AUSTRALIAN FRONTIERS OF SCIENCE, 2008

The Shine Dome, Canberra, 21-22 February

Session 6: Understanding the past, present and future of Earth’s environment
Chair: Professor Malcolm McCulloch, FAA

Malcolm McCulloch has a degree in science and a PhD from the Division of Earth and Planetary Sciences at the California Institute of Technology. He returned to Australia to take-up a Research Fellowship at the Australian National University (ANU), in the Research School of Earth Sciences. At ANU he was responsible for establishing a new range of geochemical methods to better understand how the Earth’s continental crust and mantle has grown and evolved. For the past decade he has been actively involved in issues of climate change and the effects of European settlement on river catchments and soil erosion into the Great Barrier Reef of Australia. He is currently undertaking research to better understand how increasing ocean temperatures, sea levels and acidity is likely to effect the long-term sustainability of coral reefs.

Leanne Armand's talk is on the Antarctic and some of the ecosystems that exist in that region. If you were following last night's news you would have heard Ross Garnaut talk about 90 per cent reductions in CO₂ emissions. These two things are linked, actually, because the Southern Ocean is probably one of the key regions where sequestration of CO₂ occurs, and one of the key factors controlling that is the so-called biologic pump. That is the mechanism whereby plankton and carbon consumers photosynthesise in the surface waters, take up carbon from those surface waters those surface waters are in equilibrium with the atmosphere to some extent and over time an unknown proportion of them are sequestered in the deeper oceans. That is one of the main mechanisms by which CO₂ is sequestered (as well, of course, as by physical dissolution of CO₂ in those surface waters which is then transferred into deeper waters).

As geologists and geochemists we are now starting to realise that these processes in the Southern Ocean are some of the very key parts of the climate system. What happens down there can, in fact, control what is going to happen to the rest of our whole planet in decades and centuries to come.

So Leanne's talk I think is really appropriate, because if we go past one of these thresholds which Garnaut is worrying about that is, the 450 ppm CO₂ one of the concerns is that at some kind of threshold (we don't actually know where it is) the CO₂ will start making those southern waters quite acidic or heading towards an acidic direction, and some of the calcifiers, in particular, those that make calcium carbonate, will no longer be able to do that. That would then be a major disturbance to the biologic pump which I have just described.

Also, there are going to be problems with warming of those waters, and stratification, which will stop the deep ocean sink.

So how do we get a handle on these problems? Well, we can wait and see when it happens; when we cross the threshold we can all say, 'Well, we've passed it. Things are now changed, but we know things are changing.' And of course there is a lot of effort being made now to examine these systems. Oceanographers are spending a lot of time in this region of the world's oceans.

But one of the real problems we face is that we don't have a reference point to know how resistant or how fragile and so on the systems are, and where these thresholds are and there are likely to be multiple thresholds, of course, not a single one. One way to look at that is to go back in the geologic record and look at what happened in the past. How did the system respond when we had climate change in the past? It is not exactly the same kind of climate change, but it does give us some boundary conditions which can give us some clues to what may happen in the future.

Leanne's work is quite critical in this respect because it is so important to know how the silica organisms perform. There is also pH, I should point out. There are a lot of subtleties in terms of nutrient speciation that is pH dependent, and these can have very complicated effects.