We have just completed a two week voyage around the top of Australia and along the Great Barrier Reef shelf edge on the RV Southern Surveyor, Australia’s largest research vessel. The voyage from Broome to Brisbane was to explore and study the geographic limits of the drowned (or submerged) reefs that are known to lie along the shelf edge. We wanted to find their northern and southern limits, having previously mapped about 700 km of these deep reefs.
We sailed through the Timor Sea spotting humpback whales in the distance, then across the Arafura Sea before entering the island-studded Torres Strait at the tip of Australia. Good weather meant we could then sail down the outside of the Great Barrier Reef, hugging the shelf edge and mostly following the 100 m contour to map these reefs, which are found around this depth, using the vessel-mounted EM300 multibeam sonar.
Some highlights were cruising along the outside of the northern reef while watching the shallow Ribbon Reefs pass by very close to the ship, or watching the seafloor being revealed in 3D knowing we were the first people to map the ancient coastline, formed when sea-levels were about 100 m lower in the last ice age.
Around the vast Swains Reefs in the southern Great Barrier Reef we found hundreds of coral pinnacles 5 to 20 m high lying scattered across the platform on the outside of the shallow modern reefs. We think these numerous pinnacles will be an important habitat for deep marine life and will need to be further explored.
We finished the voyage by swath surveying Gardner Bank, a rocky area just offshore Fraser Island in southern Queensland waters. This site is the focus of continuing studies to understand the past history of the Great Barrier Reef during previous warm periods (called inter-glacials) when corals grew further south than they presently do.