Continental Vegetation Research Articles

Coupled modeling of biospheric and chemical weathering processes at the continental scale

In this contribution, a reactive‐transport model describing weathering in soil profiles and at the watershed scale is coupled to a dynamic global vegetation model to calculate the dissolved load of continental waters on a 0.5° latitude × 0.5° longitude grid. The so‐called Biosphere‐Weathering at the Catchment Scale (B‐WITCH) model is applied to the Orinoco watershed (South America). We show that B‐WITCH is able to reproduce the main cation composition of the surface waters over the watershed. Sensitivity tests demonstrate that clay mineral reactivities are key factors controlling the calculated discharge of dissolved species. More specifically, our simulations show that the dissolution and precipitation rates of clay minerals in the weathering profiles are strongly intertwined, and that this coupling must be accurately described when modeling the weathering fluxes at the continental scale. A second set of sensitivity tests show that, for the tropical environment, land plants control the total base cation discharge through their impact on the soil hydrology, rather than through enhanced soil CO2 pressures. Indeed, the complete removal of the continental vegetation leads to an increase in the dissolved fluxes to the ocean by 80% because of the collapse in the evapotranspiration, resulting in a more efficient drainage of the weathering profiles. On the other hand, neglecting the root respiration and setting the soil CO2 pressure to the atmospheric level forces the total base cation discharge to decrease by only 20%.

The changing climate framework and depositional dynamics of Triassic carbonate platforms from the Dolomites

The Triassic of the Dolomites offers a valuable opportunity to investigate the relationships between climate fluctuations and the changing depositional dynamics of carbonate platforms. The reconstruction of the large palaeoclimatic modification is based on the synthesis of multiple sedimentological, palaeobotanical, pedological, and geochemical proxies. The Triassic climate fluctuations were generally fast in nature and were probably associated with a latitudinal shift of the monsoon belts. During the Triassic, the Dolomites were placed at an intertropical northern latitude of about 16–18° and were generally dominated by dry climate and elevated temperature. At least five pulses toward moister climate are however documented, dated to Early Olenekian, Middle Anisian, Late Ladinian, “Middle” Carnian, and Late Norian times. Within this variable climatic scenario, the carbonate systems record a global evolutionary trend from Late Permian–Early Triassic regional shelves, rich in loose micrites and bio-calcarenites, to Anisian–Ladinian, synsedimentary cemented, steep sided (35–40°), high-relief platforms, and back to Carnian low angle ramps. Moist transgressive episodes were surprisingly prone to the spreading of corals and other colonial reef organisms, probably because of the reduced space competition by syndepositional cementation structures. The Permo-Triassic boundary extinction dramatically impacted on the calcified organism communities, but the carbonate depositional architecture nevertheless stayed almost unaffected through the boundary. The Early Triassic and earliest Anisian were commonly associated with hyperhaline, sometimes evaporitic conditions. Intervals of moister climate and efficient river discharge are however documented by earliest Induan and early Olenekian sediments. The latter terrigenous deposits matched a crisis in the carbonate production. After a return to arid conditions, during the Anisian, a fluctuation toward moister climate developed, associated to a massive continental vegetation cover. The Anisian tectonic activation of the region fragmented the previous carbonate shelf, triggering the development of three generations of fast prograding, but globally backstepping, isolated platforms, recording an increasing role of the synsedimentary cementation. A dry climate dominated the Late Anisian and Early Ladinian interval. At the time, a fast subsidence pulse was associated with platform drowning and basinal anoxia. Only a few aggrading pinnacles were able to survive, providing the nuclei for larger prograding platforms. During a dry climate interval, massive syndepositional cementation generated a major source of carbonate. Carbonate production stayed active through the Ladinian magmatic phase, but the onset of volcanism was associated with a large modification in the platform carbonate facies, which became dominated by automicrites. Moist climate phases are well documented again during the Late Ladinian, followed by a return to dry conditions. The Late Ladinian–Early Carnian platforms prograded toward the eastern Dolomites depocentre, eventually infilling almost the whole of the accommodation space. The middle portion of the Carnian recorded renewed, sharply moist phases, associated with the demise of the rimmed platforms and with the return to loose sediment ramps. At least four separated humid fluctuations can be identified in this Carnian interval alone. Climate then returned to persistent aridity, until the Late Norian moist phase.

Experimental determination of magnesium isotope fractionation during higher plant growth

Two higher plant species (rye grass and clover) were cultivated under laboratory conditions on two substrates (solution, phlogopite) in order to constrain the corresponding Mg isotope fractionations during plant growth and Mg uptake. We show that bulk plants are systematically enriched in heavy isotopes relative to their nutrient source. The Δ 26Mg plant-source range from 0.72‰ to 0.26‰ for rye grass and from 1.05‰ to 0.41‰ for clover. Plants grown on phlogopite display Mg isotope signatures (relative to the Mg source) ∼0.3‰ lower than hydroponic plants. For a given substrate, rye grass display lower δ 26Mg (by ∼0.3‰) relative to clover. Magnesium desorbed from rye grass roots display a δ 26Mg greater than the nutrient solution. Adsorption experiments on dead and living rye grass roots also indicate a significant enrichment in heavy isotopes of the Mg adsorbed on the root surface. Our results indicate that the key processes responsible for heavy isotope enrichment in plants are located at the root level. Both species also exhibit an enrichment in light isotopes from roots to shoots (Δ 26Mg leaf-root = −0.65‰ and −0.34‰ for rye grass and clover grown on phlogopite respectively, and Δ 26Mg leaf-root of −0.06‰ and −0.22‰ for the same species grown hydroponically). This heavy isotope depletion in leaves can be explained by biological processes that affect leaves and roots differently: (1) organo–Mg complex (including chlorophyll) formation, and (2) Mg transport within plant. For both species, a positive correlation between δ 26Mg and K/Mg was observed among the various organs. This correlation is consistent with the link between K and Mg internal cycles, as well as with formation of organo–magnesium compounds associated with enrichment in heavy isotopes. Considering our results together with the published range for δ 26Mg of natural plants and rivers, we estimate that a significant change in continental vegetation would induce a change of the mean river δ 26Mg that is comparable to analytical uncertainties.

Cenozoic vegetation, climate changes and hominid evolution in tropical Africa

This paper reviews information on past vegetation of tropical Africa during the Cenozoic, focused upon the last 10 Ma, a time spanning hominid record in Central and East Africa. Summary of palaeobotanical data collected at terrestrial sites are compared with new results on the long term evolution of the continental vegetation zones documented from marine pollen record of two deep sea cores recovered from the Atlantic and Indian Oceans. Section 2 includes a summary of modern distribution of vegetation belts in the African continent and a synthesis of the results of both macrobotanical (fossil wood, leaves and fruits) and microbotanical (mainly pollen) studies presented according to time scale and geographical location. The main features emphasized by the palaeobotanical results are 1) seasonal vegetation and climate documented as soon as the Eocene in Tanzania 2) well diversified forests existing in northern West Ethiopia during the Oligocene 3) high temporal and spatial variabilities of forests composition during the Miocene when deciduous Legume woodland was documented in Ethiopia whereas wetter evergreen forests existed in Western Kenya 4) lack of evidence for an evergreen forest belt, continuous from Western Congo to East Africa. Section 3 presents new original pollen data recovered from a long core in the Gulf of Aden documenting large scale past vegetation changes in East Africa during the last 11 Ma. These results are discussed in comparison with a summarized long pollen sequence previously published from a marine core offshore the Niger delta. This comparison illustrates variations in geographical distribution of large vegetation zone at the continental scale, through time. In Section 4, vegetation changes registered during the last 10 Ma are discussed in relation with the results of isotopic studies and an updated presentation of hominids evolution in Africa. Several changes are shown in the marine records. An expansion of savanna/grassland is shown at 10 Ma in East Africa, 3 Ma earlier than in West Africa where it is documented at 7 Ma. At large geographical scale, this first increase in grass pollen simultaneously to forest increase in the marine records is interpreting as reflecting wetter conditions over the continent. Indeed, under global humid conditions, savanna could spread over the desert areas in the Northern and Eastern directions. A forest phase is well documented in West Africa between 7.5 and 7 Ma, but has not been shown in East Africa, mainly because of low resolution analysis of the DSDP East African record which needs further investigation for that period. A strong vegetation change took place between 6.3 and 6 Ma. It was marked by a trend of important decrease tree cover of the vegetation, simultaneous in West and East Africa. At that time, very arid conditions shown by scarce tree cover occurred over the whole tropical region. This happened before (or at) the early beginning of the Messinian crisis. Generally arid conditions coincide with the accepted timing for the Chimpanzee/hominid split, and record of Sahelanthropus tchadensis in Chad and Orrorin tugenensis in Kenya, although these fossils were found under locally wooded environment. The period from 6 to 4 Ma saw the appearance of Ardipithecus and diversification of Australopithecines occurring during a progressive increased tree cover in the broad-scale vegetation that culminated at 3.9 Ma, during A. anamensis time and before the first appearance of Australopithecus afarensis. Important variations in the vegetation occurred between 4 and 3 Ma, and many plant ecosystems were available to A. afarensis, a hominid which had a wide geographical distribution and persisted at Hadar under temporal climatic and environmental variability. The strongest and abrupt decline of forest pollen accompanied by an increase in the grass pollen was found at 2.7 Ma, more pronounced in the West than in East Africa. It was accompanied by a significant increase in C 4 grass proportions, well indicated in the Turkana region and likely explained by an increase in dry season length. Such marked changes correspond to the global climate change due to the establishment of the Arctic ice sheet that induced strong aridity in the tropics. Savanna expanded at the expense of rainforest, both in West and East Africa, whereas sub-desertic steppe expanded over savanna areas in the North. Mountain forests moved down slopes, closer to lowland sites in the Rift. Simultaneous faunal changes documented by the herbivores in the fauna, the appearance of early Homo and stone tools in the archaeological record of East Africa appear contemporaneous to local vegetation changes documented at terrestrial sites.

Using knowledge discovery with data mining from the Australian Soil Resource Information System database to inform soil carbon mapping in Australia

We present a piecewise linear decision tree model for predicting percent of soil organic C (SOC) in the agricultural zones of Australia generated using a machine learning approach. The inputs for the model are a national database of soil data, national digital surfaces of climate, elevation, and terrain variables, Landsat multispectral scanner data, lithology, land use, and soil maps. The model and resulting map are evaluated, and insights into biogeological surficial processes are discussed. The decision tree splits the overall data set into more homogenous subsets, thus in this case, it identifies areas where SOC responds closely to climatic and other environmental variables. The spatial pattern of SOC corresponds well to maps of estimated primary productivity and bioclimatic zones. Topsoil organic C levels are highest in the high rainfall, temperate regions of Tasmania, Victoria, and Western Australia, along the coast of New South Wales and in the wet tropics of Queensland; and lowest in arid and semiarid inland regions. While this pattern broadly follows continental vegetation, soil moisture, and temperature patterns, it is governed by a spatially variable hierarchy of different climatic and other variables across bioregions of Australia. At the continental scale, soil moisture level, rather than temperature, seems most important in controlling SOC.

Mata Atlântica: uma abordagem geográfica

According to the ecologist, the tropical rain Forest is a big ecosystem or a biome. Under the geographic optics, it is a type of sub continental vegetation that it is part of the humid tropical physiographic system, and occupies a considerable geographic space in Brazil and in some neighboring countries. Geographers, biologists and other scientists have been studying this evolution in geological time, under the focus of the paleoclimates of the Quaternary. However, it is transforming, in recent historical time, due to a considerable devastation and environmental impacts, in the same time, it has been attracting the researchers and ecotourists’ attention. For all this reasons, the government organs adopt the conservationist policies that aim to preserve what there is left. This article tries to approach these aspects concerning the Atlantic rain forest.

MATA ATLÂNTICA: UMA ABORDAGEM GEOGRÁFICA

According to the ecologist, the tropical rain Forest is a big ecosystem or a biome. Under the geographic optics, it is a type of sub continental vegetation that it is part of the humid tropical physiographic system, and occupies a considerable geographic space in Brazil and in some neighboring countries. Geographers, biologists and other scientists have been studying this evolution in geological time, under the focus of the paleoclimates of the Quaternary. However, it is transforming, in recent historical time, due to a considerable devastation and environmental impacts, in the same time, it has been attracting the researchers and ecotourists’ attention. For all this reasons, the government organs adopt the conservationist policies that aim to preserve what there is left. This article tries to approach these aspects concerning the Atlantic rain forest.

Exploring the climatic impact of the continental vegetation on the Mezosoic atmospheric CO<sub>2</sub> and climate history

Abstract. In this contribution, we continue our exploration of the factors defining the Mesozoic climatic history. We improve the Earth system model GEOCLIM designed for long term climate and geochemical reconstructions by adding the explicit calculation of the biome dynamics using the LPJ model. The coupled GEOCLIM-LPJ model thus allows the simultaneous calculation of the climate with a 2-D spatial resolution, the coeval atmospheric CO2, and the continental biome distribution. We found that accounting for the climatic role of the continental vegetation dynamics (albedo change, water cycle and surface roughness modulations) strongly affects the reconstructed geological climate. Indeed the calculated partial pressure of atmospheric CO2 over the Mesozoic is twice the value calculated when assuming a uniform constant vegetation. This increase in CO2 is triggered by a global cooling of the continents, itself triggered by a general increase in continental albedo owing to the development of desertic surfaces. This cooling reduces the CO2 consumption through silicate weathering, and hence results in a compensating increase in the atmospheric CO2 pressure. This study demonstrates that the impact of land plants on climate and hence on atmospheric CO2 is as important as their geochemical effect through the enhancement of chemical weathering of the continental surface. Our GEOCLIM-LPJ simulations also define a climatic baseline for the Mesozoic, around which exceptionally cool and warm events can be identified.

Molecular proxies for paleoclimatology

We summarize the applications of molecular proxies in paleoclimatology. Marine molecular records especially are proving to be of value but certain environmentally persistent compounds can also be measured in lake sediments, loess deposits and ice cores. The fundamentals of this approach are the molecular parameters, the compound abundances and carbon, hydrogen, nitrogen and oxygen isotopic contents which can be derived by the analysis of sediment extracts. These afford proxy measures which can be interpreted in terms of the conditions which control climate and also reflect its operation. We discuss two types of proxy; those of terrigenous and those of aquatic origin, and exemplify their application in the study of marine sediments through the medium of ten case studies based in the Atlantic, Mediterranean and Pacific Oceans, and in Antarctica. The studies are mainly for periods in the present, the Holocene and particularly the last glacial/interglacial, but they also include one study from the Cretaceous. The terrigenous proxies, which are measures of continental vegetation, are based on higher plant leaf wax compounds, i.e. long-chain (circa C 30) hydrocarbons, alcohols and acids. They register the relative contributions of C 3 vs. C 4 type plants to the vegetation in the source areas. The two marine proxies are measures of sea surface temperatures (SST). The longer established one, (U 37 K′) is based on the relative abundances of C 37 alkenones photosynthesized by unicellular algae, members of the Haptophyta. The newest proxy (TEX 86) is based on C 86 glycerol tetraethers (GDGTs) synthesized in the water column by some of the archaeal microbiota, the Crenarchaeota.

Late Holocene environmental change in the coastal southern Somalia inferred from Achatina and rhizoliths

Surfaces of poorly cemented carbonate dunes of the coast of southern Somalia contain as exhumed bodies treelet rhizoliths and subfossil shells of the giant land snail Achatina. Present-day coastal dunes in southern Somalia are poorly vegetated and do not support living Achatinas. Thus, the presence of these subfossils provides evidence for a more humid period in the past: the subfossil giant land snails and the rhizoliths indicate a palaeoenvironment which was probably similar to the modern environment of the coastal belt of Kenya and of the southernmost corner of coastal Somalia, where living Achatinas are frequent and the forest–savannah mosaic vegetation type [Bonnefille, R., 1985. Evolution of the continental vegetation: the palaeobotanical record from East Africa. South African Journal of Science 81, 267–270] is widespread. According to radiometric ages of Achatina shells and geological observations, aridification process probably took place in the Late Holocene. Somali data are consistent with the known regional climatic trends.

Relative importance of host tree species and environmental gradients for epiphytic species composition, exemplified by pyrenomycetes s. lat. (Ascomycota) on Salix in central north Scandinavia

According to the continuum concept of vegetation, variation in species composition is primarily determined by complex environmental gradients. Species‐gradient relationships of ground‐dwelling, independent organisms are studied at scales ranging from centimetres to continents. In this study we use a balanced data set for pyrenomycetes on Salix to address if how the current species‐gradient paradigm needs to be modified to apply to assemblages of organisms that are dependent on other organisms for their existence. The data from a transect across central‐north Scandinavia included variation along climatic gradients in oceanicity (from oceanic to continental vegetation sections), and temperatures (from south boreal to alpine vegetation zones) and among five common and widely distributed Salix host species (Salix caprea agg., S. glauca ssp. glauca, S. lapponum, S. myrsinifolia agg. and S. pentandra). Ten individuals of each Salix host species were selected and carefully examined for pyrenomycetes within each combination of section and zone. Data for 28 species in the 28 combinations of section, zone and host were subjected to ordination and constrained ordination analyses. Host species was the most important source of variation in species composition, followed by zone and section which are the same major regional gradients that are important to plants. We use examples to discuss the contribution of local ecological and substrate gradients to the high variation explained by host species, concluding that host specificity per se occurs for these partly parasitic fungi. We therefore suggest that in order to account for variation in composition of species assemblages with strong degree of host dependence, general rules for species‐gradient relationships need to be extended by inclusion of host specificity as separate factor.

Millenial scale variations of the isotopic composition of atmospheric oxygen over Marine Isotopic Stage 4

During rapid events of the last glacial period (DO events), dramatic changes are recorded at high and low latitudes. Without a precise common timescale, links between changes in Greenland temperature and changes in biosphere productivity, hydrology regimes and sea level are difficult to establish. The composition of atmospheric oxygen ( δ 18O atm) is influenced by global sea level changes, the global hydrologic cycle and the biosphere productivity. Since δ 18O atm is measured in ice cores it gives the opportunity to investigate the underlying processes with no timescale uncertainty. Here, we present the first high resolution (50 yrs) record of the isotopic composition of atmospheric oxygen ( δ 18O atm) measured in the air trapped in a Greenland ice core (NorthGRIP). Our record covers a sequence of DO events (18-19-20) corresponding to the Marine Isotopic Stage 4, ∼ 75 to 60 ka ago. Our measurements reveal rapid changes of δ 18O atm associated with the DO events. With a few additional measurements of the third isotope of oxygen ( 17O) during the DO event 19, we exclude the hypothesis that sea level changes are responsible for the isotopic variations. They originate more likely from large changes in relative humidity and latitudinal repartition of the continental vegetation over the DO events.

Late Quaternary upwelling off tropical NW Africa: new micropalaeontological evidence from ODP Hole 658C

AbstractPlanktonic foraminifera and radiolaria have been analysed in a Late Quaternary (40–0 ka) sediment sequence from Ocean Drilling Program (ODP) Hole 658C located under a coastal upwelling system near Cap Blanc, offshore northwest Africa, in order to document the palaeoceanographic history of the area. Temporal variations in species abundance and faunal assemblage analysis reveal a tripartite phased sequence of palaeoceanographic change through the Late Quaternary. Phase 1 spans 40–14.5 ka and is characterised by moderate upwelling, but Heinrich event 2 is distinguished as a brief episode of strengthened upwelling. Phase 2 begins with a change in a number of variables at ca. 14.5 ka and extends to ca. 5.5 ka. This phase is characterised by a general strengthening of upwelling, but may be subdivided into three minor phases including (a) the recognition of the Younger Dryas, marked by a temporary reduction in upwelling strength, followed by (b) an intensification of upwelling, and (c) upwelling and high productivity between 8 and 5.5 ka. This phase of upwelling corresponds with maximum Holocene cooling, possibly triggered by the collapse of the Laurentide ice sheet. Phase 3 extends from 5.5 to 0 ka and is characterised by weak upwelling and significant calcite dissolution. These phases are related to climatic events, particularly the African Humid Period (AHP), which is coincident with Phase 2. The AHP is characterised by increased precipitation, linked to an intensification of the African monsoon that enhances North East Trade Wind‐driven coastal upwelling and is associated with the expansion of continental vegetation across North Africa. Copyright © 2006 John Wiley & Sons, Ltd.

Evaluating the quality of AVHRR Pathfinder NDVI data for the African continent using SPOT-4 Vegetation data

Geografisk Tidsskrift, Danish Journal of Geography 106(1):87–102, 2006 The AVHRR (Advanced Very High Resolution Radiometer) 8 km resolution Pathfinder NDVI (Normalized Difference vegetation Index) 10-day composite data set has been used for numerous local and global scale vegetation time series studies during recent decades. The dataset is a result of considerable processing and resampling from the original 1 km resolution AVHRR LAC (Local Area Coverage) data and combined with inappropriate sensor band design for vegetation monitoring these factors potentially introduce noise in the Pathfinder NDVI. The quality of the Pathfinder data has been difficult to assess but the recent release of SPOT-4 Vegetation (VGT) 10-day composite (S10) NDVI data is considered to be an improvement on the AVHRR data and offers the first possibility for a correct analysis/evaluation of the Pathfinder data.—In this study, three years of AVHRR Pathfinder and resampled SPOT-4 VGT (1998–2000) data has been evaluated/analysed using an ortho-regression analysis on 10-day, monthly and annual integrated values. Annual integrated values of AVHRR Pathfinder and SPOT-4 VGT data can be characterized by a linear relationship and correlate well on a continental scale. However the dynamic range of the SPOT-4 VGT NDVI is higher than the AVHRR Pathfinder NDVI. Analysis of individual IGBP biomes shows biome specific differences; evergreen broadleaf forest characterized by lower r values and highest RMSE values and normalized RMSE values indicate largest divergence for the shrubland biome. When performing the analysis on monthly maximum composites and 10-day composite data, intra-annual variations appear. Analyses of 10-day data also show a linear relationship between the NDVI of the two composite products; the relationship being characterized by lower r values and higher RMSE's. Monthly and 10-day maximum composites reveal intra-annual variations in the correlation between the SPOT-4 VGT and AVHRR Pathfinder data. This is attributed to different cloud masking algorithms; the SPOT-4 VGT cloud screening algorithm being insufficient thereby suppressing the rainy season ND VI. However, the correspondence between the SPOT-4 VGT and A VHRR PAL data is considerably better for a transect analysis covering an area not severely influenced by clouds when compared to the continental scale analysis. This suggests that the major part of the noise found in the continental scale SPOT-4 VGT NDVI and AVHRR PAL NDVI analyses can be attributed the different cloud masking algorithms and is to a lesser degree a consequence of the AVHRR PAL NDVI resampling. It is concluded that the quality of the AVHRR NDVI PAL is adequate for time series continental scale vegetation analysis despite the resampling scheme.

Vegetation markers of palaeoclimate cyclical changes in the Pliocene of Punta Piccola (Sicily, Italy)

Abstract Astronomically driven climate changes are recorded in mineralogical composition of marine sediments. In order to view the implications of precession cycles on continental vegetation, high-resolution records of pollen and fresh water algae are presented in five precession cycles (no. 104–108, age 3.00–2.92 Ma) from the central Mediterranean Punta Piccola section (Pliocene). Each cycle has been subdivided into four phases based on the pollen composition. Three phases represent the brown, laminated part of the cycle (formed during precession minima). Their pollen associations suggest relatively heavy precipitation and high temperatures. The fourth phase represents the light, carbonate-rich part of the precession cycles, and its pollen associations express arid conditions. This phase also experiences maxima in percentages of palygorskite and higher pollen input from the South.

The palaeoclimatic utility of terrestrial biomarkers in marine sediments

Organic compounds of known biological origin (biomarkers) and preserved in marine sediments have commonly been used to develop proxy records for past climate. While biomarkers for marine organisms are the logical target of many investigations, higher plant and other terrestrial biomarkers are also common in marine sediments and can be used to develop records of past continental vegetation, from which climatic change can be inferred. In fact, the high sampling resolution and extensive temporal record (>100 ma) of marine sediments, combined with the fact that compounds in marine sediments are delivered from a potentially vast geographical area, means that marine sediments can be more appropriate for such investigations than comparable terrestrial sedimentary sequences (lacustrine sediments, peats). Critical challenges to this approach include elucidation of the controls on delivery of organic material to marine sediments, ecological and physiological variability in biomarker distributions and isotopic compositions and the impact of diagenetic alteration on biomarker distributions. Here, we review potential terrestrial plant and microbial biomarkers, the controls on their carbon isotopic compositions and their modes of delivery to marine sediments, devoting specific attention to their utility in continental vegetation reconstruction.

Vegetation markers of palaeoclimate cyclical changes in the Pliocene of Punta Piccola (Sicily, Italy)

Astronomically driven climate changes are recorded in mineralogical composition of marine sediments. In order to view the implications of precession cycles on continental vegetation, high-resolution records of pollen and fresh water algae are presented in five precession cycles (no. 104–108, age 3.00–2.92 Ma) from the central Mediterranean Punta Piccola section (Pliocene). Each cycle has been subdivided into four phases based on the pollen composition. Three phases represent the brown, laminated part of the cycle (formed during precession minima). Their pollen associations suggest relatively heavy precipitation and high temperatures. The fourth phase represents the light, carbonate-rich part of the precession cycles, and its pollen associations express arid conditions. This phase also experiences maxima in percentages of palygorskite and higher pollen input from the South.

Glacial–interglacial organic carbon record from the Makassar Strait, Indonesia: implications for regional changes in continental vegetation

Recent studies convincingly show that climate in the Western Pacific Warm Pool and other equatorial/tropical regions was significantly colder (by ∼3–4°C) during glacial periods, prompting a reexamination of the late Pleistocene paleoenvironments of these regions. This study examines changes in continental vegetation during the last two deglaciations (Terminations I and II) using a sediment core (MD9821-62) recovered from the Makassar Strait, Indonesia. Evidence based on the lignin phenol ratios suggests that vegetation on Borneo and other surrounding islands did not significantly change from tropical rainforest during the last two glacial periods relative to subsequent interglacial periods. This supports the hypothesis that the winter monsoon increased in strength during glacial periods, allowing Indonesia to maintain high rainfall despite the cooler conditions.

Fuzzy Modelling of African Ecoregions and Ecotones Using AVHRR NDVI Temporal Imagery

Conventional methods of deriving global or continental vegetation maps from the National Oceanic and Atmospheric Administration's (NOAA) Advanced Very High Resolution Radiometer (AVHRR) time series data are based on two‐value Boolean logic, which cannot properly model the so‐called ecotone, the transition zone between adjacent ecosystems. New methods and data models that have been developed on the basis of fuzzy logic to address the “mixed pixel” issue in multi‐spectral imagery can also be used with multi‐temporal imagery to handle the mixture of vegetation types within an ecotone. This study introduces the concept of semantic space and its transformation from spectral feature space, which utilizes a fuzzy logic approach to characterize the continuum of vegetation communities in the African continent from AVHRR multi‐temporal (12 months for three years from 1986 to 1988) NDVI data. The fuzzy procedure was based on the Fuzzy c‐Means (FCM) algorithm with significant modifications to improve processing speed for handling large volumes of data. A second‐order mapping approach was also devised to explicitly represent subdominant vegetative coverage in ecotones and other heterogeneous regions. Comparisons between a Sub‐Saharan African Vegetation Map compiled by the International Union for Conservation of Nature (IUCN) in 1986 and the maps derived from this study demonstrated that fuzzy modeling and classification might provide a better and more realistic representation of the vegetative characteristics of the region.

Detecting Organic Tracers from Biomass Burning in the Atmosphere

This is a brief review key to the literature on the determination of organic tracers from biomass burning which are detectable even after long-range global transport in total extracts of atmospheric particles. The major tracers are thermal degradation products from the biopolymer cellulose, namely the didehydromonosaccharide derivatives levoglucosan, galactosan and mannosan and the resin acid derivative dehydroabietic acid, with minor β-sitosterol. Dehydroabietic acid is emitted primarily from burning of conifer fuel and these tracers are found in most aerosol samples from the North American continent. Particulate matter from the atmosphere over oceanic areas contains organic tracers from both natural and biomass burning emissions. The major biomarker compounds characterized are natural products from continental vegetation consisting primarily of epicuticular wax components and trace components from biomass burning emissions. The presence of these tracers in atmospheric particulate matter over the ocean confirms the long-range transport of smoke from biomass burning off the continents.