Paleoenvironmental dynamics in central-eastern Brazil during the last 23 000 years: tropical peatland record in the Cerrado biome

The Cerrado biome is the second largest in Brazil, but the evolution of the Cerrado during the late Quaternary is not yet fully known. This study identifies paleoenvironmental changes during the last 23 000 years, based on a tropical mountain peatland record, in the Serra do Espinhaço Meridional in central-eastern Brazil. A multi-proxy approach was used that involved palynological analysis, stable isotopes (δ¹³C, δ¹⁵N), geochemistry, radiocarbon dating and multivariate statistics derived from a peatland core from Rio Preto (Minas Gerais state). The study reveals a very humid and cold climate during the late Pleistocene, with an increase in temperature and decrease in humidity at the Pleistocene–Holocene transition. During this period there was strong instability in the landscape (episodes of erosion). At the beginning of the Holocene there was a reduction in humidity with greater landscape stability. The current sub-humid climatic conditions seem to have been established in the mid-/late Holocene, with periods of landscape instability. Our findings agree with other Cerrado records that contradict previously established hypotheses, such as the Amazonian Refuge and the Pleistocene Arc.     

Late Quaternary vegetation,climate and fire dynamics inferred from the El Tiro record in the southeastern Ecuadorian Andes

In order to study the stability and dynamics of mountain rainforest and paramo ecosystems, including the biodiversity of these ecosystems, the Holocene and late Pleistocene climate and fire variability, and human impact in the southeastern Ecuadorian Andes, we present a high‐resolution pollen record from El Tiro Pass (2810 m elevation), Podocarpus National Park. Palaeoenvironmental changes, investigated by pollen, spores and charcoal analysis, inferred from a 127 cm long core spanning the last ca. 21 000 cal. yr BP, indicate that grass‐paramo was the main vegetation type at the El Tiro Pass during the late Pleistocene period. The grass‐paramo was rich in Poaceae, Plantago rigida and Plantago australis, reflecting cold and moist climatic conditions. During the early Holocene, from 11 200 to 8900 cal. yr BP, subparamo and upper mountain rainforest vegetation expanded slightly, indicating a slow warming of climatic conditions during this period. From 8900 to 3300 cal. yr BP an upper mountain rainforest developed at the study site, indicated by an increase in Hedyosmun, Podocarpaceae, Myrsine and Ilex. This suggests a warmer climate than the present day at this elevation. The modern subparamo vegetation became established since 3300 cal. yr BP at El Tiro Pass. Fires, probably anthropogenic origin, were very rare during the late Pleistocene but became frequent after 8000 cal. yr BP. Copyright © 2007 John Wiley & Sons, Ltd.     

Lake sedimentary processes and vegetation changes over the last 45k cal a bp in the uplands of south-eastern Amazonia

This study addresses paleoclimate influences in a southern Amazonia ecotone based on multiproxy records from lakes of the Carajás region during the last 45k cal a bp. Wet and cool environmental conditions marked the initial deposition in shallow depressions with detrital sediments and high weathering rates until 40k cal a bp. Concomitantly, forest and C3 canga plants, along with cool-adapted taxa, developed; however, short drier episodes enabled expansion of C4 plants and diagenetic formation of siderite. A massive event of siderite formation occurred approximately 30k cal a bp under strong drier conditions. Afterwards, wet and cool environmental conditions returned and persisted until the Last Glacial Maximum (LGM). The LGM was marked by lake-level lowstands and subaerial exposure. The transition from the LGM to the Holocene is marked by the onset of oscillations in temperature and humidity, with an expansion of forest and canga plants. Cool taxa were present for the last time in the Carajás region ~ 9.5–9k cal a bp. After 10k cal a bp , shallow lakes became upland swamps due to natural infilling processes, but the current vegetation types and structures of the plateaus were acquired only after 3k cal a bp under wetter climatic conditions.     

A multiproxy record of late Holocene natural and anthropogenic environmental change from the Sphagnum peat bog Dürres Maar,Germany: implications for quantitative climate reconstructions based on pollen

Pollen data are well established for quantitative climate reconstructions over long timescales, including the Holocene and older interglacials. However, anthropogenically induced environmental change in central Europe was strong during the last 4 ka, challenging quantitative reconstructions of this time period. Here we present quantitative climate reconstructions based on pollen analyses and evaluate them with the peat humification record and the stable carbon isotopes of Sphagnum plant material (δ¹³C_cellulose). All analyses were carried out on the same 7.5 m long, largely ombrotrophic peat bog section from Dürres Maar. Three different methods were used for the quantitative climate reconstructions on the basis of the pollen data: (1) a probabilistic indicator taxa approach (the ‘pdf method’); (2) a modern analogue technique based on pollen taxa from modern surface samples (cMAT); and (3) a modern analogue technique expanded by plant functional types (pMAT). At Dürres Maar the peat humification is only affected by peat cutting during the Roman period and the Middle Ages. The stable carbon isotopes are seemingly unaffected by human impact. Thus both proxies provide independent data to evaluate the reconstructions on the basis of pollen data. The quantitative climate reconstructions on the basis of the individual methods are in general relatively similar. Nevertheless, distinct differences between the individual approaches are also apparent, which could be attributed to taxa that reflect human impact on a local to regional scale. While the pdf method appears to be relatively robust to all observed anthropogenically induced vegetation changes, it potentially underestimates climate variability. This method is therefore expected to be independent of local site characteristics and to provide robust quantitative estimates of climatic trends rather than of climatic variability of small amplitude. This is of value for palaeoclimate reconstructions of older interglacials, for which neither multiple sites nor independent climate proxies are available for comparison. Copyright © 2009 John Wiley & Sons, Ltd.     

Climate change during the past 1000 years: a high‐temporal‐resolution multiproxy record from a mire in northern Finland

We present a record of peatland development in relation to climate changes and human activities from the Palomaa mire, a remote site in northern Finland. We used fine‐resolution and continuous sampling to analyse several proxies including pollen (for vegetation on and around the mire), testate amoebae (TA; for mire‐wetness changes), oxygen and carbon isotopes from Sphagnum cellulose (δ¹⁸O and δ¹³C; for humidity and temperature changes), peat‐accumulation rates and peat‐colour changes. In spite of an excellent accumulation model (30 ¹⁴C dates and estimated standard deviation of sample ages <1 year in the most recent part), the potential to determine cause–effect (or lead–lag) relationships between environmental changes and biotic responses is limited by proxy‐specific incorporation processes below the actively growing Sphagnum surface. Nevertheless, what emerges is that mire development was closely related to water‐table changes rather than to summer temperature and that water‐table decreases were associated with increasing peat‐accumulation rates and more abundant mire vegetation. A rapid fen‐to‐bog transition occurred within a few years around AD 1960 when the water table decreased beyond the historical minimum, supporting the notion that mires can rapidly shift into bogs in response to allogenic factors. Copyright © 2012 John Wiley & Sons, Ltd.     

Elemental and isotopic carbon and nitrogen records of organic matter accumulation in a Holocene permafrost peat sequence in the East European Russian Arctic

A peat deposit from the East European Russian Arctic, spanning nearly 10 000 years, was investigated to study soil organic matter degradation using analyses of bulk elemental and stable isotopic compositions and plant macrofossil remains. The peat accumulated initially in a wet fen that was transformed into a peat plateau bog following aggradation of permafrost in the late Holocene (～2500 cal a BP). Total organic carbon and total nitrogen (N) concentrations are higher in the fen peat than in the moss‐dominated bog peat layers. Layers in the sequence that have lower concentrations of total hydrogen (H) are associated with degraded vascular plant residues. C/N and H/C atomic ratios indicate better preservation of organic matter in peat material dominated by bryophytes as opposed to vascular plants. The presence of permafrost in the peat plateau stage and water‐saturated conditions at the bottom of the fen stage appear to lead to better preservation of organic plant material. δ¹⁵N values suggest N isotopic fractionation was driven primarily by microbial decomposition whereas differences in δ¹³C values appear to reflect mainly changes in plant assemblages. Positive shifts in both δ¹⁵N and δ¹³C values coincide with a local change to drier conditions as a result of the onset of permafrost and frost heave of the peat surface. This pattern suggests that permafrost aggradation not only resulted in changes in vegetation but also aerated the underlying fen peat, which enhanced microbial denitrification, causing the observed ¹⁵N‐enrichment. Copyright © 2012 John Wiley & Sons, Ltd.     

Late Holocene in central Brazil: vegetation changes and humidity variability in a tropical wetland

The Pandeiros wetland is a high biodiversity ecosystem located within a semiarid region of the Cerrado biome, a neotropical savanna. This large wetland is of key importance for ecological and hydrological balance in central Brazil and for the conservation of the Cerrado fauna and flora. In this study, we present the first palaeoecological investigation of the Pandeiros wetland based on pollen analysis of a palm swamp sediment core encompassing the Late Holocene. Our results show that the wetland was subject to multicentennial-scale oscillations in water availability during the Late Holocene; in particular, higher local humidity was documented between 4100 and 3100 cal a bp and from 2600 to 1000 cal a bp , and two events of drier local conditions occurred at approximately 2900 and 900 cal a bp. Our results also indicate a general decreasing trend in arboreal density in the Pandeiros River Basin from the beginning of the Late Holocene to the present, with the greatest expansion of dry forest occurring between 3600 and 3100 cal a bp.     

Aragonite stromatolitic buildups from Santorini (Aegean Sea,Greece): Geochemical and palaeontological constraints of the caldera palaeoenvironment prior to the Minoan eruption (ca 3600 yr bp)

The pyroclastic deposits of the Minoan eruption (ca 3600 yr bp ) in Santorini contain abundant xenoliths. Most of these deposits are calcareous blocks of laminated‐botryoidal, stromatolite‐like buildups that formed in the shallow waters of the flooded pre‐Minoan caldera; they consist of (i) light laminae, of fibrous aragonite arranged perpendicular to layering, and (ii) dark laminae, with calcified filaments of probable biological origin. These microstructures are absent in the light laminae, suggesting a predominant inorganic precipitation of aragonite on substrates probably colonized by microbes. Internal cavities contain loose skeletal grains (molluscs, ostracods, foraminifera and diatoms) that comprise taxa typical of shallow marine and/or lagoon environments. Most of these forms are typical of warm water environments, although no typical taxa from hydrothermal vents have been observed. Past gasohydrothermal venting is recorded by the occurrence of barite, pyrolusite and pyrite traces. The most striking features of the stable isotopic data set are: (i) an overall wide range in δ¹³C_PDB (0·16 to 12·97‰) with a narrower variation for δ¹⁸O_PDB (?0·23 to 4·33‰); and (ii) a relatively uniform isotopic composition for the fibrous aragonite (δ¹³C = 12·40 ± 0·43‰ and δ¹⁸O = 2·42 ± 0·77‰, n = 21). The δ¹³C and δ¹⁸O values from molluscs and ostracods display a covariant trend, which reflects a mixing between sea water and a fluid influenced by volcano‐hydrothermal activity. Accordingly, ⁸⁷Sr/⁸⁶Sr from the studied carbonates (0·708758 to 0·709011 in fibrous aragonite and 0·708920 to 0·708991 in molluscs) suggests that the aragonite buildups developed in sea water under the influence of a hydrothermal/volcanic source. Significant differences in trace elements have been detected between the fibrous aragonite and modern marine aragonite cements. The caldera water from which the fibrous aragonite crusts formed received an input from a volcano‐hydrothermal system, probably producing diffuse venting of volcanogenic CO₂ gas and of a fluid enriched in Ca, Mn and Ba, and depleted in Mg and probably in Sr.     

Pollen‐based biome reconstructions for Colombia at 3000, 6000, 9000, 12 000, 15 000 and 18 000 14C yr ago: Late Quaternary tropical vegetation dynamics

Colombian biomes are reconstructed at 45 sites from the modern period extending to the Last Glacial Maximum (LGM). The basis for our reconstruction is pollen data assigned to plant functional types and biomes at six 3000‐yr intervals. A reconstruction of modern biomes is used to check the treatment of the modern pollen data set against a map of potential vegetation. This allows the biomes reconstructed at past periods to be assessed relative to the modern situation. This process also provides a check on the a priori assignment of pollen taxa to plant functional types and biomes. For the majority of the sites, the pollen data accurately reflect the potential vegetation, even though much of the original vegetation has been transformed by agricultural practices. At 18 000 ¹⁴C yr BP, a generally cool and dry environment is reflected in biome, assignments of cold mixed forests, cool evergreen forests and cool grassland–shrub; the latter extending to lower altitudes than presently recorded. This signal is strongly recorded at 15 000 and 12 000 ¹⁴C yr BP, the vegetation at these times also reflecting a relatively cool and dry environment. At 9000 ¹⁴C yr BP there is a shift to biomes thought to result from slightly cooler environmental conditions. This trend is reversed by 6000 ¹⁴C yr BP; most sites, within a range of different environmental settings, recording a shift to more xeric biome types. There is an expansion of steppe and cool mixed‐forest biomes, replacing tropical dry forest and cool grassland–shrub biomes, respectively. These changes in biome assignments from the modern situation can be interpreted as a biotic response to mid‐Holocene climatic aridity. At 3000 ¹⁴C yr BP the shift is mainly to biomes characteristic of slightly more mesic environmental conditions. There are a number of sites that do not change biome assignment relative to the modern reconstruction, although the affinities that these sites have to a specific biome do change. These ‘anomalies’ are interpreted on a site‐by‐site basis. Spatially constant, but differential response of the vegetation to climatic shifts are related to changes in moisture sources and the importance of edaphic controls on the vegetation. The Late Quaternary reconstruction of large‐scale vegetation dynamics in Colombia allows an understanding of the environmental controls on these to be developed. In particular, shifts in the character of the main climatic systems that influence Colombian vegetation are described. Copyright © 2002 John Wiley & Sons, Ltd.     

Evidence of Younger Dryas and Neoglacial cooling in a Late Quaternary palaeotemperature record from a speleothem in eastern Victoria,Australia

A calcitic stalagmite collected from a limestone cave in the Buchan area of eastern Victoria has been dated by three mass-spectrometric uranium series analyses. Two growth phases are represented: the older from 13.4 to 10.6 ka and the younger from 3.2 to 2.1 ka. Oxygen isotope analysis reveals that temperatures were below present-day values at all times, but particularly cool conditions are indicated between 12.3 and 11.4 ka, and Neoglacial conditions occurred at about 3 ka. The older cold climate event is clearly synchronous with the Younger Dryas in Europe and this is the first time that strong evidence for this event has been found in Australia. Carbon isotope variations are interpreted as indicating changes in plant productivity on the surface and are most likely controlled by variations in summer rainfall. They indicate particularly high levels of plant productivity from 11.5 to 11.0 ka. © 1996 John Wiley & Sons, Ltd.     

Timing of Lateglacial vegetation dynamics and respective palaeoenvironmental conditions in southern Estonia: evidence from the sediment record of Lake Nakri

This paper investigates a detailed well‐dated Lateglacial floristic colonisation in the eastern Baltic area, ca. 14 000–9000 cal. a BP, using palynological, macrofossil, loss‐on‐ignition, and ¹⁴C data. During 14 000–13 400 cal. a BP, primarily treeless pioneer tundra vegetation existed. Tree birch (Betula sect. Albae) macro‐remains and a high tree pollen accumulation rate indicate the presence of forest‐tundra with birch and possibly pine (Pinus sylvestris L.) trees during 13 400–12 850 cal. a BP. Palaeobotanical data indicate that the colonisation and development of forested areas were very rapid, arising within a period of less than 50 years. Thus far, there are no indications of conifer macrofossils in Estonia to support the presence of coniferous forests in the Lateglacial period. Signs of Greenland Interstadial 1b cooling during 13 100 cal. a BP are distinguishable. Biostratigraphic evidence indicates that the vegetation was again mostly treeless tundra during the final colder episode of the Lateglacial period associated with Greenland Stadial 1, approximately 12 850–11 650 cal. a BP. This was followed by onset of the Holocene vegetation, with the expansion of boreal forests, in response to rapid climatic warming. Copyright © 2011 John Wiley & Sons, Ltd.     

河北安固里淖孢粉记录的晚冰期以来的植被演替与气候变化

河北安固里淖地处东南季风的边缘地区,是研究古气候环境演化的理想地区之一。文章以安固里淖的沉积岩芯（长18.4 m）为研究对象,利用AMS ¹⁴C测年和孢粉数据,重建了安固里淖湖区14.3 cal.ka B.P.以来的植被与气候演化历史。结果表明：14.3~11.0 cal.ka B.P.期间,湖区以疏林草原植被为主,气候偏干;11.0~6.0 cal.ka B.P.以森林草原植被为主,气候湿润;6.0~3.2 cal.ka B.P.以疏林草原植被为主,气候偏湿;3.2~0 cal.ka B.P.以荒漠草原植被为主,气候干旱。总体而言,自晚冰期以来安固里淖的气候经历了由干变湿再逐渐变干的过程,全新世适宜期出现在早中全新世。通过区域对比发现,安固里淖揭示的晚冰期以来东南季风的气候演化特征与西南季风的演化具有很大的相似性,表明晚冰期以来东南季风与西南季风在轨道尺度上的演化并无太大差异,太阳辐射是二者演化的共同驱动力。

     

Dinosaur coprolites from the Late Cretaceous (Maastrichtian) Lameta Formation of India: isotopic and other markers suggesting a C3plant diet

A single locality of the Late Cretaceous (Maastrichtian) Lameta Formation at Pisdura in Central India has yielded a large number of coprolites attributed to titanosaurian dinosaurs. Internally the coprolites are dark grey and contain abundant plant tissues and other organic materials. The plant tissues are mostly of gymnospermous origin. In addition, remains of bacterial colonies, fungal spores and algae are seen in the macerated fraction under scanning electron microscope. The dark grey appearance is probably attributable to fine-grained organic matter within voids in tracheids or xylem. The average ¹³C/¹²C ratio of the organic matter in the coprolites is -24‰ (relative to PDB) suggesting that plants of C₃type were the main diet of their producers. A comparison of δ¹⁵N value (about 4‰ w.r.t. air) of the coprolites with that of faecal matter of modern herbivores and carnivores suggests that gut fermentation may not have been an active mechanism in the digestion process of titanosaurs.     

Oscillatory zoning in garnet from the Willsboro Wollastonite Skarn, Adirondack Mts, New York: a record of shallow hydrothermal processes preserved in a granulite facies terrane

Oscillatory zoning in low δ¹⁸O skarn garnet from the Willsboro wollastonite deposit, NE Adirondack Mts, NY, USA, preserves a record of the temporal evolution of mixing hydrothermal fluids from different sources. Garnet with oscillatory zoning are large (1–3 cm diameter) euhedral crystals that grew in formerly fluid filled cavities. They contain millimetre‐scale oscillatory zoning of varying grossular–andradite composition (X_Adr = 0.13–0.36). The δ¹⁸O values of the garnet zones vary from 0.80 to 6.26‰ VSMOW and correlate with X_Adr. The shape, pattern and number of garnet zones varies from crystal to crystal, as does the magnitude of the correlated chemistry changes, suggesting fluid system variability, temporal and/or spatial, over the time of garnet growth. The zones of correlated Fe content and δ¹⁸O indicate that a high Fe³⁺/Al, high δ¹⁸O fluid mixed with a lower Fe³⁺/Al and δ¹⁸O fluid. The high δ¹⁸O, Fe enriched fluids were likely magmatic fluids expelled from crystallizing anorthosite. The low δ¹⁸O fluids were meteoric in origin. These are the first skarn garnet with oscillatory zoning reported from granulite facies rocks. Geochronologic, stable isotope, petrologic and field evidence indicates that the Adirondacks are a polymetamorphic terrane, where localized contact metamorphism around shallowly intruded anorthosite was followed by a regional granulite facies overprint. The growth of these garnet in equilibrium with meteoric and magmatic fluids indicates an origin in the shallow contact aureole of the anorthosite prior to regional metamorphism. The zoning was preserved due to the slow diffusion of oxygen and cations in the large garnet and protection from deformation and recrystallization in zones of low strain in thick, rigid, garnetite layers. The garnet provide new information about the hydrothermal system adjacent to the shallowly intruded massif anorthosite that predates regional metamorphism in this geologically complex, polymetamorphic terrane.     

长春地区中更新世晚期古环境重建的沉积地球化学与孢粉学证据

通过对长春地区HDBZK-1孔沉积序列的热释光测年和沉积物粒度分析,选取对气候变化较为敏感的K₂O、Na₂O、MgO、CaO、Al₂O₃等氧化物及K₂O/ Na₂O、Al₂O₃/(Al₂O₃+CaO+Na₂O)作为环境代用指标,并与孢粉分析资料相结合,分析了长春地区中更新世晚期（约280～120 kaB.P.）的气候环境变化。结果表明：该区中更新世晚期总体经历了4次明显的冷干-暖湿气候变化,即寒冷干旱（281.6～244.0 kaB.P.）-温凉稍湿（244.0～215.0 kaB.P.）-寒冷干旱（215.0～ 131.8 kaB.P.）-以淡水藻类花粉突然增多为明显标志的暖湿（131.8～126.4 kaB.P.）;这与深海氧同位素曲线所反映的气候变化旋回有较好的对应关系。