FESD Type I Proposal: Continent-island arc fluctuations: Linking deep Earth dynamics to long-term climate

这项研究的首要主题是更好地理解是什么驱动了长期气候变化，特别是在100万年的时间尺度上温室和冰窖状态之间的振荡。这些气候振荡，整合在地球上？它的历史深刻地影响了生命的进化和地球表面。首先，海洋-大气-生物圈系统中二氧化碳收支的变化在大于10 m的时间尺度上驱动气候变化：由于大气中二氧化碳的温室效应，地球？在所有其他变量（如反照率）相同的情况下，当大气中二氧化碳含量高时，地表温度变暖，当二氧化碳含量低时，地表温度变冷。地球的碳含量？在很长的时间尺度上，地球上的火山输入控制着地球的外源系统。通过沉积埋藏和俯冲从外生体系产出。因此，长期气候变率与整个地球的碳循环密切相关，即碳在内源和外源系统之间的循环。这些输入和输出究竟是如何以及为什么随着时间的推移而变化的，这是一个问题。这项研究将重点关注最近的温室-冰窖过渡。这始于白垩纪到新生代早期（150-60万年）的温室期，当时恐龙在地球上漫游，大气中的二氧化碳压力可能是今天的4-8倍，极地冰盖没有出现，地球的大部分地区？形成了5个经济上可行的烃源岩。相比之下，中新生代（~55万年至今）的特征是地表温度较低，极地冰盖，大气CO2含量较低，哺乳动物大量繁殖。我们将评估白垩纪期间二氧化碳浓度升高的一些假设。这些因素包括碳酸盐俯冲作用增强以及随后通过弧火山释放二氧化碳，海洋地壳生成增强以及偶发性洪水玄武岩的频率增加。特别是，我们还将探索一个新的假设，即进入外源系统的二氧化碳输入受到俯冲带火山性质的长期变化的强烈影响。在大陆弧活动增强的时期，碳酸盐沉积物储存在地球上的大陆上？然而，在岛弧活动主导的时期，由于海洋上板块的碳酸盐体积变小，二氧化碳输入回到基线水平。从白垩纪温室到中新生代冰窖条件的转变可能与大陆弧火山数量的减少同时发生，这表明在俯冲带的性质之间可能存在一种驱动长期振荡的机制。这项研究的目的是评估所有这些潜在的二氧化碳来源的相对重要性，以便开发一个更完整的整个地球碳循环模型。我们特别感兴趣的是地球深处的动力学如何调节这些二氧化碳的来源。检验这些假设和地点界限这些过程,我们已经组建了一个跨学科的团队量化碳酸盐的稳定性在地壳浅和深俯冲带,映射出弧火山的分布和岩浆脱二氧化碳的程度改变了时间,全球火山输入二氧化碳量化,制定长期气候演化模型耦合到C的循环深度之间的地球和外生的系统。

The over-arching theme of this study is to better understand what drives long-term climate change, specifically oscillations between greenhouse and icehouse states over timescales of 100 My. These climatic oscillations, integrated over Earth?s history, profoundly influenced the evolution of life and the surface of the Earth. To first order, variations in the CO2 budget of the ocean-atmosphere-biosphere system drive climatic variation over timescales greater than 10 My: because of the greenhouse effect of CO2 in the atmosphere, Earth?s surface temperature warms when atmospheric CO2 is high and cools when CO2 levels are low, all other variables (like albedo) being equal. The C content of the Earth?s exogenic system, over long timescales, is controlled by volcanic inputs from the Earth?s interior and outputs from the exogenic system via sediment burial and subduction. Long-term climate variability is thus intimately linked to whole Earth carbon cycling, that is, the cycling of C between the endogenic and exogenic systems. Exactly how and why these inputs and outputs have changed through time is the question. This study will focus on the most recent greenhouse-icehouse transition. This begins with the Cretaceous to early Cenozoic (150-60 My) greenhouse interval when dinosaurs roamed the Earth, atmospheric CO2 pressure was possibly 4-8 times higher than today, polar ice caps were absent, and much of Earth?s economically viable hydrocarbon source rocks were generated. In contrast, the mid-Cenozoic (~55 My to present) was characterized by cooler surface temperatures, polar ice sheets, lower atmospheric CO2, and the proliferation of mammals. We will evaluate a number of hypotheses for elevated CO2 during the Cretaceous. These include enhanced carbonate subduction and subsequent output of CO2 through arc volcanoes, enhanced oceanic crust production, and an increase in the frequency of episodic flood basalts. In particular, we will also explore a new hypothesis that CO2 inputs into the exogenic system are strongly influenced by secular changes in the nature of subduction zone volcanoes. During periods of enhanced continental arc activity, carbonate sediments stored on the continents over Earth?s history, are magmatically liberated, whereas during periods dominated by island arc activity the CO2 inputs return to baseline levels because of the smaller volumes of carbonates in the oceanic upper plate. The transition from Cretaceous greenhouse to mid-Cenozoic icehouse conditions may have coincided with a decline in the number of continental arc volcanoes, suggesting that there may also be a mechanism driving long term oscillations between the nature of subduction zones. The goal of this study is to evaluate the relative importance of all these potential sources of CO2 so that a more complete model of the whole Earth carbon cycle can be developed. We are specifically interested in how deep Earth dynamics modulates these sources of CO2. To test these hypotheses and place bounds on each of these processes, we have assembled an interdisciplinary team to quantify the stability of carbonates in the shallow crust and in the deep parts of subduction zones, map out how the distribution of arc volcanoes and the extent of magmatic decarbonation has changed through time, quantify global volcanic inputs of CO2, and develop a model for long-term climate evolution coupled to the cycling of C between the deep Earth and the exogenic system.