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

地球上的一些海岸线对全新世海平面变化有很好的记录，但其他地方的争议仍然盛行。一个有争议的地区是美国墨西哥湾海岸，在那里，两个截然不同的模型几十年来一直存在于文献中，并得到了最近NSF赞助的研究的重新支持。一种模型认为海平面在过去的6000到7000年里一直在上升，而另一种模型认为海平面在6000到7000年前达到了现在的海拔，从那时起就在距离现在的海拔1到2米的范围内波动。过去对墨西哥湾沿岸的研究是在不同的地区进行的，由不同的调查人员使用不同的方法进行。这些相互矛盾的模型尚未得到协调，而且仍然不确定不同的结果是否反映了海平面变化固有的空间变异性、所使用的各种方法的分辨率不同，还是两者的某种组合。这项合作研究将曾经产生相互矛盾的结果的研究人员聚集在一起，但他们现在将把各自的方法应用于相同的领域。研究人员将专注于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下沉、非三角洲地点。该项目的主要目标是：(1)通过对非三角洲沼泽沉积物中的基本泥炭的研究，记录全新世(地面)水位的变化；(B)在现代Chenier和海滩脊沉积中定义精确的海平面指标；(C)在Chenier和海滩脊地层记录中跟踪海平面指标随时间的变化。这一方法预计将根据底部泥炭数据以及Chenier和海滩海脊沉积为每个研究区域制作高分辨率的相对海平面曲线，以协调这两种方法，并提供关于海平面变化及其空间变异性的内部一致的图景。每条曲线将被校准到精确的GPS高程，并将由放射性碳和/或光刺激发光数据锚定。发展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更全面的理解将具有许多学科和区域影响。现有的海平面变化模型对全球气候和冰量重建以及区域沿海地貌演变、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重大不同的影响。海平面变化也是墨西哥湾沿岸人类与环境互动中最紧迫的问题之一，特别是在密西西比河三角洲，那里将投资数十亿美元用于海岸恢复。目前，这些努力缺乏关于海平面变化的自然背景速率、其区域尺度空间变异性及其最近轨迹的基本基线。这项研究将提供这样一个基线，并将与沿海恢复工作相结合。

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.