Ross Isaacs filming at North Horn. (photo- Lance Robb- Closed Circuit Divers)
Discovered in 1803, Osprey Reef is located 120 nautical miles east of the Australian mainland, beyond the Great Barrier Reef. The reef is perched on top of an isolated seamount in the Coral Sea and is not part of the Great Barrier Reef system itself. It rises over a kilometre up from the deep-sea floor to the ocean’s surface. The north western face has vertical drop offs, which form sheer undersea cliffs plunging straight down into the cobalt depths.

Noted for undersea life, cold nutrient-rich, deep-water currents stream up the steep sides of the seamount, stimulating an abundance of plankton, which is key to feeding the plentiful marine life here. The shallow waters have only been accurately charted in modern times and deep-water habitats below 200 metres deep have been inaccessible. This location has become highly significant for oceanographers and marine biologists and a focus of some intense exploratory expeditions.

Osprey Reef is formed on the Queensland Plateau, an immense geological feature submerged on the floor of the Coral Sea off Australia’s north east coast. The Plateau was once a part of Australia, but with the continued break up of the ancient super-continent of Gondwanaland, which started 150 million years ago, it separated from the mainland. Today it’s submerged, and separated from Australia’s coast by a one-kilometre-deep rift in the sea floor known as the Queensland Trough. Osprey Reef is on the edge of the northern fringe of the plateau, next to the trough, one of several oceanic coral atolls that have grown up on the plateau’s surface.

Undersea Explorer perfect CCR platform. (photo- Lance Robb- Closed Circuit Divers)
Formed on the Queensland Plateau, an immense geological feature submerged on the floor of the Coral Sea off Australia’s north east coast. Today it’s submerged, and separated from Australia’s coast by a one-kilometre-deep rift in the sea floor known as the Queensland Trough. Osprey Reef is on the edge of the northern fringe of the plateau.
Using deep sensing technology, scientists have been able to build up a three dimensional representation of the seabed and build a 3D model of Osprey Reef. This research has revealed that below 40 metres the coral wall drops vertically down to a narrow terrace at a depth of around 110 meters. As the terrace coincides with where the sea level would have been 20,000 years ago it is thought that this terrace is a wave cut formation. This is remnants of an ancient sea in a period when the Earth was going through a glacial period of the Ice Age.

12,500 years ago the ice sheets melted and the coral reef system grew with the rising sea level creating a submerged atoll with a central lagoon 25 kilometres long, 8 kilometres wide and 40 metres deep surrounded by a wide outer reef flat. Below the wave cut terrace the coral wall falls vertically until it reaches a dramatic gradient which angles away to submarine canyons down to the floor of the Queensland Trough.

Research was clearly confined to the top shallow layers of Osprey Reef with much of the studies involving animals such as the large population of grey reef sharks. It is a tantalizing thought when one peers down into the cobalt blue beside the drop offs and ponders the mysteries which are yet to be revealed down there. Scientists had small windows to the depths by setting traps to catch the rarely seen nautilus which rise up to 100 meters at night.
Lance Robb on deco stop after 156 metre dive. (photo- Ross Isaacs- Ocean Planet Images)
The Expedition

A recent expedition to Osprey Reef comprised of scientists from Queensland University and a deep diving rebreather team which included our film crew to document this and future expeditions. The deep water surrounding are inhabited by marine animals, from prehistoric past and the team will utilize rebreathers and deep sea drop cameras to discover what lies below the 40 metre layer.

During the past 20 years, research using open circuit scuba has focussed on the top shallow 40 metre layer of around Osprey Reef. Advances in new technology has enabled researchers to investigate increasingly greater depths and record the animals living there. The layer from 40 to 150 metres is now accessible by divers using closed circuit rebreathers. Lance Robb led the rebreather team and is one of the first Megalodon close-circuit rebreather instructors in Australia. I am producer and director of a film documenting the event and the natural history of Osprey Reef. The principle objective of the deep rebreather dives was to explore this second layer and film the structure and inhabitants of the drop off to 150 metres and retrieve rock samples for later scientific analysis.

This would be the last chartered expedition of the Undersea Explorer and it would be a memorable trip with some new records being set by the teams onboard. The human perspective cannot be underestimated, analogous to people actually setting foot on the lunar surface, you get an added subjective dimension of what a place is like if you go there in person.

The northwest face of Osprey Reef is bathed in crystal clear water usually displaying extraordinary horizontal visibility. So much so that if you are frightened of heights you can experience vertigo as you leave the shallow reef flat area and launch yourself out into the deep water, hovering near the drop off as it disappears into the depths below. At places the undersea cliff faces actually go in on themselves and the sensation of diving beside these looming drop offs is exhilarating. North Horn is legendary for the large numbers of grey reef sharks, silvertip whalers and sometimes schools of hammerheads down at 50 metres. Mantas can be observed in large numbers off Ragging Horn. Admiralty Entrance and False Entrance are wonderful dive locations and perfect boat anchorages, as Osprey Reef is situated out in the open ocean of the Coral Sea and offers little protection when the wind is blowing.
Lance Robb after 156 metre dive. (photo- Ross Isaacs- Ocean Planet Images)
Diving to 156 metres is a complex and exacting procedure. There is a great deal of preparation to work out the decompression stops and choose the gases which would be required in case of bail out to open circuit scuba at any depth. Lance had five bail out tanks consisting of different gas mixtures from rich helium trimixes all the way through to 100% oxygen. The propulsion unit used to tow diver, rebreather, 5 bailout tanks and carry the video camera was a Dive X-tras, Sierra which has fabulous thrust and performance. It took 6 minutes for Lance to descend down to 156 meters, he had 3 minutes at that depth with a total run time back to the surface of 201 minutes with the majority of time spent on staged decompression stops on the way back to the surface to off gas the helium and nitrogen from his blood.

Lance’s rebreather of choice is the standard ISC Megalodon closed circuit rebreather with a Shearwater Predator integrated into the control head. Naturally Lance planned to stay on the rebreather for the entire dive. However diving to these depths it would be absurd not to take enough contingency gases to be able to safely get back to the surface with all decompression obligations taken care of. I use a spun down cave Megalodon with an integrated Shearwater Predator as I want to cut down on weight due to the fact I carry a Gates Deep Red underwater housing for a Red One digital cinema system and lights. We use Gates underwater housings because they are functional, easy to operate engineering masterpieces. Lance has his Sony EX1 in a Gates housing to compliment my Deep Red which is the main production camera for the film.

The Megalodon rebreathers performed faultlessly and we had some amazing dives along the northwest face of Osprey Reef. The scientists also deployed deep drop cameras known as “LANDERS” and filmed some weird and wonderful creatures at the next layer between 200 and 1,500 metres. The combined footage of the rebreather dives and the LANDERS cameras made a great start to begin to understand the complex biodiversity of this extraordinary, isolated location as we start to plan the next expedition to Osprey Reef.

Ross Isaacs with Deep Red camera system. (photo- Lance Robb- Closed Circuit Divers)