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

在过去的1600万年里，全球气候发生了巨大的变化。在这个时间间隔开始时(我们称之为中新世气候最佳时期的一部分)，全球气温可能比今天高4-5摄氏度，在遥远的北方观察到鳄鱼等大型冷血爬行动物，以及比现代小得多的东南极冰盖(现在是地球上最大的冰盖)。大约在1450万年前(1450万Ma‘)，伴随着东南极冰盖的形成、深水环流和经向温度梯度的加强(驱动我们当前海洋环流的因素)，发生了一个重大的、永久的冷却步骤(中中新世气候转变，MCT)。下一个主要的冷却和结冰阶段发生在500万年前之后，最终形成了巨大的北半球冰盖(这是我们所谓的冰河时代的特征)。古气候学家研究了是什么驱动了这些变化，以便我们能够更好地了解是什么驱动了我们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1600万年来气候变化的驱动因素，我们需要世界海洋许多不同部分的长期温度记录(以便我们可以绘制出海洋温度模式的变化图)，以及关于全球冰量的信息(高纬度冰盖的存在产生咸水，海水与低温一起可以通过形成致密水团来驱动‘温盐’海洋环流)。我们可以通过分析深海沉积物中收集的微小海洋生物贝壳的化学成分来获得这些记录：这些贝壳中的镁/钙比率可以告诉我们过去的水温，而它们的18O/16O比率可以告诉我们温度和陆地上锁住的冰量。有证据表明，自16 Ma以来，太平洋经历了重大的海洋学变化，但来自该洋盆的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松散的了解。赤道太平洋的一个新的Mg/Ca-18/16O记录(Lear等人，在准备中)它显示了16 Ma以来水温和全球冰量的主要变化，但提出了如下有趣的问题：a)大气二氧化碳在控制气候中的作用(二氧化碳和温度在过去6个月似乎是脱钩的，这提出了相关的问题，给出了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(尽管推断出主要的冰盖增长和其他地方此时南极冰冷水域注入太平洋的证据，但在14 Ma左右没有观察到底层水温的变化)。我们计划从西北太平洋(特别是采样不足)的微化石贝壳中建立一个新的Mg/Ca-18O/16O记录(来自深水和表层水)，以填补我们在太平洋温度变化‘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，这种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类水华。这对海洋中的碳储存有着重要的影响。我们希望使用在西北太平洋钻探的岩芯中跨越灰层的有孔虫化石的地球化学测量来确定初级生产力是否与火山事件有关，以便我们更好地了解火山活动对太平洋碳循环的影响

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