Earth Science 10: Antarctica

Latitude

angular measure of how far North or South a location is from the equator

Longitude

angular measure of how far North or South a location is from the Prime Meridian

Contour Lines

- show elevation 2D map

- connects all points that have the same elevation

- when the lines get closer together the ground is steeper

What is a map? and 3 basic map projection schemes

A map is a 2D projection of a 3D globe. 3 basic map projections schemes

1) Cylindrical projections

2) Conic projections

3) Azimuthal projections

East Antarctic Ice Sheet

- Terrestrial ice sheet

- 60m sea level equivalent

West Antarctic Ice Sheet

- Marine based ice sheet

- 6m sea level equivalent

Drainage Basin View of Antarctica

the topography of Antartica influences the size and distrubution of the ice sheets. East Antarctic ice sheet, West Antarctic ice sheet, Antarctic Peninsula Ice Sheet

Ice Sheet

massive land-based glacier

• west Antartica and east Antartica are separated by mountain range

• e.a ice sheet is much thicker

becomes a glacier when covering more than 50k km²

Underlying topography

influences size and sheet of ice sheets

Terrestrial Ice Sheet and Marine-based Ice Sheet

Terrestrial Ice Sheet: bed of ice is mostly above sea level

Marine-based Ice Sheet: bed of ice is mostly sea level

• more susceptible to melting from a warming/rising ocean

Transantartic Mountains

• 3500 km long

• important geologic boundary

• splits east & west ice sheets

Ellsworth Mountains

• highest mountains in Antartica

• highest peak - Vinson Massif

Major Seas

Weddel Sea - adjacent to Antarctic Peninsula, includes the Ronnie ice shelf

Ross Sea - includes the ross ice shelf

Surrounding Ocean - Antarctica is surrounded by the Southern Ocean, the crossing between the tip of South America and the Antarctic Peninsula is called the Drake Passage

Ice Shelves

• floating extensions of ice sheets

• attached to ice sheet but no longer resting on land

• the grounding line separates an ice sheet from an ice shelf

Antarctic Ice Shelves

Ross Ice Shelf

Ronne Ice Shelf

Amery Ice Shelf

Iceberg

formed when an ice shelf towers out of the water and breaks

Antarctica Sea Ice

• crucial for life on antarctica

  • provides food(algae) and shelter(penguins/seals)

• forms from the surface of the sea freezing

• grows thick by accumulation, repetitive freezing, and snow accumulation

• in the winter, continent doubles in size due to sea ice growth

First to arrive? to Antarctica

Polynesian people: oral history suggest that Hui Te Rangiora of Rarotanga (Cook Islands) sailed south at ~750 CE & hit Ice

• by canoe

• debated and no archeological evidence

Ancient Hypothesis: Terra Australis exists.

Ptolemy (2nd century ce): North vs. South land masses should balance. Africa may extend to South Pole

First Oceanographer

James Cook, a commander in the British Royal Navy led 3 voyages(1768-1780) across the globe.

• charted New Zealand and the Great Barrier Reef, Tonga and easter islands

• sampled marine life, plants, and animals

The first expedition to reach the South Pole was led by _____, followed shortly thereafter by the expedition led by ____

Roald Amundsen then Robert Scott

Kontinentalverschiebung

continental drift: hypothesis that continents were mobile based on:

1) fit of continents

2) glaciations at low latitudes

3) Paleoclimate belts

4) fossil distribution

5) rocks matching across oceans

Crust

thin rocky shell that we walk around

• continental (high elevation)

• oceanic(low elevation)

Mantle

made of solid silicate rock … but certain areas can flow

Core

made of metallic iron/nickel

• outer core(fluid) = liquid

  • due to high heat

• inner core(rigid) = solid

  • rigid due to high pressure

4 main physical layers

• lithosphere

• asthenosphere

• mesosphere

• core

Lithosphere(rigid)

• cold rigid outer shell (~100km thick)

• includes crust and upper mantle

lithospheric plates move atop the ductile Asthenosphere

Asthenosphere(plastic)

• hot, ductile layer that flows with a high viscosity

• extends from base of the lithosphere to ~700km deep

Mesosphere(rigid)

• rigid due to increased pressure at depth

Divergent Plate Boundaries

• mid-ocean ridges

• continental rifts

new lithosphere is created via the process of spreading/rifting

Formation of ocean crust?

in a mid-ocean ridge (spreading center), molten rock arises from the mantle and forms new oceanic crust. this then moves apart, allowing newer oceanic crust to be formed

Youngest seafloor rocks are closet to what?

spreading centers

How to create an ocean basin

1) Upwarping

2) Rift Valley (ex: Great Rift Valley in East Africa)

3) Linear Sea (ex: the Red Sea)

4) Mid-ocean Ridge in fully fledged ocean basin

Convergent Boundaries

• subduction zones

Ocean-Continent Convergence

• Ocean crust subjects beneath a continent

• Continental volcanic arc forms

ocean crust (denser) subducts beneath continental crust (less dense)

deep trench forms at collision zone

volcanoes form on continent above the subductin plate

• subduction leads to magma generation

Oceanic-Oceanic convergence

• Ocean crust subduction beneath ocean crust

• Ocean volcanic island arc forms

more dense oceanic crust subduction beneath less dense oceanic crust

deep trench forms at collision zone

volcanic island arc forms on overriding plate

Continent-Continent convergence

• continental crust collides

• neither plate fully subjects, mountains form

Transform Boundaries

• San Andreas fault, etc

• Oceanic transform faults

Oceanic Transform faults

spreading centers don’t form in a perfect line

where they are offset, oceanic transform faults occur

The vast majority of the Antarctic plate is surrounded by _____ in the form of _____

divergent boundaries, mid-ocean ridges

Continental Transform faults

• occurs when two plates move past another

• example: the san Andreas fault

South Sandwich Islands

example of a volcanic island arc

formed by oceanic-oceanic convergence

• trench also present

What large mountain ranges of West Antarctica was formed during rifting?

• Transantarctic Mountains

• Ellsworth Mountains

Continental Margins

location where oceanic crust meets continent crust

Active continental margin

Left Side of the image

• oceanic plate subjecting beneath the continent

Passive continental margin

Right Side of the image

• Oceanic lithosphere and continental lithosphere are attached

  • no tectonic plate motin between continent and ocean lithosphere

• most of antarctica has passive margins

  • an exception is the northern tip of the antarctic peninsula

Time Scale 4 units ranking: largest to smallest

Eons

Era

Period

Epoch

these divisions are largely based on fossil evidence of the evolution of life and the timing of mass extinctions

When did the Earth form?

~4.6 billions year ago

When did the Cambrian Explosion happen?

~540 million years ago

When did the first mammals exist?

~220 ma

When did the avian dinosaurs go extinct?

66 millions year ago

When did the first Homo sapiens exist?

300k years ago

When did the first ancient civilizations & cities exist?

~5k years ago

Absolute Dating

using radioactive isotopes to determine when a rock/substance formed

Relative Dating

using the spatial relationships between geologic features to the sequence of geologic events

Index fossils

using specific fossils of a known age to determine when a rock was deposited

fossil: evidence of prehistoric life

fossilized organisms sucked each other through time in a definite and recognizable order. Therefore relative ages of rocks can be recognized based on their fossil content

Index Fossil: a fossil that indicates the age of the rocks containing it

Body Fossils

fossil remnant showing the body of an organism

Trace Fossils

Fossil remnant showing the behavior of an organism

• footprint, burrow, trail, or other “trace” of an organism

nearly all fossils are preserved within sedimentary rocks

Igneous rocks

rocks that form from the solidification of molten rock

• Form at volcanoes or in magma chambers

  • Common igneous rocks: Granite, basalt, rhyolite, Andesite, and many many more

Typically associated with subduction zones and rifts

Sedimentary rocks

form from the lithification (lithos = rock) of sediment

• Form within basins (large sediment traps/catchments)

  • Common sedimentary rocks: Sandstone, mudstone, limestone (i.e. coral reefs), and many more

• Associated with oceans, lakes, rivers

Metamorphic rocks

rocks that form due to high heat and pressure within the earth

• Form deep within the earth or at convergent tectonic boundaries

  • Gneiss, Schist, Marble, and many more

• Presence of metamorphic rocks at surface usually indicates large

mountain building events

Water molecules have ____ polarity

electrical

because both H atoms are on the same side of the molecule, the electrical charge of the molecule is unevenly distributed

Cryosphere

regions of Earth’s surface where water is in the solid form

• includes sea ice, lake ice, river ice, snow cover, glaciers, ice caps, ice sheets, and frozen ground(permafrost)

• The cryosphere participates in many climate feedback loops

  • solar energy absorption/reflection

  • cloud creation and precipitation

  • atmospheric/ocean circulation

Antarctica is Earth’s largest reservoir of continental

ice

Katabatic Wind

Pushes sea ice away from the ice shelf because they occur when the slope surface is cold, cooling the air making it more dense than the air at the bottom of the slope.

Polyna

the space between the ice shelf and the sea ice

Glacier

a slowly moving mass of ice that forms from the accumulation and compaction of snow

• grows when more snow accumulates in winter than melts in summer

• as many layers of snow accumulate, those at the bottom compress and turn into ice

How to make a glacier?

accumulation of snow - more snow accumulates in winter than melts in summer, requires

• lots of snow

• low summer temperatures

• gentle slope

• protected from wind

after the snow accumulates

• burial

• compaction

• recrystalization

Mountain glacier

Glacial systems that form in the valleys of mountain ranges

multiple types: valley, tidewater, Piedmont, rock, and hanging glacier

Valley Glacier

a major outflowing glacier of a mountain glacier system

Tidewater glacier

Mountain/valley glacier that end in the ocean

Piedmont glacier

a steep mountain/valley glacier that spills and spreads into flat plains

Hanging glacier

a “stranded” glacier that ends at a steep cliff

Rock glacier

a mountain glacier composed of more rock than ice

Ice Cap

continental glacier covering less than 50k km²

Ice flows because?

gravity

2 flow drivers:

1) ice will flow downhill

• primary driver of mountain glacier

2) ice wants to flatten out

• driver of ice sheets

Brittle Zone

Ice flows via fracturing/breaking

Plastic zone

ice flows via ductile deformation

Basil slip

ice “slips” atop underlying bedrock

Brittle zone - Crevasses

crevasses are cracks in the upper part of the glacier

brittle fracturing that form as ice flows

fractures mark topographic changes of underlying bedrock

Ice Fall

if underlying topography gets very steep

Ductile flow (aka internal deformation)

glacial movements accommodated by the shape change of ice crystals

Basil Slip

base of glacier slides across bedrock

• often aided by melting at glacier/rock interface

What typically exhibits ductile flow and minimal basal slip?

Polar glaciers

What typically exhibit ductile flow + basal slip?

Temperate glaciers

Why might water melt at the base of a glacier

hydrogen bonds

regelation- pressure melting of ice

Where do glaciers flow the fastest?

Fastest = top-middle

Terminus

End of the glacier

• point where flow of glacier cannot keep balance within ablation

Calving

the process where large pieces of ice break off from the edge of glaciers, ice shelves, and ice fronts, forming new icebergs that then drift into the ocean

Ice Stream

sharp margins and can move much faster than the surrounding ice

In antarctica, 90% of ice and sediment discharge happens through ice streams

• most ice shelves are fed by ice streams

Zone of accumulation

snowfall

Zone of ablation

• melting

• calving

• sublimation

Equilibrium line

elevation where accumulation and ablation (loss) are equal

Abrasion

rock debris in base scrapes the bed

• striations

• grooves

• polished surfaces

Plucking

glacier freezing to bed, moves pulls fragments away

• fractures facilitate this process

• chattermarks: depressions carved from the removing of rock flakes

U-Shaped valleys

rivers form v-shaped valleys, or gorges or canyons

glaciers create U-shaped valleys

Moraines

Glacial moraines are accumulations of rock/debris at the edges, or within, a glacier

sediment in moraines are often angular, highlighting they weren’t transported by rivers

mapping ___, we can learn about where ice sheets extended to in the past

moraines

Cirques

Bowl-shaped, amptitheatre- like depressions formed at the accumulation zone of a glacier

Erratics

a boulder that is out of place

• studying erratics led to Ice Age discovery