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).

该项目旨在重建在过去150万年中非洲南部南洋南海地区的亚热带阵线（STF）的位置变化。洋流在全球海洋中的热量和盐分分布中起着重要作用。最终，这些电流的变化会影响海洋营养分布，大气二氧化碳的海洋吸收以及全球气候。在非洲南部，阿古尔哈斯（Agulhas）电流从印度洋南部流入温暖的咸水进入南大西洋。但是，在几乎全球冷却的时间内，人们认为，在非洲周围逃脱的温水量减少甚至停止，而STF向北迁移。由于STF的北部转移有可能扩大南洋的表面积并限制印度和大西洋之间的水交换，因此非洲南部是非洲南部的重要气候目标，可以促进我们对STF的身体运动如何影响区域和全球气候的理解。在过去的150万年中，STF的迁移相对较差，部分原因是在前移民的关键地区先前缺乏沉积物核心。这项研究结合了对STF位置敏感的海洋变化的多个代理记录，以研究STF运动如何影响海洋循环和二氧化碳的吸收。该项目将支持两个女性PI（一个早期职业）以及两个研究生和几名大学生。在K-12教室和基​​于Web的材料的背景下，计划的公共外展计划将在过去150万年中从新的国际海洋发现计划核心（网站U1475）中从印度南部的新印度海洋中恢复过来，从而从印度海洋中恢复过来，以监视​​STF的位置。他们将使用多个沉积物代理使用水温，出口产生和营养利用率的重建来生成沿STF上海洋动力学的集成重建。已经假设STF的南北迁移是控制水通过印度大西洋门户的运动，这种交流对二氧化碳的空气平衡具有重要意义，以及大西洋的子午倾覆循环的强度。所得数据将用于记录STF相对于核心部位的位置，以及在扩张发作期间，南大洋下北洋的养分状态。具体而言，研究人员将使用现代模拟技术（使用有机碳，生物基因二氧化硅和总烷酮（C37TOT））和营养的动力学（使用有限的有限层有机化的有机物（Foraminiferical Matteric Matteric Matterical formantiferical Matter），使用现代化的有机碳酮（C37TOT），使用现代化的有机碳酮（C37TOT），使用现代化的有机含量（C37TOT），使用有机碳烯（C37TOT），使用现代化的有机含量（使用现代模拟技术），将产生新的水温记录（使用UK37，TEX86和有孔虫的人口普查计数），使用了有机碳和总烷酮（C37TOT），并使用了量。 STF及其对气候变化的反应。重点将放在更新世过渡（MPT）上，这是1.25至700万年前的时间间隔，而气候周期的主要周期性在没有实质性变化的轨道强度变化的情况下从41千公斤变为100千里。重建STF跨MPT的位置是了解STF迁移可能在改变南方海洋生物泵（随之而来的大气二氧化碳变化）方面起着的作用的关键。

项目成果

Antarctic icebergs reorganize ocean circulation during Pleistocene glacials

• DOI: 10.1038/s41586-020-03094-7
• 发表时间: 2021-01
• 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-Sierra;F. Jiménez-Espejo;X. Gong;J. Gruetzner;N. Lathika;L. Levay;R. Robinson;M. Ziegler

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

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