Award: OCE-1923312

Burning of fossil fuels not only causes climate change but changes the chemistry of the oceans through the uptake carbon dioxide (CO₂) produced from human activities. Once in the ocean, this CO₂ reacts with water acting to lower the pH of the ocean, a process termed ocean acidification (OA). Although this process is occurring globally some regions experience faster rates of OA than others. Determining the amount and distribution of CO₂ the oceans take up as well as how much the pH is decreasing requires highly precise and accurate measurements spanning decades. The goals of this project were to evaluate and test current methods of pH measurement as well as other measured and calculated parameters of the CO₂ system in seawater in order to improve accuracy and precision of OA and oceanic CO₂ uptake research. Through a series of publications, we increased confidence in the long-term use of purified pH indicators, made several recommendations that can be used to increase measurement quality, and determined areas that need further research. 

 

There are four commonly measured parameters used to monitor and quantify oceanic uptake of CO₂ and OA. In principle only two need to be measured because the others can be calculated from the two measured values. However, the quality of the calculated values depends on the type and quality of values measured. Through an extensive evaluation of these measurements and calculations across a wide range of temperature, salinity, and CO₂ concentrations we found that in order to achieve the quality of measurements required for long term OA monitoring pH must be measured directly rather than calculated, and that the commonly measured pair of dissolved inorganic carbon (DIC) and total alkalinity (TA) only sometimes meets the required quality for climate level OA research. Direct measurement of pH will become more essential as CO₂ increases further. We also made several recommendations for evaluating OA measurements and areas where further improvements can be made. Uncertainties in the total boron concentration and in the second dissociation constant of CO₂ contribute to the largest uncertainties in the system. 

 

The results mean that if society is to undertake marine geoengineering solutions for climate change, also called marine carbon dioxide removal (mCDR) increased high quality measurements of pH in combination with DIC and/or TA are required for successful measurement, reporting, and verification of these technologies. The results also mean that an expansion of direct high quality pH measurements across the global ocean is highly warranted. 

 

The planned broader impacts had to be slightly curtailed do the COVID-19 pandemic, which limited the involvement of undergraduate students in conducting in person laboratory research. Despite the limitations, three undergraduate students were involved in research, mostly involving data analysis. The lab participated in Shell Day 2019, a large multi-institute community science day for citizens to collect samples of TA across the Northeast United States. A tour of the lab was also given to ~20 high school and younger students as part of Shell Day. A demonstration of pH and OA was given as part of the annual MIT Carlson Lecture. The work was presented at several conferences and involvement in two working groups, the Ocean Carbon Inter-comparability Forum and the Global Ocean Data Analysis Project have acted to incorporate the results into the broader research community and maximize their impact. 

 

Last Modified: 03/08/2024
Modified by: Ryan J Woosley