Possible effects of geomagnetic polarity transitions on the biosphere

地球拥有全球磁场至少有35亿年的历史。这个地磁场表现出主要的时间变化，其中最引人注目的是极性转变。由于在这种转变过程中，表面场几乎崩溃，因此这种崩溃可能产生的影响是一个最重要的问题。如果高能粒子在极性转变期间有更好的途径进入大气，这可能会导致大气中部一氧化氮水平增加，从而导致臭氧柱密度降低和表面UV-B辐射相应增加。为了更好地理解磁层-电离层-大气-生物圈耦合系统，我们建议建立这种UV-B水平增加对选定水生生态系统影响的详细模型。通过使用描述极性转变期间大气一氧化氮增加和相关UV-B增加的模型，生物光学和浮游植物模型以及进化模型，我们希望测试(i)生物圈对地磁场变化及其延迟时间的非线性响应，（ii）水生生态系统不同物种对极性转变引起的UV-B辐射变化的敏感性和可能的进化效应。所提出的研究的另一个目的是确定能够证明所提出的磁层-电离层-大气-生物圈系统对极性转变的反应顺序的代用物。

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.