Drill Team

So far, we steamed two days to Yap Island, worked for one day on the Yap reefs, and are now steaming two days to Woleai Atoll.  Yap Island was our first field site. I worked with the “drill team”.   

First, we all jumped in the water in snorkel gear and swam around looking for giant coral colonies. I like this part, because it is like a treasure hunt, and because the opportunity to swim long distances keeps me from getting cabin fever. We are looking for something very specific: a large Porites colony with a smooth top and a symmetrical shape. The larger the colonies are older and are thus more likely to yield skeletal material deposited over several hundred years.

We drilled a core from a medium-sized colony of Porites coral, shown in the picture.  We use an underwater hydraulic drill run by a motor on the boat.  The drill bit is like a hollow tube that takes a 'biopsy' of the coral skeleton.  When the bit has drilled all the way down its full length (80 cm or about 32 in), we pull it out and push a 'breaker' tool like a spear tip down the hole to break the core loose.  Then we use a 'grabber' tool, also a hollow tube with little teeth, to reach into the hole and pull out the core.  We add extension rods to the drill bit, breaker and grabber, and drill sections of core like this until we reach the bottom of the coral. 

We hope to drill corals that are more than 4 meters in length, because depending on the growth rate, this could yield more than 400 years of annual skeletal bands (like tree rings).

(Post adapted from an entry by Konrad Hughen).