Unifying global seawater pH measurements of ocean acidification & climate

Funded by: MIT Center for International Studies (MIT Spain INDITEX Circularity Seed Fund)

Principal Investigators: Ryan Woosley, MIT CS3; Marta Álvarez, Instituto Español de Oceanografía 

The oceans have slowed the rate of climate change by absorbing approximately a quarter of anthropogenic carbon dioxide (CO2) emissions. However, once dissolved, CO2 reacts with seawater acting to lower the pH and alter ocean chemistry in a process known as ocean acidification. Ocean acidification is known to have a myriad of impacts on ocean chemical reactions, and marine organisms and ecosystems. Determining the impacts of ocean acidification and the potential effects of marine CO2 removal (mCDR) strategies requires highly precise measurements of seawater pH, consistent across locations, decades, laboratories, and methods (manual or automatic benchtop instruments or sensor-based). Of all the seawater CO2 system variables, pH has been the most challenging to achieve such consistency, primarily due to rapid evolution of the spectrophotometric reference
method based on the addition of a dye whose color varies with the seawater pH. Although ultra-precise seawater pH measurements became common in the mid-1990s, impurities in the commercial dye used added small but detectable biases, which increase the uncertainty or render quantifying rates of ocean acidification or bulk pH changes very difficult. This collaboration aims to refine and develop techniques to account for such biases in historical pH data, and to establish protocols to account for impurities in new measurements when purified dyes are not available or economical. This effort will act to reduce uncertainty and improve coherency of pH data synthesis products and provide a better understanding of global ocean acidification rates and impacts, improving methodology for mCDR research.