5th Swiss Geoscience Meeting, Geneva 2007
Climatic record from the Late Holocene in the tropics:
case study from a middle-mountain wet zone in Central
Colombia
Muñoz Paula* & Gorin Georges*
*Département de Géologie-Paléontologie. 13 rue des Maraîchers, CH-1205 Genève
(Paula.Munoz@terre.unige.ch, Georges.Gorin@terre.unige.ch)
Climatic records from the Holocene are rare in the tropics. The palynological
study of recent continental sediments helps to reconstruct the evolution of the
vegetation and represents a proxy for the evaluation of climatic variations
synchronous with sediment deposition. Changes in the vegetal record are
particularly well expressed in high-relief areas, such as the Colombian Andes,
where vegetation belts move rapidly in relation with climatic changes.
Two shallow cores have been recovered in a middle-mountain wet zone (El
Manantial at 2.100 m high) of Central Colombia situated at ca. 4° of latitude
north, in the foothills of the western flank of the Central Cordillera. Both cores
have been dated using the 14C method. The studied interval covers the last
1.500 years of the Late Holocene. Twenty-two samples have been
palynologically prepared in each core, which gives a time resolution of ca. 70
years. The palynological constituents of the regional vegetation have been
distinguished from the more local vegetation. The regional vegetation has been
subdivided in four groups (subandine, andine and high-andine forest, and
subpáramo), which correspond to the vegetation belts with respect to altitude.
The wet zone studied is located close to the boundary between the present-day
subandine and andine forest belts.
The stratigraphic evolution of the total percentage of the forest elements
(subandine, andine and high-andine forest) with respect to the subpáramo
elements allows the evaluation of the altitude variations of the forest line
through time and, consequently, of warming (elevation of forest) or cooling
(lowering of forest) periods (Fig. 1, A). Some rare ecological groups have also
been used to tentatively estimate the degree of humidity.
The correlation of the two cores has led to the identification of a succession of
cooler and warmer periods, which are not always easy to correlate because of
lack of datations. The abundance of herbal elements characterizing an open
forest environment during the last 200 years is the only indication of human
impact, probably related to deforestation. The best dated core (M 1) has been
correlated (Fig. 1) with the only high-resolution palynological study existing in
the northern part of the Western Cordillera of Colombia (Velasquez, 2005), at a
much higher altitude (3500m; Fig. 1, B)). It has also been compared (Fig. 1, C
and D) with studies using other proxies (Cariaco Basin in Venezuela, Haug et
al. 2001 & 2003; multi-proxy global temperature reconstruction, Mann & Jones
2003). The similarities of large-scale vegetation variations between the two
zones of Colombia during the last 1.500 years reflect the signature of regional
5th Swiss Geoscience Meeting, Geneva 2007
climatic mechanisms. The correlation of some climatic events (e.g., “the
Medieval Warm Period”) with the Cariaco Basin seems to confirm the influence
of the intertropical convergence zone (ITCZ) on the Late Holocene climate in
northern and central Colombia. However, some other climatic records are not
automatically similar at a global scale: for instance, the “Little Ice Age” in
Colombia shows an overall warming trend, in contradiction with what is
observed in Europe.
Figure 1. Correlation of palynological results in El Manantial core M1 (A) and in
the northern part of the Western Cordillera in Colombia (B): the variations of the
forest line are climatically induced (intervals 1, 2 and 3). Comparison with other
climate-related proxies: C) titanium used as a hydrological-cycle proxy, and D) a
multi-proxy global temperature curve: the Medieval Warm Period coincides with
a warming-up trend in Colombia, which continues during the Little Ice Age.
REFERENCES
Haug, G.H., Hughen, K.A., Sigman, D.M., Peterson, L.C. & Röhl, U. (2001).
Southward migration of the Intertropical Convergence Zone through the
Holocene. Science, 293: 1304-1308.
Mann, M.E. & Jones, P.D. (2003b). 2’000 year hemispheric temperature multiproxy temperature reconstructions. IGPB PAGES/World data center for
paleoclimatology, Data Contribution Series #2003-051.
Velásquez R., C.A. (2005). Paleoecología de alta resolución del Holoceno
Tardío en el Páramo de Frontino (Antioquia). Universidad Nacional de
Colombia. Escuela de Biociencias, Medellín, 199p.