Sb lakes intro pt1

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  1. 1. Lakes an introduction
  2. 2. Kettle Lakes in Glacial Outwash
  3. 3. Ephemeral lake on the Great plains
  4. 4. 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
  5. 5. Major Lake Types Tectonic lakes basins formed by movements of the earths crust. Ex. Lake Tanganyika Ex. Eagle lake, CA
  6. 6. Major Lake Types Glacial lakes most common lake origin due to erosion and deposition associated with glacial ice movements.
  7. 7. II. Lakes as Archives of environmental change
  8. 8. Direct Precipitation Runoff What comes in? Water
  9. 9. Organic matter Sediments Pollen Material from the landscape
  10. 10. Organic matter SedimentsBiota Material produced within the lake
  11. 11. Two primary environmental or climate changes Precipitation/Evaporation Temperature That may initiate some response in the environment that may be recorded by lakes
  12. 12. 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
  13. 13. For example recent lake level changes in Great Salt Lake
  14. 14. And these are slight compared to ancient changes. Compare Great Salt Lake to Lake Bonneville
  15. 15. Little Mountain Shorelines Bothwell, Utah
  16. 16. 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
  17. 17. 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)
  18. 18. Paleolim 591L Core Lithology-PG1351 Silty-Clastic Layer Massive Grey Silty Clay Brownish-Grey Silty ClayOlive-Grey Laminae Deposited under anoxic conditions i.e. Glacial-type climate Lithology Depth(cm) Unit Olive-Grey Silty Clay Massive Interglacial-type sediments UnitUnit Sandy Layer Depth: 385 cm
  19. 19. Sedimentology Down-Core Sediment Properties
  20. 20. Sedimentology Down-Core Sediment Properties
  21. 21. Pollen data from Whitehead and Chrisman, 1979 FOSSIL POLLEN from BERRY POND, MASSACHUSETTS
  22. 22. 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.
  23. 23. 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.
  24. 24. Diatoms single celled algae with a shell made of silica, sensitive to salinity and pH
  25. 25. Walden Pond
  26. 26. Ostracodes small crustaceans Can also analyze shell chemistry
  27. 27. Chironomids midges, most common aquatic insect
  28. 28. Chitinous head carapaces preserved in sediemnts
  29. 29. Pollen
  30. 30. Example The Younger Dryas cold period
  31. 31. named after an indicator genus, the alpine- tundra wildflower Dryas octopetala