Australasian Science: Australia's authority on science since 1938

Corals Reveal Pacific Cycles

By Stephen Luntz

The pattern of ocean temperatures known as the Pacific Decadal Oscillation (PDO) has been detected in corals from the mouth of Queensland’s Fitzroy River.

The same University of Queensland study has picked up the legacy of the huge 2011 flood for the first time.

Floods in river catchments sweep organic material into the oceans, and this material becomes incorporated into corals growing nearby. The pattern of larger floods in La Niña years has been observed for some time.

The PDO bears some similarities to the better-known El Niño Southern Oscillation (ENSO), with the western Pacific Ocean being warmer in negative periods while positive recordings are associated with warmth to the east – as in El Niño events. However, the PDO is most strongly observed away from the Equator, and operates on a cycle of 15–30 years rather than 3–5 years for ENSO.

This longer period makes patterns harder to detect, but the signal has been observed in tree rings and corals from other regions.

“As a result of this research, we now know that corals from this area have great potential for reconstructing even longer-term historical evolution of the Pacific Decadal Oscillation,” says Prof John Pandolfi of the School of Biological Sciences. “Some bommies are 5–6 metres tall and 400 years old. They can provide us with much longer-term information than is available from satellite-based data, which goes back only 40–50 years. This will help refine future models for predicting this important climate phenomenon.”

Dr Alberto Rodriguez-Ramirez of the School of Earth Sciences says that the combination of a La Niña and a negative PDO contributed to the huge 2011 floods. “Our study suggests that this oscillation will influence the frequency and intensity of future extreme events such as floods – as well as ecological processes – in the region,” he said.

The findings were published in PLOS One, along with the fact that increased run-off due to land-use changes could also be detected in the corals.