有机碳循环速度的冰川学窗口
Glaciological window into the pace of the organic carbon cycle
摘要：
大气成分的冰川学记录表明，在过去的80万年中，O2以0.3 × 1012摩尔（Tmol）O2年-1的平均速率下降。由于地质碳循环调节长期大气氧浓度，大气O2的波动通常归因于陆地上有机碳（OC）和还原硫的风化（大气O2的汇）与海洋沉积物中OC和还原硫的埋藏（O2的源）之间的不平衡。在这里，我们编制和面对的C，Fe，S和H交换的流体地球（大气，海洋，生物圈）和岩石圈（地壳和上地幔）与脱氧记录，以量化有机碳源和汇在新生代的数据库。我们表明，俯冲的氧化海洋岩石圈和脱气的还原气体从地球内部是一个水槽的氧气，这个水槽显着超过了更新世的大气脱氧速率。新生代大气O2的相对恒定性要求有机碳循环是O2的净源和CO2的汇，在过去的5000万年中，光合作用超过呼吸作用平均约40 MtC yr-1。大气氧浓度相对不变的代价是铁和碳循环中两种光合作用驱动的不平衡共存，它们相互抵消，几乎达到完美。OC从大陆和海洋到岩石圈的微弱逃逸更令人感兴趣。它表明，有机碳循环保持在令人惊讶的强大动力学控制下，尽管进化/优化的呼吸代谢和大气中的O2超过24亿年。
英文摘要：
The glaciological record of atmospheric composition suggests O2 has declined over the last 800000 years at an average rate of 0.3 x 1012 mol (Tmol) O2 yr-1. Because the geological carbon cycle regulates long term atmospheric oxygen concentrations, fluctuations in atmospheric O2 are typically attributed to an imbalance between the weathering of organic carbon (OC) and reduced sulfur on land, a sink of atmospheric O2, and the burial of OC and reduced sulfur in marine sediments, a source of O2. Here we compile and confront a database of C, Fe, S and H exchanges between the fluid Earth (atmosphere, ocean, biosphere) and lithosphere (crust and upper mantle) with the record of deoxygenation to quantify organic carbon sources and sinks in the Cenozoic. We show that the subduction of oxidized oceanic lithosphere and degassing of reduced gas from the Earth's interior is a sink of oxygen, and that this sink significantly exceeds the rate of atmospheric deoxygenation in the Pleistocene. A relative constancy of atmospheric O2 in the Cenozoic requires that the organic carbon cycle was a net source of O2 and sink of CO2, photosynthesis outpaced respiration by an average of ca 40 MtC yr-1 over the last 50 million years. The cost for the relatively invariant atmospheric oxygen concentration is the coexistence of two photosynthetically-driven imbalances in the cycles of iron and carbon that offset each other to near perfection. The weak escape of OC from continents and oceans to the lithosphere is more intriguing. It demonstrates that the organic carbon cycle remains under surprisingly strong kinetic control, despite evolution/optimization of respiratory metabolisms and rising atmospheric O2 for more than 2.4 billion years.
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