L3: Earth's glaciation legacy

How were glaciers distributed across Earth during the last glacial maximum?

Large areas of the mid- to high latitudes of the Northern Hemisphere were covered by continental ice sheets.

What is palaeo-glaciology?

Reconstructions of former ice cover.

What four ways can palaeo-glaciology be applied?

• Former ice sheet ‘footprint’ of flow (subglacial landforms)

• Former ice sheet margings (moraines, meltwater landforms)

• Former ice sheet thickness (trimlines)

• Dating (radiocarbon, surface exposure dating)

What is the subglacial footprint and how is this useful?

• Ice flow directional indicators (e.g., fluting, drumlins, mega-scale lineations).

• Form parallel to former ice flow direction.

• Record of glacier activity at cessation of glaciation (former ice sheet flow can be reconstructed).

How can moraines aid in climate reconstruction?

• Arcuate ridge formed at the margin of the moraine can tell us about ice extent.

• Geomorphic response to climate.

When was the last period of glacier growth?

The little ice age, approx. 150 years ago.

What is another powerful signal left by glaciation that can be used for climate reconstructions?

• Glacio-fluvial processes during deglaciation create meltwater streams (and subsequently rivers/lakes) that leave distinctive landforms.

What are trimlines and how can they inform reconstructions?

• Erosional mark in the landscape that can tell us about the height of the ice.

• Below the trimline, material will be glacially scoured/eroded whilst above the line it will be frost-shattered/weathered.

• Not always reliable.

In what four ways can glacial landscapes be dated?

• Optically stimulated luminescence (radiation exposure dating)

• errestrial cosmogenic radionuclides (radiometric dating)

• Radiocarbon (radiometric dating)

• Varve dating (annually banded records)

Summarise how each of the aforementioned methods can be used to reconstruct an ice sheet?

• Subglacial landforms → ice sheet ‘footprint’ of flow

• Moraines, meltwater landforms → ice sheet margins

• Trimlines → ice sheet thickness

• Radiocarbon/surface exposure dating → dating

How can multiple glaciations be differentiated from one another?

• Dating

• Intervening interglacial deposits

• Superimposition of tills → oldest at the bottom and newest at the top

• Freshness of landforms (morphostratigraphy = subdivision of landforms based on surface form) → fresher = younger

Why are older glaciations more difficult to reconstruct than recent ones (LGM and younger)?

• There is only a partial record of glacial landforms etc. due to erosion

• Overprinting of events (palimpsest)

What are periglacial environments?

Environments with conditions, processes, and landforms associated with cold, non-glacial landscapes regardless of their proximity to glaciers. Freeze-thaw processes.

What is permafrost?

Perenially frozen soil or bedrock. Develops where mean annual air temps are >0 degrees c (26% of Earth’s surface).

What are four examples of periglacial landforms?

• Patterned ground (sorted stripes and circles) → convection during freeze-thaw process

• Blockfield (felsenmeer) and tors → frost shattering (long periods of exposure)

• Pingos → growth of ice lens in former pond site

• Ice wedges → growth of vertical ice lenses in contraction tracks

What are two relicit periglacial features that can have palaeoclimatic inferences?

• Protalus ramparts → fossil snowpatches that formed under conditions colder than today.

• Ice-wedge casts → form by contraction and ice infill (subsequently infilled with sediment).

Infer the prescence of permafrost and severe winter ground cooling.

What are pluvial lakes?

Lakes related to wetter climate. Found in low-latitudes historically.

What are pluvials and interpluvials, and what can they indicate about Quaternary climate?

• Pluvials → lengthy periods of heavy rainfall

• Interpluvials → low water or dessication

• Indicate changes in moisture balance during the late Quaternary

What can sand dunes and loess infer about Quaternary climate in low latitudes?

• Sand dunes → past periods of increased aridity. Expansion of dunefields during glacials.

• Deposition of loess (wind-blown silt) with phases of aeolian activity (=cold stage) alternating with soil formation (=warm stage).