Radiocarbon isotopic evidence for assimilation of atmospheric CO2

Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Abstract Introduction Conclusions References Tables Figures Back Close Full Screen / Esc Abstract Submerged aquatic vegetation assimilates dissolved inorganic carbon (DIC) in the water column as a carbon source across its thin cuticle layer. However, it is expected that marine macrophytes also use atmospheric CO 2 when exposed to the air during low tide, although assimilation of atmospheric CO 2 has never been quantitatively evalu-5 ated. Using the radiocarbon isotopic signatures (∆ 14 C) of the seagrass Zostera marina and DIC, we show quantitatively that Z. marina takes up and assimilates atmospheric modern CO 2 in a shallow coastal ecosystem. The ∆ 14 C values of the seagrass (−36 to −8 ‰) were significantly higher than those of aquatic DIC (−45 to −18 ‰), indicating that the seagrass uses a 14 C-rich carbon source (atmospheric CO 2 , +17 ‰). A carbon-10 source mixing model indicated that the seagrass assimilated ∼ 46 % (mean: 22 %) of its inorganic carbon as atmospheric CO 2. CO 2 exchange between the air and the sea-grass may be enhanced by the presence of a very thin water film over the air-exposed leaves during low tide. Our radiocarbon isotope analysis, showing assimilation of atmospheric modern CO 2 as an inorganic carbon source, offers better understanding of 15 the role of seagrass meadows in coastal carbon dynamics.