Comparing land-based and deep-sea rock and fossil records of microplankton to test for bias in diversity patterns through time

最近对陆地上保存了多少海洋沉积岩的研究强调了不同时期的记录在环境代表性和绝对岩石体积方面的变化。因此，我们现在知道，大陆架上的岩石记录在结构上是非常循环的。在最基本的层面上，古生代的岩石记录包括两个旋回，主要由海相岩石与陆相岩石的比例变化来定义。这些周期在北方和南半球都很明显，尽管它们的精确时间略有不同。它们的出现是对板块组装和裂谷作用的主要全球构造周期的响应。这些都是短期的叠加（约。50 My）周期，这些周期在很大程度上独立于大陆之间的时间，反映了区域构造事件和局部海平面变化。海洋生物多样性，以大型化石的数量来衡量，也显示出一种周期性的模式。这些周期与大陆洪水范围的变化相吻合，因此可能是通过两个过程之一产生的：它们可能是由于取样偏差造成的，因为最终保存下来的特定年龄的海洋沉积岩的数量随着海洋在大陆上的扩张和收缩而变化;或者生物多样性可能随着浅海航道的扩张和收缩而上升和下降。目前尚不清楚哪一种是海洋化石记录的主要驱动力，因为浅水环境中的动物群具有高度的空间异质性，导致非常强烈的物种-区域效应（采样区域越广，发现的物种就越多）。到目前为止，所有的注意力都集中在大陆架的岩石和化石记录上。对深海记录的性质以及它是否与海洋多样性相关的大规模分析从未进行过探索。有充分的理由认为，深海岩石和化石记录可能与大陆架上保存的不同。首先，大部分沉积物记录都是由几乎连续的生物沉积物组成的，这些生物沉积物来自于很少侵入大陆架很远的浮游微生物。此外，在开阔的海洋中，海洋浮游生物分布广泛，因此任何物种-面积效应都不太明显。然而，我们也知道，由于没有保存，深海中存在着间断和贫瘠的间隔，并且产生特定年龄的含矿岩石的岩心数量不太可能随着时间的推移而均匀。更重要的是，据报道，南极有孔虫的多样性显示出3000万年的周期性上升和下降。为了澄清化石多样性模式是否与岩石取样模式有因果关系，我们将重点关注两个重要的浮游生物群，颗石藻和浮游有孔虫的化石记录。我们将首先通过评估大西洋中部取样记录中的空白和非保存间断的分布来确定深海记录中可能存在的任何偏差，并测试这些实际上对多样性计数的影响有多大（对于地理分布广泛的分类群，取样密度的变化应具有最小的影响）。通过记录它们的多样性，通过时间从深海岩心和比较这与他们的多样性模式，来自陆地露头，我们希望能够显示是否30万年的周期是一个真正的生物信号或结果的程度，开放的海洋沉积侵蚀到大陆块在高海平面的立场。我们还将比较深海沉积岩和化石记录的性质与来自邻近大陆陆地部分的岩石和化石记录，以查明深海化石记录是否不受影响浅水记录的许多偏差的影响，或者两者在质量上是否存在协变。

Recent reviews of how much marine sedimentary rock remains preserved on land have highlighted just how variable that record is from different time periods, both in terms of environmental representation and absolute rock volume. As a result we now know that the rock record over the continental shelf is very cyclical in structure. At its most fundamental level the Phanerozoic rock record comprises two cycles defined primarily by changes in the ratio of marine to terrestrial rock. These cycles are evident across both Northern and Southern hemispheres although their precise timing differs slightly. They arise in response to major global tectonic cycles of plate assembly and rifting. Superimposed on these are shorter-term (ca. 50 My) cycles, which are largely independent in timing from continent to continent and which reflect regional tectonic events and local sea level changes. Marine biodiversity, as measured by counts of macrofossils, also shows a cyclical pattern. These cycles match changes in the extent of continental flooding and thus could be generated through one of two processes: they could arise because of sampling bias, as the amount of marine sedimentary rock of a particular age that is ultimately preserved varies as seas expand and contract over the continents; or biological diversity could be rising and falling in tandem with the expansion and contraction of shallow marine seaways. At present it is not clear which is the predominant driver of the marine fossil record because there is high spatial heterogeneity of faunas within shallow water environments leading to a very strong species-area effect (the wider an area sampled the more species will be found). So far all the attention has been focussed on the rock and fossil records of the continental shelves. Large scale analyses of the nature of the deep-sea record and whether it correlates with marine diversity have never been explored. There are strong grounds for thinking that the deep-sea rock and fossil records might be different from that preserved on the continental shelves. For one thing much of the sedimentary record comprises near continuous biogenic deposits derived from planktonic microorganims which only rarely encroaches far onto the continental shelves. Furthermore, in the open oceans marine plankton are widely dispersed, so that any species-area effect is much less evident. Yet we also know there are hiatuses and barren intervals in the deep sea due to non-preservation, and the numbers of cores yielding fossiliferous rocks of a specific age is unlikely to be uniform over time. What is more, planktonic foraminiferans are reported to show a 30 myr cyclical rise and fall in diversity. To clarify whether fossil diversity patterns are causally linked to rock sampling patterns we will focus on the fossil record of two important planktonic groups, coccolithophorids and planktonic foraminifera. We will first identify any possible biases in the deep-sea record by assessing the distribution of gaps and non-preservation hiatuses in the sampled record of the central Atlantic, and test how much these actually affect diversity counts (for geographically widespread taxa variation in density of sampling should have a minimal effect). By recording their diversity through time from deep-sea cores and comparing this with their diversity patterns as derived from land-based outcrops, we hope to be able to show whether the 30-Myr cyclicity is a genuine biological signal or an outcome of the extent to which open oceanic sedimentation encroaches onto the continental blocks during high sea-level stands. We will also compare the nature of the deep-sea sedimentary rock and fossil records with rock and fossil records derived from land-based sections on adjacent continents to find out whether the deep-sea fossil record is immune from many of the biases affecting the shallow water record, or whether both covary in quality.