Aragonite saturation state, June 2014 through May 2015, and 15-year monthly averages for chlorophyll a. This time series of aragonite saturation state (Ω_arag) from June 2014 through May 2015 in surface water samples form the six stations (color-coded, with locations shown in Figure 1) shows a seasonal pattern of highest values during the phytoplankton growing season (March–September). Samples were collected monthly at a depth of 5 meters, with the exception of station HCB in March 2018 (10 meters). Long-term (15-year) monthly averages of depth-integrated (0–50 m) phytoplankton biomass measured by chlorophyll a over all of Puget Sound (open green squares) shows a similar seasonal pattern compared with Ω_arag measured during 2014–2015. The horizontal line indicates the Ω_arag saturation level of 1.0; values below the line are under-saturated. DOI: https://doi.org/10.1525/elementa.270.f2