Question: What do you mean you put living things from the ocean into computer models of the whole Earth?

Andrew Yool answered on 12 Jun 2020: last edited 12 Jun 2020 7:59 am

Thanks for asking!
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Largely because we’re interested in simulating the climate and important feedbacks in it, our interest when modelling the Earth system is focused on the carbon cycle. This consists of the total amount of carbon freely cycling between the atmosphere, the ocean and the land systems, and involves processes like growth of plants on land and algae in the ocean, as these lock carbon dioxide (CO2) that can affect climate into organic material that can’t.
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In terms of how we model this in the ocean, we simulate the dissolved concentration of CO2 everywhere (i.e. where it’s high, where it’s low), and we add processes that change this concentration. An important one is the exchange of CO2 between the ocean and the atmosphere, and we have equations that relate this to wind speed (plus other factors). Another important one is this transformation of dissolved CO2 into organic material by algae. To do this, our models include a “reservoir” of organic carbon concentration that represents algae, i.e. if you were to look at all the carbon in a jam jar of seawater, you might find that almost all of it was dissolved CO2, but some of it was organic carbon in algae living in the water. Knowing how much algae there are, and how much light and nutrients they have access to, we use simple mathematical equations to calculate growth of this algae and in our model this turns dissolved CO2 into organic carbon inside algae. We can then repeatedly do this sort of calculation to work out how the concentrations of dissolved CO2 and the organic carbon in algae change in time. Of course, once algae have made this organic carbon, we need to think about other physiological processes like respiration and ecological processes like animals eating the algae change their concentration too, and we have equations that try to do this too (although processes like animals eating algae are much harder to turn into simple equations compared to growth).
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And to do this for the whole Earth, we divide the ocean’s geographical space into lots of boxes, each of which has its own concentrations of dissolved CO2 and algae in it, and we link these boxes together with equations that describe how ocean currents move things around. Then, we run all of these equations forwards in time using a supercomputer, and use this to work out where CO2 is going into the ocean, where it’s coming out, how much of it is being consumed by algae and how much of it is being turned back from algae into CO2. This gives us geographical fields of the concentrations of dissolved CO2 and algae that we can compare to observations of these properties that our colleagues have made from ships or using satellites that can detect where algae are.
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There are a lot of simplifications in what we do because living things and ecosystems are much more complicated than non-living things like the air and seawater, but we think (hope!?!) that we capture the most important processes and get an idea of how much carbon they are responsible for moving around. And one of my jobs is to check our models to make sure that they simulate the patterns of carbon, nutrients, algae, animals and many other things in ways that are realistic.
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I should add that there are lots of different ways in which living things can be simulated – this is just one of them, but it’s the sort of way we do things when we work at the whole Earth scale.
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Hope this helps!