Rasmussen Christian M Ø, Ullmann Clemens V, Jakobsen Kristian G, Lindskog Anders, Hansen Jesper, Hansen Thomas, Eriksson Mats E, Dronov Andrei, Frei Robert, Korte Christoph, Nielsen Arne T, Harper David A T
Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen K, Denmark.
Department of Geology, Lund University, Sölvegatan 12, S-223 62 Lund, Sweden.
Sci Rep. 2016 Jan 6;6:18884. doi: 10.1038/srep18884.
The Great Ordovician Biodiversification Event (GOBE) was the most rapid and sustained increase in marine Phanerozoic biodiversity. What generated this biotic response across Palaeozoic seascapes is a matter of debate; several intrinsic and extrinsic drivers have been suggested. One is Ordovician climate, which in recent years has undergone a paradigm shift from a text-book example of an extended greenhouse to an interval with transient cooling intervals - at least during the Late Ordovician. Here, we show the first unambiguous evidence for a sudden Mid Ordovician icehouse, comparable in magnitude to the Quaternary glaciations. We further demonstrate the initiation of this icehouse to coincide with the onset of the GOBE. This finding is based on both abiotic and biotic proxies obtained from the most comprehensive geochemical and palaeobiological dataset yet collected through this interval. We argue that the icehouse conditions increased latitudinal and bathymetrical temperature and oxygen gradients initiating an Early Palaeozoic Great Ocean Conveyor Belt. This fuelled the GOBE, as upwelling zones created new ecospace for the primary producers. A subsequent rise in δ(13)C ratios known as the Middle Darriwilian Isotopic Carbon Excursion (MDICE) may reflect a global response to increased bioproductivity encouraged by the onset of the GOBE.
奥陶纪生物大辐射事件（GOBE）是显生宙海洋生物多样性最迅速且持续时间最长的增长过程。究竟是什么引发了古生代海洋景观中的这种生物反应，一直是个颇具争议的话题；人们提出了多种内在和外在驱动因素。其中一个因素是奥陶纪气候，近年来，它经历了一种范式转变，从教科书式的长期温室气候模式转变为至少在奥陶纪晚期存在短暂降温期的模式。在此，我们展示了首个明确无误的证据，证明中奥陶世突然出现了冰室效应，其规模可与第四纪冰川作用相媲美。我们进一步证明，这种冰室效应的开始与奥陶纪生物大辐射事件的起始时间相吻合。这一发现基于从该时段迄今收集到的最全面的地球化学和古生物学数据集中获取的非生物和生物指标。我们认为，冰室条件增加了纬度和深度的温度及氧气梯度，引发了早古生代的大洋输送带。这推动了奥陶纪生物大辐射事件，因为上升流区域为初级生产者创造了新的生态空间。随后δ(13)C比值的上升，即中达瑞威尔同位素碳偏移（MDICE），可能反映了全球对奥陶纪生物大辐射事件起始所促进的生物生产力增加的一种响应。
