SITE SELECTION: CAVES, LAKES & MARSHES

• paleontological
• geochemical
• isotopic

AVAILABILITY:
Bog, Marsh and Lake studies predominate temperate and boreal regions
Cave studies are important in arid regions
INTERPRETATION: Proxy Indicator = f(P,D,R,I)
Production Dispersal pReservation Identification/Measurement
PDR Taphonomy: how an "organism" becomes part of the fossil record
MULTI-PROXY: pollen, macrofossils, charcoal, isotopes ...
RESOLUTION: completness, mixing, rate
SOURCE of Proxy
• Autochthonous: from within the cave - lake
  
• Allochthonous: from the region surrounding the cave - lake
  Transport
  • aeolean
  • aquatic
    
    

AQUATIC SEDIMENTS: LAKES, and MARSHES
• lake sediments provide a historical record for both watershed and lake
• bog & marsh organic sediments mostly autochthonous (airborne)
• lakes mostly allochthonous (waterborne)
  • deltas
  • sediment focusing (lake center)
• preservation excellent (cold, anoxic, invariant)

PALEOLIMNOLOGY: the study of the history of changes of lake properties
Classification of lakes (modern limnology):
a. seasonal history of overturn: dimictic, holomictic, amictic
• layers of lake separated by density gradient (pyconcline)
• upper layer (epilimnion) over lower (hypolmnion)
• separated by thermocline (chemocline, pycnocline)
  
b. productivity

• eutrophic (productive, green, stinky)
  
• oligotrophic (clear fresh)
  
Subdivisions of lakes (modern limnology):
• litoral: shallow water at lakes edge
  
• pelagic: deep water
  
• benthic: lake bottom
  

PALEOECOLOGY: possible to reconstruct the entire aquatic community, from producers (algae, aquatic flowering plants) through primary consumers (mollusks, ostracods), secondary consumers (cladocera), and tertiary consumers (fish).
succession: oligotrophic, eutrophic, bog, meadow
interaction of aquatic and terrestrial ecosystem


PALEOCLIMATOLOGY: the effect of local (watershed) environment on lake properties
• precipitation: lake level, salinity, alkalinity
  
• temperature: productivity, lake level
  
• run off: nutrients, organic matter
  



Methods of lake-sidement study

1. Palynology: Pollen and spores of aquatic and wet-ground plants e.g., sedges, pondweed, and riparian trees.
examples
Myriophyllum and Pediastrum indicate higher lake level at Pecks Lake, AZ

Bingham Cienega: Ash and bullrush expands after charcoal declines


2. Macrofossil analysis: Aquatic and wetground plants. examples
Lake Cleveland: wetground plants most abundant during mid-Holocene because lower lake level exposed littoral shelf


3. Aquatic Insects: Abundances controlled by water depth, temperature


Cadis Fly


Chironomid

4. Cladocera: Abundances controlled by lake chemistry, productivity, nutrients, and pH,

Web Site
5. Ostracods: Valves used to study water chemistry

The Ostracodologist
6. Diatoms: siliceous algae
Water depth, water temperature, water chemistry


centric

pinnate


7. Mollusks calcareous snails (gastropods) clams (bivalves)
lake level, water salinity, pH, temperature, oxygen isotopes.

8. Fish scales (bones usually dissolve)
Annual rings in scales can indicate age structure, health


9. Geochemical Analyses:

1. Weight-loss-on-ignition
   
   1. dry sample at 50 ^oC
      
   2. "burn" at 550 ^oC: % O.M. Carbon = % Wt Loss / 2
      
   3. "burn" at 900 ^oC: % CO₃ carbon = 2.27 x % Wt Loss
      
2. C-H-N analyzer (900 ^oC) + chromatography
   1. autochthonous: productivity (eutrophic - oligotrophic) of the lake
      
   2. allochthonous: fertilization, preservation
      
3. Lake Nutrients: PO₄, NO₃ e.g., (Edmondson, 1972)
   
4. Heavy Metals: pollution from lead, iron, copper used to date historic and prehistoric sediments. ¹³⁷Cs maximum in 1963 from atmospheric bomb testing
   

10. Fossil pigments: (Gorham and Sanger, 1972)

1. Specific pigments, e.g., oscillaxanthin (Oscillatoria), have been used to detect the presence of a particular indicator organism. [Marker Pigments]
   
   
2. Pigment concentration has been used to reconstruct productivity, since pigment preservation is best in the anaerobic hypolimnion of a highly productive lake.
   
   
3. Chlorophylloid / carotenoid ratios have also been used to reconstruct productivity since carotenoids are more resistant to break down
   
   
4. Pigment diversity has been used to indicate the relative importance of allochthonous vs. autochthonous input since the pigment diversity is low in allochthonous O.M.
   
   
5. Carotenoid ratios have also been used to indicate the relative importance of allochthonous vs. autochthonous input. beta-carotene (epiphasic( and leutine (hypophasic) are the most common carotenoids in forest litter. ratios of leutine to total hypophasic and beta-carotene to total epiphasic carotenoids indicate relative allochthonous input.
   
   
6. Lignin degradation products (e.g., vanillans)
   Produced by wood decay, used to indicate the presence of trees in the watershed e.g., L. Washington (Leopold et al., 1982) the lack of vanillans indicate treeless vegetation, but the sediment contains abundant tree pollen
   
   
7. "Biomarkers" (e.g., Barium)
   Marine       Freshwater


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