Inverse Model Inferred Time Series of Photosynthesis Parameters From Three Decades of Primary Production Measurements

Abstract Understanding how phytoplankton photosynthetic physiology varies over seasonal to multi‐decadal time scales is important for assessing changes in ocean productivity and its role in the carbon cycle. Here we show that, at the Bermuda Atlantic Time‐series Study and Hawaii Ocean Time‐series stations, photosynthesis parameters exhibit pronounced seasonal and shorter‐term variability but no statistically significant multi‐decadal trends over more than three decades of observations. To investigate these temporal patterns, we use in situ chlorophyll and primary production profiles together with an inverse model to reconstruct long‐term time series of photosynthesis parameters. The two time series stations have surpassed the 30‐year mark, making data collected there suitable for climatological research. A shifted Gaussian is used as a model for the chlorophyll profile and an exactly solvable model of the production profile is used to infer photosynthesis parameters from measured production profiles. The models yielded high coefficients of determination, which enabled the construction of thirty‐year‐long time series of photosynthesis parameters. The seasonal cycle and long‐term changes in the parameters were analyzed. No statistically significant long‐term trends were detected in the estimated photosynthesis parameters, while substantial variability was observed on shorter time scales. The results highlight the importance of accounting for temporal variability in photosynthesis parameters when modeling ocean primary production.