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1600万年里，全球气候发生了巨大的变化。在这个间歇期开始时（我们称之为中新世中期气候最佳期的一部分），全球气温可能比今天高4-5摄氏度，在遥远的英国北部，可以看到鳄鱼等大型冷血爬行动物，而南极东部冰盖（现在是地球上最大的冰盖）比现在小得多。大约在1450万年前（14.5亿年前），一个主要的、永久的冷却阶段（中新世中期气候转变，MCT）随之而来的是东南极洲冰盖的积累，以及深水循环和经向温度梯度的加强（驱动我们当前海洋环流的因素）。下一个主要的冷却和冰积累阶段发生在500万年前，以北半球大冰盖的形成（这是我们所谓的“冰河时代”的特征）为高潮。古气候学家研究是什么导致了这些变化，这样我们就能更好地理解是什么导致了现代气候系统的变化。海洋在控制气候方面起着重要作用。为了了解过去1600万年气候变化的驱动因素，我们需要世界海洋许多不同地区的长期温度记录（这样我们就可以“绘制”海洋温度模式的变化）以及关于全球冰量的信息（高纬度地区冰盖的存在产生含盐海水，加上低温可以通过形成致密的水团来驱动“热盐”海洋环流）。我们可以通过分析深海沉积物中收集的海洋微生物外壳的化学成分来获得这些记录：这些外壳中的Mg/Ca比值可以告诉我们过去的水温，它们的18O/16O比值可以告诉我们温度和陆地上的冰量。有证据表明太平洋自16ma以来经历了重大的海洋变化，但该洋盆的Mg/Ca和18O/16O记录有限；因此，我们对地球上最大的海洋的变化只有粗略的了解。赤道太平洋的Mg/Ca-18/16O新记录(Lear et al.；)显示了自16ma以来水温和全球冰量的主要变化，但提出了一些有趣的问题：a)大气CO2在控制气候中的作用（CO2和温度在过去6万年中似乎是分离的，这提出了相关的问题，使我们目前对二氧化碳水平上升的担忧）和b)太平洋环流模式(14ma左右没有观测到底部水温的变化，尽管推断出主要的冰盖增长和其他地方的证据此时将冰冷的南极深水注入太平洋)。我们计划从西北太平洋（特别是样本不足）的微化石壳中构建一个新的Mg/Ca-18O/16O记录（来自深水和地表水），以填补太平洋温度变化“地图”中的一个重要空白，并完善我们的全球冰量记录。我们还将研究过去西北太平洋火山活动对表层海洋初级生产力的影响。西北太平洋的火山爆发会释放出大量的火山灰。有证据表明，这些火山灰是表层海洋的有效肥料，可以在几天内产生大规模的藻华。这对海洋中的碳储存具有重要意义。我们希望利用地球化学测量在西北太平洋钻探的岩心中跨越火山灰层的化石有孔虫，以确定是否存在与火山事件相关的初级生产力变化，以便我们更好地了解火山作用对太平洋碳循环的影响