Peat Record Research Articles

Combined zinc-lead isotope and trace-metal assessment of recent atmospheric pollution sources recorded in Irish peatlands

Atmospherically-fed Earth surface archives such as ombrotrophic peatlands, lake sediments, and ice consistently show an upward increase in Zn concentrations of hitherto unclear origin. Here, we present a combined stable Zn isotope and trace element (Zn, Cd, Ni, Cu, Cr, V, Ta, Pb) dataset for a historically polluted, near-urban bog (Liffey Head) from the east coast of Ireland. This peat record is compared to an archive from a rural site at the west coast of Ireland (Brackloon Wood). Both archives show a clear near-surface increase in Zn deposition, accompanied by periodic deposition in Cr, Ni, Mo, and V suggesting a co-genetic origin of these elements. In the Liffey Head site, biologic upward distillation of nutrients can be excluded as the origin of the elemental enrichments. The differences in the excess metal ratios between the two sites (e.g., Zn/Cd of 426–1564, east, and 77–106, west) are attributed to a higher contribution from traffic emissions (diesel, petrol) and oil-burning at the near-urban site, and dominant atmospheric influence from solid fossil fuel combustion emissions (e.g., mixed fuel, coal and wood) at the rural site.The Zn isotope composition in the historically-polluted Liffey Head bog evolved from δ66/64ZnJMC-Lyon values of 0.72 ± 0.03‰ in the peat accumulated during the 19th century to lighter ratios (0.18 ± 0.03‰) towards the top of the monolith (i.e., recent). Zinc-isotope ratios are positively correlated with excess metal/Cd ratios and also with 206Pb/207Pb, collectively fingerprinting the gradual change from a mining-dominated to a traffic-dominated atmospheric pollution at the east coast over the past century. A prevalent input, interpreted to represent combustion emissions from diesel engines, is observed for the past 15 years. Combined with trace elements and radiogenic Pb isotopes, the information obtained with the Zn isotope systematics adds towards an in-depth characterisation of the pollution signals.

Evidence for increased expression of the Amundsen Sea Low over the South Atlantic during the late Holocene

Abstract. The Amundsen Sea Low (ASL) plays a major role in the climate and environment of Antarctica and the Southern Ocean, including surface air temperature and sea ice concentration changes. Unfortunately, a relative dearth of observational data across the Amundsen and Bellingshausen seas prior to the satellite era (post-1979) limits our understanding of the past behaviour and impact of the ASL. The limited proxy evidence for changes in the ASL are primarily restricted to the Antarctic where ice core evidence suggests a deepening of the atmospheric pressure system during the late Holocene. However, no data have previously been reported from the northern side of the ASL. Here we report a high-resolution, multi-proxy study of a 5000-year-long peat record from the Falkland Islands, a location sensitive to contemporary ASL dynamics which modulates northerly and westerly airflow across the southwestern South Atlantic sector of the Southern Ocean. In combination with climate reanalysis, we find a marked period of wetter, colder conditions most likely the result of enhanced southerly airflow between 5000 and 2500 years ago, suggesting limited ASL influence over the region. After 2500 years ago, drier and warmer conditions were established, implying more westerly airflow and the increased projection of the ASL onto the South Atlantic. The possible role of the equatorial Pacific via atmospheric teleconnections in driving this change is discussed. Our results are in agreement with Antarctic ice core records and fjord sediments from the southern South American coast, and suggest that the Falkland Islands provide a valuable location for reconstructing high southern latitude atmospheric circulation changes on multi-decadal to millennial timescales.

High-resolution age modelling of peat bogs from northern Alberta, Canada, using pre- and post-bomb 14C, 210Pb and historical cryptotephra

Abstract High-resolution studies of peat profiles are frequently undertaken to investigate natural and anthropogenic disturbances over time. However, overlapping profiles of the most commonly applied age-dating techniques, including 14C and 210Pb, often show significant offsets (>decadal) and biases that can be difficult to resolve. Here we investigate variations in the chronometers and individual site histories from six ombrotrophic peat bogs in central and northern Alberta. Dates produced using pre- and post-bomb 14C, 210Pb (corroborated with 137Cs and 241Am), and cryptotephra peaks, are compared and then integrated using OxCal's P_Sequence function to produce a single Bayesian age model. Environmental histories for each site obtained using physical and chemical characteristics of the peat cores, e.g. plant macrofossils, humification, ash content and dry density, provide important constraints for the models by highlighting periods with significant changes in accumulation rate, e.g. fire events, permafrost development, and prolonged surficial drying. Despite variable environmental histories, it is possible to produce high-resolution age-depth models for each core sequence. Consistent offsets between 14C and 210Pb dates pre-1960s are seen at five of the six sites, but tephra-corrected 210Pb data can be used to produce more coherent models at three of these sites. Processes such as permafrost development and thaw, surficial drying and local fires can disrupt the normal processes by which chronological markers and environmental records are incorporated in the peat record. In consequence, applying standard dating methodologies to these records will result in even greater uncertainties and discrepancies between the different dating tools. These results show that using any single method to accurately date peat profiles where accumulation has not been uniform over time may be unreliable, but a comprehensive multi-method investigation paired with the application of Bayesian statistics can produce more robust chronologies. New cryptotephra data for the Alberta region are also reported here, including the historical Novarupta-Katmai 1912 eruption, White River Ash (East), and glass from Mt. St. Helens, Mt. Churchill, and probable Aleutian sources.

Appraising the cohesion of palaeoenvironmental reconstructions in north-west Spain since the mid-Holocene from a high temporal resolution multi-proxy peat record

Investigation of abrupt palaeohydrological regime change remains challenging due to site-specific noise ratios and the limitations of dating control and spatial resolution of multi-proxy records. Some of these issues are addressed through a well dated and highly resolved record from an ombrotrophic peatland in Galicia, north-west Spain. The site is in an ideal location to record marine influences and test models of past palaeoclimatic boundaries and ocean-atmosphere linkages through multi-proxy records of macrofossils, microfossils, charcoal, peat humification and loss-on-ignition data. In conjunction with many regional proxy records of terrestrial and marine origin, the data suggest spatial coherence between 5300 and ca. 3300 cal. BP and continue to link to marine responses afterwards. After ca. 2000 cal. BP, episodes of spatially consistent palaeohydrological change persist but become more short-lived, local and sporadic in north-west Iberia. These indicate an increase in the complexity of drivers of palaeoenvironmental change in recent millennia. Fire history inferred from microscopic charcoal and apparent upland erosion indicated by the loss-on-ignition profile relate to anthropogenic pressure and appear to be linked to local deforestation phases in the Xistral uplands.

Industrial-era lead and mercury contamination in southern Greenland implicates North American sources

To study the long-range transport of atmospheric pollutants from lower latitude industrial areas to the Arctic, we analysed a peat core spanning the last ~700cal.yr (~1300–2000CE) from southern Greenland, an area sensitive to atmospheric pollution from North American and Eurasian sources. A previous investigation conducted in the same location recorded atmospheric lead (Pb) pollution after ~1845, with peak values recorded in the 1970s, and concluded that a North American source was most likely. To confirm the origin of the lead, we present new Pb isotope data from Sandhavn, together with a high-resolution record for mercury (Hg) deposition. Results demonstrate that the mercury accumulation rate has steadily increased since the beginning of the 19th century, with maximum values of 9.3μgm−2yr−1 recorded ~1940. Lead isotopic ratios show two mixing lines: one which represents inputs from local and regional geogenic sources, and another that comprises regional geogenic and pollution sources. Detrending the Pb isotopic ratio record (thereby extracting the effect of the geogenic mixing) has enabled us to reconstruct a detailed chronology of metal pollution. The first sustained decrease in Pb isotope signals is recorded as beginning ~1740–1780 with the lowest values (indicating the highest pollution signature) dated to ~1960–1970. The 206Pb/207Pb ratio of excess Pb (measuring 1.222, and reflecting pollution-generated Pb), when compared with the Pb isotopic composition of the Sandhavn peat record since the 19th century and the timing of Pb enrichments, clearly points to the dominance of pollution sources from North America, although it did not prove possible to further differentiate the emissions sources geographically.

8000 years of North Atlantic storminess reconstructed from a Scottish peat record: implications for Holocene atmospheric circulation patterns in Western Europe

ABSTRACTNorth Atlantic storminess can affect human settlements, infrastructure and transport links, all of which strongly impact local, national and global economies. An increase in storm frequency and intensity is predicted over the North‐East Atlantic in the 21st century because of a northward shift in storm tracks and a persistently positive North Atlantic Oscillation (NAO), driven by recent atmospheric warming. Although documentary records of North Atlantic storminess exist, these are generally limited to the last c. 1000 years. This paper presents a continuous high‐resolution proxy record of storminess spanning the last 8000 years from a 6 m‐long core taken from a peat bog in northern Scotland. Bromine concentrations in the peat, derived from sea spray, are used to reconstruct storm frequency and storm intensity, and mire surface wetness is used as an indicator of longer‐term climate shifts. The results suggest a relationship between positive phases of the NAO and increased North Atlantic storminess. However, subtle differences between bromine concentrations and mire surface wetness suggest that high‐intensity but perhaps less frequent periods of storminess are not necessarily associated with a wetter climate.

Periodic input of dust over the Eastern Carpathians during the Holocene linked with Saharan desertification and human impact

Abstract. Reconstructions of dust flux have been used to produce valuable global records of changes in atmospheric circulation and aridity. These studies have highlighted the importance of atmospheric dust in marine and terrestrial biogeochemistry and nutrient cycling. By investigating a 10 800-year-long paleoclimate archive from the Eastern Carpathians (Romania) we present the first peat record of changing dust deposition over the Holocene for the Carpathian–Balkan region. Using qualitative (X-ray fluorescence (XRF) core scanning) and quantitative inductively coupled plasma optical emission spectrometer(ICP-OES) measurements of lithogenic (K, Si, Ti) elements, we identify 10 periods of major dust deposition between 9500–9200, 8400–8100, 7720–7250, 6350–5950, 5450–5050, 4130–3770, 3450–2850, 2000–1450, 800–620, and 60 cal yr BP to present. In addition, we used testate amoeba assemblages preserved within the peat to infer local palaeohydroclimatic conditions. Our record highlights several discrepancies between eastern and western European dust depositional records and the impact of highly complex hydrological regimes in the Carpathian region. Since 6100 cal yr BP, we find that the geochemical indicators of dust flux have become uncoupled from the local hydrology. This coincides with the appearance of millennial-scale cycles in the dust input and changes in geochemical composition of dust. We suggest that this is indicative of a shift in dust provenance from local–regional (likely loess-related) to distal (Saharan) sources, which coincide with the end of the African Humid Period and the onset of Saharan desertification.

Maceral composition and molecular markers of two condensed Middle Holocene peat profiles in N Spain

This study deals with the palaeohydrological information obtained from lipids composition and vegetal tissue preservation of two peat cores from Asturias, North Spain. The two profiles differ in the type of peatland (raised bog in La Borbolla and blanket bog in Buelna) and the type of organic matter being more bryophytic in the raised bog and more herbaceous in the blanket bog. The peatlands are located close to the coast on impermeable, old flat erosion surfaces which favoured peat accumulation within a distance of 3.5km from each other. The accumulation rate varied between 0.05 and 0.07mm/yr and the records extend from around 9000 to 2500cal.yrBP.The main differences between the two peat sites can be summarized as follows: the raised bog has lower mineral matter content and H/C atomic ratio and higher C/N ratio and extraction yields compared to the blanket bog. It has also a higher Tissue Preservation Index for Huminite macerals and increasing Inertodetrinite Index with depth. Regarding biomarkers, the raised bog has a relatively higher concentration of n-alkane-2-ones compared to the corresponding n-alkane of similar carbon number, higher concentration of medium- vs. high-molecular-weight-methyl-ketones and higher triterpenoids/steroids ratio than the blanket bog.Alternating humid/dry periods have been recorded in both profiles based on lipid concentrations indicating that the Sphagnum-rich intervals in the raised bog are more sensitive than the herbaceous blanket peat record to climatic variations. The main humid intervals identified are dated as 5000–7500cal.yrBP in the blanket bog and as 6000–3500cal.yrBP and last 2500cal.yrBP in the raised bog and correlate with the humid periods traced in other peatlands locations in this region. The transition Middle-to-Late Holocene is characterized by humid conditions in the region which favoured the Sphagnum growth in the peats.The reflectance of huminite in these records appears to be more related with differences in the oxidative conditions than with variation of peat maturity. It is higher in the layers with high mineral matter content at the beginning of organic matter accumulation and also in the upper part of the profile subjected to seasonal desiccation. A more intense biochemical gelification coincides with higher concentration of hopanoids derived from bacteria in the upper part of the profile (acrotelm).High amount of nonadecan-2-one (K19) and high concentrations of triterpenyl acetates, which are also determined in other peat profiles from Northern Spain are also detected in these profiles. This indicates that the specific conditions required for the formation of these compounds, probably associated to wet temperate climate, dominated throughout the region.

Drought as a stress driver of ecological changes in peatland - A palaeoecological study of peatland development between 3500 BCE and 200 BCE in central Poland

We reconstructed 3300years (3500BCE and 200BCE) of the development history of the Rąbień peatland located in central Poland, using pollen, macrofossil, testate amoebae, Cladocera, Chironomidae and geochemistry. Central Europe, particularly Poland, is characterised by a transitional climate that is influenced by continental and Atlantic air masses, which makes this region very sensitive to climate change. Our results demonstrate the high potential of the Rąbień peat record to reconstruct palaeohydrological dynamics. The studied time interval is characterised by two pronounced dry periods: from ~2500 to ~1700BCE and from ~700 to ~500BCE, and two significant increases in the water table: from ~1000 to ~800BCE and from ~500 to ~250BCE. The timing of the wet shift at 600BCE corresponds to wet periods at different sites in Central and Eastern Europe. Our investigation reveals a more complicated and complex than previously assumed set of climatic relationships in Europe between 3500BCE and 200BCE, which might be linked through complex teleconnections of atmospheric circulation patterns. Only reconstructions that are based on an understanding of current observations from peatlands and lake ecosystems may lead to a better interpretation of past climate changes.

Early atmospheric metal pollution provides evidence for Chalcolithic/Bronze Age mining and metallurgy in Southwestern Europe

Although archaeological research suggests that mining/metallurgy already started in the Chalcolithic (3rd millennium BC), the earliest atmospheric metal pollution in SW Europe has thus far been dated to ~3500–3200cal.yr. BP in paleo-environmental archives. A low intensity, non-extensive mining/metallurgy and the lack of appropriately located archives may be responsible for this mismatch. We have analysed the older section (>2100cal.yr. BP) of a peat record from La Molina (Asturias, Spain), a mire located in the proximity (35–100km) of mines which were exploited in the Chalcolithic/Bronze Age, with the aim of assessing evidence of this early mining/metallurgy. Analyses included the determination of C as a proxy for organic matter content, lithogenic elements (Si, Al, Ti) as markers of mineral matter, and trace metals (Cr, Cu, Zn, Pb) and stable Pb isotopes as tracers of atmospheric metal pollution.From ~8000 to ~4980cal.yr. BP the Pb composition is similar to that of the underlying sediments (Pb 15±4μgg−1; 206Pb/207Pb 1.204±0.002). A sustained period of low 206Pb/207Pb ratios occurred from ~4980 to ~2470cal.yr. BP, which can be divided into four phases: Chalcolithic (~4980–3700cal.yr. BP), 206Pb/207Pb ratios decline to 1.175 and Pb/Al ratios increase; Early Bronze Age (~3700–3500cal.yr. BP), 206Pb/207Pb increase to 1.192 and metal/Al ratios remain stable; Late Bronze Age (~3500–2800cal.yr. BP), 206Pb/207Pb decline to their lowest values (1.167) while Pb/Al and Zn/Al increase; and Early Iron Age (~2800–2470cal.yr. BP), 206Pb/207Pb increase to 1.186, most metal/Al ratios decrease but Zn/Al shows a peak. At the beginning of the Late Iron Age, 206Pb/207Pb ratios and metal enrichments show a rapid return to pre-anthropogenic values. These results provide evidence of regional/local atmospheric metal pollution triggered by the earliest phases of mining/metallurgy in the area, and reconcile paleo-environmental and archaeological records.

Abrupt climate variability since the last deglaciation based on a high-resolution, multi-proxy peat record from NW Iran: The hand that rocked the Cradle of Civilization?

We present a high-resolution (sub-decadal to centennial), multi-proxy reconstruction of aeolian input and changes in palaeohydrological conditions based on a 13000 Yr record from Neor Lake's peripheral peat in NW Iran. Variations in relative abundances of refractory (Al, Zr, Ti, and Si), redox sensitive (Fe) and mobile (K and Rb) elements, total organic carbon (TOC), δ13CTOC, compound-specific leaf wax hydrogen isotopes (δD), carbon accumulation rates and dust fluxes presented here fill a large gap in the existing terrestrial paleoclimate records from the interior of West Asia. Our results suggest that a transition occurred from dry and dusty conditions during the Younger Dryas (YD) to a relatively wetter period with higher carbon accumulation rates and low aeolian input during the early Holocene (9000–6000 Yr BP). This period was followed by relatively drier and dustier conditions during middle to late Holocene, which is consistent with orbital changes in insolation that affected much of the northern hemisphere. Numerous episodes of high aeolian input spanning a few decades to millennia are prevalent during the middle to late Holocene. Wavelet analysis of variations in Ti abundances as a proxy for aeolian input revealed notable periodicities at 230, 320, and 470 years with significant periodicities centered around 820, 1550, and 3110 years over the last 13000 years. Comparison with palaeoclimate archives from West Asia, the North Atlantic and African lakes point to a teleconnection between North Atlantic climate and the interior of West Asia during the last glacial termination and the Holocene epoch.We further assess the potential role of abrupt climate change on early human societies by comparing our record of palaeoclimate variability with historical, geological and archaeological archives from this region. The terrestrial record from this study confirms previous evidence from marine sediments of the Arabian Sea that suggested climate change influenced the termination of the Akkadian empire. In addition, nearly all observed episodes of enhanced dust deposition during the middle to late Holocene coincided with times of drought, famine, and power transitions across the Iranian Plateau, Mesopotamia and the eastern Mediterranean region. These findings indicate that while socio-economic factors are traditionally considered to shape ancient human societies in this region, the influence of abrupt climate change should not be underestimated.

The Last Termination in the South Indian Ocean: A unique terrestrial record from Kerguelen Islands (49°S) situated within the Southern Hemisphere westerly belt

The awareness of the significance of the Southern Ocean in the Earth's climate system has become increasingly obvious. The deglacial atmospheric CO2 rise during warming periods in Antarctica has been attributed to CO2 ventilation from the deep ocean caused by enhanced upwelling around the Antarctic Divergence. It has been hypothesized that, more intense Southern Hemisphere westerly winds aligned with the Antarctic Circumpolar Current due to a southward shift of the wind belt from its Last Glacial Maximum equator-ward position, are the main drivers. Reconstructions of past changes in atmospheric circulation in the Southern Hemisphere are still scarce and the overall picture is patchy with sometimes contradictory results. For obvious reasons, most terrestrial records originate from southern South America and New Zealand. Here we present a terrestrial record from the Indian sector of the Southern Ocean, from Kerguelen Islands located at 49°S. A peat record is investigated using a multi-proxy approach (pollen and plant macrofossils, magnetic susceptibility, XRF analyses, biogenic silica content, Rock-Eval6 analysis and humification degree). Peat accumulation starts at about 16,000 cal yr BP with relatively warm and dry conditions. The most prominent change in our proxy data occurs at 13,600 cal yr BP, when peat ponds were established on the peat surface, resulting in lacustrine-type deposits, as a result of very high humidity, and with proxies implying very windy conditions. Within chronological uncertainties, this onset coincides with the onset of the so-called Oceanic Cold Reversal, based on the deuterium excess data in the EPICA Dome C ice core record. Kerguelen Islands are located in the moisture source area of Dome C and a change in atmospheric circulation at that time could explain both records. Around 12,900 cal yr BP, at the end of the Antarctic Cold Reversal, pond/lake sediments give way to more peaty deposits, with proxies suggesting slightly drier, less windy and probably warmer conditions. Kerguelen Islands became less influenced by the Southern Hemisphere westerly winds and these conditions were amplified during the early Holocene climate optimum as found in Antarctic ice core records.

A shift towards wetter and windier conditions in southern Sweden around the prominent solar minimum 2750 cal a BP

A variety of palaeoclimatic records show a shift towards cooler, wetter and windier conditions in Europe around 2800 cal a BP. The shift broadly coincides with an increase of the atmospheric 14C concentration, suggesting a connection between solar activity variations and climate change. Here we investigate a peat record from Undarsmosse in southern Sweden. In a previous study, based on a low-resolution chronology, this record showed increased aeolian sand influx and Sphagnum spore content around 2800 cal a BP, indicating high storm activity and wetter conditions. We applied the 14C wiggle-match dating technique on the same record to construct a robust chronology to evaluate the temporal relationship to solar forcing. In addition, we performed plant macrofossil analysis to determine local vegetation changes. Based on the new chronology, a shift to a Sphagnum-dominated bog, representing wetter conditions, and the onset of a period with increased storminess occurred around 2700 cal a BP. These changes are, within age model uncertainties, synchronous with climatic changes inferred from other sites in Europe, suggesting a shift in the larger scale atmospheric circulation, possibly triggered by decreased solar activity.

Comparative ecology of vascular plant, bryophyte and testate amoeba communities in four Sphagnum peatlands along an altitudinal gradient in Switzerland

Monitoring tools are needed to assess changes in peatland biotic communities and ecosystem functions in response to on-going climate and other environmental changes. Although the responses of soil organisms and plants to ecological gradients and perturbations do not always correlate, peatland monitoring is mainly based on vegetation surveys. Testate amoebae, a group of protists, are important contributors to carbon and nitrogen cycling in organic soils and are useful bioindicators in peatland ecology and paleoecology. There is however little comparative data on the value of testate amoebae, vascular plants and bryophytes as bioindicators of micro-environmental gradients in peatlands.We compared the relationships of testate amoebae, bryophytes, and vascular plants with soil temperature, water table depth, micro-habitats and the carbon and nitrogen content of Sphagnum mosses in four peatlands along a 1300m altitudinal gradient in Switzerland. We used the full diversity of vascular plants and bryophyte but only a selection of ten easily identifiable testate amoeba morpho-taxa (i.e. species or species-complexes).Indirect and direct gradient ordinations, multiple factor analysis (MFA) and transfer function models for inferring water table depth showed that a selection of ten testate amoeba taxa are more powerful (% variance explained in RDA) and accurate (discrimination among habitats) indicators of local conditions (micro-habitat type, water table depth and Sphagnum C/N ratio) than the vegetation (vascular plants and bryophytes either individually or combined and considering the full diversity).Our study showed that a limited list of ten easily identifiable testate amoeba taxa have higher bioindication value than the full bryophytes and vascular plants. Furthermore, testate amoebae can be analyzed on samples collected at any season (accessibility allowing and if precise sampling sites are well marked) – a clear advantage for biomonitoring and can be used to infer past changes from the peat record at the same taxonomic resolution. This simple approach could therefore be very useful for biomonitoring of peatlands.

Testing the cause of the Sphagnum austinii (Sull. ex Aust.) decline: Multiproxy evidence from a raised bog in Northern Ireland

We use a multiproxy palaeoecological dataset from Dead Island bog in Northern Ireland to examine the cause of the Sphagnum austinii (Sphagnum imbricatum) decline. The disappearance of this species from the peat record occurred just after the ‘AD 860’ tephra layer and is coeval with a rapid increase in bog surface wetness and increased mineral dust and charcoal abundance. Although it is difficult to identify one specific cause of the decline, the evidence for increased soil-derived dust is apparent and is supported by regional tephra-dated pollen diagrams that reveal extensive landscape changes due to agricultural intensification in early Medieval Ireland. As the decline of S. austinii occurred much later (~AD 1860) in Fallahogy bog (~1.2km away), we suggest that the decline of S. austinii at Dead Island was caused by a combination of fire and the deposition of soil-derived dust. We suggest that future studies should consider the use of multiple cores from each site to examine the within-site variability of the decline of S. austinii.

Emissions from pre-Hispanic metallurgy in the South American atmosphere.

Metallurgical activities have been undertaken in northern South America (NSA) for millennia. However, it is still unknown how far atmospheric emissions from these activities have been transported. Since the timing of metallurgical activities is currently estimated from scarce archaeological discoveries, the availability of reliable and continuous records to refine the timing of past metal deposition in South America is essential, as it provides an alternative to discontinuous archives, as well as evidence for global trace metal transport. We show in a peat record from Tierra del Fuego that anthropogenic metals likely have been emitted into the atmosphere and transported from NSA to southern South America (SSA) over the last 4200 yrs. These findings are supported by modern time back-trajectories from NSA to SSA. We further show that apparent anthropogenic Cu and Sb emissions predate any archaeological evidence for metallurgical activities. Lead and Sn were also emitted into the atmosphere as by-products of Inca and Spanish metallurgy, whereas local coal-gold rushes and the industrial revolution contributed to local contamination. We suggest that the onset of pre-Hispanic metallurgical activities is earlier than previously reported from archaeological records and that atmospheric emissions of metals were transported from NSA to SSA.

Humification in northeast Australia: Dating millennial and centennial scale climate variability in the late Holocene

The identification of wetter and drier phases from the last deglaciation to the Late Holocene has been a valuable outcome of palaeoenvironmental (chiefly palynological) studies of northeastern Australia conducted over the past 40 years. Few studies have, however, focussed on the identification of wetter and drier phases in the wet tropics, and none have set their focus on the last 4000 years, a period when northeastern Australia is generally accepted to have experienced increased El Niño/Southern Oscillation (ENSO) activity. The present study provides this palaeoclimatic information using the degree of peat humification as the main palaeoclimatic proxy. To identify regional climatic signals in the peat record and differentiate these from local signals induced by particular basin hydrology or ecology, sedimentary sequences from two geographically separated swamps on the Atherton Tableland in north Queensland are examined. Wet and dry shifts are detected in the humification records for Bromfield Swamp (core BSAT03) and Mount Quincan crater swamp (Q2). Seventeen wet shifts are detected in both records with 12 shifts showing good cross-correlation at the following dates (with 2σ range): 3990/3960 (4090–3850), 3480/3550 (3640–3420), 2950/2990 (3080–2790), 2860/2880 (2980–2700), 2560/2610 (2730–2450), 1880/1820 (2100–1740), 1430/1410 (1660–1320), 1170/1080 (1390–1020), 990/1010 (1100–790), 610/640 (710–490), 290/300 (330–180) and 120/150 (190–40) cal. yr BP. A particular dry phase, initiated by dry shifts at 4090 cal. yr BP (Bromfield Swamp) and 4330 cal. yr BP (Mount Quincan), reaches its greatest strength at 4050 cal. yr BP.

Historical trends of atmospheric black carbon on Sanjiang Plain as reconstructed from a 150-year peat record.

Black carbon (BC), one of the major components of atmosphere aerosol, could be the second dominant driver of climate change. We reconstructed historical trend of BC fluxes in Sanjiang Plain (Northeast China) through peat record to better understand its long-term trend and relationship of this atmosphere aerosol with intensity of human activities. The BC fluxes in peatland were higher than other sedimentary archives. Although global biomass burning decreased in last 150 years, regional large scale reclaiming caused BC fluxes of the Sanjiang Plain increased dramatically between 1950s' and 1980s', most likely resulting from using fire to clearing dense pastures and forests for reclaiming. The BC fluxes have increased since 1900s with increasing of the population and the area of farmland; the increase trend has been more clearly since 1980s. Based on Generalized additive models (GAM), the proportional influence of regional anthropogenic impacts have increased and became dominant factors on BC deposition.

Climate in the Western Cordillera of the Central Andes over the last 4300 years

The Distichia peat core obtained in the Carhuasanta valley near Nevado Mismi, Cordillera Chila, provides information on climatic and environmental conditions over the last ∼4300 years. The relative changes in the stable carbon isotope composition of plant remains preserved in the core reflect major temperature fluctuations in the Western Cordillera of the southern Peruvian Andes. These temperature variations can be additionally linked with the changes in precipitation patterns by analysing C% and C/N ratio in the core. Relatively warm and moist conditions prevailed from 4280 to 3040 cal. yrs BP (BC 2330–1090) with a short colder dry episode around 3850 cal. yrs BP (BC 1900). The most prominent climate changes recorded in the peat occurred between 3040 and 2750 cal. yrs BP (BC 1090–800) when the initial warming turned to a rapid cooling to temperatures at least 2 °C lower than the mean for the Late Holocene. Initially drier conditions within this event turned to a short wet phase after 2780 cal. yrs BP (BC 830) when the temperature increased again. This event coincides with significant changes in peat and ice core records in the Central Andes matching the timing of the global climate event around 2.8 cal. ka BP. Climatic conditions in the study area became relatively dry and stable after the event for about 800 years. Highly variable temperatures and humidity prevailed during the last 2000 years when an extended warm and relatively humid period occurred between 640 and 155 cal. yrs BP (AD 1310–1795) followed by predominantly colder and drier conditions. The established δ13C peat record represents the first continuous proxy for the temperature in the southern Peruvian Andes dated by the AMS 14C. Distichia peat is wide spread in the Andes and the proposed approach can be applied elsewhere in high altitudes, where no other traditional climate proxies are available.

Nothofagus forest dynamics and palaeoenvironmental variations during the mid and late Holocene, in southwest Patagonia

Southern Patagonia intersects the core of the Southern Westerlies, providing a unique opportunity for palaeo-reconstructions and the implication of past wind variations. There is a strong link between the strength of the westerlies and precipitation, which impacts vegetation communities. The palaeoenvironmental changes that occurred since the middle Holocene to present days are reconstructed from a peat record recovered in Peninsula Avellaneda (50°15′57″S; 72°50′33″W). Interpretations are based on pollen, charcoal and sediment analyses. Closed Nothofagus forest together with low fire activity characterized the region during the period c. 5500–3500 cal. yr BP, related to an increased in precipitation through an intensification of the westerlies. After 3500 cal. yr BP, shrub and grass communities became dominant at the expense of Nothofagus forest, suggesting a climatic shift to dry conditions, as a result of weaker westerlies. This patchy forest-steppe vegetation has favoured the occurrence of fire events. Subsequently, Nothofagus forest recovered for a short period between 2000 and 400 cal. yr BP. Then, major vegetation changes took place with the re-establishment of an open landscape. The calculated moisture balance index allowed us to hypothesize about the relationship between westerlies fluctuation and El Niño Southern Oscillation (ENSO) anomalies during the mid and late Holocene.