Climate swings enhance marine heatwave risks off the Kimberley coast

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Scientists have confirmed that under global warming, stronger swings of climate variability, on top of the warming trend, will enhance the likelihood of marine heatwave risks off the Kimberley coast.

The findings, published in Scientific Reports, are part of a Western Australian Marine Science Institution Kimberley Marine Research Program investigation into how sensitive the coastal marine waters off the Kimberley are to variability and changes in ocean temperature, sea level, and shelf circulations.

Lead researcher, CSIRO’s Dr Ming Feng, along with a team of scientists and students, looked at historical data and numerical modelling and found that over the past six decades, ocean temperatures off the Kimberley coast have been rising at a moderate rate of about 0.05 to 0.1°C per decade, lower in comparison to waters off the southwest coast of Australia.

“The ocean temperatures on the continental shelf off the Kimberley coast are predominantly influenced by the air-sea exchanges, instead of coastal currents,” Dr Feng said.

“Unlike ocean temperatures off the west coast, sea surface temperatures at Scott Reef  and off the Kimberley coast are warmer during El Niño events, not La Niña events, despite coastal sea levels tending to be higher during La Niña,” Dr Feng explained. “We believe this is due to weaker Australian monsoons and reduced air-sea heat losses to the atmosphere, as well as reduced cloud coverage which enhances solar radiation.”

Sea surface temperature anomaly composites in austral summer during (left panel) El Niño and (right panel) La Niña events.

A large number of the world’s coral reefs were recently influenced by one of the most severe El Niño events on record that lasted from early-2014 to mid-2016. Dubbed the Godzilla-El Niño, it caused severe coral bleaching worldwide, including in regions previously considered resilient to these effects, such as the tropical reefs in the southeast Indian Ocean.

Over the past 30 years, satellite observations have also revealed that the Kimberley coast appears to experience more frequent extreme hot temperatures during summer.

It is believed that ocean temperatures and marine species off the Kimberley coast are highly sensitive to future climate change. There is, however, a lack of knowledge on interannual and longer term variability in the region.

“Poor historical data coverage, rough topography and strong tidal currents have prevented us from gaining a better understanding of the thermodynamics in the region,” Dr Feng said.

“We believe that tidal mixing is likely to play a key role in regional heat balance and biochemical processes. Surface salinity and ocean stratification off the Kimberley coast are also strongly influenced by climate variability.

“In response to increasing greenhouse gases, extreme El Niño and La Niña events are projected to increase,” Dr Feng said. “Our work shows that under the influence of different flavours of El Niño–Southern Oscillation (ENSO), and modified by Indian Ocean and decadal climate modes (like IOD, MJO, IPO) and local air-sea interactions, the coral bleaching potentials vary across the southeast Indian Ocean, and may occur more frequently in a warming world.”

Dr Feng will be presenting the latest results at a Lunch and Learn information session at the Department of Parks and Wildlife, Kensington, Western Australia on 17 August, 2017. The presentation will be made available online at  www.wamsi.org.au/climate-change.

Results of the final WAMSI report Knowledge Integration and Predicting Biophysical Response to Climate Change are due to be published later this year.

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The $30 million Kimberley Marine Research Program is funded through major investment supported by $12 million from the Western Australian government’s Kimberley Science and Conservation Strategy co-invested by the WAMSI partners and supported by the Traditional Owners of the Kimberley.

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Kimberley Marine Research Program