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Karten in diesem Stapel (165)
- 1What is the Non-linear response of the climate system to insolation?The amount of rainfall is highly sensitive to insolation changes in one season (summer), but largely insensitive to changes in the other (winter).
- 2Who came up with the Orbital Monsoon Hypothesis?John Kutzbach (early 1980's)
- 3Where do the most strong summer monsoon occur and why?Northern Hemisphere. Because of the large landmasses (Asia, North Africa) and the high elevational levels.
- 4Name direct indications of connection to tropical monsoon fluctuations in North Africa.- Occurring of sapropels
- Distinct pulses of lake diatoms in the north tropical Atlantic oceans separated by 23,000 years and relative same strength of the pulses as the preceding summer insolation maximum
- Atlantic ocean sediments. The structure of water layers varies with prominent 23,000-year rhythm. North Africa summer monsoon imposes an atmospheric circulation pattern that overrides the local circulation. - 5What are sapropels?Sapropels are distinct layers of black organic-rich muds, that were formed at times when the water at the seafloor was anoxic.
- 6What do sapropels mark?Sapropels mark times when the deep Mediterranean Basin was deprived of oxygen because sinking of oxygen-rich waters was prevented by a cap of low-density freshwater brought in by river waters (from the Nile).
- 7Describe the waters in the Mediterranean during a weak summer monsoon.The deep water is rich in oxygen, due to the sinking of oxygen-rich surface water during winter. The water sank, due to the high salt content (excess evaporation over precipitation) and winter chilling of salty water along northern margins.
- 8Why do monsoon circulations exist on Earth?The land responds to seasonal changes in solar radiation much more quickly than the ocean does.
- 9Describe the circulation pattern during Weak North African summer monsoons.Trade winds along the equator have a strong east-to-west flow. The winds drive warm surface waters southward away from the equator, which causes a shallowing of the seasonal thermocline. As the thermocline shallows, cooler waters rich in nutrients rise toward the sea surface just south of the Equator.
- 10Describe the circulation pattern during strong North African summer monsoons.The stronger summer monsoon flow overrode the circulation pattern, like during weak monsoons. A large portion of the southern trade-wind crosses the equator, turned to the northeast --> into North Africa in the monsoonal circulation. The strengthening of the monsoon flow, weakened the westward trade-wind flow along the equator and reduced the upwelling of cold waters, leaving the surface waters poorer in nutrients.
- 11How can the changes between the circulation patterns of Weak and Strong North African summer monsoon be measured?By measuring variations in relative amounts of planktic organisms. Different species of kinds of plankton prefer different environmental conditions near the sea surface - either warm waters with fewer nutrients or cooler water with nutrients.
- 12What is the argument that states that June 21 is the best choice as the insolation forcing timing during summer monsoons.Because the summer solstice is the time of peak insolation forcing. Some kind of physical process must have retarded full development of summer monsoon by 2,000 years.
- 13What would be the argument to start that June 21 is NOT the best choice as the insolation forcing timing during summer monsoons?When the continental interiors are heated to their maximum, the temperature contrast with the cool oceans reaches a maximum. The resulting temperature differences drives the strongest monsoon circulation of the year. Choosing late July or early August as the time of critical insolation forcing would eliminate the apparent 2,000-year lag in monsoon responses.
- 14What evidence for strong monsoonal circulation were found in Asia and South-America?Records from caves show delta 18O variations so large, that they could only be explained by air mass changes linked to changes in monsoon strength in those regions.
Groundwater dripping through soils and bedrock and into cave deposits, which are constructed of CaCO3. The relative amount of 16O and 18O in the calcite layers series through time because e.g. of the changing amount of surface precipitation that feeds flow of groundwater to the caves. - 15Name 3 things how tectonic conditions control monsoons.1. Amount of landmasses, large landmasses (like Pangaea) intensify monsoons by offering a large area for the sun to heat.
2. Position of landmasses at lower latitudes
* solar radiation more direct
* albedos are much lower
3. topography
High elevation regions focus strong monsoonal rains on their margins. - 16How do tectonic and orbital controls of monsoon interact?Slow increase in the amplitude of the orbital-scale cycles causes by tectonic amplification.
'Plateau ploft sensitizes the monsoon system to insolation forcing in such a way that the combined monsoon response to uplift and insolation is stronger than a simple linear combination of the two effects. - 17The prediction of monsoon response is based on 3 assumptions, namely?1. There exists a threshold level of insolation, below which the monsoon response will be too weak to leave any evidence in the geologic record.
2. The strength of the monsoon response is directly proportional to the amount by which summer insolation exceeds the threshold value.
3. The strength of the monsoon in the past, is a composite of the average monsoon strength over many individual summers. - 18Why do the diatoms pulses found in the Tropic Atlantic ocean, that show evidence for the North African lake fluctuations, coincide with insolation minima? (Figure 9-9)Because lakes dry out when monsoons weakens, therefore the diatoms were transported and deposited during insolation minima.
- 19What is the ice mass balance?The net balance between accumulation and ablation over an entire ice sheet
- 20Explain why the ice mass balance is more positive at mean annual temperatures (-15 to -10 degrees celsius) than at very cold temperatures (below -20 degrees)?At very low temperatures, all of the precipitation is snow, but frigid air carries so little water vapor that rates of ice accumulation are low.
- 21What happens with the ice mass balance above -10 degrees celsius?It turns sharply negative, ablation accelerates and overwhelmed accumulation.
- 22What is meant with the Equilibrium line?The boundary between positive and negative mass balance of an ice sheet.
- 23According to the Milankovitch Theory; when did ice growth in the Northern Hemisphere occurs?During times when summer insolation is reduced. Low summer insolation occurs when:
- Earth's orbital tilt is small and its poles point less directly at the Sun.
- The Northern summer solstice occurs with aphelion
- orbit is highly eccentric (further increasing of Earth-Sun distance) - 24What is the most sensitive latitude for low insolation values according to Milankovtich theory?65 N. Ice sheets are the first to accumulate and the last to melt. The summer insolation varied as much as 12%!
- 25What does the Milankovtich theory proposes?When summer insolation is weak, less radiation is delivered to high latitudes, and reduction in radiation cools the regional climate. Cooling reduces the rate of summer ablation and allows snow to accumulate and ice sheets to grow.
- 26Describe the Ice elevation feedback.Tops of ice sheets can reach up to 2-3 km, where temperatures are 12-19 degrees celsius cooler than at sea surface. So when ice will accumulate, the tops will move to higher elevations, where it is even cooler. Positive feedback, until it weakens because at a certain elevation the rate of snowfall is much lower.
- 27Describe the (delayed) bedrock feedback.Bedrock will sink due to applying more pressure on top (accumulation) and will rebound again when the pressure is decreased (ablation). However, the sinking and rebounding processes have a delay. So when the pressure is already increasing, the ice sheet will stay a bit longer on the cold high elevation level, since it has not sinked in yet this gives a positive feedback.
- 28What is the bedrock response when ice sheets grow?When ice sheets grow, the pressure of their weight on the underlying bedrock increases. It could depress the underlying bedrock far beneath the level it would be if no ice sheets exists. 3,000 meter of ice is equivalent to 1,000 meters of rock.
- 29Name two key indicators of past glaciations in ocean sediments.1. Ice-rafted debris: mixture of course and fine sediments delivered to ocean by melting of icebergs that calve from ice sheet margins.
2. delta 18O records from shells of foraminifera: quantitive measure of combined effects of change in ice volume and temperature of ocean water. - 30What are the dominant cycles of the low summer insolation?23,000 and 41,000-years
- 31Describe the motion of the climate point when the ice sheet grows.The climate point is displaced to the south.
- 32What is a climate point?Location where the equilibrium line intercepts Earth's surface in the higher latitudes.
- 33Who explorated the link between insolation and ice volume?John Imbrie and colleagues
- 34Describe the used conceptual model of the link between insolation and ice volumeA conceptual model based on variations through time in the intensity of the flame in a Bunsen Burner. Changes in temperature lag behind changes in intensity of the heat source, because of water's high heat capacity (slow reaction), ice sheets have same lagged response. The phase lag is ~1/4 cycle
- 35Combined north-ward movement of climate point and bedrock depression will cause...Increase in ablation. The mass balance will turn negative.
- 36What did Hays, Imbrie and Shackleton found in the delta 18O data?That the delta 18O changes lagged behind changes in summer insolation forcing by several thousand years. This is consistent with the lag of ice volume behind summer insolation that Milankovitch had predicted.
- 37How can you interpret higher amplitude and values spaced farther away of ice volume record?Ice sheets persisted for longer intervals of time and grew larger
- 38Name two measures of ice volume- delta 18O records
- Fossil remains of coral reefs - 39Explain how ancien reefs can function as a measure of the past water level.As sea level rises and falls, coral reefs follow by migrating upslope and downslope
- 40What can we state about fluctuations of the sea over orbital cycles?These are mainly the result of ice formation
- 41Name a method to date an ice formation event- sea levels histories recorded by coral reefs are also a record of ice volume
- old reefs can be dated by radiometric decay methods (234U --> 230Th) - 42Which part of the Milankovitch theory has proven accurate?The theory explains the presence of ice volume response at 41,000 (obliquity) and 23,000 (precession) and why they lag several thousand year behind the summer insolation forcing.
- 43Which parts of the Milankovitch theory are insufficient?It fails to explain the dominance of the 41,000-year cycle of the 23,000-signal for almost 2 million years, and it does not account for the emergence of large oscillations near 100,000 year in the last million years.
- 44How can interpret negatie delta18O values from foraminiferaSmaller ice sheet and/or warmer deep-ocean temperatures
- 45Explain how the delta18O record looked prior to 2.75 million years agoIt was relative negative and there was no present of ice-rafted debris
- 46Over the last 0.6 million years, what was striking about the ice sheets interpretation?Higher amplitudes and spaced farther away indicated that the ice sheet persisted for longer intervals of time and grew larger. There were around 6. However, each followed by an abrupt deglaciation (termination)
- 47Why does the size of a growing or melting ice sheet lag well behind changes in insolation?Like the Bunsen Burner, water has a high capacity so it reacts with a lag. As summer insolation declines from a maximum value, ice begins to accumulate. The rate at which ice volume growths, reaches maximum when summer insolation has fallen to its lowest value because summer ablation is at tits minimum. Later, as summer insolation begins to increase, the ice sheet will continue to grow for a while longer because insolation values are still relatively low.
- 48Each 10-meter change in global sea level results in...an isotropic (delta18O) of 0.8-1.1 permit.
- 49Give the formula for average rate of upliftU = (H - S)/t
U is the mean uplift rate (meters per 1,000 years)
H is the present elevation of the older reef (meters)
S is the relative sea level at the time the older reef formed (meters)
t is the time in 1,000 years - 50Name two climate signals that can be obtained from cores of present ice sheets that are not available from other sources.1. Records of CO2
2. Records of CH4 - 51Name two methods ice cores can be dated1. Annual layering
2. Construction of an ice flow model based on physical properties of the ice sheet and assumption of smooth steady flow of ice - 52Describe the proces of air bubbles in ice sheets1. Additional accumulation of snow
2. compression of the weight above
3. pressure eventually transforms snow into ice crystals
4. little by little flow of air is reduced and diffuses slowly through ice crystals
5. at the end air bubbles are trapped (sintering) - 53On what does the difference in age between younger air bubbles and the older surrounding ice depends on?On the rate at which the ice accumulates. The age difference can be as large as 2,000 years or more for slow deposition rates.
- 54What is sintering?Process where air is trapped in place as small bubbles because it cannot circulate anymore at great depth (about 50 meters below surface)
- 55How can carbon that moved along several reservoirs be tracked?Through carbon isotopes
- 56What property of plants changes the carbon isotopes?During photosynthesis plants preferentially incorporate the 12C isotope into their living tissue compared to the 13C isotope.
- 57Why is the vegetation-soil reservoir not suspected when it comes to the storage of the carbon that was removed during glacial maximum?Because during glacial maximum there was a vegetation reduction between 15-30%.
- 58Why is the surface ocean reservoir not suspected when it comes to the storage of the carbon that was removed during glacial maximum?Because the surface of the ocean exchanges a lot with the atmosphere, it does not change more than 30 ppm from the atmosphere.
- 59Name the 3 reservoirs where carbon was missing from during the glacial maximum (20,000 years ago).1. atmosphere
2. vegetation-soil
3. surface water - 60What reservoir must have stored all missing CO2 during glacial maximumThe deep ocean
- 61How can the amount of carbon transferred to the deep ocean during glacial maximum be estimated?Can be estimated independently from delta13C measurements from foraminifera.
- 62Explain the correlation between delta18O and delta13C during glacial times and interglacial climates.During glacial climates: lower delta 13C should correlate with more positive delta 18O values
During interglacial climates, higher delta 13C values should correlate with less positive delta 18O values, because of the melting of delta16O-rich ice.
- 63What is the problem with increase CO2 solubility in seawater to be to transfer mechanism of carbon to the deep ocean during the glacial maximum?Colder water will leed to more solubility of CO2, however higher salinity will lead to less solubility of CO2. A high salinity is expected due to the formation of ice during the glacial maximum
- 64Name two ways to move carbon to the seawater:1. Colder water --> higher solubility of CO2
2. Biological activity - 65Describe the biological transfer of carbon from surface waters to the deep sea.CO2 is extracted from the surface waters and incorporated in organic tissues, some of which sinks to the deep ocean
CO2+H2O --> CH2O + O2 - 66Describe carbon pumpTransfer of CO2 from the surface to deep sea, because of an increase in the rate of photosynthesis --> more enriched 12C organic carbon sinking
Also more nutrients are needed to stimulate greater productivity - 67What is the problem with the reliability of the carbon pump being the transfer system of carbon during the glacial maximum?There is many evidence of depleted nutrients during glaciations
- 68Why is the deep ocean loaded with nutrients? Can these nutrients by used for biologic activity?Nitrogen and phosphorus and carbon in organic matters falls down from surface waters and oxides back to mineral form.
Remained unused in the dark, unless they are delivered back by upwelling. - 69What is the iron fertilization hypothesis?Iron is critical to marine life. Erosion of land is the main source of iron, so ocean regions could have boost if extra dust is blown in by winds. The additional iron could stimulate the productivity. The theory is still debated since the estimates of the effects differ a lot.
We do know that it blew in North Pacific Ocean and Atlantic sector of southern ocean. - 70Name two ways for transferring CO2 to the deep ocean.1. Carbon pump (Iron fertilization hypothesis?)
2. Changes in deep-water circulation - 71How can we track the deep-water circulation?Through delta13C measurements in bottom dwelling foraminifera.
1. Positive values in North Atlantic because the deep water is formed from SURFACE waters that have been greatly enriched in delta13C by photosynthetic removal of delta12C. Negative from Antarctic.
2. Through delta13C aging: as deep waters flow from their source regions to other parts, their delta13C values gradually become more negative (because of continual downward rain of 12C-enrich carbon) - 72Name 3 factors that contributed to the reduction in atmospheric CO2 concentrations during glacial intervals.1. Increased CO2 solubility in colder waters, but decreased in higher salinity...
2. Biological pumping of carbon from surface to deep waters
3. changes in deep-ocean circulation.
The size of the two later is not known. - 73Name two ways changes of the pattern of deep-water circulation affects CO2 concentration in atmosphere.1. Stronger overturn of Antarctic source waters at intermediate depths could have delivered more nutrients to surface waters - > stimulation of carbon pumping
2. Carbonate chemistry of the ocean. CO3^-2 are produced when corrosive water dissolves CaCO3 on the sea floor. CO3^-2 combines at the surfaces with dissolved CO2 to produce HCO3^-1. Therefore, if increased amounts of CaCO3 are dissolved, CO2 concentration will be reduced.
(n global average: very slow proces and several regions experienced different and often opposing changes in CaCO3 during glaciation --> cancels out)
BUT POLAR ALKALINITY COULD INCREASE FORMATION OF CaCO3 - 74What is polar alkalinity?During glaciations, the water that formed in North Atlantic sank to much shallower depth and did not intersect that much with the ocean floor. Instead, an expanded area was by more corrosive southern source water, which dissolved more CaCO3. This changes would have reduced the concentration of dissolved CO2 in Southern Ocean.
- 75To what are prominent variations in methane linked toPrimarily to changes in strength of the summer monsoon in tropical and subtropical regions
- 76What is the relationship of gas concentrations and ice response when it comes to changes in insolation changes? Give two possibilities.1. Gas concentrations nearly lead ice response:
Gas concentrations respond immediately to insolation changes. Changes in the gas concentration then join summer insolation as an ADDITIONAL forcing of ice sheet, ice sheets respond with their characteristic lag of ~5,000 years.
2. Gas concentrations lag behind insolation changes and are in phase with ice response:
Greenhouse gases do not respond directly to insolation changes, but react through a positive feedback that is tightly linked to the ice sheets. Summer insolation drives the ice sheets, which create conditions to control the concentrations of greenhouse gases.
* ice growth --> less gas --> cooling --> more ice growth
* ice melt --> more gas --> climate warms --> melting accelerates - 77What features of ice core CH4 signal suggest a link to tropical monsoons?(1) control of size of north-tropical wetlands by summer monsoon rainfall
(2) control of emission from circumarctic bogs by midsummer warmth driven by insolation heating of northern continents - 78What effect does fractionation have on carbon isotope values?The delta13C values of inorganic and organic carbon differ mainly because of changes that occur during photosynthesis, a process by which plants create organic carbon from inorganic sources. During photosynthesis, plants preferentially incorporate the 12C isotope into their living tissue compared to the 13C isotope.
- 79Explain how carbon isotope delta13C changes trace shifts of carbon the land to ocean.The amount of carbon transferred from the land to the deep ocean can be estimated independently from delta13C measurements from foraminifera that lived in the ocean. Organic carbon in terrestrial vegetation is taxed with an average delta13C value of 25 permit, the amount of inorganic carbon in ocean has an average near 0 permit. Although a small fraction of the terrestrial organic carbon delivered to the ocean remain as organic matter, most of it is converted to inorganic carbon that retains the very negative delta13C composition.
- 80What two characteristics of ice response to orbital variations did Milankovitch theory predicted?(1) Presence of ice volume changes at major period of orbital variations
(2) Ice volume changes with timing consistent with northern hemisphere summer insolation as critical space setter.
--> despite evidence in favor of the theory, the tempo of ice sheet variations does not match the rhythms of insolation changes. - 81Name reason why ice sheets can become drivers of the climate.(1) Calve icebergs --> deliver cold fresh water to ocean
(2) Large albedo contrast
(3) Height of the ice sheets. High ice sheets form massive obstacles to free circulation of winds in lower atmosphere - 82Name two mechanisms that have the potential to propagate ice sheets behind high Northern Latitudes.(1) Storing ocean water in the ice sheets --> sea level drops and exposes more land. General response will be more tendency toward locally drier climates with stronger seasonal temperature extremes.
(2) Fully global reach: changes in CO2 concentrations that accompany ice sheet growth and melting. - 83The persistence of the sawtoothed oscillation at ~100,000-year period extending well into the Southern Hemisphere is a surprise. Name mechanism that this cannot be driven by and mechanism that are plausibleCannot be driven by:
(1) Ice driven, in the sense of being created by changes in northern sea ice or atmospheric winds
(2) Pushing of the ITCZ. Pushing the ITCZ would produce a southern signal reveres in seas from that in north, with the warmth of the southern ITCZ margin pushed south into cooler middle latitudes. Instead the southern pollen signals have the same sense of timing as those in the north.
(3) Fluctuations in Antarctic ice sheet. It covered 97% of the continent, even during present warm interglacial intervals and cannot have covered a much larger area during glacial climates.
Plausible mechanisms for transferring a signal of norther origin to south:
(1) changes in sea level can effect climate in coastal regions that are alternately flooded and exposed by vertical movements by shallow sea. HOWEVER, many regions that show sawtoothed oscillations are located at high altitudes well into continental interiors (not that sensitive to sea level change)
(2) Variations in greenhouse gases (CO2 primarily) - 84Ice should could have altered CO2 concentration by several mechanisms. And are these plausible to have caused the northern signal at ~100,000 to transfer south?(1) Strong winds picked up the dust --> blew out to ocean --> fertilization by iron --> strengthen carbon pump mechanisms --> reduced CO2 concentration
(2) If ice sheets causes a decrease in the depth of sinking of North Atlantic deep water, the resulting drop in the CO3^-2 ion concentration in south polar waters could have caused a CO2 decrease.
(3) If ice sheet growth helped to cool deep-water temperatures --> CO2 solubility mechanism would have reduced atmospheric CO2 concentrations.
Yes, evidence suggests that that ice sheets did drive dust concentrations and also affected the flow of North Atlantic deep water. - 85Describe the mystery of the 41,000-year glacial world.Evidence of 41,000-year variations in ice sheets during 2.75-0.9 Ma (base on delta18O values)
Temperature variation are half because of this cycle
Ice volume variations mainly because of the cycle
HOWEVER, strong insolation forcing at 23,000-period? - 86Name 3 possible explanations for the mystery of the 41,000-year glacial world.(1) Insolation varied mainly at 41,000 years
Mismatch between insolation and ice volume prior to 0.9 Ma --> incorrect choice of insolation index
- Mismatch not as large when caloric seasons of Milankovitch were used.
- Huybers: Changes are cancelled by reduction in length summer season (Keplers 2nd law --> at perihelion Earth moves faster).
However, why would the 23,000-year signal be completely absent from 2.75-0.9 Ma, yet clearly present since then?
(2) Antarctic ice changes at 23,000-year cancel northern ones
Raymo: NH ice sheets did respond to insolation forcing with 23,000-period. However, the global response was averaged by 23,000-year response of Antarctica. From seasonal point of view, changes in precession occur at opposite times in NH and SH.
Problem, evidence of sediment cores nearby north atlantic ocean during 1.5-1.2 Ma --> key ice driven responses: dominance 41,000-year cycle.
3. Positive CO2 feedback at 41,000-years
Close relationship delta18O and CO2 800,000 years --> suggest positive feedback relationship between ice volume and CO2 levels. - 87What is the mystery of the ~100,000-year glacial world?After 0.9 Ma fluctuations center near period of 100 ayr. And centre problem: Insolation forcing provides almost no direct forcing at this period.
"Why did the ice sheets fluctuate at this period, especially given the lack of direct insolation forcing?"
"What explains the slow buildup of ice cover periods averaging 100,000-years and abrupt deglacial terminations?" - 88What evidence from delta18O trends did lead to the conclusion that glacial maximum ice sheets were almost certainly smaller in volume (2MA)?Combined effects of ice volume and deep-ocean temperature were smaller.
- 89How do we know that the ice sheets during glacial maximum (2MA) were thinner?Evidence from delta18O trends --> combined effects of ice volume and deep ocean temperature were smaller, SO ice sheets were certainly smaller.
HOWEVER, did reach to the same extent, so they were thinner - 90Describe the mechanism by Peter Clark to explain thinner ice sheets.Under normal circumstances: weight of overlying ice melts bottom layer of ice --> meltwater trickles down into underlying sediments --> sediments saturated with water are more easily deformed --> base of ice sheets to slip and slide.
Ice sheets that formed earlier built up on top of thick layers that had not been glaciated for preceding hundred of millions of years --> water saturating these thick underlying layers would have reduced friction with bottom layer of ice sheet --> frequent sliding
Today, very little original soil and sedimentary rock cover across north-central Canada is left --> without soft substrate, later ice sheets have not been as susceptibel to sliding --> reduction sliding could have allowed them to growth thicker - 91Describe how Long-term cooling could have occurred the shift from 41,000 to 100,000-year dominance after 0.9 MA.The slow cooling, would have reduced ice ablation in high northern latitudes. After 0.9 MA, ice sheet growth still occurred mainly during 41,000-year insolation minima but some ice remained unmelted during relatively weak summer insolation maxima --> unmelted ice the survived would grow thicker during subsequent intervals of low insolation --> producing glacial cycles of longer duration
THE PERSISTENCE OF UNMELTED ICE TRANSFERRED PART OF THE ICE SHEET RESPONSE FROM A 41,000-YEAR CYCLE TO A LONGER PERIODE (~100,000-YEAR) RESPONSE - 92Explain the timing of deglacial terminations and what the role of the 100,000-period is.Insolation changes are dominated by changes in 23,000-year precession cycles. Obvious modulation of precession signal by eccentricity period near 100,000-years.
Modulations produces clusters of unusually high insolation maxima at intervals of ~100,000-years. Ice sheets that are able to grow to a large size during intervals when isolation maxima were small would be vulnerable to rapid melting when insolation maxima grew larger at intervals of ~100,000 years.
Ice melting is sensitive to the "upper-side" of the envelope of modulation by eccentricity. - 93Non of the intervals between successive termination is actually at the 100,000 years, but near it. Explain* Precession
Deglaciation are constrained to occur on or near major insolation maxima at precession cycles and only after the ice sheets had grown to large size
- 4 or 5 23,000-year insolation maxima (~92,000-~115,000)
* Obliquity
Because a relative large volume of ice has to accumulate in order for a amor deglaciation to be possible, tends to position terminations at multiples of 41,000-year ice growth cycle
- 2 or 3 41,000-year ice growth cycles (~82,000 - ~123,000)
So, would melt at interval of ~82,000-~92,000 or ~115,000-~123,000 years - 94The larger ice sheets that grow in a series of 41,000-year steps eventually produce internal responses that fasten their own destruction during intervals of increased insolation. Name these:(1) Large ~100,000-year ice sheet developed extensive margins that fronten on ocean and rested on bedrock lying below sea level --> more vulnerable to sea level rises that "lift" them from their bedrock
(2) Cooling produced by large northern ice sheet caused large amounts of sea ice to expand across nearby high-latitude oceans
--> reduced extraction of moisture that could be delivered to ice sheets
HOWEVER, ice accumulation is a relatively weak term in mass balance of ice sheets compared to ablation. Moisture starvation should have had a small effect on changes in ice volume during terminations.
(3) Wind of early melting just after glacial maxima produced thin coating of dust on lower southern margins of ice sheets --> lower albedo --> more incoming radiation --> more warming
HOWEVER, just a slightly thicker coating of dust can have the opposite effect --> insulating ice surface from solar heating and reducing rate of ablation - 95What is a relaxation oscillator?Varying between slow destabilization zone phase (gradual build up of ice) and fast relaxation phase (rapid ice melting)
--> concept analogous to behaviour of spring: source of fast relaxation rebound lies in system itself, as in the tension imposed by stretching the spring
RELAXATION OSCILLATOR CONCEPT VIEWS DEGLACIATIONS AS RETURNING THE SYSTEM TO ITS STABLE INTERGLACIAL STATE - 96Explain why it is questionable if the true stable state of the Earth can been seen as the interglacials (like according to the relaxation oscillator concept)Ice sheets of some size have been present in NH for 90% of the last 0.9 Ma. Seems more likely that the true stable state of the climate system has been one with a least moderate-size ice sheet present
- 97Name an ice-drive response and explain its originThe colder temperature over the ice sheet, combined with clockwise flow of winds around central ice dome, sends very cold winds blowing south-eastward over the western North Atlantic Ocean. Cold air is send into to western maritime parts of Europe. Precipitation fall significantly because the colder ocean gives off less water vapor to the atmosphere.
- 98What evidence suggests that the orbital-scale changes in northern hemisphere ice volume changes in atmospheric CO2, rather then opposite?The evidence that suggest ice sheets did drive dust concentrations in the Northern Hemisphere and also affect the flow of North Atlantic deep water.
- 99Name the revolutions of knowledge in Earth's history.(1) Development by Charles Darwin and other in 19th century of the theory of evolution.
(2) Theory of plate tectonics during 1960-1970s
(3) Expanding efforts to understand climate changes during late 1900s and early 2000s - 100Name the fundamental kinds of climate forcing.(1) Tectonic processes
(2) Changes in Earth's orbit around the sun --> alter the amount of solar radiation
(3) Changes in the strength of the sun - 101What is 'forcing' and 'response'?Forcing: factors that drive or cause changes
Response: resulting climatic shifts - 102What is response time?Measure of time it takes to react fully to the imposed change.
- 103When is the rate of response of the climate system the fastest?When the climate system is farthest form its equilibrium value.
- 104What are feedbacks?Feedbacks are processes that alter climate changes that are already underway, either by amplifying them (positive feedback) or suppressing them (negative feedback).
- 105How does climate differ from weather?Climate change specifically applies to longer term variations in contrast to the shorter fluctuations in weather that last hours, days, weeks.
- 106In what form does energy travels through space from the sun?In the form of electromagnetic radiation.
- 107What is the electromagnetic spectrum?Entire range of wave sizes
- 108What is the incoming radiation at the Top Of Atmosphere (TOA)?1,362 W/m^2
- 109What is the average radiation received per unit of surface area on Earth?1,362/4 ~ 340 W/m^2
Earth is a sphere, so the average radiation received per unit of surface area on a sphere is only 1/4 - 110How much of the shortwave radiation passes through the atmosphere and enters the climate system? And how much is absorbed by Earth's surface and atmosphere?70% of the shortwave radiation passes through atmosphere
2/3 absorbed at Earth's surface
1/3 absorbed by clouds and water vapor in atmosphere - 111What is back radiation?Heat loss that Earth loses to remain a constant temperature through time which is equal to the amount of retained energy (238 W/m^2)
- 112What is albedo and how does it vary over Earth's latitudes?Albedo is the percentage of incoming radiation that is reflected rather than absorbed by a particular surface.
* varies with angle at which incoming solar radiation arrives. For example of an overhead sun (low latitude): water reflects 5%, but 33% for a lower sun (higher latitudes)
* Snow for example (most present at the higher latitudes) has a very high albedo - 113Why are absorption and storage of solar heat strongly affected by the presence of liquid water?Liquid water has a high heat capacity.
water : ice : air : land ; 60 : 5 : 2 : 1 - 114What are difference in thermal inertia? And what are the thermal inertia's of land and ocean?Differences in amplitude and timing of response between land surfaces and the upper ocean layers.
Fast-responding land: low thermal inertia
Slow-responding ocean: high thermal inertia - 115Name two forms of heat transformation:1. Sensible heat
Product of the temperature of the air and its specific heat. Carried by convection (process of warming parcel, expands, becomes lighter and rises higher in atmosphere).
2. Latent heat
Heat carried by air is temporarily hidden in latent form as water vapor. Powerful process transferring heat long distances.
Occurs in two steps:
1. initial evaporation of water and storage of heat in water vapor
2. later release of stored heat during condensation and precipitation
Both affected by convection - 116Where is the sensible heating greatest? And where is it the lowest?Greatest:
* at low latitude (overhead sun)
* over land (low heat conductance, air heats)
* dry regions (low humidity)
Lowest:
* over oceanic regions - 117Describe mixing by sensible heat.convection driven by sensible heat
- Air parcels rise if the become heated and less dense than surrounding air
- as air parcels rise: air expands, air cools, becomes less dense, stop rising
Heat transferred vertically. Since air forced from high to low pressure, heat also moves horizontally. - 118Describe mixing by latent heat.Water vapor is less dense than mixture of gases composing the atmosphere.
Evaporation adds water vapor to the atmosphere --> density lowers
Moist air rises, expands and cools until dew point reached.
When air becomes fully saturated, condensation begins and air releases laten heat. - 119Why does atmospheric pressure increases toward lower elevations?Because air is incompressible, most of the air is held close to the surface by gravity.
- 120What forces limit the amount of vertical air motion?1. Compressed air (has nowhere to go) --> pushes back --> resistance directed upward
2. downward pull of gravity
Stable but delicate balance that limits the amount of vertical air motion - 121What is a lapse rate?The rate at which Earth's atmosphere cools with elevation.
- 122Why do dry regions have a lower lapse rate?Because the only factor that works on rising air parcels is adiabatic expansion and cooling
- 123Explain the process of the Hadley cell.1. warm air rises in giant columns, due to evaporation of water vapor from tropical oceans and subsequent condensation at high altitudes
2. condensation produces a narrow zone of high rainfall in rising part of Hadley cell near the Equator.
3. Transporting sensible heat and other energy from lower to higher latitudes
4. Air sinks toward the surface at 30 degrees --> sinking air is warmed by increasing pressure at lower elevations (adiabatic proces) --> drier --> latitudes: zone of low average precipitation and high evaporation
5. Hadley cell circulation is completed at Earth's surface by trade winds from both hemisphere blow from subtropics toward tropic and replace the rising air. Trade winds carry warm air and pass over tropical ocean - 124What is ITCZ?Intertropical Convergence Zone. Region near the equator where the northern and southern trade winds meet.
- 125What is orographic precipitation?Heavy precipitation that occurs on the side of mountains that face upwind towards warm oceans, because when air that carries large amount of water vapor (from ocean) it is blocked by mountain and forced to rise higher, where it condenses.
-->
air that has been stripped of its water vapor sinks on the downwind side of the mountain --> moves to lower elevation --> compressed and warmed --> gains in capacity to store more water without condensation --> lee or rain shadow sides of mountain - 126What are jet streams?Narrow ribbons of faster flow that flow steadily from west to east at higher elevations in the mid-latitude.
- 127What is the Coriolis Effect?Apparent deflection to the right from an Earthbound perspective due to the direction of movement.
- 128Explain how spinning gyres occur at the subtropical latitudes.Spinning gyres are the result of an initial push of the winds on the ocean surface and the Coriolis deflection of the moving water. Winds drive the uppermost layer of water into the centre and pile up a sense of warm water. The top layer pushes that underlying layers a bit further towards the right (NH) and are slowed by friction.
- 129What is the North Atlantic Drift?Continuation of the gulf stream that transports polewards. The gulf stream emerges from the Gulf of Mexico, so it forms a narrowly concentrated outflow of warm salty water headed North.
- 130What is the thermocline and give two types.Thermocline is a zone of rapid temperature changes between warm upper layers and cold water filling the deeper ocean basins.
two types:
1. Deeper permanent maintained throughout the year
2. Shallower that changes as result of seasonal heating by sun - 131Formation deep water?When water becomes more dense than the underlying water it will sink.
1. Seawater is 3.5% more dense
2. Cold water is denser than warm water (water is compressible) - 132Explain North Atlantic deep water.Salt water from the Atlantic is carried northward by the Gulf stream and North Atlantic Drift. Air masses from the surrounding continents extract sensible heat from the water in winter --> density increase.
- 133Why is the Atlantic saltier than equivalent latitudes in the Pacific?Evaporation happens in the Atlantic at subtropic latitude. Some of the water vapor taken form the Atlantic is exported westward over the low mountains of Central America into the Pacific Ocean.
- 134Explain Antarctic bottom water.Even colder and denser water mass formed in the Antarctic region that flows northward in the Atlantic. It forms near the Antarctic coast by the chilling by very cold air masses and the formation of sea ice.
- 135What is the sealing effect of sea ice?Sea ice seals off the underlying ocean from interaction with the atmosphere. With this seal, heat release stops and reflective surface absorbs little incoming solar radiation --> winter air temperatures can cool by 30 degrees or more in regions that develop a sea-ice cover.
- 136Where does downwelling occur?In areas of convergence.
1. Equatorial Divergence.
As surface water diverges, sea level falls, surface layer thins and cold water “upwells”
2. Coastal divergence results in upwelling as cold water rises to replace surface water
3. Surface water piles up in center of gyre.
Sea level in the center of gyre increases -->
Surface layer of water thickens -->
Accumulation of water causes it to sink
4. Southern Ocean around Antarctic. Deep water from Atlantic flows toward surface.
- 137Name the two glacier ice types on land:1. mountain glaciers
2. continental ice sheets - 138What are mountain glaciers?Glaciers found in mountain valleys at high elevations. Typical mountain glaciers are a few km in length and to hundreds of meters in width and thickness.
- 139What are continental ice sheets?Glaciers of much larger form than mountain glaciers. Typically hundreds to thousands of km in horizontal extent and 1-4 km in thickness.
- 140Give two reasons for the occurring of ice streams.1. pressure from weight of overlying ice increases --> some ice of bottom will melt and creates a thin layer of water, on which the ice can slide.
2. Water may percolate into and saturate soft unconsolidated sediments lying beneath --> lose mechanical strength --> slide - 141What are ice shelves?Thick floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and into the ocean surface (gravity pulls ice out of the interior of the continent)
- 142what are tabular icebergs?Broken pieces of ice that broke off of ice shelves and float away.
- 143What are marine ice sheetsBase of the ice sheets lies below sea level. Highly vulnerable to sea level changes.
- 144What is calving?Shedding of icebergs to ocean or lakes. Ice bergs leave the main mass and move elsewhere to melt.
- 145What is the vegetation-precipitation feedback?Trees transpire much large volumes of water vapor than grass or desert scrub.
- 146What are moraines?Long curving ridges of unsorted debris carried by ice, ranging from large boulders to very fine clay, that are left behind after the retreating of ice sheets.
- 147LoessSilt-sized grains that are deposited in sequences in regions where the winds weaken
- 148When are sediments most useful as climate archives?When the deposition is uninterrupted.
- 149Why are deep ocean sediments useful as climate archive?Deep ocean is a generally quiet place with relatively continuous deposition. It therefore usually yields climate records of higher quality than records from land with repeatedly erosion of deposits.
However, there is still erosion on the deep sea:
1. physical erosion
2. reworking of current on sea floor
3. chemical dissolution of corrosive water in deeper basins - 150In what latitudes are trees as climate change archive best developed?In mid-latitude and high-latitude regions, because of the large seasonal changes
- 151What is radiometric datingDating based on radioactive decay of parent isotope to daughter isotope. This occurs at a known rate (decay constant). Likelihood of one parent-to-daughter decay per amount of present parent per unit of time
Clock starts when system is closed (only changes occur by radioactive decay) - 152What is radiocarbon dating?1. vegetable and animal life forms extract carbon from atmosphere
2. Death closes off carbon exchanges with the atmosphere
-->
decay clock starts ticking
14C parents decays to 14N daughter
(back to about 30,000 till max 50,000 years) - 153On what can we count annual layers?1. Ice
Alternations between darker layers that contain dust blown in from continental source regions during dry cold windy season.
2. Lakes
varves: annual couplets from seasonal alternations between deposition of light mineral-rich debris and darker sediment rich in organic material
-->
mostly common in deeper parts of the lake, due to lack of oxygen --> less bioturbation
3. Trees
Tree Rings: Alternations between thick layers of light wood (rapid growth in spring) and thin dark layers
4. Corals
Coral bands: record seasonal changes in texture of calcite in skeletons. Light: intervals of fast growth. - 154Name two commonly used proxies:1. Biotic proxies
based on changes in compositions of plant and animal groups
--> requires a reliance on general resemblance of past forms to their modern counterparts
2. Geological-geochemical proxies
measurements of mass movements of material through climate system (as discrete particles or in dissolved chemical form) - 155Why are plankton and pollen especially useful as climate proxies?1. both are widely distributed
2. fossil remains of these two groups are abundant in sediments
3. populations in different areas tend to be dominated by small number of species with well-defined climate preferences - 156Sediment is eroded from land and deposited in ocean basin in two forms, namely:1. Physical weathering
examples, ice-rafted debris, eolian sediments, fluvial sediments
2. Chemical weathering
a. dissolution
carbonate rocks and evaporate rocks are dissolved
b. hydrolysis
Weathering process adds water to mineral derived from continental rocks made of silicates - 157Why aren't models of the atmosphere and ocean allowed to interact continuously?Air and water respond to climate changes at different rates that impose different computational demands. Ocean models can ignore interactions on small time scale, because these short-time changes have negligible effects on most ocean circulations.
- 158Describe the interactive way recent vegetation models use1. Climate data derived as output from a A-GCM or A/O-GCM are used as input to vegetation model --> simulates resulting changes in vegetation
2, Simulated changes in vegetation are used as input to another A-GCM or A/O-GCM --> simulates additional climatic feedback effect caused by the changes in vegetation. - 159What are mass balance models?Models that trace movement among reservoirs (atmosphere, ocean, ice, vegetation and sediments)
- 160What is the plane of ecliptic?Plane in which Earth moves around the sun
- 161What is modulation?Behaviour in which the amplitude of peaks and valleys changes in a repetitive or cyclic way. Modulation creates an envelope that encompasses the changing amplitude that occur at specific cycles.
- 162What does eccentricity describe?Eccentricity describes the changes in the shape of the Earth's orbit from almost circular to slightly eccentric.
- 163What is axial precession?Earth's wobbling motions. Caused by gravitational pull of the sun and Moon on the slight bulge in Earth's diameter.
- 164What is the precession of the ellipse?The entire elliptically shaped orbit of the Earth rotates.
- 165Describe the geometrics characteristics of precessional motion?Angle between two imaginary lines:
1. Sun to Earth's position at perihelion (elliptical shape of orbit)
2. Sun to Earth position at March 20 Equinox (tied to varying position of seasons with respect to elliptical orbit)
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