Hikurangi Trough late Pleistocene palaeoceanography, biostratigraphy and Cretaceous Ocean Anoxia Events (OAEs)

第一部分：世界上与南极洲接壤的海洋区域对控制地球气候至关重要。首先，环绕南极大陆的洋流(南极绕极洋流，ACC)在很大程度上不受阻碍地通过，使其巨大的大陆冰盖得以继续维持。其次，在该区域的副热带辐合(STC)中，水团之间的永久热边界延伸到海洋表面。因此，由于富含微量营养素的亚热带水域(STW)和富含大量营养素的亚北极水域(SAW)的混合，这是一个生物生产力高的地区。因此，由于初级生产力水平很高，STC是大气二氧化碳的一个非常重要的汇。这一区域还受到南极西部冰盖(WAIS)的存在和范围的影响。这一冰盖的范围已经被证明改变了南半球STC的纬度位置，与晚更新世(最后800 ka)的冰期-冰间旋回相比，变化幅度高达7度，并可能随后部分地使全球气候与大气二氧化碳分压脱钩。以前的研究突出了西南太平洋内晚更新世海面和中间水域的演变，表明在这段时间内，副热带锋(STF)行为复杂。利用来自Hikurangi海槽(探险375)内的U1520D站点的样品，我们建议对晚更新世有孔虫进行高分辨率(&lt；1KYR)研究，以更好地约束过去130 ka的区域古海洋学，以及这与气候强迫的关系。我们的目的是通过对浮游有孔虫和底栖有孔虫的氧同位素和镁/钙微量元素比值的配对测量来更好地了解STC。球藻是一种共生体贫乏的机会性物种，常在有孔虫动物群和海底沉积物组合中占据主导地位，因此是古海洋学研究的重要地球化学信息来源。Peregrina是一种底栖生物，在上新世-更新世期间也被广泛用于计算中间水的性质。这些稳定的同位素和痕量金属记录是评估表层和中间水温以及整个STC盐度的规模和时间所必需的。这些数据随后将有助于我们了解在冰冻圈发展的关键时期WAIS和经向梯度变率对轨道强迫的响应程度和影响。第二部分：通过化石群的重大更替和碳同位素正漂移(通常与富含有机碳的黑色泥灰岩或页岩有关)，可以在远洋碳酸盐岩相全球对比塞诺马尼亚-图罗尼亚界线(CTB)。岩性的巨大变化归因于海洋周转速度的增加和营养丰富的深水团的上升流，以及高地表水生产力。在过去的地质历史中，地球海洋的氧气枯竭和富营养化一直与变暖有关，目前的观察表明，现代氧气最低限度区域正在扩大。弄清这些海洋缺氧事件的性质和机制，以及它们对生命的影响，对于我们理解人为气候强迫可能对现代海洋生物多样性造成的影响是至关重要的。我们计划利用来自Hikurangi海槽内IODP探险375孔1520C的样品，在那里发现了一个详细描述塞诺马尼亚-图罗尼亚边界的扩展部分。通过有孔虫动物群分析和氧、碳同位素的配对测量，我们旨在阐明Hikurangi海槽内的CTB的性质，这是一个罕见的、保存完好的白垩纪OAEs的高纬度例子。

Part I:The regions of the world's oceans, which border Antarctica, are critical for controlling the Earth's climate. Firstly, the largely unhindered transit of ocean currents (the Antarctic circumpolar current, ACC) that circle and Antarctic continent enables the continued maintenance of its huge continental ice sheets. Secondly, a permanent thermal boundary between water masses extends to the ocean surface within the Subtropical Convergence (STC) in this region. Consequently, this is a region of high biological productivity due to the mixing of micronutrient-rich subtropical waters (STW) with macronutrient-rich subantarctic waters (SAW). As such the STC is a highly important sink for atmospheric CO2 due to high levels of primary productivity. This region is also influenced by the presence and extent of the Western Antarctic Ice Sheet (WAIS). The extent of this ice sheet has been shown to alter the latitudinal positioning of the Southern Hemisphere STC by up to 7 degrees from stadial-interstadial cycles of the Late Pleistocene epoch (last 800 ka), and may subsequently partially decouple global climate from atmospheric partial pressure of carbon dioxide. Previous studies highlighting the Late Pleistocene evolution of sea surface and intermediate waters within the southwest Pacific have indicated complex behaviour of the subtropical front (STF) throughout this interval. Utilizing samples from site U1520D from within the Hikurangi Trough (Expedition 375), we propose a high resolution (<1 kyr) study of late Pleistocene foraminifera to better constrain the regional paleoceanography over the last 130 ka, and how this relates to climate forcing. We aim to better understand the STC through paired measurements of oxygen isotopes and Mg/Ca trace element ratios of both planktonic (Globigerina bulloides) and benthic foraminifera (Uvigerina peregrina). G. bulloides is a symbiont-barren, opportunistic species which often dominates the foraminifer fauna, and sediment assemblage of the ocean floor, and is therefore an important source of geochemical information for palaeoceanographic studies. U. peregrina is an infaunal benthic species, which has also been used extensively to calculate intermediate water properties throughout the Pliocene-Pleistocene. These stable isotope and trace metal records are required to assess the scale and timing of surface and intermediate water temperature, and salinity across the STC. This data will subsequently contribute to our knowledge of the extent and influence of the WAIS and meridional gradient variability response to orbital forcing during a critical period of cryosphere development. Part II:The Cenomanian-Turonian boundary (CTB) can be correlated globally in pelagic carbonate facies by a major turnover in fossil groups, and by a positive carbon isotope excursion, typically associated with dark marls or shales enriched in organic carbon. The dramatic changes within lithology are attributed to increased rates of oceanic-turnover and upwelling of nutrient-rich deep water masses, and high surface-water productivity. Oxygen depletion and eutrophication of the Earth's oceans has been associated with warming in the geological past, and current observations show expansion of modern oxygen minimum zones. Clarifying the nature and mechanism of these oceanic anoxia events (OAEs), and there effect upon life is imperative to our understanding the possible implications that anthropogenic climate forcing may have upon the biodiversity of the modern ocean. We plan to utilize samples sourced from IODP Expedition 375 Hole 1520C, within the Hikurangi Trough, where an expanded section is been identified detailing the Cenomanian-Turonian boundary. Through foraminiferal faunal analysis and paired measurements of oxygen and carbon isotopes we aim to elucidate the nature of the CTB within the Hikurangi Trough, which represents a rare, well-preserved high-latitude example of a Cretaceous OAEs.