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PAst Links in the Evolution of Ocean’s Global ENvIronment and Ecology

Final Report Summary - PALEOGENIE (PAst Links in the Evolution of Ocean’s Global ENvIronment and Ecology)

Species do not live in total isolation to their surroundings, but adapt and ultimately, evolve, in relationship with other species as well as with their chemical and physical environment. In the ocean, this can be a two-way street – the conditions at the ocean surface affect the makeup of the plankton ecosystem, but at the same time, the particular species that are present can affect how efficiently organic matter (and with it carbon) is removed from the surface and transported to great depth in the ocean – a process that in turn influences the amount of carbon dioxide in the atmosphere and hence climate. (Then climate in influences which plankton are there, which affects carbon cycling and CO2 ... in a chicken-and-egg sort of situation). Understanding this complex interlinked system is essential if we are to correctly interpret the geological record and how plankton and marine ecosystems recover from major environmental catastrophes (and make correct projections of the future ocean!). The proposed project – ‘PALEOGENiE’ – has addressed these challenges by developing a unique computer model representation of what plankton and their ecosystems might have looked like, and functioned, in the geological past.

We started with the geological record of plankton – represented by invisible-to-the-naked-eye ‘nannofossils’. These, we analyzed, in unprecedented detail from the end of the Cretaceous (65 million years ago), when the Earth was hit by a giant asteroid, and for 13 million years after, following how plankton and marine ecosystems (the base of the food chain in the ocean) evolved and recovered from the catastrophe. We find, after about 2 Myr of exceptional ecosystem instability which saw a repeated pattern of species evolving, briefly ruling the ocean, and then going extinct again (as if a god kept re-rolling the dice), that a ‘healthy’ global carbon cycling was re-established with only relatively few different species of plankton (i.e. a ‘low species diversity’). It then took about 8 Myr for plankton diversity comparable to pre-extinction levels (or the modern ocean) to finally re-establish but to no apparent further affect (on the global carbon cycle). Ecosystem stability therefore seems not to be determined by sheer numbers of species, but rather, through the establishment and/or retention of some key individual taxa that fulfill specific and vital ecological and/or biogeochemical roles. In other words: ecological diversity does not seem to matter in the bigger picture (of global carbon cycling), just as long as the key players in the ecosystem are all present.

We then moved to the virtual world, and numerical models. We created a novel new ecosystem and added this to a computer representation of global carbon cycling and climate. We have found that this combined model was (pleasingly!) capable of reproducing many of the key features of plankton productivity in the ocean today. Then, for good measure, we allowed the plankton to evolve in the model. Having so many possible different plankton species appearing then got too numerically expensive to calculate, so we went back to our basic high school maths and the multiplication of matrices (but in a rather powerful and efficient way on supercomputer-power chips) to calculate how the ocean circulates and moves dissolved nutrients and plankton cells around. Combining brute computing power with an advanced marine ecosystem model then gave us a unique virtual world of interacting environment (nutrient recycling in the ocean interior and supply to the ocean surface) and life (plankton evolving or going extinct in response to their competitors and predators and changing food/nutrient availability) that we could play games (god) with.
Currently, we are bringing the new model and data together in a unique attempt to better understand how sensitive marine ecosystems are to global environmental change as well as how (or if) they recover. (Watch this space ...)