Active uptake of bicarbonate by diatoms

Abstract

Marine diatoms play a predominant role in the biological carbon pump¹ transferring carbon dioxide from surface to deep waters. Laboratory studies show that a number of species take up HCO₃⁻ and concentrate inorganic carbon intracellularly allowing rapid growth despite low CO₂ availability²,³. In contrast, many oceanographers, particularly when interpreting carbon isotope data⁴,⁵, have made the assumption that diatoms do not utilize the abundant HCO₃⁻ in seawater but rather take up CO₂ by diffusion⁶. This has led to the hypothesis that large diatoms may be CO₂-limited in the oceans⁷. We now demonstrate active uptake of HCO₃⁻ in the field and a carbon-concentrating mechanism in coastal Atlantic diatoms. By manipulating $p_{{\text{CO}}_2}$ we show that growth of large diatoms in the California upwelling is not limited by ${\text{CO}}_{\text{2}}$ availability.