High-resolution (15-minute frequency) monitoring of pH, dissolved oxygen, salinity, temperature, depth, and chlorophyll was conducted from July 15-October 1, 2015 in a shallow, subtidal seagrass bed in Puget Sound, WA, USA. Grab samples for instrument validation and carbonate chemistry analysis were periodically taken next to the in-situ instrumentation. This dataset is associated with the following publication: Pacella, S., C. Brown, G. Waldbusser, R. Labiosa, and B. Hales. Seagrass habitat metabolism increases short-term extremes and long-term offset of CO2 under future ocean acidification. PNAS (PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES). National Academy of Sciences, WASHINGTON, DC, USA, 115(15): 3870-3875, (2018).