Alkalinity refers to seawater’s ability to neutralize acids, such as those that form when atmospheric carbon dioxide reacts with seawater. Seawater alkalinity controls how much carbon dioxide the ocean absorbs from and releases to the atmosphere and is thus a key component of the global carbon cycle. Vegetated coastal ecosystems such as mangroves, seagrasses, and tidal marshes could be a significant source of alkalinity to the coastal ocean but currently we do not know how much alkalinity is produced in these environments. Seagrasses are vegetated coastal ecosystems that exist on the coastlines of every continent except for Antarctica. This research will measure how much alkalinity is being produced in seagrass ecosystems and will investigate the processes controlling alkalinity production. The project will evaluate the safety and efficacy of emerging marine carbon dioxide removal (mCDR) technologies that are designed to increase the amount of carbon dioxide the ocean can naturally absorb from the atmosphere by artificially increasing alkalinity in coastal environments.<br/><br/>A stronger understanding of alkalinity cycling in the coastal ocean is not only critical to constraining oceanic and global carbon budgets, but also to predicting how these budgets could be perturbed by ongoing anthropogenic impacts and emerging mCDR technologies. This work will quantify sediment total alkalinity fluxes and investigate the biogeochemical processes controlling them across two contrasting seagrass ecosystems. A multi-analyte approach under both in situ and laboratory settings using microelectrode profiling, chamber incubations, and pore water analyses is planned. This combination of high-resolution measurements and characterization of sediment alkalinity cycling in seagrasses are designed to improve our understanding of alkalinity and carbon dynamics within seagrass ecosystems. Experiments will also be conducted to understand the impact of proposed ocean alkalinity enhancement strategies (enhanced silicate weathering) on sedimentary alkalinity production in seagrasses. The project includes training in interdisciplinary oceanographic measurements and techniques and a group mentoring network for graduate and undergraduate students as well as paid research opportunities for community college students through the Santa Rosa Junior College-Bodega Marine Laboratory Internship Program.<br/><br/>This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.