Quaternary Flashcards

Question

impact of eccentricity on precession

Answer 1

strongly eccentric orbit increases the importance of precession 'precession parameter'

Answer 2

Milankovitch cycles conditions favouring cooler NH summers and Ice growth - low obliquity - high eccentricity - precession causeing NH summer at aphelion three main orbital parameters that affect how much solar radiation (insolation) Earth receives, especially during Northern Hemisphere summers NH important as it has the most landmass and icesheets, ice melts more on land than ocean Hayes et al 1976 timing of IG-G cycles still not fully explained, role of obliquity and precession unclear therefore internal feedbacks must play a role

Answer 3

onset of NH glaciation MPT Saw-toothed pattern

Answer 4

a critical threshold at which a tiny perturbation alters the state of a system

Answer 5

3Ma, gradual onset presence of "untouched" organic tundra soils date to 2.7Ma onset coincides with decreasing CO2 in atm (can be reproduced with models) question as to why CO2 decreased

Answer 6

from genetic studies, Acceleration in rate of disperial of terrestrial mammals between continents just before 2.7Ma sudden increase in surface ocean salinity carribean becomes warm and salty Density meridional gradients permits onset/intensification of Atlantic Gulf stream (which transfers both heat and moisture northward - need moisture to generate ice sheet)

Answer 7

shallowing of seaway intensified gulf stream intriduced warm water masses to high northern latitudes enhanced Northward moisture transport More moisture (precipitation) on the NH continents Freshwater run-off decreases salinities at high latitudes: Closure of isthmus → warming → increased moisture → sea ice formation → cooling

Answer 8

cause of MPT characterization of the entire Early Pleistocene as having 41-kyr periodicity is a simplification Before MPT, suggested that global temperatures (during insolation minima) were warm enough that the ice sheets were too small to survive an insolation maximum MPT marks point in time where temps became cold enough for ice sheets to reach size of threshold for surviving the next insolation maximum Then this ice sheet can accumulate until it reaches the next threshold, where it becomes unstable, when the next insolation minimum occurs, triggers a deglaciation - interglacial state

Answer 9

Berends et al 2021 atmospheric property based on adiabatic cooling as parcel of air moves up, pressure drops, air expands and cools Since the mass balance of an ice sheet, and in particular the melt, strongly depends on temperature, this leads to a positive feedback, where ice-sheet growth leads to a surface cooling, reducing melt and enhancing the growth

Answer 10

disappearance of regolith cover beneath the North American and Eurasian ice sheets can explain the MPT before onset of G-IG cycles, continents were covered by 10-50m layer of regolith easily deforms under stress of ice sheet, higher basal velocity than an ice sheet on top of hard bedrock (ice sheet is wider and thinner) gentle slopes = larger ablation zone, more sensitve to changes in climate in early pleistocene, this threshold was never reached, therefore every insolation max = deglaciation as regolith deformed and eroded, it is advected along direction of ice flow MPT is point where regolith was eroded away, and bedrock became exposed thicker (more stability through alt-temp feedback) and narrower ice sheets

Answer 11

Using a coupled ice-sheet – climate – carbon cycle model 100-kyr cycles can occur both with and without a prescribed regolith cover, but that the combination of both a prescribed global cooling trend, and a prescribed gradual removal of regolith during the Pleistocene, gave them the best fit to the observed δ18O record.

Answer 12

increased atmospheric dust at erosion of NA ice sheet complex some of this dust precipitated onto the ice sheet, the resulting decrease in albedo could have accelerated the retreat of the ice sheet (Peltier & Marshall, 1995)

Answer 13

Ocean is large carbon resovoir, connected to atm, air-sea gas exchange On G-IG timescales, variations in atm CO2 are influenced by - -ocean temps -ocean circulation -marine biological pump

Answer 14

colder water holds more CO2 glacials = more CO2 in water

Answer 15

southern ocean deep water holds large amounts of carbon changes in upwelling bring to surface sea ice at high latitudes limits the gas exchange during glacials

Answer 16

phytoplankton at surface die and sink efficiency dependent of nutrients and sunlight glacials = more nutriens (stronger wind blown dust, mroe river run off), but sea ice limits sunlight

Answer 17

Environmental records (GHG, ice volume, dust) combined with energy budget modelling can calculate direct effect of each feedback on earths radiative budget therefore global mean ST

Answer 18

27-60 kyr BP around 25 recognised D-O events in greenland ice cores during past 100,000y occur only during glacials fluctuations in strenght of AMOC abrupt warming events in greenland followed by gradual cooling

Answer 19

well-mixed atmospheric gas with a ~10 yr atmospheric residence time.

Answer 20

controlled by tropical hydro-climate which influences low‐latitude wetland CH4 emissions.

Answer 21

Greenland and Antarctica allows investigation of interhemispheric climate teleconnections and heat exchange within ~decadal-scale precision.

Answer 22

Interpolar phasing of warming and cooling transition, cold in greenland = warm in antarctica Abrupt Greenland warming leads the corresponding Antarctic cooling onset by ~200 years Clear north-to-south directionality of the abrupt climatic signal. The centennial-scale response of Antarctic climate must be associated with slow oceanic rather than fast atmospheric processes

Answer 23

North Atlantic gulf stream is key for moderating temp gradients between low and high latitudes NA is a key region for DWF freshwater alters composition, light and buyant, hampers

Answer 24

"On" - strong - warm salty water flows northward at surface, cold dense sinks in NA, keeps europe warm "Off" - weak - triggered by freshwater input, inhibits DWf, circulation slows or stops

Answer 25

system gradually approaches a critical threshold, when crossed, sudden collapse of amoc cahnge in external forcing (freshwater) reshapes stability of the landscape

Answer 26

system (amoc) can flip due to randomness or 'noise' climate noise, wind stress, ocean eddies, eruptions can be enough to trigger a flip

Answer 27

a periodic signal (freshwater ice melting) is too small alone to reach tipping point when a random internal variability is added, signals can resonate and amplify effects, meaning amoc crosses tipping point

Answer 28

stadials - warm salty water pushed under cold surdace layer capped by sea ice sea ice cover hinders venting of heat to atm = sub-surface warming sea ice melts, heat lost, AMOC begins again rapid warming phase = DO interstadial

Answer 29

significant iceberg discharge events from the Laurentide Ice Sheet 6-7 times during last glacial every 7-10kyr Ice rafted debris layers in marine sediments

Answer 30

rapid cooling episode during the holocene 1-3 degree lasted 150-400y final collapse of laurentide ice sheet, drainage of glacial lake agassiz into NA via hudson bay disrupted AMOC greenland ice cores, lake sediments and speleothems , archeological and historical records

Answer 31

16th-19th century NH focused colder winters, shorter growing seasons volcanic activity, land use changes, solar minimums, orbital forcing

Answer 32

warmer global temps 9-5kyr bp 0.5-2 degrees warmer than today not globally uniform sahara, greener and wetter, eurasia, warmer summers, northward expansions of forests orbital forcing - higher summer insolation in NH due to tild and orbit - some internal feedbacks

Answer 33

AD 700-1300 europe, longer growing seasons, North america, tree ring evidence suggests warming sunspot highs, decreased volcanic activity, stronger amoc

Answer 34

precession, shortest periodicity, most improtant changes make little difference to total solar insolation, change distribution and season of energy today, summer in NH is at aphelion, SH at pherelion (greater seasonality) 1/2 precession cycle has shifted the distribution over the holocene Early Holocene NH summer at perihelion (now nearer aphelion) so summer insolation at all NH latitudes was higher than today Decreased obliquity during the holocene, reduced insolation at high latitudes, and increased at tropics

Answer 35

Early holocene albedo decreases caused by- Ice sheet decay Vegetation expansion Sea level rise booth et al 2024 - reconstructed radiative forcing due to ice sheet driven albedo changes since LGM - combined proxy data and climate model simulations albedo forcing remained important and continued warming up until 6ka bp - explained regional warming patterns

Answer 36

direct measurment from ice cores Co2 rise since LGM correlated with temp increase Elsig et al. (2009) * 8 ppmv decline 10.5 - 8.2 ka BP then gradual 25 ppmv increase from 7–1 ka BP

Answer 37

Sunspot activity and solar flares affect solar constant Variations in solar output of 0.1% = 0.2C in global temp 11yr cycles 400 years of sunspot observations Maunder minimum - prolonged period of reduced solar activity, overall cooler conditions

Answer 38

Release of Sulphur produces sulphur dioxide and H2SO4 aerosols which back scatter solar radiation Pinatubo 1991 - 15m tonnes of SO2, global aerosol veil after 1 year, 2 years of global cooling, provides parameters for volcano-climate models

Answer 39

forams - unicellular creatures found at depths in polar, tropical and temperate marine environments benthic forams live close to sea floor - environment is relatively insulated from the shifts in temperature shells of CACO3

Answer 40

Anchoring marine isotope records to astronmical cycles - integrating the frequency of the 3 variables is mathematically complex - no single universally accepted model, varying wavelengths can be generated Lisiecki and Raymo anchored one solution to the LR04 isotopic stack, alternative solutions are equally possible Tuning precludes possibility of testing for leads and lags in global climate system

Answer 41

Annualy resolved extending back to last interglacial Idea that interstadial warming could be extremely abrupt (coope, 1975), had little validation until ice-core records Greenland archive has revealed 25 interstadial episodes (D-O events)

Answer 42

greater in older deposits Errors in ice core estimated to be 45 years at ca 8 ka, 1900 years at ca. 47 ka (Blockley et al., 2012) Arise from uncertainty in identification and counting of annual ice lauers , gaps in record, operator bias Resulting ‘maximum counting error’ is proportional to number of layers counted (hence increases linearly with depth)

Answer 43

Cheng et al 2016 Cave climate records have been important in characterising AM changes and causes U-Th dating methods, direct comparison with orbital cycles without tuning Approach hindered by limited temporal coverage Heinrich stadials or ice rafted debris events coincide with weak monsoon intervals in china Delta O 18 data from sanbao cave china Lower O18 implies higher spatially integrated monsoon rainfall between tropical monsoon sources and cave site Strong monsoon = low O18 100kyr problem - - Each of last 4 terminations characterised by one or 2 Weak Monsoon Intervals (WMI) - coincide with Heinrich events - Abrupt WMI endings are synchronous with abrupt inc in atm CH4 in antarctic ice cores

Answer 44

Rudduman 1989 - Uplift of Tibetan-Himilayan Plateau - altered circulation of atmospheric planetary waves, summer ablation is decreased (most uplift occured earlier) Emergence of panama isthmus - strengthened AMOC, increased NA temps, increased evaporation and precipitation (Keigwin, 1982) paradox Most generally accepted explanation - decrease of atmospheric CO2 concentrations, though they are not independent of the other mechanisms Lunt et al 2008, CO2 was main driver of greenland glaciation, Increase in snowfall alone is not sufficient for a greenland glaciatio

Answer 45

glacial cyales changed periodicity from 41,000 years to 100,000 Reasons proposed - nonlinear feedbacks, solid earth, ocean circulation carbon cycle