Time Travel into Palmyra’s Past

Environmental forensic detective Jessica Carilli and other members of the Paleo-Benthic Team have started probing into Palmyra Atoll to extract and decipher the record of its troubled past.


Jessica Carilli and colleagues at work in the lagoon at Palmyra using their push-coring device (and their muscles) to sample the corals of the past.

by Jessica Carilli, head researcher on the Paleo-Benthic Team

While Palmyra Atoll was occupied by the military during WW II, the lagoon was significantly altered (check out the earlier blog entry for more info). As a result, today many parts of the lagoon have little to no live coral cover whatsoever. What types of corals were living here in the past? To investigate that, the Paleo-Benthic team has begun collecting push-cores in the lagoon. Because both the living corals and the accumulating sediments build upwards over time, by collecting a core down into the sediments (which include fragments of dead corals, which were visible on the surface as well), we can essentially look back through time to see how things have changed. Our push-coring device consists of a thick aluminum pipe, a collar that fits snugly around the pipe, and a heavy steel sleeve that is manually hammered onto the collar. It’s a lot of work, but using this tactic we can sample down through several meters of sediment and coral rubble—traveling back in time hundreds or thousands of years. We’re also going to be very fit by the end of this trip!

Extracting a core sample from a mounding coral to expose the annual growth rings—a natural record of past growth rates.

We’ve also begun collecting core samples from large mounding coral colonies here, a task we will repeat on other atolls, as well. These will be used to investigate how the coral growth rates have changed over time and how frequent were bleaching events in the past. We expect to find that the stressed corals at the islands with higher human impacts grow more slowly and bleach more frequently. We will have to wait for the answers, though, because we won’t be able to see the coral’s growth rings until after the cruise. Back home we will CT scan the samples to produce 3D images of the annual layers of skeleton, the coral equivalent of tree rings.

 

 

 

During today’s coring dives on the southwestern fore-reef, we enjoyed the company of multiple black-tip reef sharks, and a gorgeous spotted eagle ray stopped by to check out the operation. Such awesome sidewalk superintendents! (Scroll down.)

Handsome company on the reef at Palmyra.