Collaborative Research: Tracking the Subtropical Front across the Mid Pleistocene Transition Using Sea Surface Temperature and Nutrients

合作研究：利用海面温度和营养物追踪中更新世过渡期的副热带锋

• 批准号: 1736938
• 负责人: Rebecca Robinson
• 金额: $ 39.06万
• 依托单位: University of Rhode Island
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-09-01 至 2022-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736938&HistoricalAwards=false
• 关键词: Collaborative; Research; Tracking; Subtropical; Front

This project seeks to reconstruct changes in the position of the Subtropical Front (STF) in the Agulhas region of the Southern Ocean south of Africa over the last 1.5 million years. Ocean currents play a significant role in the distribution of heat and salt in the global ocean. Ultimately, changes in these currents influence marine nutrient distribution, ocean uptake of atmospheric CO2, and global climate. South of Africa, the Agulhas Current moves warm, salty water from the southern Indian Ocean into the South Atlantic Ocean. However, during intervals of near-global cooling, it is thought that the amount of this warm water escaping around Africa decreases or is even stopped, cutoff by a northward migration of the STF. Because a northward shift of the STF has the potential to both expand the surface area of the Southern Ocean and limit water exchange between the Indian and Atlantic Oceans, the region south of Africa is an important climate target to advance our understanding of how the physical movements of the STF may impact regional and global climate. Migrations of the STF are relatively poorly resolved for the past 1.5 million years, in part due to a prior lack of sediment cores in the critical region of front migration. This research combines multiple proxy records of ocean changes at a location sensitive to STF position to study how STF movement may have influenced ocean circulation and CO2 uptake. The project will support two female PIs (one early career) as well as two graduate students and several undergraduates. Broader public outreach is planned in the context of K-12 classroom and web-based materials.The investigators will generate an integrated reconstruction of upper ocean dynamics along the Subtropical Front over the last 1.5 million years from sediments in a new International Ocean Discovery Program core (Site U1475) recovered from the southern Indian Ocean at a location well suited to monitor STF position. They will use multiple sediment proxies to generate an integrated reconstruction of upper ocean dynamics along the STF using reconstructions of water temperature, export production, and nutrient utilization. North-south migrations of the STF have been hypothesized to control movement of water through the Indo-Atlantic Gateway, an exchange that has important implications for the air-sea balance of CO2 and the strength of the meridional overturning circulation of the Atlantic. The resulting data will be used to document the location of the STF with respect to the core site and the nutrient status of the subantarctic region of the Southern Ocean during episodes of expansion. Specifically, the investigators will produce new high-resolution records of water temperature (using Uk37, TEX86, and foraminiferal census counts using a Modern Analog Technique), export production (using total organic carbon, biogenic silica, and total alkenone (C37tot) content), and nutrient dynamics (using foraminiferal-bound organic matter d15N) for the last 1.5 million years to constrain the history of the STF and its response to climate change. Emphasis will be placed on the Mid Pleistocene Transition (MPT), the time interval between 1.25 and 0.7 million years ago when the dominant periodicity of climate cycles changed from 41 kiloyears to 100 kiloyears in the absence of substantial change in orbital forcing. Reconstructing the location of the STF across the MPT is key to understanding the role that STF migration may have played in altering the Southern Ocean biological pump (with consequent changes in atmospheric CO2).

该项目旨在重建过去 150 万年来非洲南部南大洋厄加勒斯地区副热带锋 (STF) 位置的变化。洋流在全球海洋热量和盐分的分布中发挥着重要作用。最终，这些洋流的变化会影响海洋营养物分布、海洋对大气二氧化碳的吸收以及全球气候。在非洲南部，厄加勒斯洋流将温暖的咸水从南印度洋流入南大西洋。然而，在近乎全球变冷的时期，人们认为非洲周围的暖水逸出量会减少，甚至停止，因为STF向北迁移而被切断。由于STF的北移有可能扩大南大洋的表面积并限制印度洋和大西洋之间的水交换，因此非洲南部地区是一个重要的气候目标，可以促进我们对物理运动如何进行的理解STF 的影响可能会影响区域和全球气候。在过去的 150 万年里，STF 的迁移问题解决得相对较差，部分原因是在前沿迁移的关键区域之前缺乏沉积岩芯。这项研究结合了对 STF 位置敏感的地点海洋变化的多个代理记录，以研究 STF 运动如何影响海洋环流和二氧化碳吸收。该项目将支持两名女性 PI（一名早期职业生涯）以及两名研究生和几名本科生。计划在 K-12 课堂和网络材料的背景下进行更广泛的公众宣传。研究人员将根据新的国际海洋发现计划核心中的沉积物，对过去 150 万年沿副热带锋面的上层海洋动力学进行综合重建（站点 U1475）从南印度洋回收，位置非常适合监测 STF 位置。他们将使用多个沉积物代理，通过水温、出口生产和养分利用的重建，生成 STF 沿线上层海洋动力学的综合重建。据推测，STF 的南北迁移是为了控制水通过印度-大西洋门户的运动，这种交换对二氧化碳的海气平衡和大西洋经向翻转环流的强度具有重要影响。由此产生的数据将用于记录 STF 相对于核心地点的位置以及扩张期间南大洋亚南极地区的营养状况。具体来说，研究人员将生成新的高分辨率水温记录（使用 Uk37、TEX86 和使用现代模拟技术的有孔虫普查计数）、出口生产（使用总有机碳、生物二氧化硅和总烯酮 (C37tot) 含量） ，以及过去 150 万年的营养动态（使用有孔虫结合的有机物 d15N）来限制 STF 的历史及其应对气候变化。重点将放在更新世中期（MPT），即 1.25 至 70 万年前的时间间隔，在轨道强迫没有发生实质性变化的情况下，气候周期的主要周期从 41 公里变为 100 公里。重建 MPT 中 STF 的位置是了解 STF 迁移在改变南大洋生物泵（从而导致大气二氧化碳发生变化）中可能发挥的作用的关键。

项目成果

Antarctic icebergs reorganize ocean circulation during Pleistocene glacials

更新世冰川期间南极冰山重组海洋环流

• DOI: 10.1038/s41586-020-03094-7
• 发表时间: 2021-01-01
• 期刊: Nature
• 影响因子: 64.8
• 作者: A. Starr;I. Hall;S. Barker;T. Rackow;Xu Zhang;S. Hemming;H. V. D. van der Lubbe;G. Knorr;M. Berke;G. Bigg;A. Cartagena;F. Jiménez;X. Gong;J. Gruetzner;N. Lathika;L. Levay;R. Robinson;M. Ziegler
• 通讯作者: M. Ziegler

Latitudinal Migrations of the Subtropical Front at the Agulhas Plateau Through the Mid‐Pleistocene Transition

中更新世过渡期厄加勒斯高原副热带锋的纬度迁移

• DOI: 10.1029/2020pa004084
• 发表时间: 2021-07-01
• 期刊: Paleoceanography and Paleoclimatology
• 影响因子: 3.5
• 作者: A. Cartagena;M. Berke;R. Robinson;B. Marcks;I. Castañeda;A. Starr;I. Hall;S. Hemming;L. Levay
• 通讯作者: L. Levay