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

这项研究的主题是更好地了解是什么驱动了长期的气候变化，特别是在100 My的时间尺度上温室和冰库状态之间的振荡。 这些气候振荡，在地球上整合？地球的历史，深刻地影响了生命和地球表面的进化。 首先，海洋-大气-生物圈系统的CO2收支变化在大于10百万年的时间尺度上驱动气候变化：由于大气中CO2的温室效应，地球？当大气中的CO2含量高时，地球的表面温度会变暖，当CO2含量低时，地球的表面温度会变冷，所有其他变量（如CO2）都是相等的。 地球的碳含量？的外生系统，在很长的时间尺度，是由火山输入从地球？外生体系通过沉积埋藏和俯冲作用输出。 因此，长期气候变化与整个地球的碳循环密切相关，即内生和外生系统之间的碳循环。 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。这项研究将集中在最近的温室-冰库过渡。 这开始于白垩纪到新生代早期（150-60 My）的温室间隔，当时恐龙在地球上漫游，大气中的二氧化碳压力可能比今天高4-8倍，极地冰盖不存在，地球的大部分地区？的经济上可行的烃源岩生成。相比之下，新生代中期（约55百万年至今）的特点是地表温度较低，极地冰盖，大气二氧化碳含量较低，哺乳动物的繁殖。 我们将评估白垩纪期间二氧化碳浓度升高的一些假设。这些包括增强的碳酸盐俯冲作用和随后通过弧火山的CO2输出，增强的海洋地壳生产，以及增加的幕式溢流玄武岩的频率。特别是，我们还将探讨一个新的假设，即CO2输入到外生系统的强烈影响的长期变化的性质俯冲带火山。在大陆弧活动增强的时期，储存在地球上方大陆上的碳酸盐沉积物？的历史，是岩浆解放，而在岛弧活动为主的时期，二氧化碳的输入返回到基线水平，因为在海洋上层板块碳酸盐的体积较小。 从白垩纪温室到中新生代冰库条件的转变可能与大陆弧火山数量的下降相吻合，这表明也可能存在一种驱动俯冲带性质之间长期振荡的机制。 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，以便可以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部动力学如何调节这些二氧化碳来源。 为了测试这些假设并对每个过程进行限制，我们组建了一个跨学科的团队，以量化浅地壳和俯冲带深部碳酸盐的稳定性，绘制出弧火山的分布和岩浆脱碳的程度如何随时间变化，量化全球火山二氧化碳输入，并建立一个长期气候演变模型，该模型与地球深部和外生系统之间的碳循环相耦合。

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.