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.

before
after
Download images

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.

 

 

 

Chemical and geochemical preparation of samples:

  • Acid digestion – dissolves a sample in a dilution of hydrochloric acid (HCl) to remove any inorganic carbon present in the sample in preparation for elemental or isotope analysis.
  • Elemental Analysis – a CE Thermoscientific FlashSmart elemental analyzer is used to determine the weight and percent composition of the elements carbon, hydrogen, and nitrogen that are present in a sample.
  • Cellulose extraction – isolates cellulose from plant macrofossils for the purpose of performing isotope analysis on the extracted cellulose.  This process includes chemical and physical treatments requiring specialized equipment such as a centrifuge, chemical fume hood, and freeze-dryer.