Holocene vegetation reconstruction
- Proxies
Preserved physical characteristics of the past that stand in for direct
meteorological measurements
Allow for the reconstruction of climatic conditions over a longer fraction of
the Earth’s history
Ideal Proxies:
- Sensititve too environmental change
- Highly mobile
- Abundant and well preserved fossil record
- Readily identifiable to species level
- Narrow ecological tolerances
Diatoms
- Microscopic, unicellular algae
- Secrete a siliceous shell - ‘frustule’
- Frustule can range in length from 5 um to 2
mm, depending on species
- Frustule composed of an amorphous hydrated
silica, which enhances preservation potential
Frustule
- Composed of 2 overlapping valves or thecae, the larger – epitheca –
fitting over the smaller – hypotheca – like a pill box
- Valves linked by connecting of girdle bands
- Commonly circular or ellipitcal to rod-like
- Often perforated by tiny apertures
- Other surface features: ribs, canals, reticulations
Where are diatoms
, - Found in range of aqueous to sub-aqueous environments (oceans,
lakes, peat bogs, etc)
- limited to photic zones of water bodies (where light is)
- Distribution of diatom species is determined by:
salinity,
aciditiy,
temperature,
o2
nitrogren availability
Fresh water species are particularly affected by salinity, pH, and tropic
conditions
Marine species are affected by sea surface temperatures, nutrient
availability and the structure of the ocean
Diatoms are best preserved in fine-grained sediments, not susceptible to
oxidising and are fragile
Problems of diatoms
- Mixing of assemblages
- Light and easily transported
- Estuarine sediments contain a mixture of marine, brackish and
freshwater species
- Lacustrine sediments contain species from the lake and ones
transported into the lake
- Stronger frustules are preserved in greater quanitites than fragile
valves
Diatom salinity preference classification
The halobian system
- Polyhalobous (marine): thrive in salt water
- Mesohalobous (brackish) thrive in slightly salty water (0.2% - 30%)
- Oligohalobous (freshwater) - lakes and rivers (<0.2%)
- Halophobous – can't tolerate salty water at all
Sea-level variations
- Proxies
Preserved physical characteristics of the past that stand in for direct
meteorological measurements
Allow for the reconstruction of climatic conditions over a longer fraction of
the Earth’s history
Ideal Proxies:
- Sensititve too environmental change
- Highly mobile
- Abundant and well preserved fossil record
- Readily identifiable to species level
- Narrow ecological tolerances
Diatoms
- Microscopic, unicellular algae
- Secrete a siliceous shell - ‘frustule’
- Frustule can range in length from 5 um to 2
mm, depending on species
- Frustule composed of an amorphous hydrated
silica, which enhances preservation potential
Frustule
- Composed of 2 overlapping valves or thecae, the larger – epitheca –
fitting over the smaller – hypotheca – like a pill box
- Valves linked by connecting of girdle bands
- Commonly circular or ellipitcal to rod-like
- Often perforated by tiny apertures
- Other surface features: ribs, canals, reticulations
Where are diatoms
, - Found in range of aqueous to sub-aqueous environments (oceans,
lakes, peat bogs, etc)
- limited to photic zones of water bodies (where light is)
- Distribution of diatom species is determined by:
salinity,
aciditiy,
temperature,
o2
nitrogren availability
Fresh water species are particularly affected by salinity, pH, and tropic
conditions
Marine species are affected by sea surface temperatures, nutrient
availability and the structure of the ocean
Diatoms are best preserved in fine-grained sediments, not susceptible to
oxidising and are fragile
Problems of diatoms
- Mixing of assemblages
- Light and easily transported
- Estuarine sediments contain a mixture of marine, brackish and
freshwater species
- Lacustrine sediments contain species from the lake and ones
transported into the lake
- Stronger frustules are preserved in greater quanitites than fragile
valves
Diatom salinity preference classification
The halobian system
- Polyhalobous (marine): thrive in salt water
- Mesohalobous (brackish) thrive in slightly salty water (0.2% - 30%)
- Oligohalobous (freshwater) - lakes and rivers (<0.2%)
- Halophobous – can't tolerate salty water at all
Sea-level variations
