Documenting 10,000 years of sea-level change to better understand 21st century sea-level rise
Marguerite Toscano, Smithsonian Institution
This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). To predict present and future rapid coastal evolution, we must first reconstruct the long-term rates of local-relative sea-level rise in response to non-anthropogenic climate change, and document the ability of coral reef-mangrove environments to keep pace with these varying rates over time. The geologically stable Caribbean region is the most appropriate physical setting, containing the highest-quality mangrove peat and coral reef deposits for this purpose. Mangrove peat is a biogenic deposit that is a reliable long-term indicator of changing coastal environments. The shallow tropical marine coral reef and mangrove ecosystem is sensitive to varying rates of climate and sea-level changes. As such, the spatial extent and health of these interconnected environments are impacted by rapid environmental change. Therefore, alterations in these environments impact the viability of coastal populations and fisheries that depend on them. Given the large and growing concentration of population and economic activity in the coastal zone, as well as the importance of coastal ecosystems, the potential impacts of sea-level rise have elicited widespread concern for more than two decades. Accurate estimates of sea-level rise in the pre-satellite era are needed in order to provide a context for these 21st century estimates and calibrate climate models. During the 20th century the global rate of sea-level rise recorded by tide gauges was 1.7 to 1.8 mm/yr. However, the limited number, distribution and duration of tide gauges preclude efforts to test robustly the climate-sea level hypotheses and establish the driving mechanisms responsible for change. With recent advances in sea-level studies, these instrumental records can be augmented with sea-level records derived from mangrove and coral sedimentary sequences. An interdisciplinary team of senior scientists and their students will produce a quality-controlled, spatially and temporally comprehensive Caribbean sea-level database to reconstruct sea-level changes recorded simultaneously by coral reefs and intertidal mangroves. We will concentrate on collecting new sea-level index points for the Holocene (last 10,000 years) from thick mangrove peat deposits, with precision elevation measurements. The vertical precision of sea-level index points will be constrained by microfossil assemblages and the index points will be radiocarbon dated using the latest Accelerator Mass Spectrometric (AMS) methods. These data will produce a sea-level reconstruction at cm to dm scale vertical resolution and centennial to decadal scale temporal resolution. This comprehensive record will allow us to decipher the influence of ocean-temperature and salinity changes, mass changes of ice sheets and the isostatic response of the solid earth to Holocene sea-level changes. More recent mangrove sediments will be analyzed in greater detail using isotopic methods to bridge the gap between instrumental and established geologic records of sea-level change. Such data are a key variable in future modeling experiments to assess coastal response to sea-level change, inform national and regional hazard assessments and better understand local geomorphologic responses where sea-level rise interacts with sediment supply and wind/wave processes.