My Ocean Acidification Apprenticeship: Learning about Ocean pH Levels

(Mesocosms in position on the Friday Harbor Laboratory dock)

Last spring, I participated in an Ocean Acidification Apprenticeship at Friday Harbor Laboratories at the University of Washington. This apprenticeship was a perfect opportunity to receive training on best practices for ocean acidification research which will directly contribute to the focus of my dissertation. Ocean acidification is the process by which the ocean absorbs the excess atmospheric CO₂ resulting in lowering pH (more acidic conditions). Acidic oceans are problematic for marine organisms that secrete calcium based skeletons because the lower pH conditions may dissolve their shells. Part of my dissertation will evaluate the effects of lower ocean pH on the biology of marine crustaceans. The apprenticeship provided an opportunity to work closely with experts in the ocean acidification field while conducting my research.

The apprenticeship began by setting up mesocosms with different carbon dioxide (CO₂) concentrations to mimic what scientists project for future oceans (mid-century and end of the century). The mesocosms look like space-age domes and are six-meters tall. Each mesocosm serves as a “mini ecosystem” that can hold 3000L of water. The goal of the experiment was to evaluate how higher CO₂ conditions impacted plankton like diatoms, protists and microzooplankton. Since all of these organisms are microscopic, we had to slowly fill each mesocosm (which took three days) using a specialized pump that would not kill the fragile microscopic organisms.

Our experimental design consisted of three mesocosms that were held at 650 ppm of CO₂.  These were our controls since the water at Friday Harbor is influenced by strong upwelling and it already has high dissolved CO₂.  Another three mesocosms were “drift” replicates.  The “drift” replicates started with the same CO₂ concentration as the controls, but we did not try to keep the dissolved CO₂ elevated.  Finally, we had three mesocosms that were our high CO₂ treatment (1,200 ppm).  Since the CO₂ gradually declines within the controls and high replicates due to biological activity from planktonic organisms, we analyzed our water chemistry samples immediately, so that we could inject additional CO₂ to keep the same pCO₂ throughout the experiment. After the experiments were set-up, we collected our data daily for 22 days straight. Daily sampling required us to be on the dock every morning regardless of the weather conditions, which were often windy and rainy in April.

Our team was fortunate that its work was the highlight of several press releases during the first week of the experiment.  Our experiment was featured locally on the University of Washington’s website, and made international science news on the European Project on Ocean Acidification news stream. Stay tuned to this blog to learn what our data revealed.