Coloured Dissolved Organic Matter Dynamics in the Great Barrier Reef

The coloured dissolved organic matter (CDOM) pool was studied to provide information about the characteristics and dynamics of the dissolved organic carbon (DOC) fraction in the largest contiguous coral reef system in the world, the Great Barrier Reef, Australia. The large-scale dataset consisted of 793 discrete measurements collected in offshore and coastal regions in the period from 2004 to 2017. The study demonstrates that despite spatialtemporal variations, the CDOM values in the Great Barrier Reef are comparable to those found in other oligotrophic coastal waters. The CDOM optical properties suggest a higher terrestrial contribution and low photochemical degradation of CDOM during the Austral wet season, which is in line with the higher river inputs and overcast conditions during this period compared with the other seasons. The study also revealed a strong relationship between the DOC normalized CDOM absorption coefficient at 350 nm and the spectral slope between 275 nm and 295 nm (S275-295), suggesting that the correlation between DOC and CDOM varies depending on the DOC properties or source. The poor relationship between CDOM and salinity could be explained by a range of factors, but is likely primarily linked with the extensive photochemical degradation and generally low river inputs in the Great Barrier Reef.