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.
