sb lakes intro pt1
TRANSCRIPT
Lakes an introduction
Kettle Lakes in Glacial Outwash
Ephemeral lake on the Great plains
Major Lake Types• Volcanic lakes
– basaltic so relatively unproductive because nutrient concentrations are low.
– Two types: • Maars - small depressions in
craters of explosive origin resulting from lava coming into contact with groundwater or degassing of magma;
• Caldera - formed by collapse of the roof of partially empty magma chamber.
Big Soda lake, NV
Crater Lake, OR
Major Lake Types
• Tectonic lakes – basins formed by
movements of the earth’s crust.
• Ex. Lake Tanganyika• Ex. Eagle lake, CA
Major Lake Types• Glacial lakes
– most common lake origin due to erosion and deposition associated with glacial ice movements.
II. Lakes as Archives of environmental change
Direct Precipitation
Runoff
What comes in? Water
Organic matter Sediments
Pollen
Material from the landscape
Organic matter Sediments Biota
Material produced within the lake
Two primary environmental or climate changes
• Precipitation/Evaporation• Temperature
That may initiate some response in the environment that may be recorded by lakes
Possible lake responses to climate• Physical
– Change in water balance and lake level– Change in sediments delivered to lake
• Biological– Diatom assemblages– Ostracode assemblages– Insects, e.g. chironomids
• Chemical– Isotopic ratios of lake water, e.g. D/H– Change in salinity
For example – recent lake level changes in Great Salt Lake
And these are slight compared
to ancient changes.
Compare Great Salt Lake to Lake Bonneville
Little Mountain Shorelines – Bothwell, Utah
Major shorelines of Lake Bonneville and the early Great Salt Lake
Shoreline Name
Elevation*** at Antelope
Island
Approximate Age in Calendar
Years before Present
Gilbert* 4,275 12,800 - 11,600
Provo** 4,840 16,800 - 16,200
Bonneville** 5,220 18,000 - 16,800
Stansbury** 4,445 24,400 - 23,200
* Great Salt Lake shoreline ** Lake Bonneville shoreline ***Feet above mean sea level
Change in Sediments• Lithostratigraphy
– Color, grain size, bedding, structures
– Etc.• Water content• Petrographic examination
and x-ray• Image Analysis• Phys. Properties
– Magnetic suspectibility– GRAPE (gamma ray
attenuation (density)
Paleolim 591L
Core Lithology-PG1351
Silty-Clastic Layer
Massive Grey Silty Clay Brownish-Grey Silty ClayOlive-Grey Laminae
Deposited under anoxic conditionsi.e. Glacial-type climate
LithologyD
epth
(cm
)
UnitOlive-Grey Silty Clay
Massive Interglacial-type sediments
UnitUnit
Sandy Layer
Depth: 385 cm
SedimentologyDown-Core Sediment Properties
SedimentologyDown-Core Sediment Properties
Pollen data from Whitehead and Chrisman, 1979
FOSSIL POLLEN from BERRY POND, MASSACHUSETTS
Paleoclimatogical reconstructions based on biota
• Based on the concept of ecological niche (a given population is adapted to survive and reproduce under a set of biotic and abiotic conditions).
• A niche can be devised as a multi-dimensional space in which the axes represent variables.
• In paleoclimatology, useful species are those with limited niches; whose abundance, distribution, and presence or absence are controlled by climatic factors.
• However, one needs to keep in mind that niches are dynamic and transient and that species can evolve and adapt.
Diatoms – single celled algae with a ‘shell’ made of silica, sensitive to
salinity and pH
Walden Pond
Ostracodes – small crustaceans
Can also analyze shell chemistry
Chironomids – midges, most common aquatic insect
Chitinous head carapaces preserved in sediemnts
Pollen
Example – The Younger Dryas cold period
named after an indicator genus, the alpine-tundra wildflower Dryas octopetala