This study presents results fromii a multi-proxy anialysis of cores taken in a crater-lake sequence fromll Eski Acigol in centr-al Turkey which cover the period fromii pre-c. 1600X) cal. yr BP to the present. The sediments comiiprise an upper unit of enerally non-laminated, banded to massive silts and peats of mid-to late-Holocene age, oveilying a laminated tinit of late-Pleistocene to early/miid-Holocenie age. The lamiinlae, comprising mainily aragonite. amorphous silica (diatom trustules) and organic mattei were formed in a relatively deep, dilute. meromiiictic lake. Pollen data indicate an abrupt replacement of Ar;eyisi'io-chenopod steppe by grass-oakterebinth parkland during the period of laminae deposition, imiar-king the start of the Holocenie. A gradual Li i E ;i E; increase in tree pollen during the early Holocene came to a i n end c. 6500 cal. yr BP (U-series and adjusted 4C timescale), when mesic deciduotLs taxa declined at the same timiie as lake levels fell. Human impact on regional vegetation is infened from a sharp decline in oak arotind 4500-.4(X0)0 cal. yr BP. Diatom, isotopic anid mineralogical data indicate that during the second half of the Holocene the lake became relatively shallow and A oscillated between fresh and brackish/evaporated water conditions. The contrast between wetter early-and drier HOLOCENE late-Holocene climatic conditions is matched bv other eastern anid central Mediterranean proxy climate data. SPECIAL ISSUEWhile the Eski Acigol seqtLience resembles Holocene hydroclimatic changes in the Saharo-Arabian zone and was also apparenitly linlked to orbital forcing, it is unlikely to have had the samlle direct cause, i.e., an expansion and subsequent retreat of monsoon rainfall.

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This review paper synthesizes the recent published palaeoecological results obtained in Atlantic Equatorial Africa (ECOFIT program) on the history of forest ecosystems and inferred climate changes during the past 4000 years. Evidence are mainly provided by pollen analysis carried out at nine sites from Congo, Cameroon and Ghana, locally supported by macroflora remains, phytoliths, diatoms, 13 C and mineralogical data. At all the sites, except Lake Bosumtwi (Ghana), following a large expansion of rain and mesophilous forests until 3000 years BP, a major change is registered, affecting floristic composition, structure and geographical distribution. According to the hydrological sensitivity of the different sites, local openings of the forests with development of heliophilous formations and/or isolated enclosed savannas are observed at the most humid sites; complete disappearance of forested formations at the driest. The agreement between pollen records, hydrological and hydrobiological data definitely demonstrates that an arid event has been the primary driving factor of this change and is responsable for the main features of the modern landscapes in Atlantic Equatorial Africa. Moreover, the most recent palaeoecological data obtained in Congo (Lake Sinnda), indicate that this Late Holocene increasing aridity was of longer duration, from 4000 to 1300 years BP, and more progressive than previously inferred. A new expansion of forests is locally detected c. 900-600 BP despite increased human impact.

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Today, precipitation over tropical South America is largely controlled by the seasonal movements of the Inter-Tropical Convergence Zone (ITCZ). During the summer, the ITCZ is shifted southward due to the warming of the continent. Paleoclimate data from southeastern Amazonia and the central Andes indicate that these two areas evolved similarly during the last 30,000 yr. However, between 12,400 and 8800 cal yr B.P., eastern Amazonia received substantial moisture whereas the Bolivian Altiplano was arid. This suggests that the ITCZ during summer was then farther north than it is today.

Pollen analysis of two cores from the Lake Sinnda, located in one of the driest areas of the southern Congo, reveals a history of vegetation and climate in this region during the past 5000 yr. A major change centered around 3000–2500 yr B.P. is indicated by an abrupt decrease in forest pollen and by a corresponding increase in grassland pollen. Concurrent drying up of the lake shows that climate, in particular aridity, was the major cause of this change. This paleoclimatic reconstruction conforms with evidence for drier conditions in other parts of western equatorial Africa, such as the development of isolated enclosed savannas and of heliophilous forested formations. The aridity is recorded more fully at Lake Sinnda than at the previous studied ones. It probably lasted longer, from 4200 to 1300 yr B.P., and was more progressive than previously inferred. The aridity predates agriculture marked by pollen of the oil palm at Lake Sinnda.

Environmental conditions of the lowland tropical forests during the last glacial maximum (LGM) between ca 20,000 and 18,000 14C yr B.P., are reevaluated in terms of dating control and lithology analyzed in seven pollen records from South America. The reevaluation shows that probably in none of the published records are LGM sediments present or abundant. This conclusion is based on the occurrence of abrupt lithologic changes coupled with changes in sedimentation rate interpolated from radiocarbon dates. These findings suggest that the LGM was represented probably by a hiatus of several thousand years, indicative of drier climates than before or after.

The study of weathering and erosion processes requires the establishment of a mass balance of minerals from the soils towards the sedimentation,area. This calls for the development of quantitative tools that can be applied to mixtures of finely divided and sometimes poorly crystallized minerals found in soils and sediments. We present here the use of Fourier transform infrared (FTIR).absorbance spectroscopy in the mid-infrared as a method to calculate mineral modes for such materials. Samples were prepared using the KBr disc method. This ensures that Lambert-Beer's law is valid. A quantitative determination of the mineral content from various blends was performed by making a multicomponent analysis of the experimental spectrum using the spectra of each component in the mixture. To check the validity of the procedure, the multicomponent analysis was performed on spectra from synthetic mixtures of standard minerals (quartz, kaolinse, gibbsite, amorphous silica). Good agreement between actual and computed wt % was obtained in the range 1315-315 cm-l. This application of FTIR spectroscopy was used to quantify the mineral components of a lacustrine sediment cored at Salitre, Minas Gerais, Brazil. The major phases are organic matter, kaolinite, gibbsite, quartz, anatase, and amorphous silica (Phytoliths and sponge spicules). Fifty-three samples were analyzed. Quantitative results from FTIR spectroscopy were compared to chemical analyses to assess the validity of the method for the natural sediments. Phases with no sharp diag-2 6 nostic spectral features, such as anatase or amorphous silica, were quantified using the multicomponent analysis. The variations of the main mineral phases along the core reflect the mechanisms of transfer from the surrounding soils to the sediment area and the role of the vegetal cover over the drainage area. ~ U) .e ' formation of various form. They are an integration of components from CJ 8) two distinct environments (Dean 1993): (1) the extemal terrestrial environt c r Q 0 ment of the drainage basin and beyond (allochthonous components, mainly U , 0 from soils), and (2) the intemal lake environment (autochthonous components). The allochthonous components are tracers of weathering and erosion processes. Their behavior during their transport from soils to the lake results from several factors, including the type of soils, the vegetation cover, the climate, and the drainage pattem over the drainage basin. The autochthonous components are indicators of processes acting within the lake and within the postdepositional (diagenetic) environment. In order to assess environmental conditions prevailing during sedimentation it is useful to perform mass-balance calculations among these various sources. However, quantitative determination of major mineral phases in soils or sediments remains a difficult task, because the complexity of these natural mixtures leads to the difficulty of using conventional methods such as X-ray diffraction or optical microscopy. The methodology presented in this paper was de...