Tropical climates in the game of two hemispheres revealed by abrupt climatic change

Abstract

The climatically sensitive equatorial regions provide important information for evaluation of the phasing between high-and low-latitude climate variability. A high-resolution pollen record from northern Brazil demonstrates a significant abrupt and rapid environmental change associated with the Northern Hemisphere Younger Dryas temperature reversal. This finding is consistent with the model in which the Younger Dryas had a stronger influence on temperature in the Northern Hemisphere than south of the equator because of the larger temperature gradient between pole and equator in the Northern Hemisphere than in the Southern Hemisphere. One consequence of the Younger Dryas changes would be the location of the Intertropical Convergence Zone in a southern position, so that even tropical regions would have been under Arctic influence.

Major environmental changes recorded by lacustrine sedimentary organic matter since the last glacial maximum near the equator (Lagoa do Caçó, NE Brazil)

“…These interpretations on phases I and II are in good agreement with palynological data showing sparse and residual vegetation at the end of the LGM (Ledru et al, 2002). Our results are also consistent with Stute et al (1995) who hypothesized that the LGM was cooler but also more arid than presently, as demonstrated by the partial replacement of the Amazonian rainforest by savanna (van der Hammen and Absy, 1994;Colinvaux et al, 1996).…”

“…The mean annual temperature is 26°C. Located on the edge of the Amazon Basin, the vegetation in this region displays a strong zonation ranging from Restinga (grass steppe) near the coast, to Cerrado (shrub savanna) inland followed by Cerradao (woody savanna) in the more humid regions (Ledru et al, 2002). The lake (ca.…”

“…Nevertheless, major controversies still remain, for example on the respective contribution of the Intertropical Convergence Zone (ITCZ) and Polar Advections on regional climate variability (Ledru et al, 2002). These controversies emphasize the need to better document the climatic fluctuations that affected this area since the Last Glacial Maximum (LGM).…”

Paleohydrological changes during the last deglaciation in Northern Brazil

“…For example, a globally drier climate is suspected for the LGM. The extent to which this supposedly dry episode impacted the Amazon rainforest surface is strongly debated (Colinvaux et al, 2000;Turcq et al, 2002).…”

Pentacyclic triterpene methyl ethers in recent lacustrine sediments (Lagoa do Caçó, Brazil)

“…1). The sedimentary filling has been studied using various approaches to better document palaeoclimatic development since the Last Glacial Maximum (LGM) in the Tropics (Ledru et al, 2001;2002;Sifeddine et al, 2003;Jacob, 2003;Jacob et al, 2004a and b). Here we report on the GC-MS characteristics of several series of pentacyclic triterpene methyl ethers (PTMEs) that are present in the lipid extracts of Quaternary sediments from this tropical setting and their significance as plant source indicators or diagenetic indicators.…”