Factors affecting broadscale variation in nearshore water-column organic carbon concentrations along the Great Barrier Reef

Organic carbon is a key energy source in marine food-webs, but elevated concentrations can have negative ecological impacts. We used 12 years of marine physiochemical, climate, and near-surface sea and meteorological condition data to investigate broadscale correlates and potential drivers of variability in dissolved and particulate organic carbon (DOC and POC, respectively) concentrations in coastal waters of the Great Barrier Reef (GBR), Australia. DOC concentrations were higher when salinity was lower, when the Southern Oscillation Index was more positive, and at times of greater northward wind speeds. POC concentrations were higher in shallower waters and were positively correlated with total suspended solids and chlorophyll a concentrations. Latitude was important for structuring variation in organic carbon concentrations, likely reflecting terrestrial material from rivers and broader marine processes. We conclude that variability in broadscale patterns of DOC concentrations in GBR coastal waters is likely most sensitive to material discharge from rivers as well as oceanographic and climatic processes and forcing. Variability in broadscale patterns of POC concentrations in coastal waters of the GBR is likely most affected by sediment resuspension and phytoplankton biomass accumulation.