A PHase-Specific geochemical study of marine PRoductivity and nutrient cycling during the end-Permian mass extinction (PHoSPhoR)

我想研究导致二叠纪末期大灭绝的海洋生产力和营养物质可获得性的变化。这一事件代表了过去5亿年来最戏剧性的动物更替，随后是长达2-500万年的海洋生态系统不稳定时期。这一事件的起因(S)仍有很大争议。一个悬而未决的问题是，这一事件是否与海洋(几乎)贫瘠的生命(初级生产力崩溃)有关，或者相反，这一事件代表了多细胞真核生物之间的生物多样性崩溃，但在其他方面，海洋生产力水平普遍较高。(由于有氧和无氧呼吸的增加，营养物质通量的增加会刺激有机质的产生，并导致氧气耗竭和硫化氢富集区的扩大。)我将通过一项对关键海洋沉积档案的高度新颖的地球化学研究来检验这些关于二叠纪末生物多样性崩溃的相互竞争的假说。采用这种方法，将更全面地了解地球历史上这一关键时期海洋氧化还原条件、营养循环和生物地球化学循环之间的反馈。这项研究的核心是使用最新开发的Fe形态形成技术(该技术以前只应用于任何二叠纪-三叠纪剖面)对海洋氧化还原条件进行详细评估，此外还利用我们对痕量金属在不同氧化还原条件下的不同行为的理解的最新进展。这将产生敏感和可靠的代理记录，用于识别一系列氧化还原制度(缺氧、缺氧、缺氧-硫酸盐或缺氧-铁质)。这些分析将为下一个地球化学阶段奠定基础，该阶段将涉及磷形态形成技术和钡浓度的高度新颖的应用，以提取关于古代营养通量(和再循环)和海洋生产力的信息。这是必要的，原因有两个：(1)块状岩石的元素分析(标准技术)不能提供生物可用元素通量或相的指示，而是包括碎屑组分，以及(2)在某些环境条件下这些活性元素的沉积后(重新)动员只能通过相特定的技术实现。我将改进这些研究，对更有可能包含主要海洋信号的特定沉积相进行地球化学分析，这些信号将坚定地设置在每个样品的精确氧化还原环境中。这将与硫同位素分析相结合，以进一步了解对水柱氧化还原条件的控制。

I want to study changes in marine productivity and nutrient availability that contributed to the end-Permian mass extinction. This event represents the most dramatic faunal turnover during the last 500 million years, followed by a prolonged 2-5 million-year period of marine ecosystem instability. The cause(s) of this event are still much debated. One open question concerns whether the event is associated with an ocean (almost) barren of life (a primary productivity collapse), or conversely, that the event represents a biodiversity crash amongst multi-cellular eukaryotes, but with otherwise generally high-marine productivity levels. (Elevated fluxes of nutrients stimulate organic matter production and result in expansion of oxygen depleted and hydrogen-sulphide enriched zones, caused by increased aerobic and anaerobic respiration.) I will test these competing hypotheses for the end-Permian biodiversity collapse through a highly novel geochemical study of key marine sedimentary archives. Taking this approach, a more comprehensive understanding of feedbacks between marine redox conditions, nutrient cycling and biogeochemical cycles will be achieved for this critical interval of Earth history. Central to this study will be a detailed evaluation of ocean redox conditions, using the most recently developed Fe speciation technique (which has only once previously been applied to any Permo-Triassic sections), in addition to utilising recent advances in our understanding of the differential behaviour of trace metals under different redox conditions. This will yield sensitive and robust proxy records for identifying a range of redox regimes (oxic, dysoxic, anoxic-sulphidic, or anoxic-ferruginous). These analyses will set the scene for the next geochemical phase, which will involve the highly novel application of phosphorus speciation techniques and barium concentrations to extract information about ancient nutrient fluxes (and recycling) and marine productivity. This is essential for two reasons: (1) Elemental analyses of bulk-rock (the standard technique) does not give an indication of bioavailable elemental fluxes or phases, but instead includes the detrital fraction, and (2) post-depositional (re)mobilization of these reactive elements under certain environmental conditions can only be achieved with phase specific techniques. I will improve on these studies by conducting geochemical analyses of specific sedimentary phases that are more likely to harbour a primary marine signal, which will be set firmly within the precise redox context of each sample. This will be combined with sulphur isotope analyses to provide further insight into controls on water column redox conditions.