Late Quaternary (esp. post-LGM) environmental change in the humid and seasonal tropics laeoprecipitation: was the LGM drier (and by how mu alaeotemperatures: was the LGM much cooler? - South American and PNG evidence getation and faunal response: the rise (and fall?) of refuges - South America, Africa and Indo-Austra olocene droughts and cultural responses - the Mayan example
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Late Quaternary (esp. post-LGM) environmental change in the humid and seasonal tropics KPalaeoprecipitation: was the LGM drier (and by how much)? K Palaeotemperatures:
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Late Quaternary (esp. post-LGM) environmental change in the humid and seasonal tropics
Palaeoprecipitation: was the LGM drier (and by how much)?
Palaeotemperatures: was the LGM much cooler? - South American and PNG evidence
Vegetation and faunal response: the rise (and fall?) of refuges - South America, Africa and Indo-Australia
Holocene droughts and cultural responses - the Mayan example
Cautionary note: geo-generalizations ahead!(blame large scale and a low
density of palaeo-sites)
200 sites? 20 sites?
Were the tropics arid during the
LGM ? (climate
model output)
from: Ganopolski et al., (1998) Nature, 391, 351-6
LGM aridity:
the evidence from the Amazonian fan and
Lake Junin, Peru
from:Maslin and Burns (2000) Science, 290, 2285-2287.
African lake level status at LGM
Status
LowIntermediateHighNo record (= dry?)
LGM and Holocene pollen record, Lake Victoria
From
: Sta
ger
et
al. (
1997)
Qu
ate
rnary
Rese
arc
h, 4
7, 81
-89.
Palaeo-lake shorelines inEast Africa
+100
0
-100
0 10 20 30
L. Victoria
L. Turkana (Rudolf)
?
?
? ?
ka, BP
metr
es
(rel. t
o P
D)
200 kmBase map: Good’s Atlas
LGM palaeo-temperature:the CLIMAP model (1970’s).
Apart from the areas influenced by the eastern boundary currents, tropical SST values at the LGM were estimated (from foram 18O values) to be only about 1°C less than at present.
SST (August)CLIMAP Project Members, (1976)
The surface of the ice-age Earth. Science 191, 1131-1137
Coupled-climate model
output of glacial
conditions: tropical air
temperatures about 5°C less; SST 3-4°C less than at present
from: Ganopolski et al., (1998) Nature, 391, 351-6
LGM palaeotemperatures:evidence from tropical ice
cores
From: Thompson et al., (2000) Quaternary Science Reviews, 19, 19-35.
Sajama
LGM palaeotemperatures:evidence from tropical ice
cores0 5 10 15 20 25 ka BP
From: Thompson et al., (2000) Quaternary Science Reviews, 19, 19-35.
4.5°C
5°C
5°C
LGM palaeotemperatures:palaeoecological evidence
18O values from corals dating from 18 ka BP in Barbados indicate SST values ~5° C lower than at present (de Villiers, et al., (1995) Science 269, 1247-1249.)
changes in vegetation at numerous sites in the montane tropics suggest that the altitudinal limits of vegetation belts were ~ 900 m lower at LGM than at present (equivalent to a temperature lowering of 5°C) (Bush, et al., (2001) in Markgraf (ed.), Interhemispheric Climate Linkages, Academic Press, pp. 293-306.)
LGM palaeotemperatures in the Neotropics
El Valle Panama 8 N 500 -6 14San Juan BoscoEcuador 3 N 970 -7.5 35Lagoa Pata Brazil 0 300 -5 17Lagoa Verde Brazil 0 300 -5 ?Carajas Brazil 6 S 700 -5 10Serra Grande Brazil 7 S ? -5 ?Aguas EmedadasBrazil 15 S 1040 -5 17Serra Negra Brazil 19 S 1170 -5 ?Salitre Brazil 19 S 1050 -5 13Catas Altas Brazil 20 S 755 -7 21-31 Botucatu Brazil 23 S 770 -5 to -7 ?
Site Country Lat. Alt (m)Cooling(°C)Age(cal ka)
from: Bush et al., (2001) in Markgraf (ed.) “Interhemispheric Climate Linkages”, Academic Press, Table 1.
The effects of a 5°C lowering of air temperature at LGM in the
Neotropics
Temperature (coldest month) in the tropics at LGM compared to
from: Tallis (1991) Plant Community History, Chapman and Hall
The demise of refuge theory?The Lake Pata record
from
: C
olin
vaux e
t al., (1
99
6)
Sci
ence
, 2
74
, 8
5-8
8.
Tree
s
Is a compromise possible?
2
1 3
Lake Pata, Brazil1. Laguna Chaplin, Bolivia2. Laguna Sardinas, Colombia3. Lago do Pires, BrazilMaps: Good’s Atlas
The palaeoclimatic record from
eastern Bolivia
from: Mayle et al (2000) Science, 290, 2291-2294.
Late Holocene expansion of
Amazonian rainforests“... the humid evergreen rain forests of eastern Bolivia have been expanding southward over the past 3000 years and that their present-day limit represents the southernmost extent of Amazonian rain forest over at least the past 50,000 years. This rain forest expansion is attributed to increased seasonal latitudinal migration of the Intertropical Convergence Zone, which can in turn be explained by Milankovitch astronomic forcing.”
Mayle et al., (2000) Science. 290, 2291-2294.
from: Grimm et al., (2001) in Markgraf (ed.) “Interhemispheric Climate Linkages”, Academic Press, pp. 324-367.
The palaeo-climatic record from east-
central Brazil
The palaeo-climatic record from
north-eastern
Colombia
from: Grimm et al., (2001) in Markgraf (ed.) “Interhemispheric Climate Linkages”, Academic Press, pp. 324-367.
Long core sites (Australia-Indonesian region)
12
3
4
Numbers refer to cores on next slide
1 2 3 4
Long cores: Australia-Indonesia
Lyn
ch
’s C
rate
r: Q
ueen
sla
nd
Holocene climate change in East Africa
hu
mid
peri
od
Late Holocene droughts on the margins of the humid tropics: the collapse of
Mayan civilization
Historical droughtsA sustained drought in AD 1648-1654 left painful memories in the Yucatan:
“ The starvation as it developed was terrible and desolating…The poor, wasted and gaunt, …pulling up grass and roots, ate them to avoid starvation; public places were sown with corpses; the inhabitants looked more like specters than living men, entire places were abandoned … the best populated sites of Yucatan were threatened with being left deserted and barren”
Molina Hübbe (1941, p 20-21), quoted in Gill (2000)
“The Great Maya Droughts”, University of New Mexico Press, p. 305
Cultural chronology in the Mayan area
Source:David A. Hodell
Department of Geology, University of Florida
Growth and demise of classic Maya culture
Source: David A. Hodell, Department of Geology, University of Florida
810860
890-910
Clusters of abrupt events
(last dates on Maya
monuments)
[after Gill (2000)p. 326].
Symptoms and possible causes of the Maya
collapseSymptoms:• Rapid depopulation of the countryside and
ceremonial centres in 50-100 years;• Abandonment of administrative centres and
palaces;• Cessation of building, monument construction,
and pottery manufacture; demise of classic calendrical and writing systems.