Leveraging a more robust sea level interpretation from Last Interglacial coral reefs

Abstract:

Fossil coral reefs have long been used to reconstruct the position of sea level through time. Though most of the Pleistocene reef record is submerged by present sea level and hence generally less accessible, corals above sea level from past warm periods such as the Last Interglacial have been the focus of many studies at sites around the globe. Though the ability of corals to be radiometrically dated can provide tight temporal constraints on sea level change, their porous skeletons and aragonite mineralogy has presented diagenetic challenges to establishing accurate and precise chronologies at many Last Interglacial fossil reef sites. Additionally, uncertainties related to several factors, including paleowater depth habitats, glacial isostatic effects, tectonics and the influence of dynamic topography, have confounded attempts to ascertain accurate and precise estimates of the absolute magnitude of sea-level rise relative to present sea level.

Despite these challenges with respect to establishing both the magnitude and timing of sea level change from the fossil coral archive, placing the age and elevation data into a more robust context that considers the sedimentology, stratigraphy, geomorphology, diagenesis, taphonomy, and vertical land motion related to tectonics, glacial isostatic adjustment, and dynamic topography can enable insights into sea level change, and hence ice sheet dynamics, that are not possible by relying only on the age and elevation data of corals.

Here, we provide some examples from fossil reef sites around the globe to demonstrate how this richer geologic context can be used to assess the evolution of sea level change during the course of the Last Interglacial sea level highstand using simple principles of relative stratigraphy and sedimentology to reconstruct relative changes in rate and magnitude of sea level rise. Despite differences in relative sea level due to glacial isostatic adjustment at geographically diverse sites, a consistent pattern of episodic reef growth around the globe has emerged that suggests a pulsed nature to Last Interglacial sea-level rise. We propose that this pattern of reef accretion in the tropics reflects the dynamic interplay between the out-of-phase contributions of polar ice sheets in Antarctica and Greenland.