Wednesday, September 11, 2013

The hunt is on – fossil coral collecting on Kiritimati Island

By Pamela Grothe

Coral rubble field on Christmas Island


That is “hello” on Kiritimati (Christmas) Island, one of only three words I learned during my two-week field trip to this special place last month. Luckily, my science was a bit more productive than my Gilbertese lessons!

First off, I must thank Showtime and the Years of Living Dangerously crew for putting on this trip. Even though the primary focus was filming the wonderful science Kim does and all she has learned about climate change from Christmas Island corals, it provided me the opportunity to explore my own science goals, collect my own samples, and learn valuable fieldwork skills. It really was a trip of a lifetime, and even though I’m sure I’ll have more trips to come, this first one will always be extra memorable.

Before diving straight into the field trip itself, I think it is important to convey the science questions I am after. My overall goal is to reconstruct climate change in the central tropical Pacific over the last 6,000 years. This includes understanding changes in mean climate on different timescales (i.e. 100-yr and 1000-yr) and variations in the El Nino Southern Oscillation phenomenon, such as the intensity and frequency of El Nino events. More importantly though, is to convey to you WHY this is important. This region experiences a high-degree of natural variability in the climate system on decade-long timescales. This makes it hard for us to observe what recent changes in climate are caused by human-induced warming since instrumental data in this region only go back to the mid 20th century. In addition, future climate projections, especially for El Nino events, are not well constrained, despite having major global consequences on temperature and precipitation patterns. Additional climate data beyond the instrumental record would help us assess what current changes are due to human-induced warming and better assess model predictions for future climate changes.

Fossil coral rubble specimen - Porites
This is why we have turned to the corals, as they have proven to be reliable records for changes temperature and precipitation at a monthly resolution. These records provide us an opportunity to understand the background climate state of the central tropical Pacific and how it has changed during periods in the past. And if you recall from my earlier posts, I am trying a new ensemble method where I will be using hundreds of short fossil coral segments of ~10yr-long records, or “rubble” to reconstruct these climate changes.

With that being said, my time on Kiritimati Island was spent fossil hunting for Porites fossil corals! My previous work on dating provided a map with the distribution of ages of fossil coral on the island. This was extremely useful in determining where to focus my efforts.

My first objective was to collect samples on the leeward side of the island where most of the coral date to several thousand years old. Here, the corals are scattered around town, in piles in people’s yards, and even piled high in rock walls. This was exciting because it afforded us the opportunity to talk to the locals (before stealing coral out of their yards), play with pigs (OK, I wasn’t really a fan of the pigs, especially when it was standing on top of my backpack), and reconstruct rock walls after removing beautiful samples from them (I felt bad removing corals from their well constructed walls that I felt the need to replace them). Also, these samples are generally much larger, so through much effort of hauling rocks around the island, we took the samples back to Dive Kiribati and drilled them into 3-inch cores – this was by far my favorite task!

Collecting fossil coral from the local's property means getting up close and personal with the pigs!
Full pile of large rubble to drill!
And there's still more.
Full day of drilling fossil coral -
showing off my longest core.
Example of the clear ridge lines of coral rubble
My second objective was to target the open ridge fields on the windward side of the island, where the ages are distributed from the last century near the shoreline to just over 1000 years in the ridges farther back from the shore. My work on the age distribution of these ridges is only in its infancy, so the goal was to map out the ridges in more detail and collect samples from each of the ridges and from multiple sites that I can date. This area is really unbelievable in the magnitude of fossil coral and with precise age distribution maps we can really create a focused sampling plan for each time we come back.

Out on the rubble field collecting fossil coral

All in all, I collected several hundred samples and brought back almost half for dating (either the samples themselves or chips from them). A super productive trip I’d say! In addition, I have come away with an appreciation for each sample I collected – the painstaking work of searching for and lugging rocks around on a tropical island with limited shade is not easy! And THANK YOU Lauren Toth for all your help in doing this!

With that, I say goodbye – Tiabo!

Kim and I posing for an underwater shot.