Evidence of Atmospheric Paleocirculation over the Gulf of Guinea since the Last Glacial Maximum

Abstract

High-resolution pollen and eolian input studies from core KS 84063 in the Gulf of Guinea record the response of the tropical atmospheric circulation to global paleoclimatic events during the last glacial/interglacial transition. Two depositional phases centered around 15,000 and 10,300 yr B.P. are characterized by maximum values of pollen concentration and of eolian activity index (EA1). Pollen spectra record the significant presence of Artemisia and Ephedra of Saharan origin and the scattered occurrence of Podocarpus from Guinean mountain forests; these demonstrate the intensity of the meridional atmospheric circulation over equatorial West Africa during dry periods. The early Holocene humid phase, ca. 8500 yr B.P., is marked by minima in pollen concentrations and EAI. Saharan taxa are absent and, in contrast, Podocarpus reached its highest relative values. This evidence has been interpreted as reflecting a weakening in the continentocean eolian transport and the importance of monsoonal fluxes. Downcore variations in Podocarpus percentages are used to identify the atmospheric circulation patterns over the low latitudes of West Africa during extreme (dry/humid) climatic conditions.

Genetic differentiation between Príncipe Island and mainland populations of the grey parrot (Psittacus erithacus), and implications for conservation

“…2006, respectively). During the glacial cycles the influence of the northern dry harmattan winds extended southwards (Lézine et al . 1994) favouring this route, and the land area of Príncipe could increase by almost 10 times making colonizations more likely.…”

“…This is in agreement with results reported for other aerial colonizers such as angiosperms and blackflies (Simuliidae), which have their source populations in Nigeria and Cameroon rather than in Gabon (Exell 1973;Mustapha et al 2006, respectively). During the glacial cycles the influence of the northern dry harmattan winds extended southwards (Lézine et al 1994) favouring this route, and the land area of Príncipe could increase by almost 10 times making colonizations more likely. Furthermore, the only forests in the north capable of sustaining a grey parrot population were located in the Upper Guinea refuge that coincides with the current distribution of timneh; the erithacus populations currently found in Nigeria would not exist (Fig.…”

The blackflies (Diptera: Simuliidae) of Bioko (Republic of Equatorial Guinea) and the Gulf of Guinea with a description of the larvae of the ‘Pomeroy’ form of Simulium cervicornutum

“…The intertropical convergence zone (ITCZ), where the northern, dry harmattan winds meet the southern monsoon winds, moves north in the rainy season, whereas the monsoon winds predominate and back south during the dry season when the harmattan is dominant. The ITCZ rarely lies south of Bioko (de Terán, 1962), but pollen core studies have shown that, during the last glacial maximum, the ITCZ moved markedly further south than it is today (Lézine et al ., 1994, 1995), and the extended harmattan winds possibly provided the means of transport of species to São Tomé and Príncipe.…”

Evolution of the West African Mangrove During the Late Quaternary: A Review

“…In West Africa, pollen data from late Quaternary mangroves are discontinuous owing primarily to the irregular, often truncated nature of the related nearshore sediments (Lézine, 1987). Recent data on long, well calibrated and continuous sequences from deep oceanic sediments collected at a short distance from the coasts (Rossignol-Strick and Duzer, 1979;Hooghiemstra, 1988;Lézine and Vergnaud-Grazzini, 1993;Lézine et al, 1994 fill the gap in the record of the mangrove history during the last glacial-deglacial transition. I present here a review of studies on mangrove pollen deposition in (sub-)recent and Pleistocene sediments to discuss the different signals recorded in both littoral and deep-sea records.…”