Response of the Labrador Sea and south Greenland Ice Sheet to the mid-Pliocene climate optimum: sedimentary, magnetic and geochemical evidence from the Eirik Drift

拉布拉多海和南格陵兰冰盖对上新世中期气候最佳状态的响应：来自埃里克漂移的沉积、磁性和地球化学证据

• 批准号: 1352008
• 负责人: Anders Carlson
• 金额: $ 40万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-01 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1352008&HistoricalAwards=false
• 关键词: Response; Labrador; Sea; south; Greenland

In 2013, atmospheric carbon dioxide (CO2) concentrations reached 400 ppm, raising questions as to how the Earth will respond to this unprecedented forcing in human history. A major concern is the response of Earth's remaining ice sheets to present-day (and future) CO2 levels, and their attendant contribution to sea-level rise. In the case of the Greenland Ice Sheet (GIS), models suggest a threshold behavior where the GIS will completely melt once a certain temperature is exceeded. However, different models suggest different thresholds, so it is unclear whether the Earth has already crossed an ice-free Greenland tipping point. The last period when atmospheric CO2 reached ~400 ppm was during the mid-Pliocene climate optimum 3.3-3.0 million years ago, providing a past analogue to Earth's present climate. Climate and ice-sheet models simulate a warmer Earth with a smaller GIS, but show a range of responses. Pliocene sea-level records are significantly complicated by movement of the crust from advance and retreat of later ice sheets, preventing clear documentation of global ice volume. This project will investigate the response of the south GIS and adjacent Labrador Sea to elevated CO2 in the mid Pliocene using marine sediment archives preserved in the Eirik Drift off of south Greenland. Specific questions to be addressed are: 1) How warm was the Labrador Sea during the mid-Pliocene optimum?, and 2) Did south Greenland completely deglaciate in response to this warmth? Results of this study will help establish whether the Earth has already crossed a tipping point that will lead to an ice-free Greenland.The research team will answer these research questions using methods developed for tracking GIS behavior during Quaternary interglacials. Question 1 will be addressed through foraminifer census data and measurement of d18O and Mg/Ca on planktonic foraminifera in the Eirik Drift across the mid-Pliocene optimum sequence recorded in International Ocean Discovery Program (IODP) Site U1307. Question 2 will be answered through the tracing of the sources of mid-Pliocene detrital sediment in the Eirik Drift using silt-size Sr-Nd-Pb isotopic signatures and silt- and clay-size magnetic properties. The team's extensive provenance work has shown that silt-size particles with Precambrian isotopic signatures, high magnetic concentrations, and coarse magnetic grain-sizes are only produced on Greenland through GIS erosion of the bedrock; Iceland has distinctively different magnetic and isotopic signatures. GIS melting provides the mechanism to deliver these silt particles to the Eirik Drift. If a south Greenland terrane deglaciates removing the erosive agent and transport mechanism, the terrane's isotopic and magnetic signatures are largely absent in Eirik Drift sediment. These records will determine the Labrador Sea and south GIS response to present-day CO2 levels including the impact of long-term feedbacks necessary for assessing Earth-system sensitivity. The combination of ocean climate and south GIS records will test if the climate threshold necessary to deglaciate Greenland lies at ~400 ppm atmospheric CO2 concentration. This project will support a postdoctoral researcher and undergraduate students in multi-proxy approaches in the fields of paleoceanography, paleoclimatology, geochemistry, environmental magnetism, and glacial geology to address societally relevant climate/sea-level questions. Under-represented groups in the geosciences will take precedent in recruitment of the postdoctoral researcher and undergraduate students.

2013年，大气中的二氧化碳（CO2）浓度达到400 ppm，提出了有关地球将对人类历史上这种前所未有的强迫做出反应的问题。一个主要问题是地球剩余的冰盖对当今（和未来）二氧化碳水平的反应，以及他们对海平面上升的贡献。在格陵兰冰盖（GIS）的情况下，模型提出了阈值行为，一旦超过一定温度，GIS将完全熔化。但是，不同的模型暗示了不同的阈值，因此目前尚不清楚地球是否已经越过了无冰的格陵兰临界点。大气二氧化碳达到约400 ppm的最后一个时期是在上新世气候中最佳3.3-3-30万年前，这提供了与地球当前气候的过去类似物。气候和冰片模型模拟具有较小GIS的温暖地球，但显示了一系列响应。上新世海平面的记录显着复杂，因为外壳从前进和后来的冰盖撤退中移动，从而阻止了全球冰量的清晰记录。该项目将使用保存在南格陵兰岛的Eirik漂移中的海洋沉积物档案中调查南GIS和邻近的拉布拉多海对高架新世中期二氧化碳的反应。要解决的具体问题是：1）中新世最佳中的拉布拉多海有多温暖？和2）南格陵兰岛是否完全反应这种温暖？这项研究的结果将有助于确定地球是否已经越过临界点，这将导致无冰的格陵兰岛。研究团队将使用用于在第四纪间冰期期间追踪GIS行为的方法回答这些研究问题。问题1将通过有孔虫的普查数据以及在EIRIK跨越国际海洋发现计划（IODP）中记录的中新近最佳序列的EIRIK漂移中的D18O和MG/CA对浮游有孔虫上的测量来解决。问题2将通过使用淤泥大小的SR-ND-PB同位素特征以及淤泥和粘土大小的磁性特性来追踪Eirik漂移中中新世碎屑沉积物的来源。该团队的广泛出处工作表明，具有前寒武纪同位素特征，高磁性浓度和粗磁晶粒尺寸的淤泥大小的颗粒仅通过基岩的GIS侵蚀在Greenland上产生。冰岛具有明显不同的磁性和同位素特征。 GIS熔化提供了将这些淤泥颗粒传递到EIRIK漂移的机制。如果南格陵兰式地形脱位去除侵蚀剂和运输机构，则在Eirik漂移沉积物中，地形的同位素和磁性特征在很大程度上不存在。这些记录将确定拉布拉多海和南格斯对当今二氧化碳水平的反应，包括评估地球系统敏感性所需的长期反馈的影响。海洋气候和South GIS记录的结合将测试是否需要脱胶格陵兰的气候阈值约为400 ppm大气二氧化碳浓度。该项目将支持古文化，古气候学，地球化学，环境磁性和冰川地质学领域的多种方法的研究人员和本科生，以解决与社会相关的气候/海平面问题。地球科学中代表性不足的群体将在招募博士后研究员和本科生方面先例。