Response of Rwenzori (Uganda – DR Congo) Glaciers and Mountain Lake
Ecosystems to Climate Change: Past, Present, Future
Hilde Eggermont, Ghent University, Belgium
James Russell, Brown University, Providence, US
Dirk Verschuren, Ghent University, Belgium
Outline
• Study area ‘Mountains of the Moon’
• Context & Aims
• Strategy & Preliminary results
• Avenues for future research
DR Congo
UGANDA
Observations of glacial termini confirm rapid glacial recession from 1906 to present
From R. Taylor et al. (2007; ECRC Research report N° 113).
Redrawn and adapted from Kaser and Osmaston (2002; ISBN 0 521 63333 8)
Controlling factors of deglaciation are still the subject of debate...
• Rising temperatures in recent decades
(e.g. Bradley et al. 2006; Thompson et al. 2006; Taylor et al. 2006a-b)
• Decrease in humidity at the end of the 19th century (ca. 1880)
(e.g. Kaser et al. 2004; Mölg and Hardy 2004; Mölg et al. 2006)
Lack of continuous quantitative records of alpine glacial extent in tropical East Africa prior to the 20th
century has left the precise timing and drivers of recent glacial recession in the region equivocal
Resilience of afroalpine glaciers and ecosystems against global warming remains largely unknown
Overall Aim – To gain key insights into
(1) Modern climatic, limnological and ecological conditions
i.e. establishing (ecological, biological, physico-chemical) baseline data for the still relatively pristine
Rwenzori lakes against which to compare future changes
(2) Century-scale variability in rainfall and temperature and their impacts on alpine glaciation in central
equatorial Africa during the mid-to late Holocene
- development/calibration of climate proxies (e.g. Rainfall-independent paleothermometers)
- long-term multi-proxy reconstructions in multiple lake sites (i.e. to separate regional climate signals
from site-specific ecological processes)
Strategy and preliminary results
Fieldwork:
July 2005 (dry season)
July 2006 (dry season)
May 2007 (wet season)
Lakes
Pools
Eggermont et al. 2007. Hydrobiologia 592: 151-173
East Bukurungu, 3801 m, 17.3 m depth
Lake Mahoma, 2990 m, 25.6 m depth
Lake Bigata, 3998 m, 18.0 m depth
East Bukurungu, 3801 m, 17.3 m
depth
Lake Batoda, 3890 m, 15.0 depth
Lake Bujuku, 3891 m, 13.5 m depth
Upper Kitandara, 4009 m, 14.5 m depth
Lower Kitandara, 3989 m, 11 m depth
Lac du Speke, 4235 m, 17 m depth
Mutinda Pool, 3507 m
Kamsongi’s
Pool,
Jesephat’s
Pool, 4100
m
Baguma’s Pool, 3993 m
4490 m, 0.8 m depth
Salomon’s Pool, 4480 m
Strategy and preliminary results
1. Determination of topography and vegetation
2. Determination of lake bathymetry
3. Recovery of continuous profiles of T,
conductivity, pH and oxygen
4. Collection of water samples in lakes and rivers to determine
general water chemistry
Eggermont et al. 2007. Hydrobiologia 592: 151-173
Strategy and preliminary results
5.
Sampling of the modern (living) biota in littoral, pelagic, benthic, epibenthic and epiphytic
habitats (> 150 samples from various spots and seasons)
Strategy and preliminary results
6. Determination of oxygen and hydrogen isotopic composition (d18O and dD) of river and lakes
Russell et al. unpublished data
Stable Isotope Compositions in western Uganda
50
40
Ruwenzori Lakes
African Rainfall Station
Lowland Lakes
30
20
GMWL
Lowland Rivers
Ruwenzori Rivers
2006 Rwenzori lakes
10
dD
0
2006 Rivers
Linear (African
Meteoric Water Line)
-10
-20
-30
-40
-50
-8.0
-6.0
-4.0
-2.0
0.0
2.0
4.0
6.0
d18δ18O
O
=> dD of aquatic lipids will provide direct insight into changes in the isotopic
composition of precipitation in tropical East Africa, which varies as a function of
rainfall amount.
Strategy and preliminary results
7.
Collection of intact surface-sediment samples for analysis of various climate-proxy indicators:
geochemical biomarkers, fossil diatoms, algal pigments, pollen, and chironomids
Strategy and preliminary results
8. In view of accurate T calibration
and long-term T monitoring, we deployed
16 T loggers between ~1800-5000 m asl
(recording 12 times/day since 2005/2006)
Lakes
Pools
T-loggers
From Eggermont et al. (2007; Hydrobiologia DOI 10.1007/s10750-007-0741-3)
Strategy and preliminary results
Chironomids as paleothermometers
0
10
Taxon number
20
30
40
50
60
0
MAT 5.5°C
MAT 9.5°C
3800 m
3000 m
5
Eggermont et al. unpublished data
10
15
WA optimum (°C)
20
25
30
Strategy and preliminary results
Chironomids as paleothermometers
WA
25,0
r²jack = 0.96
22,5
RMSEP = 1.59°C
Predicted MAT (°C)
20,0
17,5
15,0
12,5
10,0
7,5
5,0
2,5
0,0
0,0
2,5
5,0
7,5 10,0 12,5 15,0 17,5 20,0 22,5 25,0
Observed MAT (°C)
Eggermont et al. unpublished data
Strategy and preliminary results
9. Recovery of short sediment cores of recent sediments (150-700 yrs old)
Strategy and preliminary results
9. Recovery of short sediment cores of recent sediments (150-200 yrs old) to
- Assess archival quality of the lake sediments
- Assess lake sensitivity to glacier retreat
Russell et al. unpublished data
- changes in the siliciclastic content of glacial lake sediments reflect fluctuations of glacial extent
- signals of glacier dynamics can be isolate through comparative limnological studies
Strategy and preliminary results
9. Recovery of short sediment cores of recent sediments (150-200 yrs old) to
-
Assess archival quality of the lake sediments
-
Assess lake sensitivity to glaciers retreat
-
Gather info on timing/triggers of deglaciation
Russell et al. unpublished data
Avenues for future research
... Long-term climatic, limnological and ecological monitoring
... Further development of climate proxies
*Quantification of the relationship between changes in the stable isotopic composition of meteoric waters in the
Rwenzori mountains and regional rainfall, T and atmospheric circulation using observational and climate
modelling data
*Optimalisation of the chironomid-based T models
... Multi-proxy study of long sediment cores (~mid- to late Holocene) from selected lake sites
Conclusion
-
Rwenzori mountain lakes constitute a unique laboratory to do paleoclimate research
-
Our study will produce new records of Holocene climate variability to assess the coherency and spatial
extent of climate changes within Africa and their relationships to global climate variability, solar forcing, and
modes of tropical ocean circulation and temperature.
-
Our studies will provide baseline data to evaluate ongoing and future climate and environmental changes in
this sensitive, alpine tropical area. Are recent changes unusual within the context of the mid- to late Holocene?
-
By providing climate records of temperature and rainfall that can be compared against independent records
of tropical glaciation, our results will be important to ongoing studies evaluating the sensitivity of tropical
glaciers to climate change
Acknowledgements
UNCST, UWA and Rwenzori Mountaineering Services for invaluable assistance in the field
Fund for Scientific Research Flanders (Belgium), Leopold-III fund (Belgium), US National Geographic Society,
Salomon Fund (Brown University) for sponsoring