MOlybdenum in the Oceans ('MOO')

我们未来的海洋可能与今天大不相同。燃烧化石燃料排放的一些二氧化碳被海洋表面吸收，改变了海水的酸度，而与大气中二氧化碳浓度升高相关的变暖正在降低氧气的溶解度，导致更深层次动物可获得的氧气减少。酸度和氧合的变化对海洋的许多其他化学性质都有影响，并可能对与底层沉积物的化学交换以及生物如何在海洋中循环碳产生连锁影响。但是，尽管气候系统主要涉及物理，尽管大多数学生可能从学校得出结论：物理很简单，但在海洋中，各种生物驱动和相互关联的化学循环的动力学是关键，而这些远不容易完全理解。地质记录在这方面可以提供帮助，因为几乎所有可能发生在海洋生命身上的事情都曾经发生过，从部分冻结的“雪球”状态到大家都说更像热硫磺汤的东西。岩石记录不仅包含了这些事件期间海洋环境条件的地球化学线索，还包含了海洋生物和生态系统如何反应的信息。这里特别有趣的是，大约1亿年前，当恐龙在陆地上漫游时，海洋中出现了广泛的氧气消耗（“脱氧”）。这些脱氧事件通常与气候变暖有关，有时与生物灭绝有关，而且总是与沉积物中大量有机碳的埋藏有关——这些碳构成了我们今天燃烧的大部分石油和天然气。在更久远的年代（大约十亿年前），海洋首先通过一系列步骤成为含氧的，这些步骤似乎与光合作用生物的进化和向咸水环境的扩散以及后来多细胞动物的出现密切相关。氧合作用的变化与地球上生命进化的关键事件之间的关系也需要充分了解。我们在这里的重点是更好地了解过去地质时期海洋的氧化程度是如何变化的。为此，我们将应用各种尖端工具：从实验室实验，到测量古代泥浆中外来金属同位素组成中最微小差异的机器，再到计算机模型和量子力学计算。具体来说，我们将研究钼元素，这种元素在商业上用于专业炼钢和催化剂。钼在像我们今天这样富含氧气的海洋中相对丰富，但随着海洋中氧气的缺乏，钼呈现出越来越多的不溶性形式，并流失到沉积物中。钼的不同同位素被移除的效率略有不同，这为我们提供了一种重建过去海洋状况的额外方法。计算机模型将在我们的工作中发挥核心作用，因为我们既没有地球的备用副本可供实验，也没有时光机让我们直接了解过去的情况。模型将使我们能够探索过去海洋氧合变化的特征如何记录在沉积物中（从而记录在地质记录中）。我们对过去海洋氧合作用的研究结果，与对海洋生物和生态系统如何随着时间的推移而进化和反应的更好理解相结合，不仅会使我们更好地理解生命和地球的共同进化，而且还会为我们未来可能在海洋中看到的生物变化提供见解。

Our future ocean may look very different from today. Some of the carbon dioxide (CO2) emitted from the burning of fossil fuels is taken up by the ocean surface and changes the acidity of seawater, while the warming associated with higher concentrations of CO2 in the atmosphere is reducing the solubility of oxygen, leading to less oxygen available to animals deeper down. Changes in acidity and oxygenation have implications for a host of other chemical properties of the ocean and may have knock-on impacts on chemical exchanges with the underlying sediments as well as how organisms cycle carbon through the ocean. But while the climate system mostly involves physics and despite what most students may conclude from school: physics is easy, in the ocean, the dynamics of a wide variety of biologically driven and inter-linked chemical cycles are key, and these are far less easy to understand in full.The geological record can help here, because almost everything that could possibly have happened to life in the ocean has happened at one time or another, from partially frozen 'snowball' conditions to something by all accounts more like a hot sulphurous soup. The rock record not only contains geochemical clues about the environmental conditions in the ocean during these events, but also information about how the marine organisms and ecosystems respond. Of particularly interest here are occurrences of intervals of widespread oxygen depletion ('de-oxygenation') in the oceans about 100 millions years ago when dinosaurs roamed the land. These de-oxygenation events are generally associated with climate warming, sometimes with biological extinctions, and always associated with the burial of large amounts of organic carbon in accumulating sediments -- carbon that formed much of the oil and gas we are burning today. Much further (some billion years) back, the oceans first became oxygenated in a series of steps that appear intimately coupled with first the evolution and spread to saltwater environments of photosynthesizing organisms, and later, the appearance of multicellular animals. The relationship between changes in oxygenation and key events in the evolution of life on this planet also demands a full understanding.Our focus here is to gain a better understanding of how the degree of oxygenation of our oceans has changed in the geological past. To do this we will apply a variety of cutting-edge tools: from laboratory experiments, machines to measure the tiniest of differences in the isotopic composition of exotic metals in ancient muds, to computer models and quantum mechanical calculations. Specifically, we will be looking at the element Molybdenum, used commercially in specialist steel making and in catalysts. Molybdenum is relatively abundant in a well oxygenated ocean like we have today, but takes on increasingly more insoluble forms and is lost to the sediments as oxygen becomes scarce in the ocean. Different isotopes of Molybdenum differ slightly in how efficiently they are removed, giving us an additional way of reconstructing past ocean conditions. Computer models will play a central role in our work, as we have neither spare copies of our planet to experiment on, nor a time machine to allow us to get a direct picture of past conditions. Models will allow us to explore how the signature of past changes in ocean oxygenation are recorded in sediments (and hence in the geological record).The result of our work on past ocean oxygenation will, when combined with improved understanding of how marine organisms and ecosystems evolved and responded through time, will lead not only to a better understanding about the co-evolution of life and the planet, but will also provide insights into the biological changes we might expect to see in the ocean in the future.