Monday, May 28, 2012

Fossil Coral Mountains

By Liz Wiggins, Undergraduate Research Assistant Extraordinaire

With our time on the island quickly coming to an end, we were down to the daunting final task of taking inventory of all the fossil corals we collected. By this point there were mountainous piles of coral that had slowly accumulated at our temporary home, Dive Kiribati. We decided to sort the corals depending on how pristine they looked and took data on the species collected, length of the growth axis, and condition of the piece. All together we ended up with a respectable grand total of 671 fossil corals. Although most will be stored here on the island for now, the best of the best will be taken home for U/Th dating and analysis.

As part of my summer project as an undergraduate student, I will be investigating how dissolution affects the geochemistry and morphology of corals. While we were completing the inventory, if any piece looked particularly altered it went into a special “Wiggins” pile that was reserved for small and pitiful corals. Any piece that made my fellow paleoclimatologists cringe only added to my excitement! I chose 10 fossil corals that represented a gradient of diagenesis ranging from a nearly unaltered sample to a calcite ridden and visibly dissolved poor excuse of a fossil coral.

These “special” Wiggins corals will come home with us to Atlanta where they will undergo geochemical analysis and later be placed in a device that simulates rain falling on the coral for a certain length of time. Dubbed the “Rain Machine” this instrument is a self-filling reservoir that slowly drips water onto a piece of coral at a constant rate, basically creating artificial rainfall.  Afterwards, they will be reanalyzed to see exactly how the geochemistry and morphology changed. This has important implications for paleoclimate reconstructions using fossil corals as climate proxies, because nearly all of the corals in question will have been dissolved in some way. Although the effects of some types of diagenesis such as forming calcite or secondary aragonite have been thoroughly tested, how dissolution alters the coral is not well understood. Christmas Island has awarded me with excellent, horrible fossil corals that fit perfectly for the job.
To relieve our boredom during the long days of cataloging, our breaks consisted of visiting some of the local shops for souvenirs to bring home for our friends and family. This island very obviously doesn’t have many tourists, as most of the stores were laden with canned goods and necessities for island life with very little in the way of souvenirs. During one of our many stops we parked at a small community that swarmed with small native children. They excitedly ran up to the truck and began rubbing and even kissing (poor Diane) our comparatively pale arms while happily chanting “white skin” in Gilbertese, the local language. Following the truck all the way to the road, they cheerfully waved and yelled good-bye until we were out of sight. But all hope was not lost, our local caretaker, Anami, led us to some interesting native vendors that had very unique souvenirs to take back with us, complete with jewelry and tasty treats all made on Kiritimati.
Sadly, this is our last night of the expedition and all the final packing is nearing completion. Tomorrow we will be sure to include one more post during our extended layover in Hawaii, complete with a blurb from each of the remaining members of our team.