Palaeoceanographic records from the NW Pacific, 16-0 Ma (using samples from Exp 350)

来自西北太平洋的古海洋记录，16-0 Ma（使用来自 Exp 350 的样本）

• 批准号: NE/M005232/1
• 负责人: Caroline Lear
• 金额: $ 5.66万
• 依托单位: CARDIFF UNIVERSITY
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2014
• 资助国家: 英国
• 起止时间: 2014 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FM005232%2F1
• 关键词: Palaeoceanographic; records; NW; Pacific; 16

Global climate has changed dramatically over the last 16 million years. Global temperatures at the start of this interval (part of what we call the middle Miocene Climatic Optimum) were perhaps 4-5 degrees C warmer than today, with large cold-blooded reptiles such as crocodiles observed as far north as the UK, and a much smaller-than-modern East Antarctic Ice Sheet (now the largest on the planet). This was followed around 14.5 million years ago (14.5 'Ma') by a major and permanent cooling step (the middle Miocene Climate transition, MCT) associated with the build up of ice sheet in East Antarctica and strengthening of deep water circulation and meriodional temperature gradients (what drives circulation in our current oceans). The next major phase of cooling and ice build up occurred after 5 million years ago culminating with the formation of large northern hemisphere ice sheets (that characterised our so-called 'ice ages'). Palaeoclimatologists investigate what drove these changes so that we can better understand what drives changes in our modern climate system. The ocean plays a major role in controlling climate. To understand drivers of climatic changes over the last 16 million years, we need long-term records of temperature from many different parts of the world's oceans (so that we can 'map' changes in oceanic temperature patterns) as well as information about global ice volume (the presence of ice sheets at high latitudes generates saline seawater which together with cool temperatures can drive 'thermohaline' ocean circulation by forming dense water masses). We can obtain these records by analysing the chemistry of the shells of microscopic marine organisms that collect in deep-sea sediments: Mg/Ca ratios in these shells can tell us about past water temperatures and their 18O/16O ratio can tell us about temperature and the amount of ice locked up on land. There is evidence that the Pacific experienced major oceanographical changes since 16 Ma but Mg/Ca and 18O/16O records from this ocean basin are limited; we therefore only have a loose understanding of changes in the Earth's largest ocean. A new Mg/Ca-18/16O record from the equatorial Pacific (Lear et al., in prep.) shows major changes in water temperature and global ice volume since 16 Ma but raises interesting questions about a) role of atmospheric CO2 in controlling climate (CO2 and temperature appear to be decoupled for the last 6 Myrs which raises pertinent questions give our current concerns over rising CO2 levels) and b) patterns of Pacific ocean circulation (no bottom water temperature changes were observed around 14 Ma despite inferred major ice sheet growth and evidence elsewhere for injection of cold deep Antarctic waters into the Pacific at this time). We plan to construct a new Mg/Ca-18O/16O record (from deepwaters and surface waters) from microfossil shells in the NW Pacific (particularly undersampled) in order to fill an important gap in our 'map' of temperature changes in the Pacific ocean and refine our records of global ice volume. We will also look at past effects of NW Pacific volcanism on primary productivity in the surface ocean. Explosive volcanism in the NW Pacific would have released vast amounts of volcanic ash. There is evidence to suggest that this ash is an effective fertiliser of surface oceans and can produce massive algal blooms within days. This has important implications for carbon storage in the ocean. We would like to use geochemical measurements in fossil foraminifera spanning ash layers in cores drilled in the NW Pacific, to determine whether there were changes in primary productivity associated with volcanic events so we can better understand the influence of volcanism on carbon cycling in the Pacific

在过去的1600万年中，全球气候发生了巨大变化。在此间隔开始时的全球温度（我们称之为中新世中期气候最佳最佳的一部分）可能比今天温暖4-5摄氏度，其中大量冷血爬行动物（如鳄鱼）北部到达英国的北部，而比模型的东方冰层（现在是大于这个星球上的最大）。紧随其后的是大约1450万年前（14.5'MA'），这是一个主要的永久冷却步骤（中新世中期气候过渡，MCT）与南极洲东部冰盖建立相关的，并加强了深水循环和Meriodional温度梯度（这导致了我们目前的大洋洲的循环）。下一个主要的冷却和冰堆积的阶段发生在500万年前之后，最终形成了大型北半球冰盖（这是我们所谓的“冰年”的特征）。古气候学家研究了什么变化，以便我们可以更好地了解现代气候系统中的变化。海洋在控制气候中起着重要作用。为了了解过去1600万年中气候变化的驱动因素，我们需要从世界海洋的许多不同地区的温度长期记录（以便我们可以“映射”海洋温度模式的变化）以及有关全球冰量的信息（在高纬度地区存在冰盖的冰盖存在，它们会与凉爽的温度一起产生凉爽的温度，从而使“热层” coundulation's house counduallation'海洋循环。我们可以通过分析以深海沉积物收集的微观海洋生物的壳的化学方法来获得这些记录：这些壳中的mg/ca比率可以告诉我们过去的水温及其18o/16o的比例可以告诉我们温度和冰块锁定在陆地上。有证据表明，自从16 Ma，但Mg/ca和18o/16o记录中，太平洋经历了重大的海洋学变化，来自该海洋盆地的记录有限。因此，我们对地球最大的海洋的变化只有松散的理解。 A new Mg/Ca-18/16O record from the equatorial Pacific (Lear et al., in prep.) shows major changes in water temperature and global ice volume since 16 Ma but raises interesting questions about a) role of atmospheric CO2 in controlling climate (CO2 and temperature appear to be decoupled for the last 6 Myrs which raises pertinent questions give our current concerns over rising CO2 levels) and b) patterns of Pacific ocean circulation (no bottom water temperature changes were尽管此时推断出主要的冰盖生长和其他地方的证据，但此时发现了大约14 Ma的大约14个MA）。我们计划从西北太平洋地区的微化石壳（尤其是不足的采样）中构建新的MG/CA-18O/16O记录（来自深水和地表水），以填补太平洋天气中温度变化的重要空白，并改善我们的全球冰量记录。我们还将研究西北太平洋火山对地面海洋初级生产力的过去影响。西北太平洋地区的爆炸性火山将释放大量的火山灰。有证据表明，这种灰烬是表面海洋的有效肥料，可以在几天内产生巨大的藻华。这对海洋中的碳存储具有重要意义。我们想在西北太平洋钻探的岩石层中使用化石有孔虫中的地球化学测量，以确定与火山事件相关的一级生产力是否有变化，因此我们可以更好地了解火山循环对太平洋碳循环的影响