Variability in the Atlantic Meridional Overturning Circulation During Marine Isotope Stage 3

海洋同位素第三阶段大西洋经向翻转环流的变化

• 批准号: 1558341
• 负责人: Delia Oppo
• 金额: $ 48.65万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-04-15 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558341&HistoricalAwards=false
• 关键词: Variability; Atlantic; Meridional; Overturning; Circulation

Paleoclimate data show that the Earth's climate varied dramatically during the last ice age. Abrupt transitions from cold to warm North Atlantic climate states, spaced several millennia apart, were generally associated with increases in atmospheric carbon dioxide concentrations. While surface climate also varied on shorter, millennial time scales, atmospheric carbon dioxide variability on this time scale was negligible. Changes in atmospheric carbon dioxide concentrations on the longer times scale, and surface climate on both time scales, are generally attributed to changes in circulation within the deep ocean, but our knowledge of deep ocean circulation variability during the last ice age is limited. Detailed knowledge of glacial circulation variability is required to understand the influence of deep ocean circulation variability on surface climate and atmospheric carbon. This project supports education and training of an undergraduate student and a post-graduate investigator. All data generated as part of this study will be made publicly available. The data will also be valuable to the climate modeling community, which uses paleoclimate data to test the same models used to predict future climate change.Bottom water temperature estimates, determined from elemental ratios of benthic foraminifera, from a tropical North Atlantic sediment core, will be used to identify times of deep ocean circulation change during the last 65,000 years. Models predict large and rapid warming at the location and depth (~550 m) of the sediment core in association with a weakening of deep Atlantic water originating from the North Atlantic region. The sediment core has high accumulation rates (30 cm/kyr), and variations in magnetic susceptibility that can be tied directly to Greenland ice core δ18O variations. Proposed radiocarbon and planktonic foraminiferal δ18O analysis will further refine the chronology. Reconstructing deep ocean variability during the last ice age is critical to understanding the role of deep ocean circulation in driving glacial atmospheric carbon dioxide variability, which generally varies significantly only on longer, multi-millennial, time-scale. On the other hand, confirming that deep ocean circulation did (or did not) vary on the shorter millennial time scale will help determine whether or not observed large climate shifts in, for example, tropical Atlantic hydrology, occurred in the absence of deep ocean circulation change. Such a finding would imply that episodes of North Atlantic cooling have significant and widespread climate impacts in the absence of changes in ocean dynamics.

古气候数据显示，在最后一个冰河时期，地球的气候发生了巨大变化。北大西洋气候状态从寒冷到温暖的突然转变，相隔数千年，通常与大气二氧化碳浓度的增加有关。虽然地表气候在较短的千年时间尺度上也有变化，但大气二氧化碳在这一时间尺度上的变化可以忽略不计。大气中二氧化碳浓度在较长时间尺度上的变化，以及地表气候在两个时间尺度上的变化，通常归因于深海环流的变化，但我们对上一个冰河时期深海环流变化的了解有限。要了解深海环流变化对地表气候和大气碳的影响，就需要详细了解冰川环流变化。该项目支持一名本科生和一名研究生调查员的教育和培训。作为本研究一部分生成的所有数据将公开提供。这些数据对气候模拟界也很有价值，他们使用古气候数据来测试用于预测未来气候变化的相同模型。根据来自热带北大西洋沉积物岩心的底栖有孔虫的元素比率确定的底层水温估计值将用于确定过去65，000年中深海环流变化的时间。模型预测，随着来自北大西洋区域的大西洋深层水的减弱，沉积物芯的位置和深度（~550米）将出现大幅度和快速的变暖。沉积物核心有很高的积累率（30厘米/千年），和磁化率的变化，可以直接联系到格陵兰冰芯#948; 18 O的变化。拟议的放射性碳和浮游有孔虫#948; 18 O分析将进一步完善年表。重建最后一个冰河时期的深海变化对于理解深海环流在驱动冰川大气二氧化碳变化方面的作用至关重要，而这种变化通常只在更长的数千年时间尺度上发生显著变化。另一方面，确认深海环流在较短的千年时间尺度上确实（或没有）发生变化，将有助于确定在没有深海环流变化的情况下是否发生了所观察到的大气候变化，例如热带大西洋水文。这一发现意味着，在海洋动力学没有变化的情况下，北大西洋的冷却会对气候产生重大而广泛的影响。