Sydney Research Visit

Neill Mackay

University of Exeter


Image: Giving a seminar both online and in person to scientists at the Climate Change Research Centre, University of New South Wales

In April 2022 I travelled to Sydney, Australia for a 2-week collaborative visit to the Climate Change Research Centre (CCRC) at the University of New South Wales. The trip had been long anticipated as an opportunity to meet face-to-face with a colleague of mine who is based there, Dr Jan Zika, and was finally made possible this year by a combination of a relaxation of covid-19 travel restrictions and the Challenger Society Stepping Stones Bursary.

The primary purpose of the visit was to lay the groundwork for developing a new method to diagnose the uptake of carbon dioxide (CO2) from the atmosphere by the ocean and its redistribution within the ocean interior. The topic is of significance to both the marine science community and the wider world, because the ocean’s ability to absorb atmospheric CO2 and sequester it deep down has a mitigating effect on climate change. The challenge is that the drivers of the uptake are complex, and there has been significant variability observed over the last few decades that is yet to be fully understood. The task at hand for my visit to Sydney was going to be a difficult one to achieve in such a short space of time, but I was determined to make the best I could of the opportunity!

I began by delivering a seminar to some of the researchers at the CCRC, which gave me the opportunity to introduce myself, and to explain the purpose of my being there. It also gave me the chance to talk through the work I had been doing in preparation for the trip: an attempt to extend a method I had developed for studying the ocean circulation and apply it to ocean CO2 uptake. The method draws on something called water mass theory, which is a powerful framework that allows the complex three-dimensional ocean circulation to be simplified with minimal loss of information. My expectation at this point, however, was to go back to the drawing board, since some months of effort had lead me to the conclusion that this particular method is not well-suited to the problem we are trying to solve. After my talk, I sat down with Jan, and with Dr Taimoor Sohail, another member of the research group who has been working on similar methods using water mass theory, to figure out the best way forward. We quickly agreed on an alternative approach, using a method based on very similar principles to that which I had been testing, but with a somewhat different implementation.

Over the next two weeks, I worked closely with Taimoor and Jan developing the new approach. Making use of some model data that I had brought with me, we were able to extend their methodology, which had thus far been used to study the physical circulation, to incorporate the ocean’s uptake of carbon. By the time I left Sydney, we had succeeded in a proof-of-concept of the new method, something we had not been able to achieve in the last several months of collaborating remotely. It was more than I had hoped I would be able to accomplish in such a short time, and I returned to the UK reassured that the long journey with its associated costs (not to mention CO2 footprint) had been more than worthwhile. Since returning I have continued to make progress with the method development, and kept in touch with my colleagues via Slack and video conferencing. I have also been reminded; post pandemic, of the benefits - and the joys - of working with people face-to-face!

Neill Mackay is a physical oceanographer working at the University of Exeter. His research to date has focused on the polar regions, using both models and observations to try to understand their role in the oceanic overturning circulation. In particular, he is interested in applying water mass theory and inverse modelling to resolving questions about the role of the circulation in the climate system. In recent years, his work has moved into the realm of biogeochemistry, studying the uptake of carbon in the Southern Ocean. Currently he is involved in a project entitled ‘Understanding Interdecadal Changes in the Ocean Carbon Sink (UNICORNS), which aims to reconcile reconstructions of the carbon inventory in the ocean interior with those of the air-sea CO2 flux using a combination of observations, machine learning, and numerical and inverse modelling. The project hopes to answer the question of whether recent decadal variability in the global carbon sink can be explained through changes in the physical ocean circulation.

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