Research frontiers in the analysis of coupled biogeochemical cycles

Adrien C Finzi, Jonathan J Cole, Scott C Doney, Elisabeth A Holland, and Robert B Jackson. 2011. Research frontiers in the analysis of coupled biogeochemical cycles. Frontiers in Ecology and the Environment 9: 74–80.

This is an interesting paper discussing research frontiers in global biogeochemistry. The authors identify our understanding of the coupling between the major (C,P,N,Si) elemental cycles with trace element cycles as being particularly lacking. For example, the coupling between the nitrogen and carbon cycles and the iron (Fe) and molybdenum (Mo) cycles. Fe and Mo are required for N-fixing apparatus in photosynthetic organisms, which allow plants to grow and thus take up carbon by taking nitrogen from the atmosphere when it is otherwise unavailable. This sets up a potentially important coupling between e.g. weathering of iron (Fe) and Molybdenum (Mo) on land and carbon uptake in the ocean.

They also identify the cross-boundary linkages between ecosystems as key understudied areas, for example streams, connecting the terrestrial biosphere with rivers and the ocean, or wildfires connecting terrestrial biomass and soils with the atmosphere and ocean and rebalancing soil nutrient stoichiometry.

In the context of understanding what mankind’s activity might do to the climate and ecosystem functioning of our planet we need predictive capacity and therefore better regional and global models of the Earth-system (so-called ‘coupled’ models which include physics, chemistry and biology all interacting simultaneously). As the authors recognise, to better constrain these models we need better understanding of the key underlying processes (often even to identify which processes are key!) and high qualtiy, high resolution time-series data with which to validate the biogeochemical interactions in the models. This is fundamental to being able to predict what might happen in the future – as multiple interacting processes can lead to highly non-linear responses to perturbations in the systems. 

“Feedback” is a word that appears only once in the paper, which is maybe a little surprising as this is ultimately what the understanding of the planet’s complex biogeochemistry is all about – how the whole system, or important parts of it, respond to the major changes we are visiting upon it? Will the Earth ‘bounce back’ from the huge temperature, carbon and nitrogen perturbations of the current period (negative feedback), or will it fly off to a new state that is much less hospitable to humans and the other inhabitants of this planet (positive feedback)? The Earth-system is made up of many interacting feedback loops, any of which may involve a number of different elemental cycles, physical and chemical processes, ecosystems and geographical regions in the ocean, atmosphere and on land. We can’t hope to identify all these ‘by hand’ so our best option is to represent all processes in coupled Earth-system models and  hope that the right balance of feedbacks falls out of the models at the end! Without the major ones being identified, we can’t hope to predict what effect our planet-wide changes are going to have, or what the side-effects of possible action (geoengineering) to ameliorate our negative effects could be.

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