Felicity McAllister

Source of trace element variability in Great Barrier Reef corals affected by the Burdekin flood plumes

Abstract Massive corals in the Great Barrier Reef, analyzed at high-resolution for Sr/Ca (thermal ionization mass spectrometry) and trace elements such as Ba and Mn (laser ablation inductively coupled plasma mass spectrometry), can provide continuous proxy records of dissolved seawater concentrations, as well as sea surface temperature (SST). A 10-yr record (1989 to 1998) from Pandora Reef, an inshore reef regularly impacted by the freshwater plumes of the Burdekin River, is compared with an overlapping record from a midshelf reef, away from runoff influences. Surface seawater samples, taken away from river plumes, show little variability for Sr/Ca (8484 ± 10 μmol/mol) and Ba (33.7 ± 0.7 nmol/kg). Discrete Ba/Ca peaks in the inshore coral coincide with flood events. The magnitude of this Ba/Ca enrichment is most likely controlled by the amount of suspended sediments delivered to the estuary, which remains difficult to monitor. The maximum flow rate at peak river discharge is used here as a proxy for the sediment load and is shown to be strongly correlated with coral Ba/Ca (r = 0.97). After the wet summer of 1991, the coral Ba/Ca flood peak is followed by a plateau that lingers for several months after dissipation of plume waters, signifying an additional flux of Ba that may originate from submarine groundwater seeps and/or mangrove reservoirs. Both Mn and Y are enriched by a factor of ∼5 in inshore relative to midshelf corals. Mn/Ca ratios show a seasonal cycle that follows SST (r = 0.7), not river discharge, with an additional high variability in summer suggesting a link with biological activity. P and Cd show no significant seasonal variation and are at a low level at both inshore and midreef locations. However, leaching experiments suggest that part of the coral P is not lattice bound.

Dispersion and fate of produced formation water constituents in an Australian Northwest Shelf shallow water ecosystem

This was a study of produced formation water (PFW) discharged into a shallow tropical marine ecosystem on the Northwest Shelf of Australia. A combination of oceanographic techniques, geochemical tracer studies, chemical and biological assessment methods, and dispersion modelling was used to describe the distribution and fate of petroleum hydrocarbons and added nutrients discharged from an offshore production platform. Using fine scale volatile hydrocarbon data, the horizontal and vertical diffusion parameters for a three dimensional dispersion model were calibrated under local conditions. Trace hydrocarbon chemistry studies and integration of the data into a mass balance model, facilitated a comprehensive description of dispersion and degradation pathways and rates. Bio-accumulation into bivalves and water column microbial growth inhibition studies confirmed the chemistry and model predictions that the area of potential biological impact extended to 0.5 nautical miles (∼900 m) from the discharge with additional skewing in the direction of the predominant tidal flows. Impact would be expected to be concentrated in transient surface slicks and near surface seawater. Dispersion and degradation processes were fast enough to prevent any long-term build-up of contamination within the system. Trace levels of oil in the near field sandy sediments were directly related to the magnitude of the daily discharge. The study is a benchmark to help predict the effects of further oil industry expansion in this pristine coastal region.

Chapter 15 Merging scales in models of water circulation: perspectives from the great barrier reef

Publisher Summary This chapter describes the technique chosen to include the effect of the oceanic circulation in a 2-D model of the large-scale circulation on the continental shelf. This circulation is found to be modulated at an intermediate spatial scale by the interaction of the tidal circulation with individual reefs, and this process is modeled by merging large-scale and reef-scale 2-D circulation models. The oceanography of the Great Barrier Reef (GBR) is made particularly complex by the extraordinary complex bathymetry. In the GBR, the obstruction of the flow by the presence of reefs steers and modifies, even at these large scales, the oceanic inflow and the longshore currents. Obstruction by large reefs or a reef matrix steers prevailing currents toward areas of low reef density. This provides the modeler the challenge to merge the large-scale oceanic circulation with the shelf-scale general distribution of reefs over the shelf. The resulting currents through a reef matrix, and the deflection of the prevailing currents around a reef matrix, are modulated by the tides.

Advancing Ocean Monitoring Near Coral Reefs

Corals, the foundation of tropical marine ecosystems, exist in a symbiotic relationship with zooxanthellae (algae). The corals obtain much of their energy by consuming compounds derived from photosynthesis by these microorganisms; the microorganisms, which reside in the coral tissue, in turn use waste products from the corals to sustain photosynthesis. This symbiosis is very sensitive to subtle changes in environment, such as increased ocean acidity, temperature, and light. When unduly stressed, the colorful algae are expelled from the corals, causing the corals to “bleach” and potentially die [e.g., van Oppen and Lough, 2009].