International team of scientists try to unravel the Ontong Java Plateau mystery | POGO

International team of scientists try to unravel the Ontong Java Plateau mystery

In January 2015, Hobart hosted a visit from Schmidt Ocean Institute’s (SOI) international oceanographic research vessel (RV) Falkor, arriving from the northwest Pacific Ocean before heading to the Tasman Sea. SOI offers ship time to technology-focused science projects through awards given to researchers from around the world, whose proposals are successfully selected through a competitive process.

Prof Mike Coffin, a marine geophysicist and Executive Director of the University of Tasmania’s Institute for Marine and Antarctic Studies (IMAS), is just back from leading a voyage between the Solomon Islands and Micronesia.


The largest volcanic eruption in the planet’s history most likely formed the Ontong Java Plateau, a submarine elevation the size of Western Australia that mostly falls within the marine jurisdiction of the Federated States of Micronesia, Papua New Guinea, and Solomon Islands.

It is a region little-known for anything other than perhaps the last confirmed position of Amelia Earhart’s plane in 1937 as she attempted the first global circumnavigation by a woman. What caused the massive volcanic eruption 122 million years ago remains a mystery, one that has engaged me for two decades.

To try to unravel the Ontong Java Plateau mystery and a host of other secrets, the RV Falkor took an international team of scientists from Australia, Europe, North America, and Pacific Islands to the region in a search for clues that might help explain what happened. Fossils found in drillcore sediment samples immediately overlying the volcanic rock forming the Plateau are from the same geological age—Aptian, in the Early Cretaceous epoch. That’s why scientists are reasonably confident that the plateau was formed in a single, massive release of magma lasting on the order of one million years. The total release is estimated to have been more than a million times larger than the largest volcanic eruption in recorded history.

Multibeam echosounders constituted the primary tool for our RV Falkor expedition. Multibeam echosounding sweeps across the seafloor mapping its contours or bathymetry using acoustic signals. Highly accurate navigation and state-of-the-art multibeam echosounding were the two technological keys to the success of this expedition and Falkor excelled at both.

Multibeam echosounding was developed in the early 1960s by the US Navy, and the first commercial system became operational in 1977, on the Australian survey vessel HMAS Cook. In the intervening 37 years, commensurate with exponential increases in computer capabilities, the technology has undergone several generational advances. Falkor’s Kongsberg 30 kHz EM302 and 70-100 kHz EM710 are the latest generation of multibeam echosounders, with operating ranges in water depths of 10-7000 meters and 3-2000 meters, respectively.

The augmented Global Positioning System (GPS) currently installed on Falkor provides an accuracy of 10 centimeters anywhere in the ocean. This level of accuracy was unimaginable even a few years ago, yet with multiple satellite navigation systems now operational - US (GPS) and Russian (GLONASS) – or under construction - European (Galileo) and Chinese (BeiDou) – accuracy will likely continue to improve.

As chief scientist, this was my sixth expedition to the region and my 30th bluewater research cruise. It was a voyage of promise when the planning process commenced more than two years ago, but the loss earlier this year of the hybrid remotely operated underwater vehicle Nereus, the only active vehicle capable of exploring the deepest parts of our oceans, was a definite setback. Operated by the Woods Hole Oceanographic Institution (WHOI), Nereus imploded at ~10,000 m water depth during a mission in the Kermadec Trench northeast of New Zealand.

Despite this setback, the objectives of our voyage were clear – to search for evidence that may help explain what happened during and following the plateau’s main constructional phase; identify any links between the only proximal subaerial features - two atolls – and a nearby major submarine canyon (Kroenke Canyon); and understand how atolls and canyons evolve on oceanic plateaus, isolated from terrestrial influences and subject to sea level fluctuations. Finally, our work should contribute to understanding tsunami risk on low-lying atolls.

Canyons, whether on land or underwater, have to start somewhere. We hypothesized that Kroenke Canyon originated from Ontong Java and Nukumanu atolls. Atolls are circular groups of coral islets, synonymous with lagoon islands. Both atolls are presumed to be the remnants of major volcanoes, which through erosion and subsidence evolved to barrier reef islands and eventually atolls, where only the fringing reefs remain. Charles Darwin published this theory of atoll formation in 1842, on the basis of his observations in the South Pacific while he was aboard HMS Beagle’s circumnavigation of the world from 1831 to 1836, and his theory has survived the test of time.

Both Ontong Java and Nukumanu atolls, although lying within Melanesia, are inhabited by Polynesians, with some 2000 people living on the former, belonging to the Solomon Islands, and 700 people on the latter, belonging to Papua New Guinea. The new seafloor mapping data will be of particular significance for them, for the first time allowing accurate estimations of tsunami risk for these two atolls, with a maximum elevation of 13 metres, in this tsunami-prone region.
Submarine canyons are ubiquitous in the oceans, commonly incising the continental shelf and slope along continental margins, and acting as conduits for transporting sediment from the continents to the deep sea. Global estimates of the number of large submarine canyons exceed 5,800, of which 83% are found on continental margins. The other 17% are located on the flanks of islands. ‘Large’ is defined as spanning at least 1000 meters in water depth, having a width/depth (incision) ratio less than 150:1, and incision exceeding 100 meters.

Two factors that make Kroenke Canyon fascinating are its setting and scale. Kroenke Canyon cuts through sediment and possibly igneous rock of the Ontong Java Plateau to a maximum depth of 1000 meters, and the distance from the atolls to the Nauru Basin is approximately 500 kilometers. Presumably the potential causes of this erosion are slumping, submarine landslides, and turbidity currents, similar to the causes around major landmasses. But where and when did the incision of Kroenke Canyon start?

Our working hypothesis is that erosional processes on one or both of the presumed ancient volcanoes continued into the subsea and caused the formation of Kroenke Canyon. When this may have happened is not known. However, evidence suggests that Tauu Atoll, which lies 270 kilometres west of Ontong Java Atoll, formed as a volcanic island between 45 and 24 million years ago. If Ontong Java and Nukumanu atolls originated as volcanoes around the same time, erosion would have commenced at the time of formation, and continued through the barrier reef island and atoll phases of development. Furthermore, throughout the last 2.6 million years, significantly greater portions of the atolls would have been subject to erosion during glacial maxima. For example, during the last glacial maximum 20,000 years ago, sea level was 125 meters lower.

Full analysis of our data will allow us to test our hypothesis. We expect there will be other significant geoscience findings from this voyage, reflecting the objectives of the Schmidt Ocean Institute, which in a world of shrinking funding resources for marine and ocean science, offers the Falkor for use as a platform to oceans scientists without charge. It allowed us to map 23,439 square kilometres of seafloor – about one-quarter the size of Tasmania – along 6,266 kilometres of ship track in water depths ranging from 87 to 4,444 metres. Further support for this voyage came from the Australian Research Council, the UK’s Natural Environment Research Council, and IMAS.

We completed two circumnavigations of the Ontong Java and Nukumanu atolls, and we mapped the canyon from the atolls across the Ontong Java Plateau to the adjacent Nauru Basin, albeit only sketchily in its upper reaches proximal to the atolls. We identified several tributaries, although we did not have time to map perhaps the most significant one. We mapped the transition of the canyon from the Plateau to the Nauru Basin, where the material eroded in forming the canyon reaches its final resting place. The data provide considerable new insights into the processes responsible for formation and evolution of the canyon, and we have identified quite a few new seamounts.


But the reality is that what we now know is just a fraction of what science would like to know about the deep ocean the world over, and the mysteries that new technologies and vessels such as Falkor, can help us resolve.

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