Collaborative Research: Middle to Late Holocene Sea-Level Change and Coastal Evolution, Northern Gulf of Mexico Coast

地球上的许多海岸线都有关于全新世海平面变化的详细记录，但在其他地方却存在争议。一个有争议的地区是美国墨西哥湾沿岸，在那里，两种截然不同的模型在文献中持续存在了几十年，并在最近由美国国家科学基金会赞助的研究中得到了新的支持。一种模式认为海平面在过去的6000到7000年里不断上升，而另一种模式认为海平面在6000到7000年前达到现在的高度，从那时起海平面在比现在的高度低1到2米的范围内波动。过去在墨西哥湾沿岸进行的研究是在不同的地区由不同的研究者使用不同的方法进行的。这些相互冲突的模式尚未得到协调，而且仍然不确定不同的结果是否反映了海平面变化的内在空间变异性、所使用的各种方法的分辨率差异，或两者的某种结合。这项合作研究将产生相互矛盾结果的研究人员聚集在一起，但他们现在将各自的方法应用于同一领域。研究人员将把重点放在路易斯安那州西南部、阿拉巴马州和佛罗里达州西北部的非沉降、非三角洲地区。该项目的主要目标是：(1)通过对非三角洲沼泽沉积物中基底泥炭的研究来记录全新世（地下）水位变化；(b)确定现代烟囱和滩脊沉积物的精确海平面指标；(c)在切尼尔和滩脊地层记录中追踪海平面指标高程随时间的变化。这一方法预计将根据基底泥炭数据和chenier和海滩脊沉积物为每个研究区域产生高分辨率的相对海平面曲线，以便调和这两种方法，并提供海平面变化及其空间变异的内部一致图像。每条曲线都将被校准到精确的GPS高度，并将通过放射性碳和/或光学刺激发光测年来固定。对美国墨西哥湾沿岸相对海平面变化及其空间变异性的更精确和综合的理解的发展将具有许多学科和区域意义。现有的海平面变化模型对全球气候和冰量重建、区域沿海景观演变、人类对过去海平面变化的适应以及沿海系统可能对未来气候和海平面变化作出反应的方式的研究具有显著不同的意义。海平面变化也是墨西哥湾沿岸人类与环境相互作用中最紧迫的问题之一，尤其是密西西比河三角洲，那里将投入数十亿美元用于海岸恢复。目前，这些努力缺乏关于海平面自然背景变化率、区域尺度空间变异性及其近期轨迹的基本基线。这项研究将提供这样一个基线，并将与海岸恢复工作结合起来。

A number of Earth's coastlines have well-constrained records of Holocene sea-level change, yet controversy prevails elsewhere. One controversial area is the U.S. Gulf of Mexico coast, where two contrasting models have persisted in the literature for decades and have seen renewed support from recent NSF-sponsored research. One model views sea level as continually rising through the last 6,000 to 7,000 years, whereas the other holds that sea level reached present elevations 6,000 to 7,000 years ago and has oscillated within 1 to 2 meters of present elevations since that time. Past research along the Gulf Coast has been undertaken in different areas and by different investigators using different methods. These conflicting models have not been reconciled, and it remains uncertain whether disparate results reflect inherent spatial variability in sea-level change, differences in resolution of the various methods used, or some combination of the two. This collaborative research brings together investigators that have produced conflicting results but who now will apply their respective approaches to the same field areas. The researchers will focus on non-subsiding, non-deltaic sites in southwestern Louisiana, Alabama, and northwestern Florida. Major goals of the project are (1) the documentation of Holocene (ground) water-level change from studies of basal peats in non-deltaic marsh sediments; (b) definition of precise sea-level indicators in modern chenier and beach-ridge deposits; and (c) tracking of changes in the elevation of sea-level indicators through time within chenier and beach ridge stratigraphic records. This approach is expected to produce high-resolution relative sea-level curves for each study area from basal-peat data and from chenier and beach-ridge deposits so as to reconcile the two approaches and provide an internally consistent picture of sea-level change and its spatial variability. Each curve will be calibrated to precise GPS elevations and will be anchored by radiocarbon and/or optically stimulated luminescence dating.Development of a more precise and integrated understanding of relative sea-level change and its spatial variability along the U.S. Gulf of Mexico coast will have a number of disciplinary and regional implications. Existing models for sea-level change have significantly different implications for global climate and ice volume reconstructions as well as for studies of regional coastal landscape evolution, of human adaptations to past sea-level change, and of the ways that coastal systems might respond to future climate and sea-level change. Sea-level change is also one of the most pressing problems in human-environment interactions along the Gulf of Mexico coast, especially along the Mississippi delta, where billions of dollars will be invested in coastal restoration. At present, these efforts lack a fundamental baseline for natural background rates of sea-level change, its regional-scale spatial variability, and its recent trajectory. This research will provide such a baseline, and will be integrated with coastal restoration efforts.