Collaborative Research: Resolving the LGM ventilation age conundrum: New radiocarbon records from high sedimentation rate sites in the deep western Pacific

合作研究：解决LGM通风年龄难题：西太平洋深部高沉降率地点的新放射性碳记录

• 批准号: 2341424
• 负责人: Lowell Stott
• 金额: $ 44.38万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2024
• 资助国家: 美国
• 起止时间: 2024-06-01 至 2027-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2341424&HistoricalAwards=false
• 关键词: Collaborative; Research; Resolving; LGM; ventilation

For more than a century, scientists have sought to understand why ice sheets expanded from the polar regions into the middle latitudes, plunging the Earth into an Ice Age. In the first part of the 20th century, scientists focused on changes in solar radiation due to changes in the Earth’s orbit around the Sun. By the mid-20th century, the Earth Science community developed new methods to reconstruct climate variables, like temperature and ice volume using fossils. That important advance led to the recognition that there is a rhythmicity to Earth’s climate during the last 2.5 million years that is like that of the Earth’s orbital cycles. But there was a problem with the original theory of orbital-induced climate variability. By the late 20th century, it had become clear that ice had advanced and retreated in both hemispheres simultaneously. This is incompatible with the orbital theory unless there was something else that would increase the sun’s impact to affect the entire planet simultaneously. That was exactly what scientists discovered from ice cores. Using samples of air trapped in Antarctic ice, scientists showed atmospheric CO2 levels were 30% lower during the last ice age. With that major scientific advance came the realization that somehow orbital variations influence changes in carbon dioxide levels. But how? The connection between orbital cycles and the Earth’s carbon cycle has been a primary focus of paleoclimate research and debate for more than three decades. This project addresses the scientific debate by testing one of the prevailing hypotheses, that is “Do the ocean’s store atmospheric CO2 during ice ages?” In this work, the scientific team will test whether the circulation of the deep ocean slowed down enough during the last ice age to allow CO2 to build up in the deep ocean. Radiocarbon techniques will be used to date how long deep waters resided in the deep Pacific before returning the surface. If the ocean circulation slowed significantly during the last ice age, it would lend strong support to the notion that the oceans regulate atmospheric CO2. The radiocarbon data currently available cannot answer this question, primarily because deep sea sediments accumulate too slowly to allow precise age dating. The new research will address this challenge by recovering deep sea records from a region where sediments accumulate very rapidly, which will allow the team to precisely date how old the deep waters in the Pacific were during the last ice age. If the findings show that the deep ocean waters were not significantly older when CO2 concentrations were low, it will prompt scientists to look to other alternative explanations. This project will provide training for undergraduate and graduate students especially students from traditionally excluded groups. Students will also have an opportunity to participate in the research cruise to collect the samples. Currently available radiocarbon data from low sedimentation rate sites (10 cm/kyr) in the deep Pacific imply deep water ventilation ages were ~800-1000 years older than today, whereas high sedimentation rate sites (20 cm/kyr) indicate there was no substantial difference. The contrast is due to either: 1) bioturbation-driven biases in low accumulation rate locations, or 2) the lack of high accumulation rate records from water depths below 3 km. The research proposed will address this problem by acquiring new high-resolution stable isotope and radiocarbon data from high deposition rate sites in the western North Pacific. Filling the deep Pacific data gap is essential to assess the hypothesis that a more sluggish ocean circulation allowed respired carbon to accumulate in the abyssal Pacific, leading to lower atmospheric CO2 levels during the Last Glacial Maximum (LGM). The goal of the project is to obtain a suite of cores from the margin of Mindanao in the western Pacific to reconstruct the ventilation ages at water depths between 1000 and 3800m. The margin of Mindanao is ideally suited for this task because sedimentation rates in the region are very high, ranging from 30 cm/kyr to 75 cm/kyr. By creating new ventilation age reconstructions from the high accumulation rate sites, it will be possible to definitively test whether ventilation rates in the deep Pacific were lower during the LGM, as predicted from the ocean circulation hypothesis. The research will address one of the grand challenges in paleoclimate science: What controls atmospheric CO2 on glacial/interglacial timescales? It has been proposed that the deep ocean played a primary role in lowering atmospheric CO2 during glacial maxima by sequestering CO2 through a combination of biological and physical processes. Testing whether the ocean sequestered CO2 would be a major step forward in solving the glacial/interglacial CO2 problem. The proposed research is critical to this effort because previous attempts to evaluate whether ventilation ages were greater during glaciations has been hampered by a lack of high-resolution data sets from the deep ( 3 km) Pacific, which is the largest potential reservoir for the storage of metabolically- derived carbon. Of the data currently available to test the prevailing hypothesis, most are from very low resolution (low deposition rate cores) that have likely been contaminated by bioturbation. Furthermore, there are no ventilation age estimates from sites below 2800 m in the Pacific that have sediment accumulation rates greater than 20 cm/kyr. This project will overcome the limitations of the current database by obtaining highly resolved records from sites in the western North Pacific at depths that will confirm whether or not ventilation ages were substantially older during the LGM. The project will support the training of students with an emphasis on recruiting students from traditionally excluded groups. In addition, students from all three institutions will participate in the research cruise and collaborate in the lab.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.

一个多世纪以来，科学家一直试图理解为什么冰盖从极地地区扩展到中纬度，将地球陷入冰河时代。在20世纪的第一部分，由于地球围绕太阳的轨道变化，科学家专注于太阳辐射的变化。到20世纪中叶，地球科学界开发了新的方法来重建气候变量，例如使用化石的温度和冰量。这一重要的进步导致人们认识到，在过去的250万年中，地球气候有节奏，就像地球轨道周期一样。但是轨道引起的攀岩变异性的原始理论存在问题。到20世纪后期，很明显，冰已经简单地在两个半球上撤进并撤退了。这与轨道理论是不兼容的，除非还有其他东西会增加太阳的影响以完全影响整个星球。这正是科学家从冰芯中发现的。使用被困在南极冰中的空气样品，科学家显示上一个冰河时代的大气二氧化碳水平降低了30％。随着这一重大的科学进步，人们意识到轨道变化会影响二氧化碳水平的变化。但是如何？轨道周期与地球循环之间的联系一直是古气候研究和争论的主要重点，已有三十多年了。该项目通过检验一个普遍的假设来解决科学辩论，即“在冰时代，海洋商店大气二氧化碳吗？”在这项工作中，科学团队将测试在上一个冰河时代，深海的循环是否足够慢，以使二氧化碳可以在深海中积聚。放射性碳技术将使用在返回表面之前在深太平洋中停留多长时间。如果在上一个冰河时代，海洋循环大大放缓，它将为海洋调节大气二氧化碳的观念提供强有力的支持。当前可用的放射性碳数据无法回答这个问题，因为深海沉积物的积累太慢，无法精确的年龄约会。这项新的研究将通过从一个迅速积累的地区恢复深海记录来解决这一挑战，这将使该团队能够准确地约会太平洋深水在上一个冰河时代的年龄。如果调查结果表明，当二氧化碳浓度较低时，深海水域的年龄较大，则将促使科学家寻求其他替代解释。该项目将为本科生和研究生提供培训，尤其是来自传统被排除的小组的学生。学生还将有机会参加研究巡航以收集样品。目前，深太平洋中低沉积速率位点（10 cm/kyr）的放射性碳数据意味着深水通气年龄比今天大约800-1000年，而高沉积速率位点（20 cm/kyr）表示没有实质性差异。对比是由于：1）在低累积率位置的生物扰动驱动偏见，或2）缺乏高于3 km的水深度的高积累率记录。提出的研究将通过获取来自北太平洋西部高沉积速率地点的新高分辨率同位素和放射性碳数据来解决这个问题。填补深太平洋数据差距对于评估以下假设至关重要：假设较低的海洋循环使呼吸碳积聚在深渊太平洋中，从而在最后一次冰川最大值（LGM）中导致大气中的二氧化碳水平降低。该项目的目的是从西太平洋棉兰老岛的边缘获得一套核心，以重建1000至3800m之间水深的通风年龄。棉兰老岛的边缘非常适合这项任务，因为该地区的沉积率很高，范围从30 cm/kyr到75 cm/kyr不等。通过从高积累速率位点创建新的通风年龄重建，可以确定地测试LGM期间深太平洋的通风率是否较低，如海洋循环假设所预测的那样。这项研究将解决古气候科学的巨大挑战之一：是什么控制冰川/冰川间时间尺度上的大气二氧化碳？有人提出，深海通过生物过程和物理过程的结合来隔离二氧化碳在降低大气中的二氧化碳中起主要作用。测试海洋隔离的二氧化碳是否将是解决冰川/冰川间二氧化碳问题的重要一步。拟议的研究对这项工作至关重要，因为先前试图评估冰川期间的通风年龄是否较大，因此由于缺乏来自太平洋深太平洋（3 km）太平洋的高分辨率数据集的阻碍，这是存储代谢衍生碳的最大潜在依据。在目前可用于检验现行假设的数据中，大多数来自很低的分辨率（低沉积率核心），这些分辨率可能受到生物扰动的污染。此外，在太平洋以下2800 m以下的地点没有通风年龄的估计值，其沉积物积累速率大于20 cm/kyr。该项目将通过从北太平洋西部地区的地点获得高度解决的记录来克服当前数据库的局限性，这些记录将确认在LGM期间是否会确认通风年龄是否年龄较大。项目将支持对学生的培训，重点是从传统排除的小组招募学生。此外，来自所有三个机构的学生将参加研究巡航并在实验室中进行合作。该奖项反映了NSF的法定任务，并通过使用基金会的知识分子优点和更广泛的影响评估标准来评估，被认为是珍贵的支持。