Deep Water Hydrography in the Glacial Western North Atlantic

北大西洋冰川西部的深水水文学

• 批准号: 1558307
• 负责人: Lloyd Keigwin
• 金额: $ 56.21万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-09-15 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558307&HistoricalAwards=false
• 关键词: Deep; Water; Hydrography; Glacial; Western

This project will investigate the ocean's role in climate during the last ice age (about 20,000 years ago), a time when conditions around the North Atlantic were very different from today. The surface ocean was colder, the atmosphere was windier, there was far less carbon dioxide in the atmosphere, and sea level was 300 feet lower. Operation of the modern North Atlantic Ocean has been likened to a conveyor belt, where warm salty waters of Gulf Stream origin enter the Norwegian Sea and release heat to the atmosphere that keeps northern Europe warm. After losing their heat, surface waters sink to the bottom and flow out of the Nordic Seas and into the deep North Atlantic basin. For over three decades oceanographers and climatologists have known that this conveyor belt was interrupted at times in the past, especially during the last ice age. Instead of deep northern water in the North Atlantic, analysis of the chemical make-up of fossil shells in marine sediment cores shows that the deep waters had a southern (Antarctic) source. This view of the glacial North Atlantic has become a paradigm. Recent findings from cores in the very deep basins of the North Atlantic have challenged that conventional wisdom, suggesting that there was a northern source of bottom water after all. This project seeks to confirm that finding by collecting and analyzing new sediment cores from the deepest basins of the North Atlantic (5000 meters). Results could significantly change, or even overturn, our understanding of how the glacial North Atlantic distributed heat, salt, nutrients, and CO2. Furthermore, because glacial age data are used to test modern climate models under different scenarios, the proposed new research could lead to refinement of models that predict future climate changes. The research expedition will have about eight berths for early career professionals who are interested in learning methods of seafloor surveying and sampling, and the long sediment cores to be collected will be archived and readily available for sampling by many diverse scientists. The project will also involve international collaboration with a German research team.The centerpiece of the research is an expedition to the western North Atlantic between Cape Cod, MA and the Azores to survey the very deep seafloor for new coring locations and to sample them with different devices (multicorers, gravity corers, and piston corers). Changes in deep ocean circulation will be traced using carbon isotope ratios in shells of fossil planktonic and benthic foraminifera. The 13C/12C ratio is a proxy for deep water nutrient content, and at core sites around 4.2 km this ratio shows that during glaciation the mixture of waters from the Arctic and Antarctic was different than today and consistent with current thinking. Most likely, either the northern source produced less water because the surface in the Nordic seas was more covered with sea ice than today, or the deep water traveled more slowly and accumulated more nutrients from the surface. Existing 14C/12C data support the pattern seen in 13C/12C, and this tracer is also used to date the sediment deposits. However, below 4200 m, the pattern of these isotope pairs reverses and indicates more northern source waters with increasing depth (to 5 km). This hypothesis will be tested with coring and shore-based analytical work on sites from between 3 km and 5 km. Data from new core sites above 3 km will be collected by a German colleague, and the collaboration will result in the first high resolution depth reconstructions past hydrographic changes in the western basin of the North Atlantic.

该项目将研究海洋在上一个冰河时代（约2万年前）的气候作用，当时北大西洋周围的条件与今天大不相同。 海洋表面更冷，大气风更大，大气中的二氧化碳含量少得多，海平面低了300英尺。 现代北大西洋的运作被比作一条传送带，墨西哥湾流的温暖咸沃茨进入挪威海，向大气释放热量，使北方欧洲保持温暖。 失去热量后，表层沃茨沉入海底，流出北欧海，进入北大西洋盆地深处。 三十多年来，海洋学家和气候学家已经知道，这条传送带在过去曾被中断过，特别是在最后一个冰河时代。 对海洋沉积物岩芯中贝壳化石的化学组成的分析表明，沃茨的来源不是北大西洋北部的深水，而是南部（南极洲）的深水。 这种北大西洋冰川的观点已经成为一种范式。 最近在北大西洋非常深的盆地中的岩心发现挑战了传统的智慧，表明毕竟有一个北方的底层水来源。 该项目试图通过收集和分析北大西洋最深盆地（5000米）的新沉积物岩心来证实这一发现。结果可能会显著改变，甚至推翻我们对冰川北大西洋如何分布热量，盐，营养物质和二氧化碳的理解。 此外，由于冰川时代的数据被用来测试不同情景下的现代气候模型，拟议的新研究可能会导致预测未来气候变化的模型的改进。 研究考察将为有兴趣学习海底勘测和取样方法的早期职业专业人员提供大约八个泊位，将收集的长沉积物岩心将存档，供许多不同的科学家随时取样。该项目还将涉及与德国研究小组的国际合作。研究的核心是对马萨诸塞州科德角和亚速尔群岛之间的北大西洋西部进行考察，以调查新的取芯地点的极深海底，并使用不同的设备（多芯取样器，重力取芯器和活塞取芯器）进行取样。 深海环流的变化将使用化石浮游有孔虫和底栖有孔虫的壳中的碳同位素比率来追踪。 13 C/12 C比率是深水营养物含量的代用指标，在4.2公里左右的核心地点，这一比率表明，在冰川作用期间，来自北极和南极的沃茨的混合物与今天不同，与目前的想法一致。 最有可能的是，要么是北方的水源产生的水更少，因为北欧海的表面比现在覆盖着更多的海冰，要么是深水移动得更慢，从表面积累了更多的营养物质。 现有的14 C/12 C数据支持13 C/12 C中看到的模式，这种示踪剂也用于确定沉积物沉积的年代。 然而，低于4200米，这些同位素对的模式反转，并表示更多的北方源沃茨与深度增加（5公里）。 这一假设将通过在3公里至5公里范围内的地点进行取芯和海岸分析工作来检验。来自3公里以上新核心站点的数据将由一名德国同事收集，这一合作将导致北大西洋西部海盆水文变化之后的第一次高分辨率深度重建。