Pliocene to Pleistocene reconstruction of regional versus global ocean oxygenation from eastern Pacific anoxic sediments

从东太平洋缺氧沉积物中重建区域与全球海洋氧化的上新世至更新世

• 批准号: 467246485
• 负责人: Professor Dr. Martin Frank
• 金额: --
• 依托单位: Forschungseinheit Paläo-Ozeanographie
• 依托单位国家: 德国
• 项目类别: Infrastructure Priority Programmes
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/467246485?language=en
• 关键词: Pliocene; Pleistocene; reconstruction; regional; versus

Over the past decades the oxygen content of the ocean has decreased as a consequence of global warming. This has resulted in the expansion of oceanic regions that are highly deficient in oxygen. Such expanding oxygen minimum zones (OMZs) prevail in the eastern Pacific Ocean as a consequence of high biological productivity and subsequent remineralisation of organic matter, which is driven by upwelling of nutrient-rich waters. In order to judge if enhanced anoxia is within or outside the range of the natural variability of the past, the only access is offered by the sedimentary record. The geochemical proxies commonly used to reconstruct the strength and modes of past anoxia, however, yield controversial results, in particular in open ocean settings. Here we propose to apply new knowledge on the functioning and influencing factors of proxies for anoxic conditions obtained during recent studies of modern settings in the OMZs off Peru and in the Guaymas Basin to reconstruct the evolution of the modes of anoxic conditions over the past 3 million years. We will utilize sediments of ODP Site 680 (later redrilled as IODP Site 1228) from the present day centre of the Peruvian shelf coastal upwelling OMZ (250 m water depth) and DSDP Site 479 from the centre of the deeper Guaymas Basin OMZ (750 m water depth), which is part of the large North Pacific OMZ. The anoxic sediments of both locations cover the time period from the present to the late Pliocene. Site 680 shows a pronounced glacial/interglacial cyclicity of organic carbon contents reaching up to 15% during interglacials of the Pleistocene, whereas deeper Site 479 shows more uniform organic carbon contents near 3%. In order to determine long and short term changes of different modes of anoxia in the past we will apply a combination of proxies including different Fe pools obtained through sequential leaching of the sediments, stable Mo isotopes, redox sensitive metal concentrations and bulk sediment N-isotope compositions. Based on this suite of proxies recently calibrated for the respective modern settings it will be possible to reconstruct the variability of the modes of anoxic conditions and their potential internal and external climatic drivers in the past. In addition, comparison between the reconstructed seawater Mo isotope compositions at the two sites will allow to constrain if there were secular changes of past global seawater molybdenum isotope composition and if these changes impacted reconstructions of oxygenation and redox conditions over the past 3 million years.

在过去的几十年里，由于全球变暖，海洋的含氧量减少了。这导致了海洋区域的扩张，这些区域严重缺氧。这种不断扩大的最低含氧区在东太平洋普遍存在，这是由于高生物生产力和随后的有机物再矿化，这是由营养丰富的沃茨的上涌驱动的。为了判断缺氧的增加是否在过去自然变化的范围之内或之外，唯一的途径是通过沉积记录。然而，通常用于重建过去缺氧强度和模式的地球化学代用指标产生了有争议的结果，特别是在开阔海洋环境中。 在这里，我们建议应用新的知识的功能和影响因素的代理缺氧条件下获得的现代环境中的OMZs关闭秘鲁和瓜伊马斯盆地在最近的研究，以重建在过去的300万年的缺氧条件下的模式的演变。我们将利用ODP站点680（后来重新钻探为IODP站点1228）的沉积物，该站点位于秘鲁大陆架沿海上升流OMZ（水深250 m）的现今中心，以及DSDP站点479，该站点位于更深的瓜伊马斯盆地OMZ（水深750 m）的中心，该盆地OMZ是大的北太平洋OMZ的一部分。这两个地点的缺氧沉积物覆盖的时间段从现在到上新世晚期。680号站点在更新世间冰期有机碳含量具有明显的冰期/间冰期旋回性，达到15%，而更深的479号站点有机碳含量更均匀，接近3%。为了确定长期和短期的变化，在过去的缺氧不同的模式，我们将应用一个组合的代理，包括不同的铁池获得通过顺序浸出的沉积物，稳定的钼同位素，氧化还原敏感的金属浓度和散装沉积物N-同位素组成。基于这套代理最近校准各自的现代设置，它将有可能重建缺氧条件的模式及其潜在的内部和外部的气候驱动因素在过去的变化。此外，重建的海水钼同位素组成在两个网站之间的比较将允许限制，如果有长期的变化，过去的全球海水钼同位素组成，如果这些变化影响重建的氧化和氧化还原条件在过去的300万年。