Variability of nutrient regeneration rates and nutrient concentrations in surface sediments of the northern Great Barrier Reef shelf

Sediment nutrient concentrations and fluxes were examined on the northern Great Barrier Reef (GBR) shelf to determine the extent of temporal and spatial variability. Despite a clear sediment gradient of increasing carbonate content seaward and differences in river discharge along-shelf, no significant differences in nutrient concentrations or fluxes across the sediment–water interface were observed for most nutrients along- or across-shelf over time. Only interstitial P and DOC concentrations displayed significant differences along-shelf and only in the wet season. Rates of nutrient regeneration were highly variable, but contributed, on average, 11% of N and 22% of P requirements for phytoplankton production, similar to the benthic contribution for primary production on the central GBR shelf. The lack of clear patterns in the size of the sediment nutrient pools and fluxes are contrary to patterns on most other shelves, and may be partly the result of intense dilution, mixing and transport processes operating at small to large spatial scales over time.