The reconstruction of Holocene sea level and paleoenvironmental change

Project Description: 

Sea-level changes on the time-scale of decades to millennia are driven, predominantly, by changes in climate. The recent transition of the earth system from a glacial to interglacial state produced a dramatic global sea-level response. Puerto Rico is distant from the major glaciation centers, thus is characterized by a sea-level rise of ~120 m since the Last Glacial Maximum due, largely, to the influx of glacial meltwater to the oceans. By comparing observations of sea-level changes to model predictions, it is possible to infer parameters relating to changes in climate, the rate and geographic source of meltwater influx, the rheological structure of the solid Earth, and the spatially variable vertical land motion , a key parameter for understanding mantle flow and the tectonic evolution of our planet. The key science objectives are:
1. To collect new Holocene sea-level data from mangrove peats involving a complete suite of paleoenvironmental indices, precise elevation measurements tied to sea level, state of the art analyses and data interpretation.
2. To synthesize existing and new data to produce a quality-controlled, spatially and temporally comprehensive sea-level database for Puerto Rico and the Caribbean during the Holocene.
3. To determine the nature and magnitude of vertical land motion within Puerto Rico and the Caribbean sea-level database.
Holocene changes in RSL are commonly determined using microfossil sea-level indicators, which possess a systematic and quantifiable relationship to elevation with respect to the tidal frame. When the relationship of such an indicator to present-day sea level is determined (Figure 1), it can be applied to samples in the stratigraphic record to determine the former position of sea level. Microfossils (e.g. diatoms, foraminifera) are, however, poorly preserved in tropical environments and therefore are of little use in paleoenvironmental studies in these locations. As an alternative we wish to examine if the stable carbon isotope chemistry of bulk organic matter, which varies with vegetation zones related to elevation in the tidal frame, holds utility as a sea-level indicator (Figure 2).
Constructing Chronologies in Mangrove Sediments
There is currently no consensus on the appropriate material to date in mangrove environments. Our initial results suggest that accurate chronologies can be obtained from these environments by dating leaf or wood fragments that fall in situ on the mangrove sediment surface (Figure 3). We will assess what components of mangrove peat should be dated to construct accurate and precise chronologies in mangrove environments.
RSL Reconstruction
We have collected a series of cores from the northern and southern coasts of the island to reconstruct RSL. Comparison of these records to glacio-isostatic adjustment (GIA) model predictions and other records in the Caribbean, and construction of our records from compaction-free basal peats, which minimize local effects, should enable us to estimate the impact of local tectonics on Puerto Rico’s RSL history.

Additional funding sources
1. National Ocean Sciences Accelerator Mass Spectrometry Facility (NOSAMS) at Woods Hole Oceanographic Institution
2. British Geological Survey

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Contact Information
Person(s) Completing This Form: 
Benjamin P Horton
Benjamin P Horton Nicole Khan Chris Vane
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