Oceanographers began going to sea in ships about 200 years ago, with maybe one or two expeditions per year from the UK. That progressed to the point about 20-25 years ago when maybe 15-20 ships around the world were doing the work.
Fortunately, in the last 15 years we have a brand-new technology called Argo. This is a series of about 3000 floats drifting around in the world’s oceans that take vertical measurements every month, sinking to a depth of 2000 metres, then coming to the sea surface to transmit the information they’ve gathered to satellites. In the Southern Ocean we’re now getting more data every year from this new technology than we did in the previous century.
We also now have specialised satellites that measure the wind stress on the ocean, providing us with maps of this wind stress every few days. Other satellites measure the height of the sea surface accurate to within a millimetre or two on horizontal scales of hundreds of kilometres. It’s this height information that gives us the currents at the sea surface, because, due to the Coriolis effect, a small difference in the height of the free surface of the ocean translates into a current that is perpendicular to that gradient.
These are the technologies we’re mining to understand so much more about the ocean from observations. Supercomputers then allow us to model the ocean with better and better resolution as these computers become faster and larger.
If it wasn’t for the atmosphere and the ocean moving and thus transporting heat, the temperature differences on Earth would be extreme. This transport of heat is the basic thing that we are all studying in climate science when we are investigating climate variability and climate change.
People understand that the El Nino Southern Ocean phenomenon affects our weather patterns, along with La Nina, and these influence climate variations on a timescale of between two and seven years. But there are other changes in the planet happening over decades, and multi decades, and centuries. Climate variability such as El Nino and the Indian Ocean Dipole, occurring on time scales of two to 7 years, involves a coupled instability between the atmosphere and ocean, with the upper 200-300 metres of the ocean being involved.
But with climate change, happening over decades and centuries, you’ve got to look deeper in the ocean, down to 1000-metre and even to 3000-metres. And at these depths, under that sort of pressure, the mathematics describing the mechanisms of heat transfer is very complex.
For example, if you’re 1000 or 3000 metres deep in the ocean, it’s very hard to get the ocean to mix vertically. The rate of mixing horizontally – whether it’s of temperature, salinity, oxygen etc – is about a factor of 10 million times stronger than vertically.
You can think of it as a party drink with layers of red and yellow and green alcohol of various densities. In the ocean it’s very hard to get those coloured layers to mix. If you put a little blob of dye in the ocean at those depths and come back a year later (if you’re clever enough to find it, which we can do these days), it will be dispersed in the vertical by no more than 50 metres. But in the horizontal it will have moved around half an ocean basin – thousands of kilometres. So it’s really important in models and in interpreting observations to be able to determine the direction of this strong lateral mixing.
What I’ve been able to do is to bring some rigour to these calculations. It’s complicated, because the density in the ocean depends not only on temperature and salinity, but also on pressure, so it becomes a bit of a mathematical puzzle to try and find your way through.
One of the things I’m known for is an algorithm which people now use to label observations with a density variable that is called Neutral Density. There’s a variety of types of density, all with their complications. I was able to produce an algorithm which has become very popular – basically, anyone that does oceanography beyond a few hundred metres depth uses this variable. But there are improvements that we need to make.
You ask about early influences in my career. I knew quite early that I wanted to focus on a career in engineering, and it turned out that I was attracted to the fluid mechanics aspect of engineering, and later that progressed into oceanography. But I faced one large obstacle.
I was brought up in a closed religious cult, the Exclusive Brethren. This cult forbade social contact with anyone outside their reclusive membership. Science had no place in its culture at all – and even listening to the radio or watching TV was outlawed.
Slowly at first, and then growing into an absolute conviction, I decided that this strange religious cult made no sense. I couldn’t imagine spending my life in it. The sect was not encouraging of my interest in science at all. In fact, I was the last person in the whole world in that cult to be allowed to go to university. Every Sunday I had people preaching at me saying that I shouldn’t be studying there. So, in the last term of my fourth year at Adelaide University, I faced my parents and told them that I couldn’t remain in the sect that had directed their whole lives.
Such a life-changing decision was incredibly difficult to make. Looking back, I don’t know how I did it. But I was aware of an inconsistency in what the global leader of the church was saying publicly and what he had told myself and my father. This inconsistency made me question the whole religion, and I started to reason: what’s the chance of these few thousand people being the only correct people in the world? I knew that the minute I told my parents that I didn’t want to be part of their religion anymore that I’d never see them again. And that’s how it worked out. I never saw my sisters or brother again.
I was allowed to go back once for my father’s funeral. Some years later when my mother died, I was not informed, and found out by accident some six months after her death. They well and truly drew up the drawbridge – if I wasn’t part of their Exclusive Brethren cult, then I was worse than a nobody. But I knew that that was how it was going to be. And so I just moved on.
Having decided that I could not be true to myself while remaining in this religious cult, I felt empowered and a whole world of opportunities suddenly became possible. I started a new life at age 21. Shortly after, I found myself in Cambridge UK, and I became a new person, designing who Trevor McDougall was going to be from the ground up, and slowly purging 21 years of religious brainwashing from my head.
Looking forward from today, the next big scientific challenge for me is take some more of the theoretical mathematical concepts that have been accepted by theoretical oceanographers, and to develop them into practical tools that can be used by all observational oceanographers. We have a lot of data coming in from these new instruments, but how do we analyse this data to determine, for instance, the rate of mixing in the vertical direction? This is a whole subject in itself, and it relies on accurate practical software tools that I’m now developing.
Discovering new things in science is satisfying work, but there’s not any good news for humanity about climate change. The only positive thing I can think of is that every year the predictions of our changing climate become a bit more precise. But those predictions are not getting any easier to live with. We Homo sapiens have been around for 350,000 years, and in just a few generations we have made a huge change to the climate system of our planet, with the carbon dioxide concentration in the atmosphere being larger now than at any time in the past several million years. We, and our elected politicians, need to begin treating the climate emergency as the emergency that it is.
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