Upwelling as a Source of Nutrients for the Great Barrier Reef Ecosystems: A Solution to Darwin's Question?

Abstract

The Great Barrier Reef shelf ecosystem is examined for nutrient enrichment from within the seasonal thermocline of the adjacent Coral Sea using moored current and temperature recorders and chemical data from a year of hydrology cruises at 3 to 5 wk intervals. The East Australian Current is found to pulsate in strength over the continental slope with a period near 90 d and to pump cold, saline, nutrient rich water u p the slope to the shelf break. The nutrients are then pumped inshore in a bottom Ekman layer forced by periodic reversals in the longshore wind component. The period of this cycle is 12 to 25 d in summer (30 d year round average) and the bottom surges have a n alternating onshoreoffshore speed up to 10 cm S-'. Upwelling intrusions tend to b e confined near the bottom and phytoplankton development quickly takes place inshore of the shelf break. There are return surface flows which preserve the mass budget and carry silicate rich Lagoon water offshore while nitrogen rich shelf break water is carried onshore. Upwelling intrusions penetrate across the entire zone of reefs, but rarely into the Lagoon. Nutrition is del~vered out of the shelf thermocline to the living coral of reefs by localised upwelling induced by the reefs. Bottom chlorophyll concentrations average 0.4 mg m-3 a t the inner reefs and 0.8 mg m-3 near the shelf break while surface concentrations average 0.3 mg m-3; annual top and bottom variances are respectively 0.5 and 1.9 m g m-3 and there is no apparent seasonal cycle. The estimated onshore nitrogen flux in a 10 m thick bottom layer gives an annual nitrogen input of 20 yg at 1-' throughout the water column in a 50 km zone of reefs, a n enormous value for tropical waters.

Physical forcing of phytoplankton community structure and primary production in continental shelf waters of the Western Antarctic Peninsula

“…Subsurface intrusions and subsequent upwelling or upward mixing of oceanic waters have been observed in other regions, such as the southeastern U.S. continental shelf (Atkinson, 1977(Atkinson, , 1985 and the east coast of Australia (Andrews and Gentien, 1982). Estimates of the nutrient and carbon fluxes associated with intrusion events on these continental shelves (e.g.…”

Oceanographic forcing of nutrient uptake and release over a fringing coral reef

“…Many reefs, not just Ningaloo, are influenced by upwelling that can lower temperatures and elevate nutrient concentrations (Andrews and Gentien 1982;Gove et al 2006;Chollett et al 2010). Fore-reef NO x concentrations at Ningaloo varied substantially between the austral spring and autumn, likely in response to the spring and summer equator-ward wind regime and sporadic upwelling (Hanson et al 2005;Wyatt et al 2010).…”

Regional Variability of Surface Ocean Radiocarbon from Southern Great Barrier Reef Corals

“…Abraham Reef is located on the southeastern tip of the outer Great Barrier Reef, 200 km offshore of the Queensland coast. It lies close to the shelf break where upwelling has been observed (Andrews and Gentien 1982). The predominant flow in this region is from the westward East Australian Current (EAC).…”