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

第一部分：与南极洲接壤的世界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（南极绕极流，ACC）基本上不受阻碍地通过，使其巨大的大陆冰盖得以持续维持。其次，在副热带辐合带（STC）内，该地区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）与富含大量营养素的亚南极水域（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高，STC是大气中二氧化碳的一个非常重要的汇。该区域还受到南极西部冰盖的存在和范围的影响。该冰盖的范围已被证明改变了南半球STC的纬度定位，比晚更新世（过去800 ka）的平间旋回高7度，并可能随后部分地使全球气候与大气二氧化碳分压分离。以往的研究强调了西南太平洋晚更新世海面和中间水域的演化，表明副热带锋（STF）在这段时间内的复杂行为。利用Hikurangi海槽（Expedition 375） U1520D站点的样品，我们提出了一个高分辨率（<1 kyr）的晚更新世有孔虫研究，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。本文旨在通过对浮游生物（gloigerina bulloides）和底栖有孔虫（Uvigerina peregrina）的氧同位素和微量元素Mg/Ca比值的配对测量来更好地了解STC。G. bulloides是一种共生贫瘠的机会性物种，通常在海底有孔虫动物群和沉积物组合中占主导地位，因此是古海洋学研究的重要地球化学信息来源。U. peregrina是一种水生底栖生物，它也被广泛用于计算上新世-更新世的中间水性质。这些稳定的同位素和痕量金属记录需要评估整个STC的表面和中间水温和盐度的尺度和时间。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响应的程度和影响。第二部分：盖诺曼—turonian界线（CTB）可以通过化石群的大规模更替和正碳同位素偏移（通常与富含有机碳的暗色泥灰岩或页岩有关）在全球范围内与远洋碳酸盐岩相进行对比。岩性的剧烈变化是由于海洋更替率的增加和营养丰富的深水块的上涌，以及高地表水生产力。在过去的地质时期，地球海洋的缺氧和富营养化一直与气候变暖有关，而目前的观测表明，现代最低氧带正在扩大。澄清这些海洋缺氧事件（oae）的性质和机制及其对生命的影响，对于我们理解人为气候强迫可能对现代海洋生物多样性产生的影响至关重要。我们计划利用来自IODP远征375孔1520C的样品，该孔位于Hikurangi海槽内，在那里确定了一个扩展的部分，详细说明了Cenomanian-Turonian边界。通过有孔虫区系分析和氧、碳同位素配对测量，我们旨在阐明Hikurangi海槽内CTB的性质，这是一个罕见的、保存完好的白垩纪高纬度oae实例。

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.