Improving High Latitude Foraminiferal Paleoproxies: Insights from Northern California Current Modern and Historical Records

该项目将提高我们在高纬度地区重建过去海洋状况的能力，例如海洋表面温度。与低纬度地区相比，这些地区对气候变化的反应更为极端。研究过去海洋气候变化的最好方法之一就是研究浮游有孔虫或“有孔虫”的浮游生物化石。有孔虫是一种微小的浮游动物，已经存在超过2亿年，生活在海洋表面附近。随着这些有机体的生长，它们会形成小的贝壳。贝壳化学记录了贝壳形成时的条件。当生物体死亡时，它的外壳沉入海底，成为地质化石记录的一部分。因此，从深海沉积物中回收的化石贝壳的化学成分可以用来重建过去的表层海洋状况。这项研究将产生用于评估化石有孔虫记录的地球化学-环境关系(即校准方程)。从表层海洋中收集的活的和最近死亡的有孔虫的贝壳的组成将与它们生活的海水的条件和化学成分进行比较。这项研究的样本将包括过去十年的浮游生物样本档案。从加利福尼亚州北部、俄勒冈州和华盛顿州海岸外的整个北加州洋流地区新收集的浮游生物拖曳和水样也将被研究。尽管有孔虫在全球都有发现，但这项研究将重点放在限制生活在中高纬度地区的物种的地球化学-环境关系上，以更好地预测这些脆弱地区将如何应对不断变化的气候。研究小组还将调查有孔虫贝壳的组成在生物体的整个生命周期中可能会发生怎样的变化。这项研究将有助于确保用于解释化石记录的校准方程是准确的。该项目包括对早期职业科学家和本科生的支持。研究小组将通过几个公共推广活动与公众分享研究结果和科学过程。近半个世纪以来，通过加利福尼亚州、俄勒冈州和华盛顿州海岸的一系列水文断面，动态北加州洋流(NCC)系统一直受到广泛监测，从而产生了强大的浮游生物丝束样本和同步环境数据档案。这项研究将利用历史上的浮游生物样品，并采集新的浮游生物样品，以进一步开发一系列生活在NCC的中高纬度浮游有孔虫物种的微量元素/钙(TE/Ca)古替代物。NCC常见的种类包括温带和高纬度的Globigerina Bulloids、Neogloboquina pachyderma、N.incomta、N.dutertrei和Turborotalita ququieloba。这些物种在高纬度地区很常见，包括北冰洋，那里的温度变化对气候变化的反应往往最大。研究目标是：1)建立未被研究的温带到极地浮游有孔虫类群的镁/钙温度和钠/钙盐度校正，并调查其他TE/Ca-环境关系的可能性；2)在浮游有孔虫贝壳从生物到死亡的过程中，调查TE的潜在重要影响和机制；以及3)描述研究区域的d18O(海水)特征，建立物种特有的海水有孔方解石同位素偏移量，以限制研究类群的深层生境，这是根据“自然实验室”的数据建立校正的关键步骤。这项拟议的研究将进一步开发新的和现有的浮游有孔虫TE/Ca替代物，用于古气候和古海洋重建，特别强调提高我们重建中高纬度地区过去环境条件的能力。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project will improve our ability to reconstruct past ocean conditions, such as sea surface temperatures, in high-latitude regions. These regions experience a more extreme response to climate change than low-latitude regions. One of the best ways to study past ocean-climate change is by studying fossil plankton called planktic foraminifera or “forams”. Forams are microscopic zooplankton that have existed for over 200 million years and live near the surface of the ocean. As these organisms grow, they build small shells. The shell chemistry records the conditions at the time the shells were formed. When the organism dies, its shell sinks to the seafloor and becomes part of the geological fossil record. Thus, the chemical composition of fossil shells recovered from deep-sea sediments can be used to reconstruct the surface ocean conditions in the past. This study will generate the geochemical-environmental relationships (i.e., calibration equations) used to evaluate fossil foram records. The composition of the shells of living and recently deceased forams collected from the surface ocean will be compared to the conditions and chemical makeup of the seawater they are living in. Samples for this study will include an archive of plankton tow samples from the last decade. Newly collected plankton tow and water samples from throughout the Northern California Current region off the coast of northern California, Oregon, and Washington states will also be studied. Although forams are found globally, this study will focus on constraining geochemical-environmental relationships for species that live in intermediate- to high-latitude regions to better predict how these vulnerable regions will respond to our changing climate. The research team will also investigate how the composition of foram shells may change throughout the organism’s life cycle. This study will help ensure that the calibration equations used to interpret fossil records are accurate. The project includes support for an early career scientist and for undergraduate students. The research team will share the results and scientific process of the research with the public through several public outreach events.The dynamic Northern California Current (NCC) system has been extensively monitored for nearly half a century, through a series of hydrographic transects off the coasts of California, Oregon, and Washington, resulting in a robust archive of plankton tow samples and concurrent environmental data. This study will use historical plankton tow samples, and collect new plankton samples, to further develop a range of trace element/calcium (TE/Ca) paleoproxies for intermediate to high latitude planktic foraminiferal species living in the NCC. Species common to the NCC include temperate and high-latitude genotypes of Globigerina bulloides, Neogloboquadrina pachyderma, N. incompta, N. dutertrei, and Turborotalita quinqueloba. These species are common in higher latitude regions, including the Artic Ocean, where temperature change in response to climate change tends to be greatest. The research objectives are to: 1) establish Mg/Ca-temperature and Na/Ca-salinity calibrations for understudied temperate to polar planktic foraminiferal taxa and investigate the potential for other TE/Ca-environmental relationships, 2) investigate potential vital effects and mechanisms for TE incorporation in planktic foraminiferal shells as they transition from life to death, and 3) characterize the d18O(seawater) signature in the study region and establish species specific seawater foraminiferal calcite isotopic offsets in order to constrain the depth habitats of the study taxa, a critical step to establishing calibrations based on data in a “natural laboratory” setting. The proposed research will further develop novel and existing planktic foraminiferal TE/Ca proxies for use in paleoclimatic and paleoceanographic reconstructions, with particular emphasis on improving our ability to reconstruct past environmental conditions in intermediate to high latitude regions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.