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。在这段时间开始时（我们称之为中新世中期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，在英国北部观察到大型冷血爬行动物，如鳄鱼，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）。这之后是大约1450万年前（14.5 'Ma'）的一个主要的和永久的冷却步骤（中中新世气候转变，MCT），与南极洲东部冰盖的建立和加强深水循环和meriodional温度梯度（驱动我们目前海洋的循环）有关。下一个冷却和冰堆积的主要阶段发生在500万年前，最终形成了北方的大冰盖（这是我们所谓的“冰河时代”的特征）。古气候学家调查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，我们需要世界海洋不同区域的长期温度记录（这样我们就可以'绘制'海洋温度模式的变化）以及全球冰量的信息（高纬度冰盖的存在会产生含盐海水，与凉爽的温度一起，稠密的水团）。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比率可以告诉我们过去的水温，它们的18 O/16 O比率可以告诉我们温度和陆地上的冰量。有证据表明，自16 Ma以来，太平洋经历了重大的海洋学变化，但该洋盆的Mg/Ca和18 O/16 O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。来自赤道太平洋的Mg/Ca-18/16 O新记录（Lear等人，（正在编写中）显示了自16 Ma以来水温和全球冰量的重大变化，但提出了关于a）大气CO2在控制气候中的作用的有趣问题（过去600万年来，CO2和温度似乎是分离的，这引起了我们目前对CO2水平上升的担忧的相关问题）和B）太平洋环流模式（在14 Ma左右没有观察到底层水温的变化，尽管推断出大冰盖的生长和其他地方的证据表明此时南极深层寒冷的沃茨注入太平洋）。我们计划构建一个新的Mg/Ca-18 O/16 O记录（从深沃茨和表面沃茨）从微体化石贝壳在西北太平洋（特别是采样不足），以填补我们的“地图”在太平洋的温度变化的重要空白，并完善我们的全球冰量的记录。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，这些灰烬是海洋表面的有效肥料，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具有重要意义。我们想利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，以确定初级生产力是否与火山活动有关，以便我们能够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