Tectonics and Orbital Variability during the Quaternary Period

Question 1

Cenozoic era -> trend of cooling yet during the Quaternary Period there were climatic fluctuations of 15°C referred to as glacial and interglacial periods -> orbitally driven

Answer 1

Quaternary (Pleistocene 2.58Myr and Holocene 11.7ka) (Lowe and Walker, 2015)

Question 2

Tilt -> 23.4° and causes each hemisphere to be orientated to the sun differently

Answer 2

Orbit -> elliptical not circular leads to perihelion (earth closer to the sun) and aphelion (earth further away from the sun)

Question 3

Obliquity -> tilt of the earth’s axis at 23.4°

Answer 3

every 41,000yrs and impacts the NH and SH seasons intensities (Maslin and Ridgewell, 2005)

Question 4

Eccentricity -> shift in the earth’s orbit from circular to elliptical

Answer 4

every 100,000yrs (Maslin and Ridgewell, 2005)

Question 5

Procession -> wobble of the earth on its’ axis alters the exposed area of the earth during perihelion and aphelion and thereby intensifies winters or summers

Answer 5

every 23,000-25,000yrs (Maslin and Ridgewell, 2005)

Question 6

Orbital forcing -> devised by James Croll (Raymo and Huybers, 2008)

Answer 6

Milankovitch developed the ideas -> orbital forcing triggers latitudinal insolation shifts -> core latitude 65°N due to the earth’s asymmetry -> marine cores outlining these shifts won over support (Hays et al., 1976; Petit et al., 1999)

Question 7

Cool NH Summer

Answer 7

low tilt = NH not facing the sun so lower insolation
eccentricity = earth in aphelion so far away from the sun
procession = NH summer occurring when less solar radiation reaches the earth

Question 8

Nick Shakelton 1967 -> Oxygen Fractionation

Answer 8

produced a temperature record for marine cores

Question 9

Last Glacial Maximum -> 20,000 - 10,000 (MIS 2)

Answer 9

125m drop in sea levels, land bridges formed e.g. Beriniga Bridge, Sunda Shelf and Doggerland (Lomolino et al., 2015)

Question 10

Marine Isotope Stages -> odd numbers = interglacial and even numbers = glacial

Answer 10

stages (a-e) -> stadial and interstadial events

Question 11

Greenland Ice Core -> 130,000 yr record

Answer 11

Vostok Ice Core -> 800,000 yr record

Question 12

Spectral Analysis -> statistical time series analysis -> ice sheet volume = 41,000 yr oscillations beginning 2.58Myr

Answer 12

mid-Pleistocene Transition 1Myr -> identified in benthic δ O-18 ice cores, switch to 100,000yr oscillations (Hays et al., 1976; Maslin and Ridgewell, 2005)

Question 13

Eccentricity Myth -> appeared that after the MPT it was the core orbital forcing mechanism

Answer 13

Eccentricity merely required to amplify procession and obliquity since ice sheets had solidified via ice-albedo and oceanic shifts -> more energy needed to destabilise (Anderson et al., 2010; Maslin and Ridgewell, 2005)

Question 14

Lambart et al., 2008

Answer 14

Antarctice ice core dust records and Loess Plateau dust records -> increase in dust aligned with peaks in O-18 abundance and therefore ice volume -> in line with glaciation = increased aridity

Question 15

uncertainties -> delay in ice sheet change from orbital forcing meaning feedback mechanisms are playing a role

Answer 15

uncertainties -> glacial periods not present across the whole globe -> Last Glacial Period ice in the SH only contributed 3%, British Isles not entirely covered in ice in the glacial periods during the Early Quaternary but was later (Lowe and Walker, 2015)

Question 16

volcanic eruptions -> global cooling as cloud condensation nuclei and dust reflect insolation

Answer 16

Krakatoa and Katamai eruptions decreased solar radiation by 10-20% (Anderson et al., 2010)

Question 17

Closing of the Isthmus of Panama 3Myr -> triggered a glaciation across the NH as the merging of NA and SH shut down the North Atlantic Drift Current and led to a 2-3°C increase in North Atlantic temperatures at the end of the Pilocene

Answer 17

Benthic δ O-18 identified a 0.2% increase in sea ice volume and a drop in sea levels by 25m 2,932-2.82Myr (end of the Pliocene) aligning with the theory (Bartoli et al., 2005).

Question 18

Drake Passage closed 10Myr

Answer 18

Antarctic circumpolar current formed to insulate Antarctica leading to a glaciation (Raymo and Ruddiman, 1992)

Question 19

BLAG Hypothesis -> plate tectonic uplift = volcanic activity -> to nullify the impact weathering increases to drawdown co2

Answer 19

(Berger, Lasaga and Garrels, 1983)

Question 20

50Myr Indo-Australian Plate collided with Asian Plate -> Tibetan Plateau formed and Cenozoic cooling began by altering planetary wave structure

Answer 20

BLAG important -> increased hydrolysis and led to intense weathering of the Himalayas -> carbon drawdown e.g. 35% of the earth’s soluble load from the Himalayas and radiogenic stronium dating identified that the primary form of weathering is silicate -> Himalayas composed of silicate rock (Raymo and Ruddiman, 1992)

Question 21

Indian Ocean Monsoon 2.6Myr -> land sea thermal contrast - land heats and cools faster than the ocean = pressure gradients

Answer 21

Tibetan Plateau enhances = Somali/Findlater Jet from 25°S off the horn of Africa 15m/s -> July to September (Rajogopalan and Molnar, 2013)

Question 22

EPICA -> European Project for Ice Coring in Antarctica -> compared Greenland and Vostok Ice Core over 8 glacial cycles

Answer 22

Similarities for 4 cycles, mid-Brunhes Event in 430,000 with the temperature of interglacial periods increasing (EPICA, 2006)

Question 23

Different ways to tune marine cores from the NH and SH with to O-18 ratios from foraminifera and SSTs

Answer 23

conducted through different models:- SIMPLEX models = age depth modelling
ELBOW models = chronologically dating but not via depth -> since been replaced with TUNE-UP.
PATCH = time series using statistics to join records together (Hays et al., 1976)

Question 24

Hays et al., 1976

Answer 24

outlines the theories proposed by Milankovitch and the mid-Pleistocene transition

Question 25

co2 concentrations were linked to the feedback mechanisms implicating glacial/interglacial transitions

Answer 25

believed that co2 amplified the orbital pacemakers -> found to be the case but there was regional asymmetry to the trend (Hogg, 2008)

Question 26

procession not as significant in causing orbital forcing -> 21,000yr impacts on ice extent across the NH but the SH nullified these and prevented glaciation periods

Answer 26

explains the lack of 22,000 yr cycles across the SH (Raymo and Huybers, 2008)

Question 27

Cryogenian Period (720-635Myr) -> snowball earth hypothesis in 1949 by Mawson -> since been rejected

Answer 27

idea that ice-albedo feedbacks = 50% ice coverage would lead to global ice coverage
some evidence -> methane core ghg in controlling global temperatures, a drop = icehouse conditions, there is neoproterozoic glacial deposits across very continent indicating previous glacial extent was more widespread than previously thought (Hoffman and Schrag, 2002)

Question 28

SPECMAP -> produced by Shackleton, Imbrie and Hays -> incorporation of O-18 isotope ratios and the lag time in their shifts in response to obliquity and procession -> identified that greenhouse gas concentrations play different contributory roles between 22,000-year procession shifts and 41,000yr obliquity driven shifts

Answer 28

Ghg concentrations are more important in procession and so are higher than obliquity as the glaciation events are more intense under the 41,000yr shifts which leads to North Atlantic Deep Water growing alkaline causing carbon sequestration by the ocean, and an increase in dust concentration increases photosynthesis in algae further increasing this sequestration (Ruddiman, 2006)

Question 29

Milankovitch proposed that obliquity driven shifts at 65°N resulted in ice formation/ glaciations

Answer 29

also proposed a 5-year lag after orbital forcing (Ruddiman, 2006)