CCE_LTER_P1908 Upwelling Filament Ocean Acidification Phytoplankton Iron Incubation Experiments

Coastal upwelling regions are among the most biologically productive ecosystems in the ocean but may be threatened by amplified ocean acidification from rising atmospheric CO2. Increased acidification is hypothesized to reduce iron bioavailability for marine phytoplankton thereby expanding iron limitation and impacting primary production. Here we show from community to molecular levels, with a multi-omics approach, that iron-stressed phytoplankton in an upwelling region exhibit resistance to short-term acidification. Trace metal clean incubations were performed for up to four days and 1200 ppm pCO2; however, phytoplankton growth, nutrient uptake, and community compositions remained unchanged. Although variable, molecular-level responses suggest that resistance to changes in iron bioavailability is facilitated by iron uptake pathways that are less hindered by acidification and strategies that reduce cellular iron demand. These mechanisms, however, may only confer resistance over short time periods, and chronic long-term exposure may result in further iron stress. Alternatively, many phytoplankton taxa already flourish within the high pH variability in coastal upwelling regions, and acidification may not hinder continued high levels of productivity in these ecosystems.