Possible effects of geomagnetic polarity transitions on the biosphere

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The Earth possesses a global magnetic field for at least 3.5 billion years. This geomagnetic field exhibits major temporal variations with the most dramatic one being a polarity transition. As during such a transition the surface field almost collapses the question of possible effects of this collapse is a most important one. If energetic particles have much better access to the atmosphere during a polarity transition, this may cause an increased nitric oxygen level in the middle atmosphere with a resulting decrease of the ozone column density and a corresponding increase in the surface UV-B radiation. In order to better understand the coupled magnetosphere-ionosphere-atmosphere-biosphere system we propose to develop detailed models of the effect of such a UV-B level increase on selected aquatic ecosystems. By using models describing the atmospheric nitric oxygen increase and the associated UV-B increase during polarity transitions, a bio-optical and phytoplankton model as well as an evolutionary model we want to test (i) the nonlinear response of the biosphere on geomagnetic field changes and its delay times, (ii) the sensitivity of different species of the aquatic ecosystem to polarity transition induced UV-B radiation changes and possible evolutionary effects. Another aim of the proposed studies is the identification of proxies that show evidence for the proposed reaction sequence of the magnetosphere-ionosphere-atmospherebiosphere system on polarity transitions.