andes to amazonia: what we think we know and what we don’t. mark bush florida institute of...
TRANSCRIPT
Andes to Amazonia: What we think we know and what we don’t.
Mark BushFlorida Instituteof Technology
&
Miles SilmanWake Forest University
Some of the big questions before us:To what extent can Andean records inform us about Amazonia?How much climatic variation was there within ice age Amazonia?How robust are the data for a 5oC cooling in the terrestrial Neotropics?How dry was Amazonia during the last ice-age?
Refugia
• Raised on modern biogeographic data but no reliable paeleocological data.
• Most recent manifestation is untestable as it has no time or habitat constraints (Haffer and Prance Amazoniana 2002).
Brown (1991)
Dry Forest Arcs
• Modern biogeographic data used to suggest the presence of a past habitat bridge of dry forests.
• Assumed to be ice-age• But there is no basis for
this assumption.• Nor a real difference from
modern required to allow movement of species.
Pennington et al. ( J. Biogeogr. 2000)
Different ideas about Arcs
Pennington et al. (J. Biogeogr. 2000)Wüster et al. (Molec. Ecol. 2005)
Miles et al. (GEB, 2004)
Sites that we’ll discuss
Amazon fan
ConsueloTiticaca
Negra
Pata &Verde Maicuru
Carajas
TRMM data and paleo locations
• Not surprising that the different paleoecological records are providing a different story
Late Glacial and Holocene Vegetation from Lake Titicaca
Paduano et al. (Palaeo3 2003)
The Glad 800 drill rig (NSF/ODP) was hauled to Titicaca in 2001 and three cores were raised from deep water under the supervision of Paul Baker, Geoff Seltzer and Sheri Fritz.
Long record from core LTO1-2B,
Titicaca Probably four, full glacial
cycles.
Pollen concentration is a proxy for productivity, and indicator of near Holocene temperatures.
MIS 5
MIS 7
MIS 9
MIS 11
Long record from core LTO1-2B,
Titicaca
MIS 5e
MIS 7
MIS 9
MIS 11
Isoetes may be important for glacial temperature.
Too cold for pollen or Isoetes
D-O cycles in Titicaca
Work in progress
Work in progress
GISPTiticaca pollenconcentration
D-O cycles in Titicaca
Lake level and insolation
• Lake Titicaca and the Salar de Uyuni, Bolivia, respond to DJF insolation.
• Lake level at Titicaca varies synchronously with Pata for the last 70,000 years.
20 40K yr BP
Baker et al. (Science 2001)
Hill of Six Lakes
Lake level fluctuation in Amazonia
• Lakes Pata and Verde show continuous forest cover through last two glacial periods.
• Periods of low lake level correlate with periods of high K+ concentrations in sediment in Pata.
• Low lake level due to reduced precipitation.
Lake level and orbital forcing
• Peak low-lake level corresponds to 11 K BP and 33 K BP with 22 K BP wet (matches Titicaca).
• Aligns to orbital rhythm of variation in insolation.
• Continuous forest cover suggests decrease in precipitation in the wet season rather than dry season.
Bush et al. (J. Paleolimn. 2002)
Bush et al. (Palaeo3 2004)
Lake Pata, Brazil
10, 000
18,00022,00034,000
48,000
Cal BP
Colinvaux et al. (Science 1996)
Fusing modern ecology and paleoecology
• Linking Amazon and Andean forests– Single system– Space and Time
• Fully vouchered 1 ha plots lowlands to treeline (17 to date)
• Series of lakes along transects
• Peru and Bolivia
Andes Biodiversity Consortium
L
LLL
L
L
LLL
LL
L
LLLLLL
LLL
L
L
L
LLL
Modern Ecology: 77 ha (Peru) -17 Montane, 60 Lowland
w3 tropicos databasePaleoecology: 24 Lakes
0 1000 2000 3000 4000 5000Piper
0.0000
0.0004
0.0008
0.0012
0 1000 2000 3000 4000 5000Weinmannia
0.0000
0.0004
0.0008
0.0012
0 1000 2000 3000 4000 5000Clethra
0.0000
0.0004
0.0008
0.0012
0 1000 2000 3000 4000 5000Polylepis
0.0000
0.0004
0.0008
0.0012
Collection data for 4 genera
0 1000 2000 3000 4000 5000Piper
0.0000
0.0004
0.0008
0.0012
0 1000 2000 3000 4000 5000Weinmannia
0.0000
0.0004
0.0008
0.0012
0 1000 2000 3000 4000 5000Clethra
0.0000
0.0004
0.0008
0.0012
0 1000 2000 3000 4000 5000Polylepis
0.0000
0.0004
0.0008
0.0012
Representation of pollen taxa
Continuous wet forest taxa for 50,000 yrs
Gradual change in community composition
Bush et al. (Science 2004)
Consuelo Ordination
Two basic states(1) 30 kyr
(2) 11 kyr
Evidence of cycles
DCA Axis 1
0 50 100 150 200
Age (cal y
r bp)
0
10000
20000
30000
40000
50000
DCA Axis 1 vs. Time
• Two major forest types
• Periodic changes– ENSO, drought
cycles, D-O events
• Gradual ~8-10 ky transition
• Non-equilibrium?
0 1000 2000 3000 4000 5000
Predicted elevation (m)
0.000
0.005
0.010
0.015
0.020
0.025LG
M (21K
cal y
r B
P) Post
eri
or
Densi
ty~1200m
0.0055 °C m-1
~6.6 °C cooler
Elevation for taxa found 21,000 years ago (500 cm pollen assemblage)
Q: What does time course look like?
If taxa were found co-occurring today, most likely elevation
would be 2400m
Laguna Negra waveletsLake at 3300 m elev, 7oS.
Dry event
Bush et al. (JQS In press)
Consuelo and Pata
Pata
Pata
Maicuru
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
504200
405160
409070
6012960
601568024029550
28038890
>40000
C-14 (
years
BP)
Depth (
cm)
Litholo
gy
20% 40% 60% 80%
Arbore
al low
land for
est
20
Arbore
al fores
t (coo
l-ada
pted)
20 40
Terre
strial
herbs
20 40
Aqua
tic he
rbs
20
Unide
ntifie
d po
llen g
rains
100 200 300
Spore
s
2000 4000 6000 8000
Algae
Zone
MAI-
MAI-2
MAI-2
MAI-3
MAI-3
Percentage Sum
15-30K
hiatus
Colinvaux et al. (Amazoniana 2001)
15,000
25,000
31,000
>50,000
Carajas, eastern Amazonia
15-25Khiatus
Absy et al. (Compt Rendus 1991)
Amazon Fan data (S. Haberle 1999)
Fan deposits reflect pollen from entire basin
Ice age does not have more grass pollen than modern
Modern Grass
Ice age Grass
Amazon fan reconsidered
Discharge source and Fan data
What is cooling? All these sites provide evidence of a 5-7oC cooling at the LGM
13oC
8oC
Plants probably respond to minimum temperatures, and absolute modern minima are very different across the basin.Were absolute minima in the north reduced while monthly minima were reduced in the south?
Extract sub-region for training and recognition
One way forward: Improving pollen recognition
Using SEM and vector-based computer modeling we aim to improve identification of key taxa to species or species group.More precise taxonomy = more precise bioclimatic envelope modeling
What we think we know: Strong decline in species diversity with elevation. Species migrate individualistically in response to climate change. Strong cooling signature in all Pleistocene records with some
species’ ranges typically moving 1000 m -1500 m downslope. Lowland taxa are adapted to Pleistocene cooling. Amazonian paleoclimates were temporally and spatially
heterogeneous. Refugia and savanna corridors are not grounded in reality.
What we don’t know:Do we have to reconcile the terrestrial record with the marine record?Difference in temperature could be absolute minima (NH) or mean temperature (SH)? To what extent forest structure changed.Fine-resolution climate change from the lowlands.The full impact of Holocene human activities.
The Coring Gang
Andrea Gomez
Alex CorreaDunia Urrego
Jen Hanselman
Dr. Will Gosling