CO2-CarbonCycle-Climate-Interactions (C4I)

海洋占地球表面的70%，支持着巨大的生物多样性，并为人类提供主要的食物资源。自工业革命以来，海洋通过吸收化石燃料燃烧和水泥生产产生的约50%的二氧化碳，限制了全球变暖的程度。二氧化碳溶解在海水中时会形成碳酸，并降低环境pH值，这种现象被称为“海洋酸化”。海洋酸化的一个重要方面是海洋中碳酸盐离子浓度的下降，碳酸盐离子是一种溶解碳，当二氧化碳加入海水时，它会在酸化反应中耗尽。这是至关重要的，因为许多海洋生物的外壳和骨骼是由碳酸钙（CaCO 3）组成的，碳酸钙在低碳酸根离子浓度（称为“欠饱和”条件）下溶解。然而，破坏的生态阈值可能早在饱和度不足的条件实际发生之前就已经越过，海洋生物的外壳开始溶解，因为随着碳酸盐离子浓度的下降，碳酸钙外壳和骨骼将需要更多的代谢能量来维持其厚度。实验室和野外的实验已经证明了这种效应，并发现称为颗石藻的钙化藻类通常在酸性条件下产生较少的CaCO 3外壳材料。减缓生活在海洋表面的藻类产生CaCO 3的速度可能会通过帮助中和化石燃料CO2而产生“有益”的影响，但随着生态系统的破坏，这种影响是有害的。这也可能对海底生物的有机碎屑供应产生严重影响，因为人们怀疑这种食物供应在很大程度上依赖于CaCO 3颗粒来减轻蓬松的有机物并帮助其下沉。海洋酸化的其他影响可能包括海洋中产生的有机物质的数量和营养成分的变化，以及营养物质的损失：将硝酸盐转化为强大的温室气体一氧化二氮。海洋碳循环是如何“工作”的，CaCO 3颗粒是否真的对减轻蓬松的有机物很重要，以及像颗石藻这样的藻类将如何对海洋化学变化做出反应，这些都受到很大的不确定性的影响。这意味着我们无法知道单个计算机模型对未来的预测是否正确。在这个项目中，我们将解决这个不确定性的问题--通过使用描述现代海洋“看起来”像什么的大量数据集（根据沉积物中记录的营养物质分布和模式）来约束模型群，使它们都同意现代海洋开始的样子，我们将得到很大的帮助。我们的工作成果首先将是更好地了解现代海洋碳循环，这对于在担心未来之前做好准备至关重要。我们还将预测未来海洋碳和营养循环的变化范围，以及海洋如何通过排放或多或少的温室气体（如二氧化碳和一氧化二氮）来影响未来变暖的程度。

Oceans represent 70% of Earth's surface, supporting vast biodiversity and providing major food resources for humankind. Since the industrial revolution, the oceans have restricted the extent of global warming by taking up approximately 50% of the CO2 from fossil fuel burning and cement manufacture. CO2 forms carbonic acid when dissolved in seawater and lowers ambient pH in a phenomenon known as 'ocean acidification'. An important facet of ocean acidification is a decline in the concentration of carbonate ions in the ocean, a form of dissolved carbon that is depleted in the acidification reaction when CO2 is added to seawater. This is critical, because the shells and skeletons of many marine organisms are made of calcium carbonate (CaCO3) which dissolves at low carbonate ion concentrations (known as 'under-saturated' conditions). However, ecological thresholds of disruption may be crossed long before conditions of under-saturation actually occur and marine organisms' shells start dissolving around them, because calcium carbonate shells and skeletons will require more metabolic energy to maintain their thickness as carbonate ion concentrations fall. Experiments in the laboratory and field have already demonstrated this effect and find that calcifying algae called coccolithophorids generally produce less CaCO3 shell material in more acidic conditions. Slowing the rate of production of CaCO3 by algae living in the ocean surface may have a 'beneficial' impact by helping neutralize fossil fuel CO2, but a detrimental impact as ecosystems are disrupted. There may also be serious implications for the supply of organic detritus to organisms on the seafloor, as it is suspected that this food supply depends heavily on particles of CaCO3 to weigh down the fluffy organic matter and help it sink. Other impacts of ocean acidification may include changes in the amount and nutritional content of organic matter produced in the ocean, and loss of nutrients: converting nitrate to the powerful greenhouse gas nitrous oxide. How the ocean carbon cycle 'works' and whether CaCO3 particles are really important to weighting down fluffy organic matter as well as how exactly algae like coccolithophorids will respond to changing ocean chemistry are subject to significant uncertainties. This means that we would have no way of knowing whether a single computer model prediction for the future is correct or not. In this project we will tackle this question of uncertainty head-on - running out computer models of ocean carbon cycling and climate hundreds and hundreds of times to see what future impacts are possible and what are not. We will be greatly helped in this by using vast datasets describing what the modern ocean 'looks' like (in terms of the distributions of nutrients and patterns recorded in the sediments) to constrain the swarm of models so that they all agree on what the modern ocean looks like to begin with. The outcome of our work will firstly be a better understanding of the modern ocean carbon cycle, which is essential to get right before worrying about the future. We will also make predictions about the range of changes in ocean carbon and nutrient cycles we can expect in the future and how the ocean may affect the degree of future warming by emitting more or less greenhouse gases such as carbon dioxide and nitrous oxide.