Tracing the effects of the Little Ice Age in the tropical lowlands of eastern Mesoamerica

Abstract

The causes of late-Holocene centennial to millennial scale climatic variability and the impact that such variability had on tropical ecosystems are still poorly understood. Here, we present a highresolution, multiproxy record from lowland eastern Mesoamerica, studied to reconstruct climate and vegetation history during the last 2,000 years, in particular to evaluate the response of tropical vegetation to the cooling event of the Little Ice Age (LIA). Our data provide evidence that the densest tropical forest cover and the deepest lake of the last two millennia were coeval with the LIA, with two deep lake phases that follow the Spö rer and Maunder minima in solar activity. The high tropical pollen accumulation rates limit LIA's winter cooling to a maximum of 2°C. Tropical vegetation expansion during the LIA is best explained by a reduction in the extent of the dry season as a consequence of increased meridional flow leading to higher winter precipitation. These results highlight the importance of seasonal responses to climatic variability, a factor that could be of relevance when evaluating the impact of recent climate change.climate variability ͉ Late Holocene ͉ Mexico ͉ seasonality ͉ tropical ecosystems T he Little Ice Age (LIA) (1350-1850 A.D.) has been identified as one of the most important climatic oscillations of the late Holocene and the last of several centennial to millennial scale Holocene cooling events centered over the North Atlantic (1-4). Low-latitude cooling during the LIA is evident from tropical glacier advances (5, 6), and reduced sea-surface temperatures in the Caribbean (7-9). Dry LIA conditions in the Caribbean are relatively well documented and explained by a change in the position of the Intertropical Convergence Zone (ITCZ) (10, 11), but little is known about the impact that this climatic event had on the lowland tropical ecosystems of the Americas. Lago Verde, near the coast of the Gulf of Mexico (Fig. 1), is a highly sensitive record of recent climate change (12,13) where the response of the tropical vegetation and the lake system to the LIA cooling can be clearly traced, without any significant human impact. Multiproxy data from this lake show that in this tropical region the LIA is recorded by the deepest lake level and the densest forest cover of the last two millennia. In this article, we present arguments evaluating the role of solar forcing as an important element explaining climatic variability in the tropics and the North Atlantic region. We also discuss the role of regional moisture balance as a condition for the expression of regional precipitation trends, and, finally, we present an argument about the importance that changes in the seasonality of precipitation can have over the Gulf of Mexico coastal region, mitigating the dry LIA trend recorded in some areas of the Caribbean. Study SiteThis study is based mainly on pollen, charcoal particles, and diatom analyses on the sediment record from Lago Verde, a small, closed-basin lake at 200 m above sea level, on the outskirts of ...

Detrended correspondence analysis: A useful tool to quantify ecological changes from fossil data sets

“…Apparently, before 800 CE the territory was heavily occupied by people, who maintained a regime of heavy disturbances over the forest (Lozano-Garcia et al, 2007). Human abandonment of the area has been reported as taking place between 750 and 900 CE (Santley and Arnold III, 1996), coinciding with the inflection point of DCA axis 1 for both proxies.…”

“…The ecological space as defined by species arrangement in the reduced biplot suggests that axes have environmentallyassociated distributions along axes 1 and 2 (for species environmental associations see Lozano-Garcia and Martínez, 1990;Lozano-Garcia et al, 2007. For pollen, taxa associated with open forest (e.g.…”

“…Sediments have been extensively analyzed for pollen, diatoms and geochemistry, and results have been published elsewhere Ortega et al, 2006;Lozano-Garcia et al, 2007Ruiz-Fernández et al, 2007).. Here we use the pollen and diatoms records of Lago Verde Lozano-Garcia et al, 2007) to derive ecological changes through two DCA analyses performed independently on each data set. We present data for the last 2100 years with CE and BCE refering to "common era" and "before common era", respectively.…”

“…Urrego et al, 2009;Correa-Metrio et al, 2012b;Restrepo et al, 2012;). Because of this essential reason, our paper focuses on the description of some technicalities of the method, along with the development of a worked example using pollen and diatoms from Lago Verde (see Caballero et al, 2006;Ortega et al, 2006;Lozano-Garcia et al, 2007).…”

“…However, there is an inherent relationship between lake trophic levels and geologic materials and weathering rates, which are in turn Conclusively, pollen and diatom records complement each other (e.g. Lozano-Garcia et al, 2007), providing information that leads to environmental reconstructions at scales that range from local to regional. Both proxies indirectly reflect biotic communities that should be governed by ecological principles.…”