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

在大约12.5万年前的最后一次间冰期(LIG)变暖期间，全球平均气温估计只比今天略有上升(可能上升了1-2摄氏度)。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，全球海平面比现在上升了约6-9米。今天如此高的海平面将使多达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，海洋热膨胀和山脉冰川融化可能各占约0.5米，但南极洲肯定占了其中的大部分。融化发生在哪里？据推测，南极洲的一个特殊部分(西南极冰盖，WAIS)是推测融化的地点。南极西部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，阻碍了对它们的解释，因为过去WAIS不稳定。这一建议测试了一种相对较新的方法，包括由沉积物本身记录过去的地磁场，该方法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中WAIS的不稳定性，从而导致我们目前的气候/海平面两难境地。在过去20年中，相对(地磁)古强度(RPI)指标与北大西洋第四纪沉积物中的氧同位素数据相结合，目的是将RPI作为一种高分辨率地层对比工具。地磁场强度的变化速度相对较快(目前约为每世纪5%)，而沉积速率约为50 cm/Kyr的沉积物可能只记录到磁场的主要轴向偶极分量，这意味着RPI有望提供一种高分辨率的全球对比工具。现在有几个串联关联的例子，涉及过去几个MyR的RPI和氧同位素数据，通过“匹配”等自动匹配协议实现。结果为RPI(如PISO)生成了经过时间校准的参考栈，可与氧同位素数据结合使用，以提高第四纪地层学的分辨率。这项提议是为了测试RPI作为一种地层工具在南极半岛和别林豪森海的海洋沉积物漂流中的使用，使用2015年初在RRS詹姆斯·克拉克·罗斯号JR298巡航期间发现的七个活塞岩芯。南极西部地区是对相对古强度(RPI)指标的地层学作用的重要检验，因为南极沉积物漂移的沉积历史是从西南极冰盖(WAIS)和南极半岛冰盖(APIs)的不稳定性来解释其沉积历史的关键。高纬度地区有孔虫碳酸盐的稀少意味着该地区沉积物中的年龄模式不能依赖氧同位素数据。这些南极漂流中的年龄模式依赖于高生物成因硅质/碳酸盐百分比(以及从磁化率、湿体积密度和生物成因Ba含量代替高生物成因含量的指标)与间冰期海洋同位素阶段的联系。这些方法并不理想，因为它们的分辨率较低，并且会对沉积物记录施加解释。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岩心扫描数据和冰筏碎屑(IRD)替代物，根据WAIS和API的不稳定性。这个项目将由一名本科生研究员协助完成。

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.