Macrofossil and Sediment Processing Laboratory

Science Center Objects

In the Macrofossil and sediment processing lab we analyze the physical, biological, and geochemical characteristics of peat and sediment samples collected from lake, wetland, and peat cores as proxies for past changes to these depositional environments on timescales of decades to millennia. We primarily study terrestrial wetland ecosystems from subtropical to arctic regions in order to understand how they have responded to changes in climate, sea level, and land-use changes. Recent study sites include peat bogs and permafrost plateaus in Alaska, forested swamps in Virginia, and mud islands in Florida Bay. All cores are collected manually. Depending on the depositional environment and types of information we hope to recover, we use a range of coring equipment, including Russian Corer, freeze corer, and vibracorer. In the field, each core is measured, photographed and described in our field log for later reference. Upon return from the field, all core sections are scanned on the GeoTek core logger and stored in our refrigerated core repository. Permafrost cores are kept frozen until they are sampled.

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Sphagnum moss leaves viewed under a microscope. 

Analyses in our Lab:

Loss-on-Ignition (LOI) analysis calculates the amount of organic material in a sediment sample by determining the amount of inorganic material remaining after the sample is combusted in a furnace. LOI is performed on volumetric wet samples in order to also obtain the bulk density of a sample.

Macrofossil analysis: Macrofossils are the remains of previously living plants that are large enough to be seen without the aid of a microscope. They can provide information about the types of plants living at the sampling location through time. As conditions changes, plant macrofossil assemblages change.  We perform plant macrofossil analysis using semi-quantitative methods that includes sieving a uniform quantity of peat or sediment through a 250-µm sieve. All remaining material on the sieve is washed into a petri dish and examined under a dissecting or compound microscopes to aid in taxonomic identification of the macrofossils. Individual specimens (seeds, leaves, needles, charcoal) are tallied, while relative percentages of the dominant the organic matter type (herbaceous, ligneous, humified) are recorded. Where needed, macrofossils are picked and cleaned for radiocarbon (age dating of sediments and peat) analysis.

Elemental analysis: We prepare and analyze organic sediments and peat for their carbon, nitrogen, and hydrogen composition to better understand carbon and nutrient cycling, changes in carbon density, and carbon accumulation rates in wetland sediments.

Stable isotope analysis: We prepare a range of sediment and peat types for stable isotope analysis to better understand processes from carbon and nutrient cycling (δ13C, δ15N) to Holocene hydroclimate (δ18O of peat cellulose).

Lab Capabilities:

  • Fume hood for acid digestion and cellulose extraction
  • Drying oven
  • Furnace
  • Mass balances (including microbalance)
  • Centrifuges
  • Freeze dryer