Continuous Measurement of the CO2 System in Waquoit Bay, a Coastal System with Groundwater Input

William Martin, Marine Chemistry and Geochemistry


Project summary

Recent studies have started to demonstrate the role of the coastal ocean in the earth-surface CO2 cycle.  In addition, a small number of studies have shown that the acidification of the ocean as a result of elevated atmospheric CO2 levels can have important effects on the chemical and ecological balances of the coastal ocean.  However, these studies have made it apparent that, since regional and local effects are important, and since short-term fluctuations (tidal, diurnal) and discrete events can be of paramount importance in coastal systems, autonomous, in situ measurements for extended time periods are essential for understanding the coastal environment.

Here at WHOI over the last several years, Fred Sayles (with recent help from Martin and Dan McCorkle) has developed an instrument (“RATS”) that meets the requirements for study of the CO2 system in coastal (and other) environments.  It measures TCO2 and pH with a time resolution of ~ 2 hours, over unattended deployments as long as 6 weeks. In addition to direct measurement of pH, its data can be used to calculate both pCO2 (needed to assess air-sea exchange) and the carbonate ion concentration (needed to assess the saturation state of seawater with respect to carbonate minerals) with the accuracy and precision needed for oceanographic studies.  This instrument is now ahead of others in its development, and the time is right for demonstration of its capabilities in a scientific study.  We will use RATS to examine the CO2 cycle in Waquoit Bay, a well-studied example of a coastal water body that is heavily impacted by groundwater.  The study will have local significance, as preliminary work indicates very low pH values during summer in the Bay; and will have broader significance as a study of a groundwater-impacted coastal system.  The work will enable Martin and McCorkle to establish a track record in the collection and interpretation of data from an autonomous, CO2-system instrument.  It will serve as a “demonstration project” to show the effectiveness of RATS.  We expect that the results of this study will place us in a strong position to apply for funds to use RATS in a broad range of biogeochemical studies requiring autonomous instrumentation.