When did Australia’s climate become so dry? When did tropical reefs around Australia develop? And what will happen to Australia’s climate and reefs in the future?
The answer to these questions can be found by digging into the distant past. That means digging deep into the Earth’s crust, and you don’t always need to be on dry land to do that.
The US scientific ship JOIDES Resolution is capable of drilling deep under the ocean’s floor. It will depart Fremantle, in Western Australia, next month on a two month expedition to help shed light on some of the mysteries about Australia’s past. On board will be an international team of 30 scientists co-led by myself.
The JOIDES Resolution is named in honour of HMS Resolution that was commanded by Captain James Cook more than 200 years ago when he explored the Pacific Ocean. It is the flagship of the International Ocean Discovery Program (IODP), the world’s largest Earth science program whose country members include Australia and New Zealand.
The plan is to travel from Fremantle to Darwin and drill a series of cores of up to a kilometre deep into the seabed. This will give us a five million year history of climate and environmental change off the west coast of Australia.
Ocean drilling is the best method to directly sample the layers beneath the sea bed and it tells us how the Earth has worked in the past, how it is working now and how it might work in the future.
The origin of Australia’s western tropical reefs
The history of Australia’s climate is linked to oceanic conditions off its coastline.
Tropical reefs such as the Houtman-Abrolhos reefs off western Australia are controlled by the warm southward flowing offshore Leeuwin Current. This current is related to the global circulation system of ocean currents that travels through the Indonesian archipelago, called the Indonesian Throughflow.
Global ocean circulation controls the Earth’s climate. It transports water heat from the Pacific to the Indian Ocean and then to the poles.
Previous research has shown that ocean circulation in the Indian Ocean slowed down or nearly stopped near the Indonesian archipelago many times in the past. Every time this happened, the global climate changed, leading to cooling of the Indian Ocean and drier climates.
Our expedition hopes to study fossils and sediments in the layers from below the seabed to chart the history of these ocean features over millions of years. We seek to understand how global ocean circulation has changed and its climatic consequences.
The aim is to establish when tropical conditions suitable for reef growth first occurred and whether these conditions have changed over millions of years.
Looking into the past history of these reefs and ocean currents will improve our understanding of how modern reefs and currents off west Australia might behave with future climate change.
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