Collaborative Research: Millennial-Scale Records of Sea-level Change Along the Atlantic Coast of the United States

这项研究将产生美国大西洋沿岸从康涅狄格到佛罗里达的纬度梯度上近2000年来海平面变化的高分辨率重建。需要对前卫星时代的海平面上升进行准确估计，以便为21世纪的预估提供适当的背景，并验证地球物理和气候模式。记录海平面的地理趋势很重要，因为由于固体地球的均衡（陆地）运动、海洋和冰盖之间的质量交换驱动的重力和旋转变化、温度和盐度变化引起的海洋密度（立体）变化以及其他因素，海平面变化在全球范围内并不均匀。对盐沼沉积物微化石的分析将产生传递函数，以±0.1-0.3米的垂直分辨率记录史前海平面。沉积物的年龄将由补充测年法确定。海平面重建将根据陆地水平运动和海洋密度影响进行调整，以解决海平面变化的潜在机制，重点是格陵兰和南极西部冰盖的不同影响之间的相互作用。在美国大西洋沿岸，格陵兰冰盖在海平面上升幅度上从北向南产生显著的纬度梯度，而南极西部冰盖的影响在空间上是均匀的。对海平面上升时间和幅度的四个具体研究假设进行了验证：①20世纪海平面上升时间在各站点之间是同步的，且海平面上升幅度由北向南递增；(2)与小冰期（公元1500—1850年）相关的海平面上升减速幅度由南向北增加；(3)中世纪气候异常时期（公元1000—1500年）海平面上升幅度由南向北递增；(4)从公元0年到公元1000年，海平面上升速率保持不变。海平面上升是气候变化的重要晴雨表，在21世纪可能对沿海地貌、人口和基础设施造成毁灭性后果。对过去2000年海平面变化的认识是有限的，对中世纪气候异常、小冰期和20世纪变暖等已知气候偏差的响应是未知的。该项目将增加对海平面变化驱动机制的理解，提高对21世纪海平面上升的预测能力。这种预测必须根据限制海平面时空变化的观测结果加以验证。这个项目的结果将有助于评估与海平面上升和沿海反应有关的国家危害。

This research will produce high-resolution reconstructions of sea-level change for the last 2000 years along the latitudinal gradient of the Atlantic Coast of the United States from Connecticut to Florida. Accurate estimates of sea-level rise in the pre-satellite era are needed to provide an appropriate context for 21st century projections and to validate geophysical and climate models. Documenting geographic trends in sea level is important because sea-level changes are not globally uniform owing to isostatic (land-level) movements of the solid Earth, gravitational and rotational changes driven by the exchange of mass between oceans and ice sheets, ocean density (steric) changes from temperature and salinity variations, and other factors. Analysis of microfossils from salt marsh sediments will generate transfer functions that document prehistoric sea level at a vertical resolution of ±0.1-0.3m. The age of the sediments will be determined from complementary dating methods. Sea-level reconstructions will be adjusted for land-level movements and ocean density influences to address the underlying mechanisms of sea-level change, focusing on the interplay between the contrasting influences of both the Greenland and Western Antarctic Ice Sheets. Whereas the Greenland Ice Sheet produces a significant latitudinal gradient in the magnitude of sea-level rise from north to south along the Atlantic Coast of the United States, the influence of Western Antarctic Ice Sheet is spatially uniform. Four specific research hypotheses related to the timing and magnitude of sea-level rise will be tested: (1) The timing of 20th century sea-level rise was synchronous between sites and the magnitude of this rise increased from north to south; (2) The magnitude of a deceleration in sea-level rise associated with the Little Ice Age (AD 1500-1850) increased from south to north; (3) The magnitude of sea-level rise during the Medieval Climate Anomaly (AD 1000-1500) increased from south to north; and (4) The rate of sea-level rise was constant from AD 0 to 1000.Sea-level rise is a vital barometer of climate change, with potentially devastating consequences in the 21st century for coastal landforms, populations and infrastructure. Knowledge of sea-level variability during the past 2000 years is limited and the response to known climate deviations such as the Medieval Climate Anomaly, Little Ice Age and 20th century warming is unknown. This project will increase comprhension of the driving mechanisms of sea-level change and enhance the ability to predict 21st century sea-level rise. Such predictions must be validated against observations that constrain spatial and temporal variability in sea-level. The results of this project will contribute to the assessment of national hazards with respect to sea-level rise and coastal responses.