Abrupt Sea Level Change in the Geologic Record: Reconciling Contradictory Evidence
SummaryThis proposal seeks funding to investigate potential geologic evidence of abrupt sea level on the island of Barbados. Geologic evidence provides important constraints on past rates of sea level change prior to the period of historical and modern observations. These constraints are crucial for refining predictions of future sea level change, a question of significant societal relevance. Evidence for sea level change in the past comes from the dating of fossil coral reefs that mark former highstands of the sea. Early dating of the uplifted coral terraces on Barbados, West Indies and the Huon Peninsula in Papua New Guinea suggested that sea levels during MIS 5a, relatively warm period approximately 80-85 thousand years ago, peaked at a level approximately 15 to 20 meters below its present level, and these early results have been supported by subsequent work. However, later work on the U.S. Atlantic coastal plain suggested that relative sea levels during MIS 5a were above present sea level. It was subsequently suggested that this discrepancy could be resolved by accounting for whole earth gravitational, rotational, and isostatic changes imposed by the waxing and waning of the glacial ice sheets (glacial isostatic adjustment (GIA)). However, recent evidence from the island of Mallorca, Spain also indicates that MIS 5a relative sea levels were about the same as present. In April of 2012, an NSF-sponsored workshop in Mallorca, Spain (Sea level changes into MIS 5: from observations to predictions) highlighted the serious conflict in relative sea level data for the Marine Isotope Stage (MIS) 5a highstand. A primary conclusion of the workshop was that the Mallorca evidence could not be reconciled with data from Barbados and Huon by accounting for GIA.
There are two potential explanations for the significant relative sea level discrepancy: 1) The island of Mallorca has undergone substantial tectonic uplift since MIS 5a, a possibility that is contradicted by Last Interglacial fossil beaches found at the expected elevation on Mallorca, or 2) evidence for a rapid 15 to 20 m oscillation of sea level has been overlooked on Barbados. There is some recently developed Barbados field evidence supporting the possibility of (2) and this proposal seeks funding to investigate this hypothesis with exploratory field sampling and high-precision U-Th dating. Preliminary results obtained through this proposal would provide the proof of concept necessary for leveraging a larger NSF-funded research project.
Sea level change during MIS 5a is a crucial piece of earth and ocean history, and the significant discrepancy between relative sea levels inferred from Barbados and Mallorca pinpoint a crucial gap in knowledge that should be immediately addressed. A more detailed history of MIS 5a will provide information on past rates of sea level change, constraints on GIA adjustment models, and improvements in projections of future sea level change. Conclusive evidence of a large oscillation of sea level during MIS 5a would be a significant and transformative contribution to the present state of knowledge. Barbados is an ideal field site for detecting MIS 5a sea level anomalies and the PI is uniquely qualified to carry out this investigation, given extensive experience in fossil reef field work, high-precision U-Th dating, and overcoming the diagenetic challenges of dating older corals.