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）在很大程度上不受阻碍的过境使其巨大的大陆冰盖得以继续维持。其次，在该地区的副热带辐合带（STC）内，水团之间的永久热边界一直延伸到洋面。因此，由于富含微量营养素的亚热带沃茨（STW）与富含大量营养素的亚热带沃茨（SAW）的混合，这是一个高生物生产力的区域。因此，由于初级生产力水平高，STC是大气CO2的一个非常重要的汇。该地区还受到南极西部冰盖（WAIS）的存在和范围的影响。这片冰盖的范围已被证明可以改变南半球STC的纬度定位，从晚更新世时期（过去800 ka）的stadial-interstadial周期中可达7度，并可能随后部分地将全球气候与大气二氧化碳分压脱钩。以往的研究突出了晚更新世的海面和中间沃茨在西南太平洋的演变表明，复杂的行为的副热带锋（STF）在整个这段时间。 利用来自Hikurangi海槽（远征375）内的U1520 D站点的样本，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。我们的目标是更好地了解STC通过配对测量的氧同位素和镁/钙微量元素比值的浮游生物（Globigerina bulloides）和底栖有孔虫（Uvigerina peregrina）。G. bulloides是一种共生贫瘠的机会性物种，通常在有孔虫动物群和海底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。联合peregrina是一种底栖动物，也被广泛用于计算上新世-更新世的中层水性质。需要这些稳定同位素和微量金属记录来评估整个STC的表层和中层水温以及盐度的规模和时间。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和纬向梯度变率对轨道强迫的响应的程度和影响。第二部分：Cenomanian-Turonian边界（CTB）可以在全球范围内相关的远洋碳酸盐相的化石群的主要营业额，并通过积极的碳同位素漂移，通常与深色泥灰岩或页岩富含有机碳。岩性内的巨大变化归因于海洋周转率的增加和富含营养的深水团的上涌，以及地表水的高生产力。 地球海洋的氧气耗尽和富营养化与过去地质学上的变暖有关，目前的观测表明现代氧气最低区的扩大。阐明这些海洋缺氧事件（OAEs）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对现代海洋生物多样性的可能影响至关重要。我们计划利用来自Hikurangi海槽内IODP Expedition 375 Hole 1520 C的样本，在那里确定了详细描述Cenomanian-Turonian边界的扩展部分。通过有孔虫动物群分析和配对的氧和碳同位素的测量，我们的目标是阐明的性质的CTB内的希库朗吉槽，这是一个罕见的，保存完好的高纬度的例子白垩纪OAE。

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.