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L'intérêt est grandissant pour le potentiel présenté par les acccumulations cavernicoles de guano de chauves-souris et d'oiseaux en tant qu'enregistrements stratigraphiques continentaux, complémentaires voire alternatifs aux archives étudiées généralement (sédiments lacustres, palustres, tourbeux, etc.). Ces dépôts permettent des reconstructions de la variabilité climatique à haute résolution pour des échelles de temps récentes à plus anciennes, grâce à la calibration de nouveaux proxies susceptibles d'enregistrer ces variations. Ainsi la comparaison du contenu pollinique et des traceurs isotopiques delta 13C et delta D des n-alcanes du guano de différents animaux insectivores, les salanganes diurnes (Collocalia spodiopygia) et les chiroptères nocturnes (Micropterus robustior) cohabitant dans de nombreuses grottes de Nouvelle-Calédonie, met en évidence une grande variabilité. Celle-ci est à l'image des cibles de nourrissage des proies appétées et de leur interaction avec les composantes de l'écosystème, en particulier les plantes. La grande richesse du contenu pollinique observée dans les deux types de guano, bien que présentant 50 % de taxons communs, souligne des aires de nourrissage préférentielles. Elle montre aussi des fluctuations interannuelles, marqueurs probables de changements environnementaux, sinon climatiques. Cet article présente des premiers résultats obtenus sur le sondage HAK1 prélévé dans un amas de guano de salanganes de la grotte Hama sur l'île de Lifou, l'une des îles Loyautés. La comparaison entre les données de géochimie isotopique moléculaire (isotopes du carbone delta 13C et de l'hydrogène delta D du n-alcane C29) et les données pluviométriques met en évidence une bonne covariation interprétée comme marqueur du signal climatique ENSO contemporain des dépôts de guano analysés. Ce travail préliminaire confirme le fort potentiel des amas de guano cavernicoles pour étudier à haute résolution les changements paléo-environnementaux.

International audience; Here we present the first terrestrial record of mid-Holocene environmental changes in Vanuatu. This preliminary multi-proxy analysis of core Tfer 06 from Emaotfer Swamp (Efaté Island) indicates changes in environmental conditions are mainly related to variations in climate over the last 6500 cal yr BP. Drier periods are broadly correlated with an increase in sustained El Niño events recorded in the Pacific on a decadal timescale. The earliest change is the disappearance of mangroves adjacent to the site around 3200 cal yr BP, this could well be due to both local tectonic uplift with subsequent hydrostatic adjustment and the onset of a drier period. From c. 3250-2500 cal yr BP the prevailing drier conditions can be linked to more persistent El Niño conditions. Local volcanic events had limited ecological impact on the area. Freshwater diatoms indicate a hydroseral succession, species living on submerged plants being common in muds from c. 3250-1500 cal yr BP, but rare in fibrous peat deposited later. Palaeoecological indicators of human impact have not been identified throughout this work.

International audience; Climate changes, sea-level variations, volcanism and human activity have influenced theenvironment of the southwest Pacific Islands during the Holocene. The high-resolutionpalynological analysis presented here concerns two specific levels (main lithologicalchanges) of a well-dated Holocene core, Tfer06, collected from Emaotfer Swamp, EfateIsland (Vanuatu). Our aim is to understand the role of climatic variability and humanactivities in shaping vegetation during these changes. Between 3790–3600 cal yr BP, thedevelopment of vegetation marked by disturbance is a marker of an increase in sustainedEl Ni˜no events, also observed in many Asian-West Pacific areas. Between 1500–900 cal yrBP, the increase in introduced taxa and in microcharcoal particles is interpreted as humanimpact. In a forthcoming paper, the ongoing high-resolution palynological analysis of thewhole core will be compared and integrated into regional palaeoecological data.

The recognition of key coral species (KCS) in the geological record, i.e. those that contribute to reef formation and maintenance of coral reef ecosystems, is important for understanding the development and evolution of reef ecosystems and for forecasting their responses to climate change and anthropogenic impacts in the near future. This study examined the contribution to reef formation and maintenance of KCS from Pleistocene and Holocene barrier reefs in New Caledonia, based on analyses of six cores retrieved from three different reefs: Islets Kendec, Amédée, and Bayes. Our results indicate that at least 19 genera and 33 species of corals contributed to reef formation and maintenance during the Holocene in New Caledonia. Among them, Goniastrea retiformis, Isopora palifera, Dipsastraea pallida/speciosa complex, corymbose Acropora sp., massive Porites sp., and encrusting Porites sp. were KCS during the Holocene. This observation suggests that KCS will potentially contribute to the formation and persistence of reefs in the near future under conditions of estimated global sea-level rise of 0.2–0.6 m/100 years. However, the distributions and abundances of these species are currently decreasing. This study emphasizes the need for further research on the restoration and conservation of potential KCS.

Lithostratigraphic and palynological analysis of two cores recovered from the ‘Grand Lac’ (New Caledonia), combined with 35 14C AMS dates, yields a paleoenvironmental record spanning the last 2000 yr. The lithology is represented mainly by clayey or laminated layers. A catastrophic event, which is marked by very coarse deposits, occurred probably between ca 1070–960 cal yr B.P. and possibly is associated with an unusually severe La Niña event. Before and after this event, a similar combination of the two main sediment types is recorded. The repeated alternation of laminated and clayey layers is interpreted as the response to local hydrologic forcing, which may reflect a shift from relatively wet to relatively drier conditions, respectively. Variable amount of micro-charcoal is detected all along the profile. Without additional evidence, notwithstanding the initial local human settlement documented since ca 2900 14C yr B.P., micro-charcoal occurrence and variability cannot be linked directly to an anthropogenic origin. No distinct palynological zonations in relation to the lithology are observed, and the vegetation changes may only represent minor transitions across environmental limits.

The organic matter of lake sediments contains information that allows for the reconstruction of past environmental and climatic changes. The elemental composition and isotopic characteristics of sedimentary organic matter enable discrimination between allochthonous (vegetal matter from within the catchment) and autochthonous (phytoplanktonic and fixed algae) components. This approach makes it possible to distinguish between the inputs of organic matter from C 3 - vs. C 4 -type land plants. Sedimentary records from South America and Africa provide examples of applications of organic bulk composition in palaeoenvironmental reconstructions. The records from two African lakes show that, during the Last Glacial Maximum (LGM), the distribution of C org /N org – δ 13 C pairs indicates the dominance of organic material having a C 4 terrestrial origin. These inferences are supported by pollen analysis, which indicates opening up of the forest at both sites, consistent with drier climatic conditions than present. The record from Siberia Lake (Bolivia), ca. 3000 m altitude, shows that, during the LGM, the sedimentary organic matter is dominated by the phytoplanktonic fraction, as indicated by the C org /N org – δ 13 C pairs. The petrographic analyses show that this material is not well preserved, suggestive of drier conditions, consistent with interpretations from the pollen record. The beginning of the Holocene is marked by a shift from a scattered C 4 signal to one with a greater terrestrial C 3 and aquatic phytoplanktonic influence. These results indicate climatic amelioration towards more humid and warmer climatic conditions, leading to forest development in the lake catchment, together with increasing lake levels conducive to greater phytoplankton production. These conditions persisted during the Holocene, as shown by the C org /N org – δ 13 C pairs in all lakes, with a terrestrial C 3 signal predominating at the Carajas and Siberia lakes. Only Dom Helvecio Lake shows a different pattern during the beginning of the Holocene in the distribution of C org /N org – δ 13 C pairs. This pattern indicates that the sedimentary organic material is dominated by C 4 terrestrial material coming from savanna expansion in the lake catchment during a period of relative aridity in central Brazil.

Minerals derived from catchment soils were determined using FTIR spectroscopy in the well-dated core OW4 from Lake Ossa, a lowland rainforest area in Cameroon. This quantification provides a hydrologic record indicating that the magnitude of runoff events, and by inference, rainfall pattern, has varied during the Late Holocene. The comparison between minerogenic inputs and vegetation changes improves the understanding of the inferred climate dynamics. Since at least 5400 cal yr B.P., the paleomonsoon rainfall intensity decreased, as shown by a general decrease in mineral fluxes. This observation is consistent with a gradual weakening of the boreal summer insolation in tropical latitudes. However, the major vegetational change lags behind the onset of the decrease in mineral fluxes. From 2800 to ca 1000 cal yr B.P., the forest receded: the amount of rainforest taxa decreased and is replaced by pioneer trees and Poaceae, when the mineral fluxes attained their lowest values. This episode of maximum dryness is attributed to an abrupt climatic event of global significance which is superimposed onto the paleomonsoon variability. It is related to a cold event, which in turn produced a change in the lower atmospheric circulation that was characterized by a strengthening of northern trade winds, probably correlated with sea-surface temperature variations in the eastern tropical Atlantic area.

This paper presents the most recent and detailed Holocene palynological research carried out on the Congolese Atlantic littoral, in the region of Pointe-Noire, as part of the ECOFIT program (CNRS-IRD). The results are obtained on two continental sedimentary sequences (core S2 from Songolo site: 4 degrees 45'51"S, 11 degrees 51'55"E, alt. 5 m and core 2 from Coraf site: 4 degrees 45'S, 11 degrees 51'E, alt. 1 m). Pollen data and interpretation are completed on the Songolo sequence by mineralogical (quartz, kaolinite, TOM) and isotopic (delta 13 C on organic matter) analysis allowing a continuous reconstruction of the Congolese littoral palaeoenvironments from 7000 yr. cal B.P. onwards. The Congolese coastal plain is today a mosaic of forest-grassland. Sandy open short savanna largely occurs with as dominant grass Loudetia arundinacea. Locally, Symphonia globulifera swamp forests are present along rivers and in flooded areas. Mangrove with Rhizophora is not well developed except along the Kouilou estuarine. The climate is characterized by mean annual precipitation not exceeding 1300 mm and temperature ranging between 22 and 25 degrees C. The core S2 from Songolo site was extracted using a piston corer. The coring site is today a peat building swamp with abundant Cyperus papyrus. The local dominant trees are Raphia and Alstonia. The presence of Elaeis guineensis (oil palm) and Mangifera indica (mango) testifies of a recent human occupation of this area. The core Coraf 2 was collected on the beach by manual penetration of PVC tube. On the two studied cores, dating control is provided by thirteen 14 C conventional and AMS dates performed on total organic matter. The ages are reported with equivalent ranges in calendar years. The present pollen, mineralogical and isotopic records, completed by previous other data (mainly macroflora remains), give new informations on vegetation and hydrological changes at local and regional scale since 7000 yr. cal B.P. on the Congolese littoral, in relation to climatic and sea level changes. The main conclusions can be summarized as follows. During the middle Holocene (7000-3000 yr. cal B.P.), expansion of swamp dense forests with Pandanus, Anthostema, Hallea, Symphonia globulifera, Syzygium, and also of mangrove (Rhizophora), as testified by pollen analysis, gives evidence of high rainfall which is also supported at Songolo by the abundance of kaolinite and quartz, an increase in the amorphous silica and delta 13 C low values typical of C 3 biomasse until 3000 yr. cal. B.P. At the same time, the occurrence in macroflora remains of trees such as Saccoglottis gabonensis, Ongokea gore and several species of Monopetalanthus that are found today in the Mont de Cristal forest in Gabon, under 2000-2500 mm of annual rainfall, confirms this climatic interpretation. A major change is registered ca. 3000 yr. cal B.P., characterized by the regression of the swamp forests which are replaced by herbaceous formations dominated by Cyperaceae and ferns, the disappearance of mangrove near the Songolo site, an important decrease in mineral influx (quartz and kaolinite) and increase in organic matter content. Increase in delta 13 C values during this period shows that most of the organic fraction derives from C 4 plants, probably linked to local expansion of Cyperus papyrus. This change, well known at this time on several sites from Central Atlantic Africa, is mainly linked to a progressive regional deterioration of climate towards aridity. On the Songolo site, the presence of fresh water taxa such as Nymphaea lotus supports an absence of marine water influence, indicating a sea level regressive episode well known, at the same time, along the West African coast. During the most recent period, despite more favourable climatic conditions (rainfall), no re-extension of littoral swamp forests is detected. These results are mainly related to the location of the studied sites, in an area of particularly intense human impact as shown by the occurrence of Elaeis guineensis (oil palm) in macroflora remains recovered from numerous archeological sites. The multidisciplinary data presented here correlate well with previous records from Central Atlantic Africa (Congo and Cameroon). The general similarity of the registered changes during the last 7000 yr cal B.P. strongly supports a regional climatic interpretation.

Relics of human activities anterior to the seventeenth century are documented for the first time in the Lake Ossa catchment basin (Cameroon Littoral Province). The remains from two sites are composed mainly of potsherds in association with iron slags, stone implements and charcoals. The charcoal samples yield ages ranging from 1290 to 1647 calendar yr. A.D.

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.

Multiproxy analysis of three littoral cores from western New Caledonia supports the hypothesis that the main controlling factors of environmental changes are sea-level change, ENSO variability and extra-tropical phenomena, such as the Medieval Warm Period (MWP) marked by a tendency for La Niña-like conditions in the tropical Pacific. The record starts during the late Holocene sea-level rise when the terrestrial vegetation indicated wet and cool conditions. The site was a coastal bay definitely transformed into a freshwater swamp at around 3400 cal yr BP, after the rapid drawdown of sea level to its current level. Sediments and foraminiferal assemblages indicated subsequent episodes of freshwater infillings, emersion or very high-energy conditions, likely related to climatic changes and mostly controlled by ENSO variability. Between 2750 and 2000 cal yr BP, relatively dry and cool climate prevailed, while wetter conditions predominated between ca. 1800 and 900 cal yr BP. The Rhizophoraceae peak between ca. 1080 and 750 cal yr BP, coeval with the MWP, may indicate a global phenomenon. Microcharcoal particles present throughout the record increased after 1500 cal yr BP, suggesting an anthropogenic source. From ca. 750 cal yr BP the appearance of current type of vegetation marks the human impact.

Plusieurs études paléoclimatiques et paléoenvironnementales (analyses de séries coralliennes et sédimentaires) ont été menées à terre et en mer au cours des deux dernières décennies, en Nouvelle-Calédonie et dans l'archipel du Vanuatu. Bien qu'encore inachevées, elles apportent des informations majeures sur la variabilité des environnements dans cette région du sud-ouest du Pacifique depuis le dernier maximum glaciaire : les importantes fluctuations du niveau marin et des températures de surface de l'eau de mer ont contribué à la mise en place des paysages maritimes et terrestres d'aujourd'hui et joué un rôle prépondérant dans les déplacements et les implantations des populations humaines insulaires. Several paleoclimatic and paleoenvironmental studies (analyses of coral and sedimentary sequences) were conducted on land and offshore during these two last decades in New Caledonia and Vanuatu. Although the analyses are still in progress, these preliminary data provide information on the environmental variability in the south-west Pacific since the last glacial maximum : the sea-level rise and the changes of sea surface temperatures contribute to the settlement of the modern marine and terrestrial environments. Moreover, all these changes may have played a major role in the settlement of the insular population.

Lifou is an atoll uplifted to a near 100 m height near the Vanuatu Trench. Extensive karstification is recorded in the outer coral rim and to a lesser extend in the lagoon type limestones of the inner island. The orientations found in the longest karstic networks correspond rather well to the main fracture directions, but near coasts, the galleries are controlled by the paleo-shoreline, suggesting that mixing corrosion might be involved during cave formation. The freshwater level and temperature, recorded during one year inside two caves present smooth variations, if tidal components near 12 and 24 h periods are removed, and are poorly correlated with rain. Comparison with data recorded in a continental karst (Baget, Pyrenees) and in the chalk of the Paris Basin indicates that Lifou lacks an organized channel network able to collect and transfer quickly rainwater toward the phreatic zone.

precipitation are based on 85 pollen sites 14 C dated at 6000 ± 500 years B.P and distributed over the whole of Africa. To improve the reliability of the pollen-based climate reconstruction, two methods are used: the ‘‘modern analogues technique’’ (MAT) and the ‘‘plant functional types’’ (PFT) methods. We then conduct a model-data comparison for five distinct regions, allowing an evaluation of model outputs (the Sahara-Sahel, the eastern Sahara, western equatorial Africa, East Africa, and Madagascar). The pollen-inferred reconstructions are compared with 21 mid-Holocene simulations yielded by Atmospheric General Circulation Models (AGCMs), and coupled ocean-atmosphere-vegetation models (OAVGCMs). The large-scale feature of the hydrological changes is shown to be well captured by most of the models. Data show that during the mid-Holocene, the Sahara was considerably wetter than today (+200 to +700 mm/yr). The results reinforce the conclusion that the AGCMs significantly underestimate this precipitation increase in the Sahara whereas the OAVGCM simulations are in accordance with the data. Our results show that vegetation and ocean feedbacks do not have a strong impact in the intertropical zone and that models fail to properly reproduce the climatic conditions in East Africa and Madagascar. The model-data comparison also suggests that the lengthening of the dry season during boreal winter in the west equatorial region is a robust feature although the pollen-based reconstruction shows no change or only slight drying there.

Texto completo: acesso restrito. p.139–146 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2013-02-01T12:46:19Z No. of bitstreams: 1 Mourguiart.pdf: 1057020 bytes, checksum: edb5c0c5332f490022cea63513c0e604 (MD5) Approved for entry into archive by Fatima Cleômenis Botelho Maria (botelho@ufba.br) on 2013-02-04T14:12:49Z (GMT) No. of bitstreams: 1 Mourguiart.pdf: 1057020 bytes, checksum: edb5c0c5332f490022cea63513c0e604 (MD5) Made available in DSpace on 2013-02-04T14:12:49Z (GMT). No. of bitstreams: 1 Mourguiart.pdf: 1057020 bytes, checksum: edb5c0c5332f490022cea63513c0e604 (MD5) Previous issue date: 1997 Une approche multidisciplinaire a permis la reconstruction des fluctuations du lac Titicaca durant le Pleistocene terminal et à l'Holocène. Trois hauts niveaux lacustres (avant 25/28 ka BP, entre 14-10,5 ka BP et après 0,4 ka BP) et deux baisses importantes (25/28-14 ka BP and 10,5-0,4 ka BP) sont les caractéristiques hydrologiques principales de l'évolution du lac Titicaca.

Between the western and eastern Andean cordilleras in Peru and Bolivia, there are three main lacustrine basins: Lake Titicaca, Lake Poopó, and the group of Coipasa-Uyuni. For the past few millennia, highly variable environmental conditions have been recorded in their sediments. Today a latitudinal meteorological gradient influences the lakes' status, leading to specific deposits and ostracod communities. Lake Titicaca in the north is oligohaline, whereas Lake Poopó further south is polyhaline. In the south, the Coipasa-Uyuni depression is characterized by a 12,000-km2surficial salt crust. During the Late Pleistocene (ca. 40,000 to 25,000 yr B.P.), the water depth and salinity in paleolake Poopó fluctuated widely and paleolake Titicaca was slightly larger than at present. Sedimentation was mostly biocarbonate in the shallower areas and it was detrital-organic in the deepest zones. During the Holocene, a dry period transformed Lake Poopó into a "salar" with evaporite precipitation. Lake Titicaca registered a large decline in water level (8100-3600 yr B.P.) initially inducing gypsum precipitation followed by short influxes of water, with an ostracod faunal composition similar to that of the modern brines of Lake Poopó. Lake Titicacas' present condition only appeared between 2200 and 1500 yr B.P.

At an altitude of 3809 metres above sea level, Lake Titicaca, the northern lake basin on the Altiplano (a high endorheic plateau in Peru and Bolivia) is the largest navigable water body in the world lying at over 3000 metres.

Preliminary results of sedimentological and paleontological analysis of two cores taken in Lake Titicaca (Bolivia) indicate that between 7700 and 3650 yr B.P. the lake level was up to 50 m lower than at present. Evaporitic deposits occurred at the maximum low lake level.

In lake Titicaca, the distribution of the modern ostracod fauna appears to be controlled by a combination of two factors: a) the equilibrium between carbonates and organic matter, b) the ionic composition of the lake water and its tributaries. Therefore, the Limnocythere-Pampacythere group generally predominates on an alkaline-carbonate lake floor. In parts of the lake receiving an NaCI input from tributaries, Cyprideis and Cyprinotus occur. These are generally absent elsewhere. The Candonopsis group is found in the deepest part of the lake.