The Cruise

Expedition Route

The Cohen Lab is sailing around the Caribbean with Pangaea Exploration's vessel SeaDragon to learn how corals respond to changes in Atlantic and Pacific ocean climate.

Our expedition begins in St. Thomas, US Virgin Islands on December 4, 2013. We will stop at Martinique and Barbados before ending our expedition at Curacao on December 24.

At each island, we will spend several days SCUBA diving on coral reefs. We use an underwater hydraulic drill to extract cores of skeleton from massive coral colonies. The skeleton at the bottom of the cores that we collect may be centuries old! 

CAT scans of coral skeletoncores. The light 

and dark bands are high- and low- density 

skeleton, respectively. Starting at the top, we 

can count back density bands to track how 

each coral grew over time. These cores 

extend back several decades. The scalebar in 

bottom left is 5 cm.

Corals form colonies that are made of thousands and thousands of clone polyps. Day in and day out, each polyp builds skeleton out of calcium and carbonate ions available in seawater. Together, the polyps slowly build massive colonies up to several meters tall over tens or hundreds of years.

But how quickly coral colonies grow depends on the properties of seawater flowing over them. Temperature, nutrients, pH, and the amount of plankton in the water can all affect coral growth rate.

The skeleton cores that we collect will go through a CAT scanner at WHOI. These scans reveal the secrets locked in the coral skeleton. Using our cores, we can go back in time and look at how the coral was growing hundreds of years in the past.

We can track how quickly a particular coral grew over time because every year corals form one high-density band of skeleton and another low-density band of skeleton. The idea is like counting tree rings, except we count coral density bands back in time. But we do not just count the bands, we measure the distance between bands in our CAT scans. This tells us how quickly the coral grew each year.

Our expedition to the Caribbean will provide critical coral samples that tell us how corals have been growing across the Caribbean over time. Different reefs within the Caribbean are exposed to different temperature and nutrient regimes. By sampling reefs around the Caribbean, we can begin to tease apart how different environmental properties (like temperature and nutrients) are driving coral growth rates.

This information will help us answer key questions. Temperature and nutrients change naturally in the Atlantic, and may change along with a changing climate. By identifying how these factors drive coral growth, we can begin to understand how coral growth may change in the future.

We can also use corals to learn about the climate of the past. Skeleton cores that pre-date recorded temperature in the Caribbean provide us a way to 'go back in time' and learn what ocean temperature was like hundreds of years ago in the Caribbean.