RESPONSE OF GLOBAL OCEAN OXYGENATION TO EARLY CENOZOIC CLIMATE EXTREMES (RESPIRE)

地球上生命的进化与地球海洋的发展及其气候系统密切相关。科学家们通过对大陆和海洋中多年来积累的古老岩层的详细研究，建立了一幅地球历史和过去时代的动物和植物的图景。长期的相对平静和逐渐变化被地球环境突然变化的较短间隔所打断。环境的快速变化往往伴随着异常高水平的物种灭绝和多样性的变化，并往往伴随着新的物种进化模式。地球历史的一个公认的方面是，过去的气候往往比现在温暖得多。此外，人们几乎普遍认为，气候和全球平均温度与大气中的二氧化碳水平密切相关，尽管关系复杂。但是，无论气候与二氧化碳之间的关系的确切性质如何，全球变暖的一个后果是，海水中的含氧量预计将相对较低，原因有二。第一，所有气体-包括氧气-在温度较高的液体中的溶解度低于在温度较低的液体中的溶解度;第二，海洋的初级生产力直接影响氧气水平，因为生产力越高，氧气消耗量越大。因此，可以合理地预期，随着海洋变暖和河流提供更多的营养物质，海水的含氧量将在未来下降。过去50年或60年来，海洋许多地方的含氧量大幅下降，这一直接观察结果支持了这一预期。虽然这是一种全球现象，但大陆架沃茨的含氧量最敏感。这是一个令人关切的问题，因为大多数海洋物种生活在大陆架上，它们非常容易受到海水氧合变化的影响。人类正面临货架脱氧后果的严重风险：超过10亿人依赖海洋食品作为其主要蛋白质来源。然而，要准确预测未来脱氧的速度、严重程度和轨迹是非常困难的。提高预测可靠性的一个非常有效的方法是通过使用过去海水氧化的观察来“调整”预测模型。该项目（EQUIPIRE）将确定海水的氧化历史，涵盖了从大约5600万年前到2500万年前的3000多万年的时间。在此期间，地球表面环境大幅降温，既有逐渐降温，也有几次不连续的跳跃。由于没有过去海水氧化的直接记录，我们将使用反映氧化水平的地球化学指标。虽然这些地球化学测量非常困难和耗时，但我们在其开发和应用方面有多年的经验，我们已经表明，这些替代物可以作为过去短时间内氧化的可靠档案。现在的挑战是生成更长期的记录，这将帮助我们更好地了解对过去和未来海水氧合的控制。低氧海洋环境的另一个非常重要的方面是，它们是烃源岩形成的先决条件，而烃源岩满足了世界当前大部分能源需求。由于该项目将涉及野外地质学家、地球化学家、气候建模者和工业地质学家之间的密切合作，该项目将提供一个论坛，以更好地确定过去海水脱氧与碳氢化合物来源的有机物质积累之间的关系。该项目将是第一个通过提供关于海水氧合如何与全球地球系统过程相关联的综合、跨学科评估来建立海水长期氧合历史的研究。

The evolution of life on Earth has been tightly linked to the development of the planet's oceans and to its climate system. Scientists have built up a picture of Earth history, and of the animals and plants of past times, through detailed examination of ancient rock strata that have accumulated on the continents and in the oceans over the ages. Long periods of relative quiescence and of gradual change were punctuated by shorter intervals when Earth's environment changed abruptly. Intervals of rapid environmental change were often accompanied by unusually high levels of species extinctions and of changes in diversity, and were often followed by new patterns of species evolution. One well established aspect of Earth history is that past climates were often much warmer than at present. Furthermore, it is almost universally accepted that climate and mean global temperature are intimately related to the level of atmospheric CO2, albeit in a complex way. But no matter what the precise nature of the climate-CO2 relationship, one consequence of global warmth is that seawater oxygen levels are expected to be relatively low, for two reasons. The first is that all gases - including oxygen - are less soluble in warmer liquids than in cooler ones; the second is that the primary productivity of the oceans affects oxygen levels directly, as higher productivity leads to greater levels of oxygen consumption. Thus there is the reasonable expectation that seawater oxygenation will decline in the future, as the oceans warm and as rivers supply more nutrients. This expectation is backed up by the direct observation of substantially decreasing oxygen levels in many parts of the oceans over the last 50 or 60 years. Although a global phenomenon, oxygen levels are most sensitive in continental shelf waters. This is a concern, because most marine species live on the continental shelf, and they are highly susceptible to changes in seawater oxygenation. Humankind is acutely at risk from the consequences of shelf deoxygenation: more than one billion people depend on marine food as their primary protein source. However, it is notoriously difficult to predict accurately the speed, severity and trajectory of future deoxygenation. One very powerful way of improving the reliability of forecasts is to refine predictive models by 'tuning' them using observations of past seawater oxygenation. This project (RESPIRE) will define the oxygenation history of seawater covering a period of just over 30 million years, from around 56 million years ago to 25 million years ago. The Earth's surface environment cooled substantially during this period, both gradually and also in a few discrete jumps. Because there are no direct records of past seawater oxygenation, we will use geochemical proxies whose values reflect oxygenation levels. Although these geochemical measurements are very difficult and time consuming, we have many years' experience in their development and application and we have shown that the proxies can act as robust archives of past oxygenation for short time intervals. The challenge now is to generate longer-term records that will help us to better understand the controls on past - and future - seawater oxygenation.An additional and highly important aspect of low-oxygen marine environments is that they are a pre-requisite for the formation of hydrocarbon source rocks, which supply most of the world's current energy demand. Because RESPIRE will involve close co-operation between field geologists, geochemists, climate modellers and industry geologists, the project will provide a forum to better define the relationship between past seawater deoxygenation and the accumulation of organic matter from which hydrocarbons are derived. RESPIRE will be the first study to establish the longer-term oxygenation history of seawater by providing an integrated, interdisciplinary assessment of how seawater oxygenation is linked to global Earth System processes.