The carbonate factory

I really am wondering what those of you who’ve been attending the ‘Introductory Geology’ fieldtrips regularly must now be thinking! A carbonate factory on the sea floor? What on Earth is he rabbiting on about? Can I get my enrolment fees back?

Let me assure you there’s nothing to worry about. I’m not expecting you to imagine some high-tech structure reminiscent of Karl Stromberg’s Atlantis – in The Spy Who Loved Me, for those of you who need reminding. The term ‘carbonate factory’, which has been used by sedimentologists for about forty years, refers simply to an area of the sea floor where large quantities of calcium carbonate are produced relatively quickly, or at least can be produced relatively quickly. This carbonate is produced mainly by photosynthesising microorganisms.

If we’re going to make a model of a carbonate factory – and we are – then clearly we’re going to have to know the factors that control where those carbonate-producing organisms are present. The most obvious suggestion – this is the one that most people put forward – is that the main controlling factor has surely to be the physical environment on the sea floor, in particular the light intensity. (The carbonate producers are photosynthesisers, therefore they need light to live.) This suggestion sounds so reasonable that very few people trouble to look for alternatives. What a pity, for it’s completely wrong! The presence of the carbonate-producing organisms is not controlled by the physical environment; it reflects instead the extent to which those organisms have colonized the parts of the sea floor where the physical environment will let them survive. (There is a fundamental ecological principle involved here, namely that the physical environment never prescribes where organisms actually live; it acts only to limit where they can survive. Organisms do not change their distributions automatically if and when the physical environment changes.) The amount of carbonate produced in a particular area of the sea floor can accordingly be very much less than would be predicted by looking only at the physical environment; this is the case whenever the relevant carbonate-producing organisms have yet to colonize that area fully. The take-home message is that it is colonization rather than the physical environment that controls the production in a carbonate factory.

Clearly what we’re going to need as a part of our carbonate factory model is a model of the colonization process – the process by which those carbonate-producing organisms spread out over the sea floor. Do I hear the sound of pennies dropping? Yes, this is yet another stochastic spatial process, albeit one that is a little more complicated than those you saw in previous posts: see ‘Walking at random’ (8 August 2020), ‘Another stochastic process – this time with thanks to David Attenborough’ (20 July 2020), and ‘Models, and walking of course!’ (21 August 2020). This new spatial process is going to be modelled here using what is termed a cellular automaton.

OK, that’s enough for now, apart of course from the obligatory recommended reading list. (You are keeping up with your background reading, aren’t you?) (1) For a general introduction to cellular automata go to https://en.wikipedia.org/wiki/Cellular_automaton. (2) For what is perhaps the most widely known cellular automaton (Conway’s Game of Life) look at the October 1970 issue of Scientific American. (3) For an online version of the Game of Life go to https://playgameoflife.com/. (4) For a paper that describes in detail the carbonate factory model we’ll eventually be producing here go to https://www.dropbox.com/s/6pzv1khph7pla6t/Tipper%201997%20Modeling%20carbonate%20platform%20sedimentation%E2%80%94Lag%20comes%20naturally.pdf?dl=0. Send complaints about this last paper directly to its author!

Comments are closed.