Award: OCE-1744702

NSF Project Outcomes Report for the General Public Project Title: Collaborative Research: NSFGEO-NERC: A Thermodynamic Chemical Speciation Model for the Oceans, Seas and Estuaries PI: Heather Benway, Woods Hole Oceanographic Institution Award Number: 1744702 Carbon and trace metals such as iron and cadmium are critical elements for supporting marine life. Rising carbon dioxide (CO2) levels in the atmosphere have caused both warming and increasing dissolution of this greenhouse gas in seawater, which is fundamentally changing ocean chemistry, a process known as ocean acidification. Carbon and trace metals can take many different forms or species in seawater, some more available to biota than others, depending on the chemistry of the water. Understanding the cycling and distribution of these elements is critical to marine food webs, but it requires a combination of measurements and computational models that can calculate speciation. The most widely used computational approaches to date are only applicable over a narrow range of temperatures and salinities. This project has yielded a thoroughly updated modeling tool based on a well-documented set of geochemical equations based on solution activity that account for interactions between pairs and triplets of dissolved species. The model, called MarChemSpec (Marine Chemical Speciation) can predict chemical speciation and acidity (pH) in natural waters (with accompanying uncertainties) over a much larger range of compositions than existing models. This not only benefits the oceanographic community-at-large, but it will facilitate the testing and verification process for marine carbon dioxide removal approaches such as ocean alkalinity enhancement, which are likely to yield local compositional changes that cannot be characterized using traditional computational approaches. This modeling tool was developed in continual consultation with the prospective user community (surveys, town hall meetings, email lists) and has been posted on a website (marchemspec.org) along with tutorials to maximize accessibility. Last Modified: 01/10/2024 Submitted by: HeatherBenway