Science Focii
GBROOS is an observation network that seeks to understand the influence of the Coral Sea on continental shelf ecosystems in north-east Queensland including the GBR Marine Park. In the next decade, GBROOS will monitor the effect of rising ocean temperatures on the incidence of coral bleaching, and on the frequency of regional upwelling that fuels productivity in sections of the GBR. In the longer term, GBROOS will monitor the impact of global climate change upon ocean chemistry that threatens the survival of calcifying organisms.
The South Equatorial Current (SEC) is the dominant flow in the Coral Sea. On reaching the Australian coast, the SEC bifurcates into northern and southern boundary currents. The northern arm is responsible for driving a clockwise gyre in the Gulf of Papua that is a nursery for tropical rock lobster; a major resource for indigenous communities in the Torres Strait. The southern arm becomes the East Australian Current (EAC), which flows down the eastern seaboard and affects coastal climate and ecosystem performance from southern Queensland to Tasmania.
The Coral Sea also directly affects the regional climate of the GBR. Despite these regional and far-reaching influences, the Coral Sea is the least intensively studied regional sea in the Australian Marine Jurisdiction. The SEC is dynamic on annual and decadal time scales. Variations in flow of the EAC associated with the Southern Oscillation Cycle (El-Nino/La-Nina) affect the heat and carbonic acid stress on the outer barrier reef, and the replenishment of commercial fish stocks along the eastern seaboard. The latter may result from variable alongshore flows and/or eddy instabilities or they may result from variations in the productivity of coastal seas.
In the central GBR, the slope bathymetry favours intrusion of Coral Sea water onto the continental shelf and flushing of the outer Lagoon while also suppressing cross-shelf exchange. Many of these intrusions draw cool nutrient rich water from the deeper Coral Sea onto the shelf, which could explain the higher productivity of fisheries in the southern GBR. While the dynamics of the Coral Sea appear important to the normal functioning and health of coral reef ecosystems on the outer shelf, there are signs that climate change resulting in surface ocean warming will introduce new threats.
Coral bleaching and coral disease is caused in large part by rising ocean temperatures. This same warming of the oceans will suppress vertical mixing and up-welling at the shelf-break, which could starve GBR food chains of essential nutrients. Finally, continued uptake of excess carbon dioxide by the ocean is predicted to change carbonate chemistry in ways detrimental to all organisms with calcareous skeletons. While this could impair the performance of diverse animal groups, including reef-building corals, changes affecting the major planktonic calcifiers (coccolithophores, foraminifera, pteropods) could result on major disruptions to energy flows and nutrient cycles.
A recent report from the British Royal Society on global climate change concluded that the “adverse effect on calcification is one of the most obvious and possibly most serious of the likely environmental impacts of ocean acidification.” (Raven et al. 2005).
The GBROOS Science Plan is based on understanding the following issues:
- Changes in ocean chemistry from climate change
An instrumented deep-sea mooring (>1000m depth) on the Queensland Plateau will monitor long-term change in the Coral Sea (temperature, salinity, CO2 chemistry, productivity). This mooring would be part of a national network of long-term reference stations and contribute to global efforts to quantify global heat and carbon budgets from burning fossil fuels.
- Dynamics and changes in the forcing of the East Australian (boundary) Current
Instrumented slope moorings (>100m) on both sides of the bifurcation will monitor variations in the alongshore flows measured on the slope that will be related back to variability of the SEC as measured by BlueLink. Additional moorings in the southern GBR will monitor the strength of currents immediately upstream of the Capricorn gyre and relate its dynamics to upwelling events detectable on the Capricorn-Bunker Shelf.
- Dynamics and changes to up-welling in the central GBR
AIMS weather towers offshore of Townsville will be equipped to transmit real-time data on vertical temperature gradients in the Palm and Magnetic Passages. Apart from revealing the conditions that force deep water onto the shelf, real-time monitoring will allow planned experiments on heat stress, acidification and the biological impacts of up-welling events.
- Calibration and validation of satellite remote sensing products
Current satellite-derived maps of sea surface temperature and ocean colour are calibrated to northern hemisphere observing conditions that are significantly different from humid tropical atmospheres. Two research vessels operated by AIMS will be fitted with additional sensors to make underway measurements during the 700 days that they spend at sea each year.
- Shelf-scale currents
Oceanographic buoys will transmit real-time hydrodynamic properties (e.g. current velocity, temperature, salinity) from the northern, central and southern GBR Lagoon. Buoys will be located near the four Island Research Stations (Lizard, Orpheus, Heron, One Tree) to facilitate maintenance and to provide local service. The provision of real-time hydrodynamic properties from these latitudes will provide the basis for a data-assimilating shelf-scale model of circulation covering the majority of the GBR; available to all researchers.
- Demonstration sites for development and testing of sensor network technology
The island research stations will provide platforms for developing the next generation of underwater observing systems based upon wireless sensor networks. Such networks have enormous potential to measure physicochemical and kinetic environments at unprecedented resolution and are very suitable to current efforts to understand the impacts of ocean climate upon the physiological stress states of coral reef organisms.
The research challenges that the current level of knowledge and understanding produce includes:
- How to integrate the various scales of processes that determine and influence the overall movement of water through the reef matrix and to produce models and understandings that better allow us to predict the impact of change on the overall system;
- How to gain a better understanding of the impact of micro-climate on corals and other species and how their responses to temperature and other events is tied into or explained by the measured micro-climate;
- How to develop systems that can effectively monitor a system that is 1.3 times the size of the United Kingdom, complex at all scales and that is undergoing complex change in response to climate and other changes.