Late Quaternary (esp. post-LGM) environmental change in the humid and seasonal tropics

1
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

2
Cautionary note geo-generalizations
ahead!(blame large scale and a low density of
palaeo-sites)
200 sites? 20 sites?
3
Were the tropics arid during the LGM ? (climate
model output)
from Ganopolski et al., (1998) Nature, 391,
351-6
4
LGM ariditythe evidence from the Amazonian fan
and Lake Junin, Peru
fromMaslin and Burns (2000) Science, 290,
2285-2287.
5
African lake level status at LGM
6
LGM and Holocene pollen record, Lake Victoria
From Stager et al. (1997) Quaternary Research,
47, 81-89.
7
Palaeo-lake shorelines inEast Africa
100 0 -100
L. Victoria
L. Turkana (Rudolf)
?
?
metres (rel. to PD)
?
?
0 10 20 30
ka, BP
200 km
Base map Goods Atlas
8
LGM palaeo-temperaturethe CLIMAP model (1970s).
CLIMAP Project Members,  (1976) The surface of
the ice-age Earth.    Science 191, 1131-1137
SST (August)
Apart from the areas influenced by the eastern
boundary currents, tropical SST values at the LGM
were estimated (from foram d18O values) to be
only about 1C less than at present.
9
Coupled-climate model output of glacial
conditions tropical air temperatures about 5C
less SST 3-4C less than at present
from Ganopolski et al., (1998) Nature, 391,
351-6
10
LGM palaeotemperaturesevidence from tropical
ice cores
Sajama
From Thompson et al., (2000) Quaternary Science
Reviews, 19, 19-35.
11
LGM palaeotemperaturesevidence from tropical
ice cores
0 5 10 15
20 25 ka BP
4.5C
5C
5C
From Thompson et al., (2000) Quaternary Science
Reviews, 19, 19-35.
12
LGM palaeotemperaturespalaeoecological evidence

• d18O 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 5C) (Bush, et al.,
  (2001) in Markgraf (ed.), Interhemispheric
  Climate Linkages, Academic Press, pp.
  293-306.)

13
LGM palaeotemperatures in the Neotropics
Site Country Lat. Alt (m) Cooling(C) Age(cal ka)
El Valle Panama 8 N 500 -6 14 San Juan
Bosco Ecuador 3 N 970 -7.5 35 Lagoa
Pata Brazil 0 300 -5 17 Lagoa Verde Brazil 0 300 -
5 ? Carajas Brazil 6 S 700 -5 10 Serra
Grande Brazil 7 S ? -5 ? Aguas Emedadas Brazil 15
S 1040 -5 17 Serra Negra Brazil 19
S 1170 -5 ? Salitre Brazil 19 S 1050 -5 13 Catas
Altas Brazil 20 S 755 -7 21-31
Botucatu Brazil 23 S 770 -5 to -7 ?
from Bush et al., (2001) in Markgraf (ed.)
Interhemispheric Climate Linkages, Academic
Press, Table 1.
14
The effects of a 5C lowering of air temperature
at LGM in the Neotropics
15
Temperature (coldest month) in the tropics at LGM
compared to PD
Was cooling around Atlantic greater than around
margins of Indian and Pacific Oceans?
www.bgc-jena.mpg.de/bgc_prentice/ databases/ferrar
a/fig4.jpg
16
or not? (data from PNG highlands)
17
PD vs. LGM the effects of lowered temperature
and reduced rainfall
18
LGM in the humid tropics plant and animal
responses
Were tropical rain forests restricted to small
refuges at LGM?
19
The rise of refuge theoryendemism in the
Neo-tropical forest avifauna
Haffer (1969) Science, 165, 131-137.
from Prance and Lovejoy (1985) Amazonia, Oxford
U.P.
20
Ranges of related forest bird species and
subspecies
Trumpeters (Psophia)
Jacamars (Galbula)
21
Ranges of related forest bird species and
subspecies
Aracaris (Pteroglossus)
Toucans (Rhamphastos)
22
Species and subspecies rangesHeliconius
butterflies
23
Inferred LGM forest refuges based on 1.
birds2. lizards3. butterflies4. four tree
families5. scorpions
From Nores (1999) J. Biogeography, 26, 475-485
24
TRF refuges a minimalist reconstruction
Lake Pata
forest desert
from Tallis (1991) Plant Community History,
Chapman and Hall
25
The demise of refuge theory?The Lake Pata record
Trees
from Colinvaux et al., (1996) Science, 274,
85-88.
26
Is a compromise possible?
2
1
3
Lake Pata, Brazil1. Laguna Chaplin,
Bolivia 2. Laguna Sardinas, Colombia 3. Lago do
Pires, Brazil
Maps Goods Atlas
27
The palaeoclimatic record from eastern Bolivia
from Mayle et al (2000) Science, 290,
2291-2294.
28
Late Holocene expansion ofAmazonian 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.
29
The palaeo-climatic record from east-central
Brazil
from Grimm et al., (2001) in Markgraf (ed.)
Interhemispheric Climate Linkages, Academic
Press, pp. 324-367.
30
The palaeo-climatic record from north-eastern
Colombia
from Grimm et al., (2001) in Markgraf (ed.)
Interhemispheric Climate Linkages, Academic
Press, pp. 324-367.
31
Long core sites (Australia-Indonesian region)
2
1
4
3
Numbers refer to cores on next slide
32
Long cores Australia-Indonesia
1 2 3
4
33
Lynchs Crater Queensland
34
Holocene climate change in East Africa
humid period
35
Late Holocene droughts on the margins of the
humid tropics the collapse of Mayan civilization
36
Historical droughts
A sustained drought in AD 1648-1654 left painful
memories in the Yucatan The starvation as it
developed was terrible and desolatingThe 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
37
Cultural chronology in the Mayan area
Source David A. Hodell Department of Geology,
University of Florida
38
Growth and demise of classic Maya culture
Clusters of abrupt events (last dates on Maya
monuments) after Gill (2000) p. 326.
810
860
890- 910
Source David A. Hodell, Department of Geology,
University of Florida
39
Symptoms and possible causes of the Maya collapse

• Symptoms
• 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.
• Inferred Causes
• Natural - soil exhaustion, soil ersion,
  hurricanes, drought, disease
• Social - peasant revolt, civil war, invasion

40
The case for mega-droughtpalaeo-climatic
results from Yucatan lakes
Source David A. Hodell Department of Geology,
University of Florida
Chicanacanab Lake
41
Symptoms of drought in a closed lake basin in a
karstic landscape
Source David A. Hodell Department of Geology,
University of Florida
42
Symptoms of drought shelly layers point to low
accumulation of plant organics
Source David A. Hodell Department of Geology,
University of Florida
43
The Holocene record from Lake Chichancanab
Source David A. Hodell Department of Geology,
University of Florida
44
The Holocene record from Lake Chichancanab d18O
in ostracode tests
Source David A. Hodell Department of Geology,
University of Florida