Reconstruction of Burdekin River runoff from fluorescent bands in massive Porites corals from the inshore Great Barrier Reef

Full description

Coral cores, 90 mm in diameter, were collected from two inshore reefs on the Great Barrier Reef, Australia. One core was collected from a 4.0m high colony of P. Lutea on Pandora Reef, and the second core was collected from an 8.1m high colony of P. lovata on the fringing reefs surounding Havanah Island. The custom built underwater pneumatic drilling rig (Isdale and Daniel, 1989) was used to drill up to 800mm continuous lengths from coral colonies.

Coral slices of 7-mm thickness closest to their diameter were X-rayed and photographed under ultraviolet excitation. Measurements of relative fluorescence (luminescence) intensity were obtained using a purpose-built fluoromicrodensitometer (FLUORAC) and the fluorescence emitted was recorded at 0.425 mm intervals along the slice.

Streamflow data from October 1921 was supplied by the Water Resources Section of the Queensland Department of Natural Resources, Gauge Station 120001 on the Burdekin River at Home Hill. Records up to 1950s were via staff gauge and a continuous recording gauging stations was then built at Clare.


Other climate data used in the analysis included Rainfall and temperature in Queensland, as well as an index of cloud amount


This research was undertaken to develop a reconstruction of past runoff for the Burdekin River, based on fluorescence (luminescence) measurements from massive Porites corals collected from two inshore reefs, which lie in the path of the northward drift of the Burdekin River plume.


This data has been superseded by a more recent analysis with updated methods found in the record linked below "Freshwater Impacts In The Central Great Barrier Reef: 1648-2011"

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: The drilling rig used to collect coral cores is described in:Isdale PJ and Daniel E (1989) The design and deployment of lightweight submarine fixed drilling system for the acquisition of coral cores. Marine Technology Society Journal 23: 3-8.The FLUORAC system was mounted on a custom-built scanning table and controlled by a microcomputer. The coral slices were passed under a 2 mm diameter spot of 360 nm (± 20 nm) wavelength focused via an optical system from a 100-watt mercury arc lamp source. The fluorescence emitted was recorded at 0.452-mm intervals along the coral core. Since fluorescence was not measured in absolute terms, a common standard was used to ensure that consecutive determinations between core sections were comparable. A uranyl glass block, which is ultraviolet light-stable, was used as a calibration standard within and between each section and whole core.The fluorescence measuring system incorporated a small photodiode in the light path to measure the stability of the light output. No drifts or anomalies in excess of 5% in light output were detected. The raw data consisted of emission units relative to the uranyl glass standard at the same excitation level against distance along the coral core. The data were converted to a time series using a recursive-diminishing window smoothing algorithm that identified a seasonal low value for each year, corresponding to the winter dry season of little or no river flow. The accuracy of these low values was checked by reference to the photographs of the fluorescent bands in the core. Obvious mismatches (usually not more than a few positions on each core section) were corrected by inserting or deleting seasonal low values. Twelve intermediate data points were then interpolated between the two original low points of each annual cycle. The 12 relative fluorescence values between each annual minimum were then totalled to give a single annual value. This value was taken to represent the amount of fluorescing material incorporated into the coral skeleton during one seasonal wet/dry cycle. The annual time series for each core was then standardized by the appropriate long-term mean and standard deviation.

Notes

Credit
Lough, Janice M, Dr (Custodian)

Credit
Isdale, Peter J, Dr (Principal Investigator)