Saturday, June 7, 2014


The Ocean Researcher 3 sampling around Dongsha. Look
carefully and you can see the rosette of "Niskin" bottles
used for sampling resting on the starboard gunwale. Look
even more closely and you can see a strip of green seawater
just below the horizon - that is the Dongsha reef.
Coral reefs are amazingly dynamic ecosystems. Everywhere in the ocean, organisms are constantly changing the chemistry of the seawater around them. Seasonal variability often dominates in the open ocean, where the composition of the upper 100 meters changes relatively slowly as plankton photosynthesize and respire. Changes are "slow" because there is a lot of water, and plankton are very small.

On a coral reef flat, the table is turned. Here, there is much less water (1-2 meters) and reefs are teeming with life. The timescale of change shrinks. Seawater chemistry can change dramatically over the course of a day. Tracking these changes tells us a lot about the reef, such as the rates of net calcification (construction of calcium carbonate minus dissolution) and net production (photosynthesis minus respiration).

The "robot" of our sampling team, the RAS collects
seawater samples on the shallow reef flat. The smaller
instrument next to the RAS is measuring the pH of the 
But tracking changes in seawater in such a dynamic system requires an intense sampling effort. On Dongsha, we deployed the RAS (see June 1 post) to automatically collect samples every 2 hours on the reef. In addition, the research vessel Ocean Researcher 3 (OR3) steamed from Taiwan to Dongsha to collect samples just offshore of the reef every few hours for several days. During the day, we bring two more boats to the reef: the larger Atoll-2 is stationed just inside of the lagoon while the smaller Atoll-1 travels over the shallow reef to sample between the RAS and OR3. It was at these times that our months of planning truly felt worthwhile. A whole transect of sampling teams (including 1 "robot") stretched across the reef, perfectly synchronized. And at the same time, the DTS and offshore mooring (posts on June 3 & 7) are characterizing the physical processes around the atoll. Together, the samples that we collect will paint a unique picture of the dynamic processes occurring on Dongsha Atoll.

- Tom DeCarlo
Joint Program in Oceanography
Woods Hole Oceanographic Institution

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