By Pamela Grothe
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| Coral rubble field on Christmas Island |
Mauri!
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.
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| 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!
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| Collecting fossil coral from the local's property means getting up close and personal with the pigs! |
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| Full pile of large rubble to drill! And there's still more. |
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| Full day of drilling fossil coral - showing off my longest core. |
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| 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.
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| 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!
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| Kim and I posing for an underwater shot. |
