Applied photonics in the Southern Ocean
So why did I, a physicist who is most at home in the darkened, well-controlled confines of a laser laboratory, find myself dressed in high-viz clothing climbing aboard a big orange ship in Tasmania in January 2016 about to set off for a three-month trip to one of the most isolated areas of the planet?
The story starts with a technique known as Optical Coherence Tomography (OCT), an imaging technique developed in the early 1990s that has had real impact – many optometrists now rely on these systems to provide 3 dimensional images of the retina and its underlying structure and it provides a unique method of diagnosing many important visual impairments. The technique has also found application in many other fields including imaging plaques within arteries and mapping the boundaries of cancer tumours. We have used the system we developed at St Andrews in many medical areas however we have also sought to develop its application in other fields, most recently in providing high resolution structural imaging of Antarctic Krill (Euphasia Superba), one of the most important animals within the food chain of the Antarctic that stretches all the way from microscopic algae to the Blue Whale the planet’s largest animal.
OCT provides imaging of structure by relying on accurate depth measurement of light which is reflected from the boundaries between different tissue types within a sample. The depth can be measured to a thousands of a mm accuracy by relying on the phenomenon of interference, the effects produced when two waves interact with one another either causing cancellation of a large growth in the signal. A typical OCT system can give resolution of a few thousandths of a mm or better in three dimensions to depths of a few mm within living tissue.
Our studies on Krill started from important biological questions on the effects of ocean acidification on the structural development of the animals. We began by examining preserved lab specimens before shipping the system the Australian Antarctic Division aquarium in Tasmania, Australia to produce the first three-dimensional imaging of living animals.
In the last year we have also taken our technology to the Antarctic itself by taking part in the Australian Government’s K-Axis marine science voyage based on the icebreaker Aurora Australis, which brought together around 50 scientists from a range of disciplines including Physics, Biology, Oceanography, Ecology and Chemistry, to study an area of unusual productivity in Eastern Antarctic between the Kerguelen Islands and the Antarctic itself. We showed that our OCT system, which is normally used within a specifically built optics lab, can be deployed and generated high quality data within the marine science environment with measurements taken even as the ship was rolling by more than 12 degrees in each direction. We have also shown that a wide range of interesting species can be imaged using these techniques and look forward to starting a host of new collaborations with partners from a very broad group of interests contributing new knowledge to globally important effects of climate change and ocean acidification.
The work described in this post has been supported from several sources with EU funding enabling the original development of the system, EPSRC providing ongoing support through a Platform Grant and the Australian Antarctic Division, providing major in kind contributions for voyage costs and hosting experiments.
Throughout the marine science programme our photonics technology performed exceptionally and provided an important compliment to the other photonics-systems on board that provided both imaging and advanced experiments on plankton development. The fact that the ship then ran aground and we had to be rescued by a major international mission – well that might be a story for another post!
Dr Tom Brown, School of Physics and Astronomy
M.J. Cox, S. Kawaguchi, R. King, K.Dholakia and C.T.A. Brown, “Internal physiology of live krill revealed using new aquaria techniques and mixed optical microscopy and optical coherence tomography (OCT) imaging techniques”, Marine and Freshwater Behaviour and Physiology, 48, p. 455 (2015)
N. Bellini, M.J. Cox, D.J. Harper, S.R. Stott, P.C. Ashok, K. Dholakia, S. Kawaguchi, R. King, T. Horton and C.T.A. Brown, “The Application of Optical Coherence Tomography to Image Subsurface Tissue Structure of Antarctic Krill Euphausia superba”, PLOS ONE, 9, Art. No. e110367 (2014)