Late Quaternary environments of the dry tropics and subtropics

1
Late Quaternary environments of the dry tropics
and subtropics

• North Africa
• Arabia - India
• Australia
• South Africa
• South America

2
Saharan dust
In the journal of his voyage aboard HMS Beagle in
1833, Darwin commented on the atmospheric dust
off the Cape Verde Islands, dirtying everything
on board. In 1844 Ehrenberg was surprised to
find that the valves of freshwater diatoms
comprised a substantial component of Darwins
dust samples. Recent samples (e.g. those
collected in 1982 aboard the French research
vessel Le Chinon) demonstrate that about 50
these diatoms belong to planktonic taxa such as
Aulacoseira.. The remainder are freshwater
benthics. Where do they come from?
3
Saharan dust storm over adjacent Atlantic Ocean
and ODP core site
Arrows indicate dominant winter wind direction
ODP658C
image terra.
nasa
.
gov
4
ODP658C core log
deMenocal et al., (2000) Quaternary Science Rev.,
19, 347-361
5
Dust sources dried beds of early-mid Holocene
Saharan lakes
Yardangs in lake sediments, C. Sahara
Relict shorelines (in background), L. Asal,
Djibouti (PAGES News)
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Summer monsoon climates of N.Africa and the Near
East
SE Trades
SW Monsoon
lt100 mm
May 01- Sept 31
gt1000 mm
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Four N. African palaeosites
1. Sebhka Mellala 3. Oyo (West Nubia)
5. Fayum2. Lake Chad 4. Lake Abhé
1
5
3
2
4
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Palaeo-lake deposits, Sebhka Mellala,Algeria
8.2 cal ka cold snap
9
Lake Chadrecent hydrological changes
1963
50 km
1997
http//edcwww.cr.usgs.gov/earthshots/slow/LakeChad
/LakeChad
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Lake Mega-Chad
Bougdouma
1100 ft (300m) shoreline dates to 20-30 ka BP.
L. Mega-Chad covered 600 000 km2 and was 200
m deep
Kajemarum
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Palaeo-lake deposits, Bougdouma,Niger
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Late Holocene climate change, Kajemarum Oasis, NE
Nigeria
shallow saline
deep fresh
from Holmes et al., (1998) J. Paleolimnology,
20, 369-380
13
West Nubian sites
14
West Nubianpalaeo-lake
Hoelzmann et al. (2001) Palaeo3 169, 193-217.
15
Pollen evidence
from Roberts, N. (1996) The Holocene, 2 ed.
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Lake Ahbé, Ethiopia
4200 cal yr BP
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Variations in Nile discharge
The Nilometer at Roda (A.D.641 - present)
Said (1993) The River Nile Geology, Hydrology
and Utilization Pergamon Press
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Nile flow (9000 - 300 BC)
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Lake Moeris(Fayum depression)
25 0 -25 -50
?
?
Elevation (m, asl)
Birket Qarun
9 8 7 6 5 4
3 2 1 0 ka BP
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The end of the humid period and the demise of the
Egyptian Old Kingdom(2180 BC4200 cal yr BP)
Lo, the desert claims the land Towns are ravaged,
Upper Egypt became a wasteland Lo, everyone's
hair has fallen out Lo, great and small say, "I
wish I were dead" Lo, children of nobles are
dashed against walls Infants are put on high
ground Food is lacking Wearers of fine linen are
beaten with sticks Ladies suffer like
maidservants Lo, those who were entombed are cast
on high grounds Men stir up strife
unopposed Groaning is throughout the land,
mingled with laments See now the land deprived of
kingship What the pyramid hid is empty The
People are diminished. (Egyptian sage, Ipuwer)
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low dust influx
11 10 9 8 7 6 5 4
3 2 1 0 ka BP
high dust influx
ODP685C
S. Mellala
high
dry
low inter.
Lake Chad
arid wet
arid
S.W. Egypt
Oyo, Sudan
Nubia
L. Ahbé,
L. Fayum
Nile R.
Malville et al., (1998), Nature 392,
488-491 (discharge units are billion
cumecs/yr)
200 100
22
Vegetation of north and central Africa 8000 ka
BPpink desert pale yellow grass savanna
http//www.uni-mannheim.de/phygeo/8000BP.htm
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Rock art, Tassilli and Ennedi massifs, central
and eastern Sahara
a
a mouflon b, c giraffes
c
b
a and c http//ennedi.free.fr/
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Sites in Arabia and Pakistan
74KL
Yemen Oman Thar desert
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74 KL d18O, dust deposition and CaCo3 production
Dust minimum7850 8850
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Holocene climate change in Arabia
11 10 9 8 7 6 5 4
3 2 1 0 ka BP
dust minimum
74 KL
1
Calcite deposition rate in Hoti Cave (Neff et
al., (2001) Nature, 411, 290-292.
mm/yr
0
abandoned villages
YEMEN OMAN
agriculture
Archaeological record

wet hyperarid
Rock hyrax (Procavia capensis) middens
Data from
http//www.usgs.gov/public/press/public_affairs/p
ress_releases/pr1482.html
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Indian subcontinent Thar desert
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Thar desert paleolake record
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Changing palaeo-climates in southern Africa the
Mega-Kalahari
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Dune-activity phases, southern Africa
from OConnor and Thomas (1999) Quaternary
Research, 52, 44-55.
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Monsoon palaeoclimate sites, NW Australia
NE Trades (Nov. -April)
2
1
1. Gregory Lakes 2. Fitzroy R. basin
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Late Pleistocene pluvial phases in NW Australia
from Bowler et al., (2001) Quaternary
International, 83-85, 63-80.
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Post-glacial monsoon initiation
from Wrywoll and Miller (2001) Quaternary
International, 83-85, 119-128.
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Selected palaeoclimate sites, Atacama desert and
neighbouring areas
0
3
Moche culture area
2
1
30S
1. Salar de Atacama, Chile 2. Lake Titicaca,
Bolivia 3. Galapagos archipelago
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Late Quaternary wet phases, Salar de Atacama
from Bobst et al., (2001) Palaeo3, 173, 21-42.
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Late Holocene climatic variation, Bolivian
altiplano
Moche culture
from Abbot et al., (1997) Quaternary Research,
47, 169-180
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A 6000-yr record of El Niño activity from the
Galapagos Islands
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Millenial-scale variablity of El Niño events in
the Galapagos Islands
435 events in last 6000 years
Bainbridge Crater Lake During moderate El Niño
events the surface waters of this hypersaline
lake become relatively fresh and carbonates are
precipitated during severe events there is
erosion of the crater walls into the lake.
Laminae in the organic-rich salts that have
collected on the lake bed record these events
Data Riedinger et al., (2002) J. Paleolimnology
27, 1-7.