Budgeting sinks and sources of CO₂ in the coastal ocean: Diversity of ecosystems counts

TLDR

High‑latitude marginal seas absorb atmospheric CO₂, whereas subtropical and tropical marginal seas emit CO₂. The study up‑scaled air‑water CO₂ fluxes across latitudes and ecosystem types using a comprehensive literature survey. Marginal seas sequester about 0.45 Pg C yr⁻¹ of CO₂, but near‑shore coastal ecosystems emit roughly 0.40 Pg C yr⁻¹, nearly offsetting the sink and highlighting the role of ecosystem diversity.

Abstract

Air‐water CO 2 fluxes were up‐scaled to take into account the latitudinal and ecosystem diversity of the coastal ocean, based on an exhaustive literature survey. Marginal seas at high and temperate latitudes act as sinks of CO 2 from the atmosphere, in contrast to subtropical and tropical marginal seas that act as sources of CO 2 to the atmosphere. Overall, marginal seas act as a strong sink of CO 2 of about −0.45 Pg C yr −1 . This sink could be almost fully compensated by the emission of CO 2 from the ensemble of near‐shore coastal ecosystems of about 0.40 Pg C yr −1 . Although this value is subject to large uncertainty, it stresses the importance of the diversity of ecosystems, in particular near‐shore systems, when integrating CO 2 fluxes at global scale in the coastal ocean.