The Impact of Ocean Acidification on the Sorption of Trace Metals by Diatoms

Abstract

Diatoms are a major phytoplankton group that plays a critical role in aquatic biogeochemical processes. Their metabolism relies on trace metals as cofactors for numerous enzymes, and changes in seawater pH may therefore influence metal sorption. Here, we investigated the effects of pH variability on diatom growth and trace‐metal sorption using neutron activation analysis (NAA). Although NAA has rarely been applied to phytoplankton, we demonstrate its suitability for marine diatom samples. Overall, diatoms exposed to CO 2 treatment exhibited higher cell abundance but lower intracellular elemental concentrations. In particular, Nitzschia navis‐varingica showed significantly lower concentrations of Al, Ce, Co, Cr, Fe, Mg, Mn and Zn under the CO 2 treatment. These trends are consistent with previous studies. For example, Zinc, which is a cofactor in many enzymes, plays a role in inorganic carbon acquisition; under lower pH, reduced enzymatic metal requirements likely explain the lower Zn concentrations observed. Nitzschia navis‐varingica also had significantly lower levels of Co under lower pH. Both Thalassiosira pseudonana and Nitzschia navis‐varingica showed lower Fe concentrations under CO 2 treatment. As Iron is required for photosynthetic and respiratory processes that support the carbon‐concentrating mechanism (CCM), reduced CCM activity at lower pH may decrease Fe demand. Overall, this study highlights NAA as a robust approach for quantifying metal sorption in marine organisms and provides new insight into the effects of ocean acidification on the growth and elemental composition of diatoms.

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