Spatial Distribution of CO2, CH4, and N2O in the Great Barrier Reef Revealed Through High Resolution Sampling and Isotopic Analysis

Methane (CH4) and nitrous oxide (N2O) dynamics in coastal coral reef areas are poorly understood. We measured dissolved carbon dioxide (CO2) and CH4 (with delta C-13-CO2 and delta C-13-CH4 isotope fractions) and N2O in the Great Barrier Reef (GBR) to determine spatial distributions and emissions. CO2 (379-589 mu atm) was oversaturated due to calcification and riverine sources, as indicated by depleted delta C-13-CO2 values. CH4 (1.5-13.5 nM) was also oversaturated from nearshore biogenic sources indicated by depleted delta C-13-CH4 and probable offshore aerobic production. N2O (5.5-6.6 nM) was generally undersaturated, with uptake highest near the coast. Daily CO2 emissions were 5826 +/- 1191 tonnes, with CO2 equivalent ((eq)) N2O uptake (191 +/- 44 tonnes) offsetting 3.3% of CO2 or 89% of CH4eq (214 +/- 45 tonnes) emissions based on 20-year global warming potentials. The GBR was a slight CO2 and CH4 source and N2O sink during our study. However, further work is required to constrain diurnal, seasonal, and spatial dynamics.