Relative Paleointensity (RPI) and Age Control in Antarctic Marine Drift Sediments

南极海洋漂流沉积物的相对古强度（RPI）和年龄控制

• 批准号: 1542579
• 负责人: James Channell
• 金额: $ 13.13万
• 依托单位: University of Florida
• 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: 2016-05-01 至 2019-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1542579&HistoricalAwards=false
• 关键词: Relative; Paleointensity; RPI; Age; Control

During the last interglacial (LIG) warm interval, ~125 thousand years ago, mean global temperature is estimated to have been only very slightly elevated (by perhaps 1-2 °C), relative to today. At that same time, global sea level was elevated by ~6-9 m, relative to present, according to studies of exposed corals in Australia, the Seychelles, and the Caribbean. Such high sea level today would displace up to 20% of the US population. It is estimated that Greenland glacial melting could have accounted for ~2 m of sea-level rise, thermal expansion of the oceans and melting of mountain glaciers could account for ~0.5 m each, but Antarctica must account for the bulk of it. Where did the melting occur? It has been speculated that the one particular part of Antarctica (the West Antarctic Ice Sheet, WAIS) was the site of the inferred melting. The marine sediments that have accumulated off-shore West Antarctica should provide evidence of this melting, but the lack of robust age control in Antarctic marine sediments has stymied their interpretation in terms of past instability of WAIS. This proposal tests a relatively new method, involving the recording of the past geomagnetic field by the sediments themselves, that can provide age models for the Antarctic marine sediments, contribute their interpretation in terms of instability of WAIS over the last few climate cycles, and hence contribute to our current climate/sea level dilemma. Over the last 20 years, relative (geomagnetic) paleointensity (RPI) proxies have been combined with oxygen isotope data in Quaternary sediments in the North Atlantic with the objective of implementing RPI as a high-resolution stratigraphic correlation tool. The relatively rapid rate of change of geomagnetic field intensity (currently about 5% per century), and the fact that sediments with sedimentation rates ~50 cm/kyr are likely to record only the main axial dipole component of the field, means that RPI can be expected to provide a high-resolution global correlation tool. There are now several examples of tandem correlations involving RPI and oxygen isotope data over the last few Myrs, implemented through automated matching protocols such as 'Match'. The results have led to the generation of temporally calibrated reference stacks for RPI (such as PISO) that can be used, in conjunction with oxygen isotope data, to provide improvements in the resolution of Quaternary stratigraphies. This proposal is to test the use of RPI as a stratigraphic tool in marine sediment drifts off the Antarctic Peninsula and in the Bellingshausen Sea, using seven piston cores recovered in early 2015 during cruise JR298 of the RRS James Clark Ross. The west Antarctic region provides an important test of the stratigraphic role of relative paleointensity (RPI) proxies because the sedimentation history of Antarctic sediment drifts is a key to interpreting their sedimentation history in terms of instability of the West Antarctic Ice Sheet (WAIS) and Antarctic Peninsula Ice Sheet (APIS). The paucity of foraminiferal carbonate at high southerly latitudes means that age models in sediments from the region cannot rely on oxygen isotope data. Age models in these Antarctic drifts have relied on the association of high biogenic siliceous/carbonate percentage (as well as proxies for high biogenic content from magnetic susceptibility, wet bulk density and biogenic Ba content) with interglacial marine isotopic stages. These methodologies are not ideal because they have low resolution and impose interpretations on the sediment record. For these reasons, we seek new methods for determining age in these drift sediment using RPI to interpret sedimentation rates, XRF core scanning data, and ice-rafting debris (IRD) proxies, in terms of instability of WAIS and APIS. This project will be assisted by an undergraduate researcher.

在最后一次间冰期（LIG）温暖的间隔期间，大约12.5万年前，全球平均温度估计相对于今天只有非常轻微的升高（可能1-2 °C）。 与此同时，根据对澳大利亚、塞舌尔和加勒比海暴露的珊瑚的研究，全球海平面相对于现在上升了6-9米。 今天如此高的海平面将使20%的美国人口流离失所。据估计，格陵兰冰川融化可能导致海平面上升约2米，海洋热膨胀和山地冰川融化可能各导致约0.5米，但南极洲肯定是其中的主要原因。 据推测，南极洲的一个特定部分（南极西部冰盖，WAIS）是推断融化的地点。西南极洲近海积累的海洋沉积物应该提供这种融化的证据，但南极海洋沉积物缺乏强有力的年龄控制，阻碍了他们的解释，在过去的不稳定WAIS。这项提议测试了一种相对较新的方法，涉及到由沉积物本身记录过去的地磁场，它可以为南极海洋沉积物提供年龄模型，有助于解释过去几个气候周期WAIS的不稳定性，从而有助于我们目前的气候/海平面困境。 在过去的20年中，相对（地磁）古强度（RPI）代理已结合在北大西洋第四纪沉积物中的氧同位素数据，实施RPI作为一个高分辨率的地层对比工具的目标。 地磁场强度的变化率相对较快（目前约为每世纪5%），而且沉积速率约为50 cm/kyr的沉积物可能只记录到磁场的主轴偶极分量，这意味着RPI有望提供一种高分辨率的全球相关工具。现在有几个串联相关的例子，涉及RPI和氧同位素数据在过去的几个百万年，通过自动匹配协议，如“匹配”实施。结果导致产生的时间校准的参考堆栈RPI（如PISO），可以使用，结合氧同位素数据，以提高分辨率的第四纪地层。该提案旨在测试RPI作为地层工具在南极半岛和别林斯高晋海海洋沉积物漂移中的使用，使用RRS James Clark Ross的JR 298巡航期间于2015年初回收的七个活塞岩心。 西南极地区提供了一个重要的测试地层的相对古强度（RPI）代理的作用，因为南极沉积物漂移的沉积历史是一个关键，解释其沉积历史的不稳定性的西南极冰盖（WAIS）和南极半岛冰盖（APIS）。南方高纬度地区有孔虫碳酸盐的缺乏意味着该地区沉积物的年龄模型不能依赖于氧同位素数据。这些南极漂流物的年龄模型依赖于高生物硅质/碳酸盐百分比（以及来自磁化率、湿体积密度和生物Ba含量的高生物含量的代理）与间冰期海洋同位素阶段的关联。 这些方法并不理想，因为它们的分辨率低，而且对沉积物记录的解释也很复杂。出于这些原因，我们寻求新的方法来确定这些漂流沉积物的年龄，使用RPI来解释沉积速率、XRF岩芯扫描数据和冰漂流碎片（IRD）代理，考虑WAIS和APIS的不稳定性。 该项目将由一名本科研究人员协助。