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大灭绝的海洋生产力和营养物质的变化。这一事件代表了过去5亿年间最剧烈的动物更替，随后是长达2-5百万年的海洋生态系统不稳定时期。这一事件的起因仍有很多争论。一个悬而未决的问题是，这一事件是否与海洋（几乎）生命贫瘠（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。（由于有氧呼吸和无氧呼吸的增加，营养物质通量的增加刺激了有机物的产生，导致缺氧区和硫化氢富集区扩大。）我将通过对关键海洋沉积档案的高度新颖的地球化学研究来测试这些关于二叠纪末生物多样性崩溃的相互竞争的假设。通过这种方法，可以更全面地了解海洋氧化还原条件、营养循环和生物地球化学循环之间的反馈关系。本研究的核心将是详细评估海洋氧化还原条件，使用最新开发的铁形态技术（该技术以前仅应用于任何二叠纪-三叠纪剖面），此外还利用我们对不同氧化还原条件下微量金属差异行为的最新研究进展。这将产生敏感和可靠的替代记录，用于识别一系列氧化还原机制（缺氧、缺氧、缺氧-硫化物或缺氧-含铁）。这些分析将为下一个地球化学阶段奠定基础，这一阶段将涉及高度新颖的磷形态形成技术和钡浓度的应用，以提取有关古代营养流动（和再循环）和海洋生产力的信息。这有两个重要原因：(1)块状岩石的元素分析（标准技术）不能给出生物可利用元素通量或相的指示，而是包括碎屑分数；(2)这些活性元素在特定环境条件下的沉积后（再）动员只能通过特定相的技术来实现。我将通过对特定沉积相进行地球化学分析来改进这些研究，这些沉积相更有可能包含主要的海洋信号，这些信号将牢固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.