Collaborative Research: Deglacial Ice Dynamics in the Weddell Sea Embayment using Sediment Provenance

摘要：在过去的几百万年里，南极冰盖的边缘不断地前进和后退。从19000年前到9000年前的最后一次退缩中，融化的冰使海平面上升了8米或更多，但之前的退缩程度鲜为人知。该项目的主要目标是了解南极冰是如何退缩的：快速还是缓慢，循序渐进还是稳定，以及冰盖的哪些部分最容易退缩。南极洲的冰流失主要有两个过程：浮冰架底部的融化和冰山的崩解。冰山本身是短暂的，但它们携带着从南极基岩上冲刷下来的矿物颗粒和岩石碎片。随着冰山的漂移和融化，这？iceberg-rafted碎片?落在海床上，并稳定地埋在海洋沉积物中，形成冰山活动和冰盖退缩的记录。调查人员将阅读这些冰山碎片的记录，以找出过去南极冰在何时何地不稳定。这些信息可以帮助预测南极冰在变暖气候下的表现。研究区域是威德尔海海湾，位于南极洲的大西洋部分。冰山的主要来源是附近的南极半岛和威德尔海海湾，那里的冰流消耗了大约四分之一的南极冰。通过将漂流碎片（IRD）中单个矿物颗粒的地球化学指纹（如特征氩同位素年龄）与相应源区的地球化学指纹（如特征氩同位素年龄）相匹配，可以找到漂流碎片（IRD）和携带漂流碎片的冰山的来源。更详细地说，该项目将：利用进入威德尔海的每条主要冰流的样本，确定冰川侵蚀物质源区的地球化学指纹。现有资料表明，威德尔湾的腹地是由地球化学上可区分的源区组成的，因此可以应用地球化学物源技术来确定南极洲冰山的起源。这一地区的陆地沉积物样本很少，因此该项目包括实地工作，收集沉积物，以表征回收和基础冰流提供的碎屑。2. 记录了威德尔海西北部两个深水沉积物岩心中冰山漂流碎屑（IRD）和冰川侵蚀物质物源的地层变化。从海湾的冰流中分离出来的冰山被威德尔环流带着，在经过核心地点时沉积在IRD上。物源信息确定了哪组冰流正在积极侵蚀并向海洋输出碎屑（通过冰山漂流和底流），岩心的地层学显示了冰流活动随时间的相对顺序。通过使用一种新的方法在细粒物质中测量铀系列同位素，确定细粒沉积物侵蚀和沉积之间的时间滞后，进一步增加了一个维度。技术摘要：南极冰盖和冰流的行为是气候变化和未来海平面上升的关键话题。本提案的目标是限制威德尔海冰盖在最近三次冰川终止期间对气候变化的反应，作为未来潜在变暖的类比。该项目还将研究对融水脉冲1A的可能贡献，并测试南极洲东部和西部冰流的相对稳定性。南极西部的大部分冰可能在第三纪（130 - 114 Ka）融化，因此它可能是预测未来几个世纪冰减少的类似物。冰川侵蚀碎屑的地球化学物源指纹图谱为重建威德尔海这些终止期冰川退缩的位置和相对时间提供了一种新的方法。该项目的两个主要目标是：1。通过表征Ar、U-Pb和Nd同位素特征，以及来自进入威德尔海的每条主要冰流的碎屑矿物的重矿物和Fe-Ti氧化物组成，使用来自Ronne和Filchner冰架的陆上斜坡和现有沉积物岩心，确定物源区域。试验资料表明，可以明显区分威德尔海海湾东西两侧的碎屑岩；公开资料表明，威德尔海海湾腹地由地球化学上可区分的碎屑岩源区组成。这一地区的陆地沉积物样本很少，因此该项目包括实地工作，收集沉积物，以表征回收和基础冰流提供的碎屑。2. 记录了威德尔海西北部两个深水沉积物岩心中冰山漂流碎屑（IRD）和冰川侵蚀物质物源的地层变化。从海湾的冰流中分离出来的冰山被威德尔环流带着，在经过核心地点时沉积在IRD上。来源信息将确定哪些冰流正在积极侵蚀并将碎屑输出到海洋（通过冰山漂流和海底流）。岩心的地层学将显示冰流活动随时间的相对顺序。通过使用u系列粉碎年龄确定细泥沙侵蚀和沉积之间的时间滞后，增加了进一步的时间维度。

Abstract for the general public:The margins of the Antarctic ice sheet have advanced and retreated repeatedly over the past few million years. Melting ice from the last retreat, from 19,000 to 9,000 years ago, raised sea levels by 8 meters or more, but the extents of previous retreats are less well known. The main goal of this project is to understand how Antarctic ice retreats: fast or slow, stepped or steady, and which parts of the ice sheet are most prone to retreat. Antarctica loses ice by two main processes: melting of the underside of floating ice shelves and calving of icebergs. Icebergs themselves are ephemeral, but they carry mineral grains and rock fragments that have been scoured from Antarctic bedrock. As the icebergs drift and melt, this ?iceberg-rafted debris? falls to the sea-bed and is steadily buried in marine sediments to form a record of iceberg activity and ice sheet retreat. The investigators will read this record of iceberg-rafted debris to find when and where Antarctic ice destabilized in the past. This information can help to predict how Antarctic ice will behave in a warming climate. The study area is the Weddell Sea embayment, in the Atlantic sector of Antarctica. Principal sources of icebergs are the nearby Antarctic Peninsula and Weddell Sea embayment, where ice streams drain about a quarter of Antarctic ice. The provenance of the iceberg-rafted debris (IRD), and the icebergs that carried it, will be found by matching the geochemical fingerprint (such as characteristic argon isotope ages) of individual mineral grains in the IRD to that of the corresponding source area. In more detail, the project will: 1. Define the geochemical fingerprints of the source areas of the glacially-eroded material using samples from each major ice stream entering the Weddell Sea. Existing data indicates that the hinterland of the Weddell embayment is made up of geochemically distinguishable source areas, making it possible to apply geochemical provenance techniques to determine the origin of Antarctica icebergs. Few samples of onshore tills are available from this area, so this project includes fieldwork to collect till to characterize detritus supplied by the Recovery and Foundation ice streams. 2. Document the stratigraphic changes in provenance of iceberg-rafted debris (IRD) and glacially-eroded material in two deep water sediment cores in the NW Weddell Sea. Icebergs calved from ice streams in the embayment are carried by the Weddell Gyre and deposit IRD as they pass over the core sites. The provenance information identifies which groups of ice streams were actively eroding and exporting detritus to the ocean (via iceberg rafting and bottom currents), and the stratigraphy of the cores shows the relative sequence of ice stream activity through time. A further dimension is added by determining the time lag between fine sediment erosion and deposition, using a new method of uranium-series isotope measurements in fine grained material. Technical abstract: The behavior of the Antarctic ice sheets and ice streams is a critical topic for climate change and future sea level rise. The goal of this proposal is to constrain ice sheet response to changing climate in the Weddell Sea during the three most recent glacial terminations, as analogues for potential future warming. The project will also examine possible contributions to Meltwater Pulse 1A, and test the relative stability of the ice streams draining East and West Antarctica. Much of the West Antarctic ice may have melted during the Eemian (130 to 114 Ka), so it may be an analogue for predicting future ice drawdown over the coming centuries. Geochemical provenance fingerprinting of glacially eroded detritus provides a novel way to reconstruct the location and relative timing of glacial retreat during these terminations in the Weddell Sea embayment. The two major objectives of the project are to: 1. Define the provenance source areas by characterizing Ar, U-Pb, and Nd isotopic signatures, and heavy mineral and Fe-Ti oxide compositions of detrital minerals from each major ice stream entering the Weddell Sea, using onshore tills and existing sediment cores from the Ronne and Filchner Ice Shelves. Pilot data demonstrate that detritus originating from the east and west sides of the Weddell Sea embayment can be clearly distinguished, and published data indicates that the hinterland of the embayment is made up of geochemically distinguishable source areas. Few samples of onshore tills are available from this area, so this project includes fieldwork to collect till to characterize detritus supplied by the Recovery and Foundation ice streams. 2. Document the stratigraphic changes in provenance of iceberg-rafted debris (IRD) and glacially-eroded material in two deep water sediment cores in the NW Weddell Sea. Icebergs calved from ice streams in the embayment are carried by the Weddell Gyre and deposit IRD as they pass over the core sites. The provenance information will identify which ice streams were actively eroding and exporting detritus to the ocean (via iceberg rafting and bottom currents). The stratigraphy of the cores will show the relative sequence of ice stream activity through time. A further time dimension is added by determining the time lag between fine sediment erosion and deposition, using U-series comminution ages.