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，科学家们一直试图了解为什么冰盖从极地地区扩展到中纬度地区，使地球陷入冰河时代。在 20 世纪上半叶，科学家们关注的是由于太阳辐射的变化。到了 20 世纪中叶，地球科学界开发出了利用化石重建温度和冰量等气候变量的新方法，这一重要进展使人们认识到地球的运行具有节奏性。气候在过去的 250 万年里，这就像地球的轨道周期一样，但轨道引起的气候变化的原始理论存在问题，到了 20 世纪末，人们已经清楚地知道冰在这两个轨道上都发生了前进和后退。这与轨道理论不相容，除非有其他东西可以增加太阳的影响同时影响整个地球，这正是科学家从南极冰芯中发现的。科学家们发现，在上一个冰河时代，大气中的二氧化碳含量降低了 30%，随着这一重大科学进步，人们认识到轨道变化会以某种方式影响二氧化碳含量的变化，但轨道循环与地球碳循环之间的联系是如何产生的呢？三十多年来一直是古气候研究和争论的主要焦点，该项目通过测试一个流行的假设来解决科学争论，即“海洋在冰河时代是否储存大气二氧化碳？”团队将测试是否在最后一个冰河时代，深海的环流减慢到足以使二氧化碳在深海中积聚，如果海洋环流减慢，将使用放射性碳技术来确定深海在太平洋深处停留了多长时间。在上一个冰河时期，这将有力地支持海洋调节大气二氧化碳的观点，目前可用的放射性碳数据无法回答这个问题，主要是因为深海沉积物积累得太慢，无法进行精确的年龄测定。通过恢复深海记录来应对这一挑战这是一个沉积物积累非常迅速的地区，这将使研究小组能够精确测定上一个冰河时期太平洋深水的年龄。如果研究结果表明，当二氧化碳浓度较低时，深海海水的年龄并没有明显增加，它将促使科学家寻找其他替代解释。该项目将为本科生和研究生，特别是来自传统上被排除在外的群体的学生提供培训，学生还将有机会参与研究巡航，以收集目前可用的放射性碳数据。低沉降率地点 (10 cm/kyr)太平洋深部意味着深水通风年龄比今天早约 800-1000 年，而高沉积率地点（20 厘米/凯尔）表明没有显着差异，原因是：1）生物扰动驱动的偏差。低积累率地点，或2）缺乏3公里以下水深的高积累率记录。拟议的研究将通过从西部高沉积率地点获取新的高分辨率稳定同位素和放射性碳数据来解决这个问题。填补北太平洋深部数据空白对于评估海洋环流更加缓慢导致呼吸碳在太平洋深海积累、导致末次盛冰期（LGM）期间大气二氧化碳水平降低的假设至关重要。该项目的目的是从西太平洋棉兰老岛边缘获得一套岩心，以重建 1000 至 3800m 水深的通风年龄。棉兰老岛边缘非常适合。因为该地区的沉降率非常高，从 30 厘米/凯尔到 75 厘米/凯尔，通过从高堆积率地点创建新的通风年龄重建，将可以明确地测试该地区的通风率。正如海洋环流假说所预测的，末次盛冰期期间太平洋深海的水位较低，这项研究将解决古气候科学中的一项重大挑战：有人提出，深海在冰期/间冰期时间尺度上控制着大气中的二氧化碳浓度。通过生物和物理过程的结合来封存二氧化碳，在冰川盛期期间降低大气二氧化碳的主要作用是测试海洋封存的二氧化碳是否是解决冰期/间冰期二氧化碳问题的重要一步。由于缺乏来自太平洋深处（3公里）的高分辨率数据集，之前评估冰川时期通风年龄是否更大的尝试受到了阻碍，而太平洋深处是储存二氧化碳的最大潜在水库。目前可用于检验普遍假设的数据中，大多数来自极低分辨率（低沉积率岩心），这些数据可能已受到生物扰动的污染。此外，没有来自海拔 2800 米以下地点的通风年龄估计。该项目将通过从北太平洋西部的深度地点获得高分辨率记录来克服当前数据库的局限性，这些记录将确认通风年龄是否在该期间更老。 LGM。该项目将支持学生培训，重点是从传统上被排斥的群体中招收学生。此外，来自所有三个机构的学生都将参加研究巡游并在实验室进行合作。该奖项反映了 NSF 的法定使命，并被认为是值得的。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来提供支持。