High carbon dioxide emissions from Australian estuaries driven by geomorphology and climate

Estuaries play an important role in connecting the global carbon cycle across the land-to-ocean continuum, but little is known about Australia's contribution to global CO₂ emissions. Here we present an Australia-wide assessment, based on CO₂ concentrations for 47 estuaries upscaled to 971 assessed Australian estuaries. We estimate total mean (±SE) estuary CO₂ emissions of 8.67 ± 0.54 Tg CO₂-C yr^-1, with tidal systems, lagoons, and small deltas contributing 94.4%, 3.1%, and 2.5%, respectively. Although higher disturbance increased water-air CO₂ fluxes, its effect on total Australian estuarine CO₂ emissions was small due to the large surface areas of low and moderately disturbed tidal systems. Mean water-air CO₂ fluxes from Australian small deltas and tidal systems were higher than from global estuaries because of the dominance of macrotidal subtropical and tropical systems in Australia, which have higher emissions due to lateral inputs. We suggest that global estuarine CO₂ emissions should be upscaled based on geomorphology, but should also consider land-use disturbance, and climate.