Carbon Burial Rates in Sediments and a Carbon Mass Balance for the Herbert River Region of the Great Barrier Reef Continental Shelf, North Queensland, Australia

The largest century scale carbon reservoir in the Herbert River sector of the Great Barrier Reef continental shelf is carbonate carbon. This carbonate carbon is produced by corals, coralline algae, and other benthic organisms, and is stored on less than 13% of the area of the shelf. Maximum organic carbon burial rates (1–28 mol m 2 yr 1) occur within a wind-protected <20 m water depth embayment (<1% area of the shelf), where the highest bulk sedimentation rates (1–12 kg m 2 yr 1) were determined from 210Pb and 137Cs profiles in 1–4 m cores. Sediment, organic carbon (OC), and carbonate carbon (CC) accumulation rates are very low in the Great Barrier Reef lagoon shelf and slope, where most annual productivity (8–15 mol OC m 2 yr 1) is decomposed by algal and microbial respiration. A carbon mass balance indicated that approximately 1% of combined river and marine organic carbon production was preserved in across-shelf sedimentation, but 3% of river and mangrove organic carbon input was preserved in this small wind-protected embayment. An across-shelf carbon mass balance model predicted average shelf organic matter respiration correctly, and the ratio of organic carbon fixation to respiration (corrected for burial losses) was 1·06.