Producing reliable, high-resolution records of relative sea-level change from mangrove sedimentary archives

Abstract

In tropical locations, mangroves occur at the interface between terrestrial and marine environments and preserve vital archives of climatic, environmental and relative sea-level (RSL) change. These tropical locations span a gradient across the intermediateand far-field of polar ice sheets, and may provide important constraints on sea-level quivalent changes and its sources since the Last Glacial Maximum. While numerous high-resolution (decimeter vertical and decadal age resolution) RSL records have been obtained from temperate salt-marsh environments, these records are non-existent in tropical mangroves. High rates of decomposition and bioturbation may limit preservation of mangrove micro- and macrofossils and introduce complications in interpreting the indicative meaning and developing precise chronologies of RSL change. Here, we provide a review of recent methodological developments used to interpret and date mangrove archives, drawing from case studies in Florida, USA, Puerto Rico, and Bermuda. We assess controls on the vertical distribution and resolution of mangrove proxies, and offer suggestions to improve their precision when microfossils (e.g., foraminifera) are absent or poorly preserved. In addition, we examine the distribution of ages of different mangrove peat components (leaf and wood macofossils, bulk peat, fine roots) and assess the impact on the interpretation of RSL and its rates based on chronologies obtained from different components from these cores. Based on this analysis, we outline best practices for obtaining accurate chronologies from mangrove sedimentary archives. Finally, we demonstrate the successful application of these methodological advancements to produce high-resolution records of RSL change over the mid to late Holocene in Florida.