Earth 104 Exam #2
Describe a glacial valley (u-shaped). How does it form?
V-shaped valleys become U-shaped valleys (glacial trough)
What is a glacial period and an interglacial period?
Glacial periods: individual pulses of cold climate within a long-term ice age Interglacial periods: intermittent warm periods within a long-term ice age.
What is the likely culprit?
Increased temperatures and increased co2
What tectonic changes brought to the presence of ice sheets in Antarctica?
Allowed the Tasman-Antarctic and Drake Passages to open. Allowing a circumpolar current to form
What are outwash plains? What kind of sediments do they deposit?
As the end moraine forms, meltwater leaves the ice in fast streams that carry huge amount of sediment, deposited as stratified drift
What is the role of the presence of sea ice around Antarctica in ice sheet development and preservation?
Sea Ice keeps the air above the ocean cooler. (Ex: It keeps 0º water from transferring heat to a -30º air mass)
What are the predictions in terms of sea level change?
Sea levels rising - total of 79 m
In which hemisphere did ice appear first during the Cenozoic? Why?
Southern Hemisphere. Antarctica is surrounded by water and is much higher in elevation than the Arctic.
What are the main characteristics of the West Antarctic Ice Sheet?
Wet bottomed. 5-6m sea level change. Relies on Ice Shelves to help support it.
What was the Last Glacial Maximum (LMG) and when did it occur?
Wisconsin Episode began about 30,000 ya, reached its greatest advance 21,000 ya, and ended about 10,000 ya
How did the current ice age start? What were the conditions leading to it?
World's climate cooled - cool summer, mild winter Winter period become longer and shorter summers, so less melting Snowfalls accumulated as ice
North Atlantic Deep Water
a deep water mass formed in the North Atlantic Ocean. Water flowing northward from the Gulf Stream becomes modified through evaporation and mixing with other water masses, leading to increased salinity. - When this water reaches the North Atlantic it cools and sinks through convection, due to its decreased temperature and increased salinity resulting in increased density
Oligocene
a geologic epoch that extends from about 33.9 million to 23 million years before present
Fjord
a long, narrow inlet with steep sides or cliffs, created by glacial erosion
Greenhouse Earth
a period in which there are no continental glaciers whatsoever on the planet, the levels of carbon dioxide and other greenhouse gases (such as water vapor and methane) are high, and sea surface temperatures (SSTs) range from 28 °C (82.4 °F) in the tropics to 0 °C (32 °F) in the polar regions
What is an ice age?
a period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental and polar ice sheets and alpine glaciers
Gulf Stream
a powerful, warm, and swift Atlantic ocean current that originates at the tip of Florida, and follows the eastern coastlines of the United States and Newfoundland before crossing the Atlantic Ocean
Antarctic Bottom Water
a type of water mass in the Southern Ocean surrounding Antarctica with temperatures ranging from -0.8 to 2 °C (31 °F), salinities from 34.6 to 34.7psu. Being the densest water mass of the World Ocean, AABW is found to occupy the depth range below 4000 m of all ocean basins that have a connection to the Southern Ocean at that level
Erosion
actions of exogenic processes (such as water flow or wind) which remove soil and rock from one location on the Earth's crust, then transport it to another location where it is deposited
What is glacial drift? What are till and stratified drift?
all sediments of glacial origin that deposit when ice melts - Till: material deposited directly by the glacier (unsorted) -Stratified drift: sediment deposited by meltwater (sorted)
What are Marine Isotope Stages?
alternating warm and cool periods in Earth's paleoclimate deduced from oxygen isotope data Odd numbers (low δ18O) = WARM starting with the Holocene (1) (5,7)... previous interglacials (3) = mid-Wisconsin "interstadial" Even numbers (high δ18O) = COLD starting with LGM of Wisconsin Glaciation (2)
ACC or Antarctic Circumpolar Current or West Wind Drift
an ocean current that flows clockwise from west to east around Antarctica
Marine isotope stages
are alternating warm and cool periods in the Earth's paleoclimate, deduced from oxygen isotope data reflecting changes in temperature derived from data from deep sea core samples. The data are derived from pollen and foraminifera (plankton) remains in drilled marine sediment cores, sapropels, and other data that reflect historic climate; these are called proxies
What is a recessional moraine?
are formed when the ice stands still and melts
What are fjords? Where are they found?
are glacial valleys that open to the sea
Dansgaard-Oeschger events
are rapid climate fluctuations that occurred 25 times during the last glacial period
End moraine
are ridges of unconsolidated debris deposited at the snout or end of the glacier. They usually reflect the shape of the glacier's terminus. End moraine size and shape are determined by whether the glacier is advancing, receding or at equilibrium. The longer the terminus of the glacier stays in one place, the more debris accumulate in the moraine. There are two types of end moraines: terminal and recessional
How is the CO2 trend in the last ~200yr?
as a gas at standard temperature and pressure and exists in Earth's atmosphere in this state, as a trace gas at a concentration of 0.04 per cent (400 ppm) by volume, as of 2014 INCREASED GREATLY
What are glacial erratics?
boulders found in till or lying free on the surface, different from bedrock
Rock flour
consists of fine-grained, silt-sized particles of rock, generated by mechanical grinding of bedrock by glacial erosion or by artificial grinding to a similar size. Because the material is very small, it becomes suspended in meltwater making the water appear cloudy, which is sometimes known as glacial milk
Conveyor belt circulation
constant motion in the ocean caused by a combination of thermohaline currents in the deep ocean and wind-driven currents on the surface. Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface
Stratified drift
drift that has been size-sorted by the water runoff of the melting glacier
What is a moraine? How are they formed? What is the difference between end moraines and ground moraines?
layers or ridges of till = forms along the sides of a glacier. As the glacier scrapes along, it tears off rock and soil from both sides of its path GROUND: Formed as till is deposited directly beneath a glacier • Formed as ice front retreats and leaves a flatter deposit • Located behind end moraines • Gently undulating lands
Terminal moraines
mark the maximum advance of the glacier. Recessional moraines are small ridges left as a glacier pauses during its retreat. After a glacier retreats, the end moraine may be destroyed by postglacial erosion
What was the Wisconsinan Glaciation?
most recent major advance of continental glaciers such as the Laurentide ice sheet
Recessional moraine
often observed as a series of transverse ridges running across a valley behind a terminal moraine. They are composed of unconsolidated debris deposited by the glacier. They are created during temporary halts in a glacier's retreat
Icehouse Earth
the earth as it experiences an ice age. An icehouse earth has ice sheets present, and these wax and wane throughout times, in glacial periods and interglacial periods. During an icehouse earth, greenhouse gases tend to be less abundant, and temperatures tend to be cooler globally. The Earth is currently in an icehouse stage, as ice sheets are present on both poles and glacial periods have occurred at regular intervals over the past million years.
What is glacial rebound?
the rise of land masses that were depressed by the huge weight of ice sheets during the last glacial period, through a process known as isostasy (state of gravitational equilibrium between the earth's lithosphere and asthenosphere such that the tectonic plates "float" at an elevation which depends on their thickness and density).
Ground moraine
till-covered areas with irregular topography and no ridges, often forming gently rolling hills or plains
What is the Laurentide Ice Sheet?
was a massive sheet of ice that covered hundreds of thousands of square miles, including most of Canada and a large portion of the northern United States, multiple times during Quaternary glacial epochs
Wisconsin glacial episode
was the most recent major advance of the North American ice sheet complex. This advance was synchronous with global glaciation during the last glacial period. The Wisconsin glaciation extended from approximately 85,000 to 11,000 years ago
What is the Wisconsinan Glaciation? When did it take place?
was the most recent major advance of the North American ice sheet complex. This advance was synchronous with global glaciation during the last glacial period. The Wisconsin glaciation extended from approximately 85,000 to 11,000 years ago.
How did the Great Lakes form?
• Moving ice scoured bedrock surface in river valleys • Gouged valleys deeper and broader • Not until the ice melted back into S Michigan did the ice front again become separated into distinct lobes - Saginaw Lobe - Michigan Lobe - Huron-Erie Lobe
Interglacial periods
intermittent warm periods within a long-term ice age
Plucking
is a glacial phenomenon that is responsible for the erosion and transportation of bedrock especially large joint blocks
Glacial erratic
is a piece of rock that differs from the size and type of rock native to the area in which it rests
Where are lateral and medial moraines found?
- ridges along sides of the valley - single stripes of debris formed when two glaciers come together
Outwash plain
is a plain formed of glacial sediments deposited by meltwater outwash at the terminus of a glacier
Kettle lake
is a shallow, sediment-filled body of water formed by retreating glaciers or draining floodwaters
Moraines
is any glacially formed accumulation of unconsolidated glacial debris (soil and rock) that occurs in currently glaciated and formerly glaciated regions on Earth (i.e. a past glacial maximum), through gemorphological processes
Cenozoic era
is the current and most recent of the three Phanerozoic geological eras, following the Mesozoic Era and covering the period from 66 million years ago to the present.
How were sea level and vegetation different than today?
- The sea level was less than today and the vegetation was less as well
What happened during the Cenozoic leading up to the ice age?
Decreasing deep water temps, build-up of continental ice sheets
What were the major steps of the present ice age?
East Antarctic Ice Sheet: appeared ~34 mya, became permanent ~12 mya. West Antarctic Ice Sheet: appeared 6 mya, became permanent ~2 mya. Northern Hemisphere ice sheets (e.g. Greenland): appeared ~2 mya, became significant ~0.5 mya
What are kettle lakes? How are they formed?
Form when blocks of ice become buried in drift and melt leaving depressions that can be filled by water - Most are less than 2km in diameter and 10m deep
What is the role of the Tibetan Plateau in cooling the climate?
It blocks moisture from the Indian Ocean, creating cool dry air masses.
Why did ice appear first in East Antarctica?
It is colder than West Antarctica due to higher elevation
What are the main characteristics of the East Antarctic Ice Sheet?
Oldest current ice sheet. Dry bottomed. Largest Ice Sheet (17m sea level change)
Abrasion
is the mechanical scraping of a rock surface by friction between rocks and moving particles during their transport by wind, glacier, waves, gravity, running water or erosion. After friction, the moving particles dislodge loose and weak debris from the side of the rock
What is the role of ocean circulation in establishing the presence of ice in Antarctica?
When land doesn't block the Antarctic Circumpolar Current, it keeps warmer waters from entering the Antarctic region. Therefore keeping the area cooler than the Arctic.
Till
is unsorted glacial sediment. It is that part of glacial drift which was deposited directly by the glacier. Its content may vary from clays to mixtures of clay, sand, gravel, and boulders
Jet stream
fast flowing, narrow air currents found in the Earth's atmosphere. The main jet streams are located near the altitude of the tropopause, the transition between the troposphere and the stratosphere (where temperature increases with altitude). The major jet streams on Earth are westerly winds (flowing west to east). Their paths typically have a meandering shape; jet streams may start, stop, split into two or more parts, combine into one stream, or flow in various directions including the opposite direction of most of the jet. The strongest jet streams are the polar jets, at around 7-12 km (23,000-39,000 ft) above sea level, and the higher and somewhat weaker subtropical jets at around 10-16 km (33,000-52,000 ft). The northern hemisphere polar jet flows over the middle to northern latitudes of North America, Europe, and Asia and their intervening oceans, while the southern hemisphere polar jet mostly circles Antarctica all year round
What are glacial striations?
grooves created by rocks scratching against bedrock at the base of a glacier
What is the situation today in terms of ice coverage for ice sheets , alpine glaciers, sea ice, and permafrost?
ice - melting, ice coverage decreasing acceleration of melting in greenland permafrost - less than before
Glacial periods
individual pulses of cold climate within a long-term ice age
What are Dansgaard/Oeschger (D/O) events?
rapid climate fluctuations that occurred 25 times during the last glacial period Ø In the Northern Hemisphere, they represent rapid warming episodes each followed by gradual cooling over a longer period
Last glacial maximum
refers to a period in the Earth's climate history when ice sheets were at their most recent maximum extension, between 26,500 and 19,000-20,000 years ago, marking the peak of the last glacial period. During this time, vast ice sheets covered much of North America, northern Europe and Asia
What is the last glacial maximum?
refers to a period in the Earth's climate history when ice sheets were at their most recent maximum extension, between 26,500 and 19,000-20,000 years ago, marking the peak of the last glacial period. During this time, vast ice sheets covered much of North America, northern Europe and Asia.
Glacial drift
s a general term for the coarsely graded and extremely heterogeneous sediments of glacial origin
Glacial striations
scratches or gouges cut into bedrock by glacial abrasion