late quaternary (esp. post-lgm) environmental change in the humid and seasonal tropics...

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

PD

www.bgc-jena.mpg.de/bgc_prentice/databases/ferrara/fig4.jpg

Was cooling around Atlantic greater

than around margins of Indian and Pacific Oceans?

or not?(data from PNG highlands)

PD vs. LGM: the effects of lowered temperature and

reduced rainfall

LGM

in t

he h

um

id t

ropic

s:

pla

nt

and a

nim

al re

sponse

s

Were tropical rain forests restricted to small refuges at LGM?

The rise of refuge theory*:endemism in the

Neo-tropical forest

avifauna

from: Prance and Lovejoy (1985) Amazonia, Oxford U.P. * Haffer (1969)

Science, 165, 131-137.

Ranges of related forest bird species and

subspecies

Trumpeters(Psophia)

Jacamars(Galbula)

Ranges of related forest bird species and

subspecies

Aracaris(Pteroglossus) Toucans

(Rhamphastos)

Species and

subspecies ranges:Heliconius butterflies

Inferred LGM forest refuges

based on: 1. birds

2. lizards3. butterflies4. four tree

families5. scorpions

From

: N

ore

s (1

99

9)

J. B

iogeogr a

phy, 2

6, 4

75

-48

5

TRF refuges: a minimalist

reconstruction

Lake Pata

forest desert

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.

Inferred Causes• Natural - soil exhaustion, soil ersion,

hurricanes, drought, disease• Social - peasant revolt, civil war, invasion

The case for mega-drought:palaeo-climatic results from

Yucatan lakes

Source:David A. Hodell

Department of Geology, University of Florida

Chicanacanab Lake

Symptoms of drought in a closed lake basin in a

karstic landscape

Source:David A. Hodell

Department of Geology, University of Florida

Symptoms of drought; shelly layers point to low accumulation of plant

organics

Source:David A. Hodell

Department of Geology, University of Florida

The Holocene record from Lake Chichancanab

Source:David A. Hodell

Department of Geology, University of Florida

The Holocene record from Lake Chichancanab: 18O in ostracode

tests

860 1650

Source:David A. Hodell

Department of Geology, University of Florida