Q&A with Mike Coffin: Exploring the edge of Australia’s continental shelf

By on 2 September, 2020

Position editor Daniel Bishton spoke with Professor Mike Coffin, a marine geophysicist at the University of Tasmania’s Institute for Marine and Antarctic Studies about his recent journey to the edge of Australia’s continental shelf.

DB: Professor Coffin, you led a remarkable scientific voyage to the edge of Australia’s continental shelf earlier this year, with a potentially significant contribution to the boundaries of Australia’s marine estate and our understanding of the continent’s formation. What was the most significant and interesting aspects from your perspective?

MC: Remarkable in a single voyage was being able to investigate the conjugate William’s Ridge (Kerguelen Plateau) – Broken Ridge margins, which rifted, broke up, and separated approximately 43 million years ago. They are now 27,00 km apart, and are still moving away from each other due to seafloor spreading along the Southeast Indian Ridge. The extraordinary detail of seafloor morphology provided by the multibeam bathymetry data, the excellent quality of the subseafloor seismic reflection imagery across these margins, and the amount of rock recovered from the seafloor along these margins are all fabulous.

DB: How might data acquired during the voyage inform a decision on the expansion of Australia’s boundaries? How compelling is the evidence?

MC: The multibeam bathymetry data demonstrate the contiguity of William’s Ridge with the Central Kerguelen Plateau, which Heard Island and the McDonald Islands surmount. This serves to strengthen Australia’s original case for extending our continental shelf beyond 200 nautical miles from the islands. Once petrological, geochemical, and geochronological analyses of the rock samples are complete, the results may strengthen the case further by demonstrating similarities between the geology of William’s Ridge and that of Broken Ridge.

DB: How could data and samples collected during the voyage reshape a broader understanding of plate tectonics and Australia’s geological history?

MC: The rifting, breakup, and separation of William’s Ridge and Broken Ridge represent an end member of continental breakup. Because the two features broke up only a few tens of millions of years after they formed by massive magmatism, they don’t have the geological complexity of ancient continental crust that has experienced numerous magmatic and tectonic modifications. Study of this relatively simple end member should reveal significant insights into the fundamental processes associated with the rifting, breakup, and separation of tectonic plates.

DB: My understanding is that this voyage utilised the extent of RV Investigator’s capabilities in terms of technical acquisition capacity and vessel endurance. Can you run us through the main methods used and their application to the voyage’s objectives?

MC: The voyage certainly pushed the limits of RV Investigator’s endurance. The ship’s master constantly monitored our fuel supply to ensure that we could complete our research and then make it home! Our strategy for the voyage was to first map the seafloor using the Kongsberg EM122 deep water system, and then to choose optimal dredging sites and locations of seismic reflection transects on the basis of the newly-created bathymetric maps. We were able to map most of William’s Ridge and the conjugate portion of Broken Ridge for the first time, ~52,000 km2 and ~43,000 km2, respectively. The maps reveal patterns of ridges and troughs comprising the two features, as well as seamounts and sea knolls, which provide insights into the history of tectonism and magmatism. We dredged rocks from nine sites on William’s Ridge, eight sites on Broken Ridge, and three sites on Rig Seismic Seamount (proximal to William’s Ridge); analyses of these samples will yield the age, origin, and evolution of the features. We acquired ~500 line-km of seismic reflection data on four transects of William’s Ridge, and ~600 line-km on five transects of Broken Ridge. These data illuminate the structural development and stratigraphy of the features. We also acquired potential field data – gravity and magnetics – during the voyage, which will help to constrain the density structure of the crust and its magnetic properties, respectively. All told, we acquired the first seismic reflection data with Australia’s new system, and over the 57-day voyage mapped more seafloor (>100,000 km2) and sailed a greater distance (>10,000 nautical miles) than any previous RV Investigator expedition.

DB: Were there any unexpected challenges during such an ambitious voyage, technical or otherwise?

MC: Weather is always a major factor working in the Southern Ocean. Although RV Investigator is a relatively large research vessel, both dredging and seismic reflection data acquisition have limits with respect to weather and sea state. Fortunately, when conditions prohibited these activities, we were able to map the seafloor, albeit at reduced speed. On the transit from William’s Ridge to Broken Ridge, just inside the Roaring Forties from the Furious Fifties, a severe storm – winds exceeding 60 knots and commensurate waves – caused some damage to the ship that would have precluded us from dredging and seismic reflection acquisition. However, the ship’s crew was able to promptly execute repairs while still transiting, and our work program on Broken Ridge was saved.

The inaugural operational deployment of Australia’s new seismic reflection system meant that we were commissioning the system in the Roaring Forties and Furious Fifties, a situation preferred to be avoided, but the Marine National Facility provided outstanding technical support to ensure the system functioned. Seismic operations were limited to daylight hours, sufficient visibility, and the absence of marine mammals; fortunately only fog inhibited our seismic work.

The global Covid-19 situation, while not a direct challenge to anyone on the isolated ship, was certainly a matter of utmost concern because of families and friends ashore. On the ship we had scientists and students from Asia, Australia, Europe, and North America, as well as a New Zealand doctor and an Australian nurse. We shared information from our respective countries, and the doctor held regular briefings and consultations on the pandemic. A prime challenge for personnel on such a long voyage, with lengthy transits between work areas, is well-being, including preventing boredom. The entire science and technical team met almost every day at watch change (1400), and 65 seminars were presented over the two months. Music-making, yoga, and Assassin (https://en.wikipedia.org/wiki/Assassin_(game)) proved to be popular diversions.

DB: One of the research projects taking place on the voyage sought to accurately date a past West Antarctic ice sheet collapse using samples from the Kerguelen Plateau. Are there any results to share from this project?

MC: This evolutionary molecular biology work, led by A/Prof Jan Strugnell at James Cook University and Dr Nerida Wilson at the Western Australian Museum, is being conducted on biological bycatch recovered from the dredged rocks. It involves DNA sequencing and subsequent modelling, and is thus laboratory-based and time-consuming. As the samples only made it ashore in March, just prior to ongoing lockdowns at universities and museums across Australia, no results are available yet.

DB: Are there any discoveries you can share now that there has been some analysis performed of data and subsea samples from the voyage?

MC: As noted above, university lockdowns across Australia and the world have precluded nearly all shore-based analyses of the data and samples from the voyage. A PhD student is scheduled to start work on the geophysical data in August, and rock samples have been identified for analyses. Thus we have no analytical results to report to date.

DB: Was there any other data captured that can inform our understanding of the marine environment surrounding Australia, and may interest our readers? Any surprises from your perspective, or anything else you would like to add?

MC: Acoustic backscatter and sub-bottom profiler data, together with the multibeam bathymetry data, that we acquired will help characterise benthic habitats. Such information aids in managing and sustaining Australia’s extensive offshore marine jurisdiction. We also deployed both Argo (https://argo.ucsd.edu/) and SOCCOM (Southern Ocean Carbon and Climate Observations and Modeling; https://soccom.princeton.edu/) robotic floats, which acquire physical oceanographic and biogeochemical data that reveal properties and changes in the water column for the Australian and overseas research communities. RV Investigator also acquires copious underway ocean (e.g., temperature, salinity, acidity, oxygen, chlorophyll) and atmospheric (e.g., aerosols, reactive gases, greenhouse gases) data continuously during every voyage. All RV Investigator data are logged in a public data base that ascribes to FAIR (findable, accessible, interoperable, reusable) principles. Last but not least, the 56-strong ship’s complement was stupendous. The science party of 22 was 64 percent (14) female and 36 percent (8) male, and included 16 students ranging in age from 19 – perhaps the youngest-ever student to sail on RV Investigator – to 32. For the first time in my 35 research voyages spanning five decades, women outnumbered men in the science party, a noteworthy milestone.

DB: Congratulations on these spectacular outcomes! Many thanks for your time, Mike.

This feature originally appeared in the August/September edition of Position Magazine, with subscribers now. Not a subscriber yet? You can get yours here.

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