This study seeks to explore the impacts of warming and ocean acidification on the transition of life in freshwater to life at sea in Chinook salmon smolts. In a fully factorial experiment, we transitioned Chinook salmon from fresh- to seawater at current and future conditions of temperature (13 ◦C and 16 ◦C, respectively) and ocean acidification (400 and 1400 atm CO2), including a fluctuating CO2 treatment (between control and high CO2) that may be more representative of natural environmental conditions associated with upwelling and tidal cycling.This dataset is included in the OA-ICC data compilation maintained in the framework of the IAEA Ocean Acidification International Coordination Centre (see https://oa-icc.ipsl.fr). Original data were provided by the author of the related paper (see Related to) to the OA-ICC data curator. In order to allow full comparability with other ocean acidification data sets, the R package seacarb (Gattuso et al, 2024) was used to compute a complete and consistent set of carbonate system variables, as described by Nisumaa et al. (2010). In this dataset the original values were archived in addition with the recalculated parameters (see related PI). The date of carbonate chemistry calculation by seacarb is 2025-01-20.