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陆地植物在过去2400万年限制大气中二氧化碳下降方面的作用。

The role of terrestrial plants in limiting atmospheric CO(2) decline over the past 24 million years.

作者信息

Pagani Mark, Caldeira Ken, Berner Robert, Beerling David J

机构信息

Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA.

出版信息

Nature. 2009 Jul 2;460(7251):85-8. doi: 10.1038/nature08133.

Abstract

Environmental conditions during the past 24 million years are thought to have been favourable for enhanced rates of atmospheric carbon dioxide drawdown by silicate chemical weathering. Proxy records indicate, however, that the Earth's atmospheric carbon dioxide concentrations did not fall below about 200-250 parts per million during this period. The stabilization of atmospheric carbon dioxide concentrations near this minimum value suggests that strong negative feedback mechanisms inhibited further drawdown of atmospheric carbon dioxide by high rates of global silicate rock weathering. Here we investigate one possible negative feedback mechanism, occurring under relatively low carbon dioxide concentrations and in warm climates, that is related to terrestrial plant productivity and its role in the decomposition of silicate minerals. We use simulations of terrestrial and geochemical carbon cycles and available experimental evidence to show that vegetation activity in upland regions of active orogens was severely limited by near-starvation of carbon dioxide in combination with global warmth over this period. These conditions diminished biotic-driven silicate rock weathering and thereby attenuated an important long-term carbon dioxide sink. Although our modelling results are semi-quantitative and do not capture the full range of biogeochemical feedbacks that could influence the climate, our analysis indicates that the dynamic equilibrium between plants, climate and the geosphere probably buffered the minimum atmospheric carbon dioxide concentrations over the past 24 million years.

摘要

在过去的2400万年里,环境条件被认为有利于通过硅酸盐化学风化作用提高大气二氧化碳的消耗速率。然而,替代记录表明,在此期间,地球大气中的二氧化碳浓度并未降至百万分之200 - 250以下。大气二氧化碳浓度在这一最小值附近趋于稳定,这表明强大的负反馈机制抑制了全球硅酸盐岩石高风化率对大气二氧化碳的进一步消耗。在这里,我们研究了一种可能的负反馈机制,它发生在相对较低的二氧化碳浓度和温暖的气候条件下,与陆地植物生产力及其在硅酸盐矿物分解中的作用有关。我们利用陆地和地球化学碳循环的模拟以及现有的实验证据表明,在这一时期,活跃造山带高地地区的植被活动受到二氧化碳近乎匮乏以及全球变暖的严重限制。这些条件减少了生物驱动的硅酸盐岩石风化,从而削弱了一个重要的长期二氧化碳汇。尽管我们的模拟结果是半定量的,没有涵盖可能影响气候的所有生物地球化学反馈,但我们的分析表明,植物、气候和地圈之间的动态平衡可能在过去两千四百万年里缓冲了大气二氧化碳的最低浓度。

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