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）暖期，估计全球平均温度相对于今天只略微升高（可能升高1-2°C）。与此同时，根据对澳大利亚、塞舌尔和加勒比地区暴露的珊瑚的研究，全球海平面相对于现在上升了约6-9米。今天如此高的海平面将使美国20%的人口流离失所。据估计，格陵兰冰川的融化可能是海平面上升2米的原因，海洋的热膨胀和高山冰川的融化各可能是0.5米的原因，但南极洲肯定是其中的主要原因。融化发生在哪里？据推测，南极洲的一个特定部分（南极西部冰盖，WAIS）是推测融化的地点。积累在西南极洲近海的海洋沉积物应该提供了这种融化的证据，但南极海洋沉积物缺乏强有力的年龄控制，阻碍了它们根据过去WAIS的不稳定性进行解释。这一提议测试了一种相对较新的方法，该方法涉及沉积物本身记录过去的地磁场，可以为南极海洋沉积物提供年龄模型，根据过去几个气候周期的WAIS不稳定性提供解释，从而有助于我们当前的气候/海平面困境。在过去的20年里，我们将相对地磁古强度（RPI）指标与北大西洋第四纪沉积物的氧同位素数据相结合，目的是将RPI作为一种高分辨率的地层对比工具。相对快速的地磁场强度变化率（目前约为每世纪5%），以及沉降速率~50 cm/kyr的沉积物可能只记录了磁场的主要轴向偶极子分量，这意味着RPI可以提供高分辨率的全球相关工具。在过去的几年中，有几个例子涉及RPI和氧同位素数据的串联相关性，通过“Match”等自动匹配协议实现。这些结果导致了RPI（如PISO）的临时校准参考堆栈的产生，可以与氧同位素数据一起使用，以提高第四纪地层的分辨率。该提案旨在测试RPI作为一种地层学工具在南极半岛和别令斯豪森海海洋沉积物漂流中的应用，使用的是2015年初詹姆斯·克拉克·罗斯号JR298巡航期间回收的7个活塞芯。由于南极沉积物漂移的沉积历史是根据南极西部冰盖（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，因此南极西部地区提供了相对古强度（RPI）代用物的地层作用的重要测试。南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。这些南极漂流的年龄模式依赖于高生物成因的硅质/碳酸盐百分比（以及由磁化率、湿体积密度和生物成因Ba含量组成的高生物成因含量的代用物）与间冰期海洋同位素阶段的关联。这些方法并不理想，因为它们的分辨率很低，并且对沉积物记录进行了解释。由于这些原因，我们寻找新的方法来确定这些漂流沉积物的年龄，利用RPI来解释沉积速率，XRF岩心扫描数据，以及漂流碎屑（IRD）代理，在WAIS和api的不稳定性方面。该项目将由一名本科生研究员协助。

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.