Rights: The University of Waikato Published 21 June 2007 Download

Dr Mike Williams from NIWA explains what happens when sea ice forms and what effect it has on ocean circulation.


What happens, particularly around Antarctica, is the amount of salt we put in the water makes the water heavier. And it’s an experiment anyone can do. Just keep adding salt to the water and it will get denser and denser. So as sea ice forms, the salt is pushed out of the ice as it forms, and it’s pushed back into the ocean.

So what sea ice is doing is it’s effectively adding salt to the top of the ocean, so that salt mixes in and it wants to sink. And around Antarctica over a whole winter, the amount of salty water we get on the bottom is a key driver of deeper ocean circulation. Because we get the salty water around Antarctica and then it wants to flow off the Continental Shelf around Antarctica into the Deep Abyssal Ocean, and then it’s that movement down into the Deep Abyssal Ocean that’s important for overall ocean circulation in the globe.

While B15 was across the end of McMurdo Sound, the water structure in McMurdo Sound changed. Instead of being highly stratified with fresher water on the top and saltier water on the bottom, we found the water was very homogeneous. What this meant was that McMurdo Sound had become almost a small separate sea, where everything was just circulating around in a limited area, and it was all being mixed up.