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和气候系统密切相关。科学家们通过详细研究多年来在大陆和海洋中积累的古代岩层，已经建立了一幅地球历史和过去动物和植物的图画。长期的相对静止和逐渐的变化被短暂的间歇所打断，这时地球环境突然发生了变化。快速的环境变化常常伴随着异常高的物种灭绝和多样性变化，随后往往是物种进化的新模式。地球历史上一个公认的事实是，过去的气候通常比现在暖和得多。此外，人们几乎普遍认为，气候和全球平均温度与大气中二氧化碳的含量密切相关，尽管是以一种复杂的方式。但无论气候-二氧化碳关系的确切性质是什么，全球变暖的一个后果是海水中的氧含量预计会相对较低，原因有两个。首先，所有的气体——包括氧气——在较热的液体中比在较冷的液体中更难溶解；第二，海洋的初级生产力直接影响氧气水平，因为更高的生产力导致更高的氧气消耗水平。因此，我们有理由预计，随着海洋变暖和河流提供更多的营养物质，海水的氧合作用将在未来下降。在过去50或60年里，对海洋许多地方氧气含量大幅下降的直接观察支持了这一预期。虽然这是一个全球性的现象，但氧含量在大陆架水域是最敏感的。这是一个令人担忧的问题，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。货架脱氧的后果严重威胁着人类：超过10亿人依赖海洋食物作为主要蛋白质来源。然而，准确预测未来脱氧的速度、严重程度和轨迹是出了名的困难。提高预报可靠性的一个非常有力的方法是通过对过去海水氧合的观测来“调整”预测模型，从而改进预测模型。这个项目（RESPIRE）将定义3000多万年的海水氧化历史，从大约5600万年前到2500万年前。在此期间，地球表面环境的温度大幅下降，有逐渐下降的，也有断断续续的下降。由于没有过去海水氧合的直接记录，我们将使用地球化学代用物，其值反映氧合水平。虽然这些地球化学测量非常困难且耗时，但我们在其开发和应用方面有多年的经验，我们已经证明这些代理可以作为短时间间隔内过去氧合作用的可靠档案。现在的挑战是生成长期记录，这将帮助我们更好地了解过去和未来海水氧化的控制因素。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，而烃源岩提供了目前世界上大部分的能源需求。由于RESPIRE将涉及野外地质学家、地球化学家、气候建模师和工业地质学家之间的密切合作，该项目将提供一个论坛，以便更好地定义过去的海水脱氧与碳氢化合物来源的有机物积累之间的关系。RESPIRE将是第一个建立海水长期氧合历史的研究，它将对海水氧合与全球地球系统过程的联系提供一个综合的、跨学科的评估。

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.