the north Pacific, drawing in elephant seals with the promise of food.

The eddies peel off the Alaska gyre – a large current that circles the Gulf of Alaska – and linger in slow rotation for as long as a year at a time. Called “mesoscale eddies” because they’re big but not really big, they can be hundreds of miles across and 300 feet or more deep. (The black lines in the Seawifs picture above are roughly 300 miles apart.) They can be warmer or cooler than the surrounding water. Other qualities, like salinity, can differ also.

At the AGU meeting today, I met some scientists from University of California, Santa Cruz who follow elephant seals by tracking battery-powered tags they glue onto the seals’ heads. The tags don’t disturb the animals, but transmit information on where the seals are, how often and how deep they dive, and characteristics of the water they’re in.

The seal location reports, which arrive by satellite at least daily, often show seals altering course as if seeking out these eddies, said Samantha Simmons, one of the UCSC team.

Eddies can be either warmer or colder than the surrounding water. And just like their atmospheric counterparts, cold eddies spin counterclockwise and warm ones spin clockwise. As they do so, cold eddies bring water and nutrients up from the depths, aiding phytoplankton blooms but dispersing animals at the surface, like water coming up out of a fountain. Warm eddies drive water down and may help concentrate the seals’ food of squid and fish collected from 1,000 feet or deeper, said Luis Huckstadt, Simmons’s colleague.

I talked to these helpful folks at a poster session that was supposed to feature their colleague Scott Shaffer’s work on albatrosses collecting sea surface temperature readings. But Shaffer ran out of time and didn’t prepare his poster – you’ll have to read the BBC News report instead.