Evidence for past climates L2- L5 Flashcards
LANDFORMS - Glacial cirques
Glacial cirques are concave landforms formed at the sources of mountain glaciers
How are glacial cirques formed? (2)
1) Hollows are sheltered from heat - leads to accumulation of snow and ice and ultimately glaciers; enlarged by freeze-thaw weathering and glacial erosion
How are glacial cirques used in climate reconstruction?
Ancient snowlines can be compared with present day snowlines, and temperature changes calculated
What is crag and tail?
Asymmetric hills
How do crag and tail form?
C+& are formed by the inflow of glacial sediments into a cavity produced in the lee of the rock obstruction, and hence have tails composed of unconsolidated sediments.
What are morraine’s?
any accumulation of unconsolidated debris, sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice sheet.
What are drumlins?
Oval mounds of glacial till, elongated parallel to the axis of ice flow.
How do drumlins form?
formed by a successive build of sediment to create the hill (ie deposition or accretion)
What are eskers?
sinuous ridges of glacial-deposited material
How do eskers form?
when sediment carried by glacial meltwater gets deposited in subglacial tunnels,
what are kames?
mounds of glacial deposited material
how do kames form?
deposited on depressions on ice of retreating glacier, deposited on land as ice melts
What are tuyas?
A tuya is a flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are rare worldwide, being confined to regions which were covered by glaciers and had active volcanism during the same period.
what are the sub-glacial characteristics of a tuya?
Steep sided (magma under ice cools quickly and doesn’t flow far) with magma characteristics associated with subaqueous environment.
what are the sub-aerial characteristics of a tuya?
flat lying lavas of a lava pond, with magma characteristics associated with eruption in air.
what are deserts?
Accumulations of wind-blown particulates
How do deserts form?
Large continental sand dunes only develop where precipitation is <100 mm a-1
If precipitation >100 mm a-1, vegetation cover reduces sand movement and encourages soil development
How are deserts used on climate reconstruction?
Fossil sand dunes currently found in areas of high rainfall indicate that rainfall has increased since dune formation
What is palynology?
the study of plant pollen, spores and certain microscopic plankton organisms (collectively termed palynomorphs) in both living and fossil form.
how is palynology used in climate reconstruction?
- Sediments may contain pollen grains (palynomorphs) derived from local/regional vegetation; analysis of abundance/type of pollen grains provides a picture of vegetation at the time of deposition.
- Different types of vegetation are specific to different temperature zones, e.g. palm trees versus tundra
What are diatoms?
A diatom is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world.
How are diatoms used in climate reconstruction?
- Diatoms preserved in lake/ocean sediments;
- Sensitive to different environmental conditions reflected in variations in species abundance
- analysis of abundance/type provides a picture of water quality (e.g. salinity, nutrients, temperature) at time of deposition (fall to ground… core)
CASE STUDY: use of diatoms in Tanginika - what was the purpose?
to reconstruct late holocene climate (meeker et al)
CASE STUDY: Tanginika - what was the project?
- 109 m length lake core
- Location in lake chosen where shielded from terrigenous input
- Radiocarbon dating still to be undertaken
- Core sampled at 5 cm intervals, species abundance noted.
