Icy isobaths at the Jetty

Quick definition at the beginning of this post: an isobath is a contour line at a specific water depth, and is often used for underwater mapping, science, and navigation. We use isobaths in our project as a way to distinguish areas of work.

In many marine systems, depth is already a strong driver of ecosystems, from significant changes in pressure to light penetration. In McMurdo sound, it also constitutes how deep anchor ice can form! Anchor ice is ice that forms on the seafloor, and has been documented down to about 30 meters, or 90 feet. It can separate the ecosystem of a single site, where large die-offs of organisms occur each year in the anchor ice zone.

The Jetty dive site is an excellent example of this phenomenon. This year, at the 60 foot isobath, life is thriving with fish, urchins, sponges and more cast across the seafloor.

A Trematomus bernacchii sits atop atop the deeper rocks at the Jetty. also pictured: urchin, feather duster worms, nudibranch, and much more!

In comparison, any point shallower than 45 feet at this site has a staggering amount of ice cover. Life is few and far between.

Anchor ice covers the shallows at the site