The oceans play a major role in the carbon cycle, storing about 50 times more carbon than the atmosphere. The rise in atmospheric CO₂ as a result of human activities (burning fossil fuels, cement production, etc.) has been significantly slowed by the uptake and storage of about a third of this carbon by the oceans. This carbon storage by the oceans slows the rate of climate change, but not without harmful effects on the oceans, namely a lowering of the pH (termed ocean acidification). Measuring ocean acidification and the effects on marine organisms, particularly calcifying organisms, like corals, requires very precise measurements of pH.

pH is measured by adding an indicator dye, which turns the water purple, and precisely measuring the color with a spectrophotometer. Although the measurements are simple to make, the instrument is not always available and preparing the samples requires special care, so as not to allow any CO₂ to escape and alter the pH.  It would be much easier for many to collect samples and ship them back to a lab, rather than measuring them immediately on board the ship, but since CO₂ loss and biological activity can contaminate the sample it is currently unknown if it is possible to preserve the samples for measurement in the lab.

On this cruise, I am collecting 2 samples of pH from several stations and water depths. I measure one sample immediately on board. The second one, I add mercuric chloride to halt all biological activity, and seal the bottles tightly to prevent any CO₂ loss. The second bottle will then be shipped back to the lab and measured. The two measurements will be compared to determine if the pH is stable and can be measured in the lab, rather than on board.

Posted by Ryan