Daniel Palacios, at NOAA in Pacific Grove. Where is Penelope, the elephant seal, going? Penelope, the red animal icon on the TOPP.org home page map (and on her species page map), left Año Nuevo State Reserve in June. She is making a beeline for the central North Pacific. If you and I were out there, it would all look like vast empty expanse of blue ocean to us. But Penelope is probably heading for the TZCF.

Transition Zone Chlorophyll Front. This is the term used by oceanographers to refer to the boundary between two different ecosystems; one that doesn't have much plant life (in the form of the tiny plankton called phytoplankton) to the south and one that has a lot of plant life, to the north. The TZCF, which spans across the North Pacific at a latitude of about 40-45°N in summer, is readily detected from space by NASA's ocean color sensor satellite. The satellite detects chlorophyll, which is what makes plants on land or in the ocean green.

So, why's she going there, given that elephant seals' favorite food is squid, several steps up in the food chain from plants? (The chain: tiny plants are eaten by tiny animals are eaten by larger animals are eaten by large animals.) As it turns out, the TZCF is where different masses of water converge (in this case, one with a lot of nutrients and one without many nutrients: think fertilizer). These convergence areas are very dynamic, and in addition to fueling local phytoplankton blooms, food chains build around them, including top predators like elephant seals.

Here's a map of three elephant seal tracks from September 2004 that I put over the corresponding false-color chlorophyll image. You can see how the elephant seals skirt right along the TZCF, represented by the rapid change from blue to green in the ocean color. I altered the lower image to only show the areas with greatest changes in ocean color, from one pixel to the next. Not surprisingly, most of these areas are in the vicinity of the TZCF. It looks like the seals are working the front looking for groups of squid or other animals that they like. For us, the ocean color data is very useful for pinpointing the location of the front.

Here are images from the TOPP researchers' data page that shows Penelope's track married with the image from NASA's satellite that tracks chlorophyll.

When TOPP began in 2000, we knew very little about why elephant seals went to the central North Pacific, seemingly in the middle of nowhere. Now we're learning more about why they go there.