Low Latitude - Issues and Key Themes

Question 1

glacial-interglacial framework

Answer 1

high latitude cooling = steeper meridional temperature gradient = H.C. intensification and wind speeds enhanced = lower sea levels (Anderson et al., 2010)

Question 2

general rules for climate oscillations

Answer 2

higher latitudes = temp change w/ ice growth/retreat
lower latitudes = precipitation change w/humidity or aridity

Question 3

vostok ice core identified the LGM as

Answer 3

110-11.5ka (Petit et al., 1999)

Question 4

LGM was around 20ka

Answer 4

triggered by solar forcing
climate models forced latitudinal LGM and there was a global temp drop of 5.8°C while l.l. did not change in temp (Schenider von Deimling et al., 2006)
proxies indicate a 4°C temp change (Annan and Hargreaves, 2013)
sea levels dropped 120m (Waelbroech et al., 2002) = 45% reduction in precipitation rates (van der Hammen and Hooiemestra, 2000)

Question 5

Issues with the LGM

Answer 5

l.l. -> not covered by ice, 1/3 of global land covered, SH = ice free
maximum extent variable across the globe e.g. West Antarctica (29-33ka) other regions around 26.5ka (Clark et al., 2009)

Question 6

glacial-aridity hypothesis (Sarnthein, 1978)

Answer 6

increased dust plumes (Harmattan) in sediment core taken of western coastline of N.A = increased aridity during glacial periods due to an enhancement of the p.g. (Sarnthein, 1978)

Question 7

controversy of the glacial-aridity hypothesis

Answer 7

spatial complexity to patterns
dust in icre cores = glacial foreland erosion not deserts (Machowal et al., 1999).
BUT -> trace dust sources via geochemical means e.g. analysing radiogenic Sr-Nd isotopes = dust in Greenland cores from N. Mongolia and Chinese Loess Plateau (Ujvari et al., 2015)

Question 8

support for the glacial-aridity hypothesis

Answer 8

glacial periods = aeolian deposits across Australia (Hesse, 1994) and the south atlantic (Stuut, 2004)
glacial periods = more dust in EPICA and Vostok ice cores (Lambert et al., 2018)
BIOME3 dust flux modelling = 20x more dust in the last glacial section of cores (Mahowald et al., 1999)

Question 9

l.l. change in the LGM

Answer 9

lower obliquity caused the LGM
sea ice extent over Antarctic Sea increased -> enhanced p.g. -> intensified westerlies and led to more moisture advected from Atlantic Ocean into S. Africa = more precipitation (Chase and Meadows, 2007) -> but no precipitation across eastern S. Africa

Question 10

Amazonian Forest Birds (Haffer, 1969) -> early devising of the Tropical Refugia Theory

Answer 10

Aridity expanded during glacial periods.
Led to wet forest being replaced by savannah e.g. Amazon Basin and Congo Basin -> tropical rainforest pushed to isolated mountain locations = geographic isolation and speciation/genetic drift.
Sand dunes replaced savannah regions.
Further enhanced by tectonic processes e.g. Uplift of Andes end of Tertiary prior to Quaternary

Question 11

evidence for the Tropical Refugia Theory

Answer 11

analysed Roondonia (S.A.) that there was savanna pollen, but tropical rainforest pollen is located above (van der Hammer, 2000)

Question 12

criticisms of the Tropical Refugia Theory

Answer 12

little evidence of savannah, and the extremity of the hypothesis was over exaggerated (Haberle and Maslin, 1999)
speciation occurred prior to the Quaternary (Ribas et al., 2012)
C-isotope analysis of soils = no C4 plant (savannah-favouring) evidence where C3 plants are located (Freycon et al., 2010)

Question 13

landbridges = facilitated the movement of species

Answer 13

Sunda Shelf = indonesia to Malaysia
Isthmus of Panama = N. America to S. America
(Lomolino et al., 2016)

Question 14

limitations of pollen

Answer 14

not a reliable proxy in drylands due to oxidation (Thomas and Burrough, 2012)

Question 15

africa proxy records

Answer 15

pollen in terrestrial regions (Scott et al., 2012) and in marine regions e.g. ‘Site 1078C’ off the coast of Angola (Dunpont et al., 2008)

Question 16

geochemical data from leaf wax in Lake Tanganyika sediment cores E. Africa (Tierney et al., 2010)

Answer 16

LGM = 32% decrease in lake volume, 4-5°C temp change
caused by changes to the Indian Ocean Monsoon + SSTs

Question 17

geoproxies = geomorphological features

Answer 17

inferences are harder due to diagenesis e.g. sediment reshaped after deposition (Chase and Meadows, 2007)

Question 18

multivariate calibration-functions = pollen records in S. Africa (Scott et al., 2012).

Answer 18

lower temps during HS1 and HS2 -< increased humidity during the YD across S. Africa but not uniform (Scott et al., 2012)
Start of Holocene = precipitation increased over N.E. Africa due to procession weakening the SSTs in the Indian Ocean -> lagged across central S. Africa as ITCZ was displaced southward

Question 19

lower latitude insolation changes influence the net radiation budget = temp changes also important at low latitudes e.g. African Humid Period and THC

Answer 19

LGM -> THC (AMOC slowed) = warmer temperatures were trapped at lower latitudes (Broecker, 1998)

Question 20

African Humid Period (14.8ka-5.5ka) -> intensification of the African monsoon due to 8% increase in orbital forcing

Answer 20

procession = perihelion + boreal summer
more northerly position of rainbelt = 40% increase in precipitation led to vegetation + lakes over Sahara (deMenocal et al., 2000)
end driven by vegetation shifts -> modelled by CLIMBER 2 (deMenocal et al., 2000)

Question 21

African Humid Periods

Answer 21

20 humid periods across N. Africa over 0.8 million yrs (Armstrong et al., 2023)
Site 658C Cap Blanc (offshore west of N. Africa -> dust supplied by the Sahara (deMenocal et al., 2000)
HadCM3B model = simulates the humid period well
amplitude of AHPs = high variability -> eccentricity on ice sheets and a suppression of the monsoon formation through cooling effects
Lake Tanganyika -> geochemical leaf wax proxy = overflowed during AHP (Tierney et al., 2010).
AHP -> not in S. Africa but lake levels were higher (Burrough and Thomas, 2013)

Question 22

Arabian Humid Period?

Answer 22

subtropical rain belt extended over Arabia (Woor et al., 2022)
evidence in Nafud Desert, Saudi Arabia (Parton et al., 2018) and grassland in Arabia (Dinies et al., 2015)