Faculté des sciences

Phosphorus, a Servant Faithful to Gaia ? Biosphere Remediation Rather Than Regulation

Föllmi, Karl B. ; Tamburini, Federica ; Hosein, Rachel ; Van de Schootbrugge, Bas ; Arn, Kaspar ; Rambeau, Claire

In: Scientists Debate Gaia. The Next Century, 2004, vol. 2, p. 79-92

The global cycles of the biophile elements phosphorous and carbon are closely linked through their profound implication in two major biogeochemical processes, photosynthesis and biochemical weathering. In photosynthetic processes phosphorous may limit the transformation of atmospheric CO2 into organic carbon, and in biochemical weathering processes atmospheric CO2 may limit the mobilization of... Plus

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    Summary
    The global cycles of the biophile elements phosphorous and carbon are closely linked through their profound implication in two major biogeochemical processes, photosynthesis and biochemical weathering. In photosynthetic processes phosphorous may limit the transformation of atmospheric CO2 into organic carbon, and in biochemical weathering processes atmospheric CO2 may limit the mobilization of phosphorous. During environmental change, changes in both cycles are coupled and associated feedback mechanisms have important implications on the biosphere. In this chapter, we study the character of the coupled changes in the phosphorous and carbon cycles during the last 160 million years and propose feedback mechanisms between the two cycles. We explore the effects of the proposed feedback systems on the biosphere and especially their capacity to regulate environmental conditions in a Gaian sense. For this purpose, we use marine phosphorous and carbon burial rates, a modeled atmospheric CO2 curve, and stable carbon isotopes and proxies for temporal change in the global phosphorous and carbon cycles. Based on the temporal changes within these proxies, we postulate a period on fundamental change in feedback between weathering, productivity, and climate at around 32 million years ago, which is explained by the onset of major glaciation. This suggests that feedback mechanisms may not be uniform throughout Earth’s history but may change during environmental change. We also observe evidence for complex interactions between the carbon and phosphorous cycles, which suggests that the two cycles are not necessarily coupled in a linear fashion. Our general conclusion is that the phosphorous and carbon cycles are characterized by interactions and resulting feedback mechanisms, which show stabilizing effects only to a certain extent. The effects of global change extrinsic to the biosphere, such as volcanic events, changes in orbital parameters, and impacts, and intrinsic change related to biological evolution appear to overrule the tendency toward stable conditions, and the associated feedback mechanisms are considered to be remediative rather than regulatory.