Smithsonian Institution

Department Member, National Museum of Natural History

Smithsonian Research Associate

About

I am a Smithsonian Research Associate, based in the Paleobiology Department of the National Museum of Natural History. I have research interests in estuarine and fluvial geomorphology, paleohydrology and sedimentology, paleoecology, biogeochemistry (stable isotopes), alluvial geoarchaeology, and Quaternary landscape/geomorphic evolution.

I have specific research interests in the reconstruction of Holocene relative sea-level and estuarine paleosalinity (and paleo-river discharge); and in the reconstruction of mid-late Holocene climate variability using various geomorphic, paleoecological and biogeochemical proxy records.


Qualifications

- BSc Geology, Uni of Derby 1999
- MSc (with Distinction) Environmental Sedimentology and Geomorphology, Uni of Reading 2001. Dissertation advisors: Dr D. Lawrence and Prof J.R.L. Allen.
- PhD Geography, Exeter Uni 2009. Thesis: "Palaeosalinity change in the Taw Estuary, south-west England: response to late Holocene river discharge and relative sea-level change". Thesis advisors: Prof T. Brown, Prof C. Caseldine and Dr J. Jordan. 


Description of recent postdoctoral research (I was a Smithsonian Postdoctoral Fellow from April 2009 - August 2011).

Research project: “Diatom distribution and δ13C variability along the Patuxent River Estuary: environmental controls and implications for reconstructing Holocene paleosalinity and river discharge”. This study uses both variation in marsh sediment δ13C and the contemporary distribution and salinity preferences of diatoms along the Patuxent Estuary salinity gradient to quantitatively reconstruct paleosalinity in a dated Holocene sediment core.

Seven tidal marshes were investigated in the Patuxent River Estuary, a sub-estuary of Chesapeake Bay with marshes located in freshwater tidal, oligohaline and mesohaline environments, enabling diatom communities to be identified within a range of salinity regimes. Samples were taken from the marsh sediment surface (from tidal flat, low marsh and high marsh altitudes) sequentially over a 12 month period, so as to incorporate a range of seasonal and hydrological conditions. A range of environmental variables were measured at each site, including salinity, altitude in the tidal frame, nutrient concentration, sediment organic matter content, pH and sediment grain size. Variation in marsh sediment δ13C, δ15N and C/N was also examined along the salinity gradient of the estuary. The δ13C value of organic marsh sediment is a reflection of the relative proportion of C3 vs C4 plants occupying the marsh surface, with C4 plants (e.g. Spartina spp.) becoming more abundant with increasing salinity. Vegetation surveys of each marsh enabled 52 vascular plant species to be identified. The δ13C, δ15N and C/N signature of each species was measured.

The first aim of this project was to determine the main environmental controls on diatom species distribution and marsh sediment δ13C variability in a microtidal estuary. Using canonical correspondence analysis (CCA), salinity was shown to be the variable that explained most of the variation, with the results of this project providing a modern analog of diatom-salinity and δ13C-salinity relationships. The second aim of the study is to produce a new late Holocene climate record based on changes in estuarine paleosalinity. The contemporary dataset is being used to calibrate diatom species and marsh sediment δ13C values to salinity. Predictive transfer functions are then being applied to the diatom and δ13C records of a Holocene marsh sediment core (sampled at 1 cm intervals) enabling paleosalinity to be quantitatively reconstructed for the last 3000 yrs. Changes in estuarine paleosalinity can be used to infer decadal-centennial scale fluctuations in late-Holocene river discharge, allowing a precipitation-driven climate record to be reconstructed for the eastern US mid-Atlantic region.