Mired in the past — looking to the future: Geochemistry of peat and the analysis of past environmental changes

Peat cores from ombrotrophic bogs have been used as a valuable archive to study environmental change for over a century. Much of this focus on the peat record has been on biological proxies of environmental change, such as pollen and peat-forming macrofossils, but there is growing interest in the geochemical record to study environmental changes. Several studies of long-term peat records in Europe have reconstructed past changes in atmospheric lead pollution, for example, and the general cohesiveness of the results and their agreement with known historical trends in metal production exemplify the best potential of peat geochemistry as an environmental archive. Based on the success with lead, a current emphasis in peat reconstructions is to assess the record of past mercury deposition and results thus far show generally consistent trends, e.g., a pre-anthropogenic mercury accumulation rate of about 0.5–1.5 μg Hg m^− 2 year^− 1. Despite this general consistency there is increasing concern that there may be diagenetic effects on the quantitative record of some metals, which can be inferred based on a strong relationship between mercury and other organically bound elements and proxies for peat decomposition (C/N ratio). However, it is possible that changes in decomposition and the alteration of some metal records could provide climatic information. A few recent studies show that closer examination of the geochemical matrix, in some cases along with biological proxies, can provide valuable information on landscape changes and climate; for example, partitioning metals into different weight fractions and source regions can be applied to climate studies. The best interpretations of the peat geochemical record in the context of environmental and climate change will likely come when geochemical and biological records are considered simultaneously.     

A peat core based estimate of Late-glacial and Holocene methane emissions from northern peatlands

We estimate the intensity of Late-glacial and Holocene methane emissions from peatlands based on their paleo net primary production (PNPP). The PNPP is derived from the carbon accumulation rates of the studied bog profile (Etang de la Gruère, Switzerland), which are corrected for the degree of peat degradation. The obtained PNPP curve is taken as a proxy for methane emissions. It shows relatively high values (90 g C m^− 2 yr^− 1) early in the Bolling/Allerod and drops to low values (40 g C m^− 2 yr^− 1) during the Younger Dryas cold period. With the onset of the Holocene the PNPP increases strongly up to 150 g C m^− 2 yr^− 1 around ca. 10,000 Cal. yr bp. This is followed by a decline to minimum values (30 to 40 g C m^− 2 yr^− 1) between 6500 and 4000 Cal. yr bp. Thereafter, the PNPP starts to increase again to reach its highest value (175 g C m^− 2 yr^− 1) around 1000 Cal. yr bp.The PNPP curve correlates well with the evolution of the atmospheric methane concentrations as derived from Greenland ice-cores. For example, minima in atmospheric methane reported during the Younger Dryas and around 5200 Cal. yr bp are coinciding with the lowest values of PNPP and the negative atmospheric methane peak at 8200 Cal. yr bp corresponds to a marked decrease in PNPP.Our PNPP curve suggests that the methane emissions from northern peatlands evolved similar to those of low latitude wetlands and together they largely determined the evolution of atmospheric methane throughout the Late-glacial and the Holocene. The abruptness of the rise of atmospheric methane at the end of the Younger Dryas probably points to an additional source (e.g. marine gas hydrates), but very early in the Holocene the peatlands have likely become the dominant source of atmospheric methane.     

A multitracer study of peat profiles from Tunguska, Siberia

Two peat columns from Tunguska (Siberia) were analysed for pollen, spores, charcoal, trace elements and γ-emitters in order to identify the fingerprints of the impact of a still unidentified cosmic body (TCB), which occurred in the summer of 1908, and the level of environmental pollution in a background area of central Siberia. Peat layers were subject to non-destructive γ-ray spectrometry to derive radiochronology by the excess ²¹⁰Pb method. The age-to-depth relationship was crosschecked by using both 1963 horizon of ¹³⁷Cs associated to maximum global fallout deposition and palynological data profiles. Vertical distributions of trace elements in the peat columns were obtained by PIXE multielemental analysis allowing determination of the levels of environmental contamination in a background region of the Siberian taiga.The association of heavy metals such as Ni, Co and Cu in the profiles suggests the connection of the area with mining and metal smelting activity in the north of the region through atmospheric circulation. As concerns global scale contamination, the inventory of the artificial radionuclide ¹³⁷Cs (4.6 kBq m^− 2) shows a value typical of remote slightly contaminated areas resulting from global scale redistribution of radioactive fallout from Cold War nuclear weapon testing. The atmospheric inventory of the natural radionuclide ²¹⁰Pb, for which a mean annual flux of 200 Bq m^− 2 yr^− 1 has been calculated, is typical of continental regions.The influence of Tunguska Cosmic Body in the peat is recognizable by a large discontinuity in the palynological profile of the peat monolith at a depth coinciding with the 1908 layer as determined by the ²¹⁰Pb technique, showing a large peak of total pollen counting attributed to the impact of the shockwave on the area in which huge tree stands were destroyed. Following the event, tree pollen concentration decreases abruptly showing the temporary inception of a mire environment with an increase of Sphagnum spore concentrations. Results of elemental analysis so far available do not show anomalies in the concentration profiles at depths coinciding with the Tunguska event layer indicating the need for pre-concentration technique enabling the detection of element associations typical of extraterrestrial materials.     

Estimation of net accumulation rate at a Patagonian glacier by ice core analyses using snow algae

Snow algae in a 45.97-m-long ice core from the Tyndall Glacier (50°59′05″S, 73°31′12″W, 1756 m a.s.l.) in the Southern Patagonian Icefield were examined for potential use in ice core dating and estimation of the net accumulation rate. The core was subjected to visual stratigraphic observation and bulk density measurements in the field, and later to analyses of snow algal biomass, water isotopes (¹⁸O, D), and major dissolved ions. The ice core contained many algal cells that belonged to two species of snow algae growing in the snow near the surface: Chloromonas sp. and an unknown green algal species. Algal biomass and major dissolved ions (Na⁺, K⁺, Mg²⁺, Ca²⁺, Cl⁻, SO₄²⁻) exhibited rapid decreases in the upper 3 m, probably owing to melt water elution and/or decomposition of algal cells. However, seasonal cycles were still found for the snow algal biomass, ¹⁸O, D-excess, and major ions, although the amplitudes of the cycles decreased with depth. Supposing that the layers with almost no snow algae were the winter layers without the melt water essential to algal growth, we estimated that the net accumulation rate at this location was 12.9 m a^− 1 from winter 1998 to winter 1999, and 5.1 m from the beginning of winter to December 1999. These estimates are similar to the values estimated from the peaks of ¹⁸O (17.8 m a^− 1 from summer 1998 to summer 1999 and 11.0 m from summer to December 1999) and those of D-excess (14.7 m a^− 1 from fall 1998 to fall 1999 and 8.6 m a^− 1 from fall to December 1999). These values are much higher than those obtained by past ice core studies in Patagonia, but are of the same order of magnitude as those predicted from various observations at ablation areas of Patagonian glaciers.     

Estimation of the energy used to melt snow in the Tien Shan mountains and Japanese Islands

The heat needed to melt snow over the Tien Shan mountains and Japanese Islands for 10-day period (TDP) was estimated. Melting curves and a map of snowmelt duration were obtained through the long-term data from 79 stations in the Tien Shan mountains and 20 stations in the Japanese Islands. At high elevations in the mountains, about 40% of the snow melts during penultimate 10 days of snow cover. In the Japanese Islands, about 80% of the snow melts during the last 20 days of snow cover. Over the mountains, 0.13×10⁴ MJ m² year⁻¹ is needed to melt snow in the northern and western Tien Shan where maximum snow accumulation occurred. The volume of air cooled 10 °C by snowmelt amounted to 4.4×10⁶ km³ year⁻¹ over the Tien Shan mountains and 3×10⁶ km³ year⁻¹ over the Japanese Islands. The most significant impact of snowmelt on air temperature was observed at an elevation of 2500 m in the western and northern Tien Shan. Air that was cooled 10 °C could reach an elevation of 2.1 km day⁻¹. Over the Japanese Islands, energy losses from snowmelt amounted to 0.26×10¹⁴ MJ year⁻¹ and the maximum occurred over Honshu Island. The heat loss from snowmelt in the Tien Shan mountains and Japanese Islands amounted to about 2/3 of heat loss in the Eurasian continental plains.     

Sources and distribution of trace elements in Estonian peat

This paper presents the results of the distribution of trace elements in Estonian mires. Sixty four mires, representative of the different landscape units, were analyzed for the content of 16 trace elements (Cr, Mn, Ni, Cu, Zn, and Pb using AAS; Cd by GF-AAS; Hg by the cold vapour method; and V, Co, As, Sr, Mo, Th, and U by XRF) as well as other peat characteristics (peat type, degree of humification, pH and ash content). The results of the research show that concentrations of trace elements in peat are generally low: V 3.8 ± 0.6, Cr 3.1 ± 0.2, Mn 35.1 ± 2.7, Co 0.50 ± 0.05, Ni 3.7 ± 0.2, Cu 4.4 ± 0.3, Zn 10.0 ± 0.7, As 2.4 ± 0.3, Sr 21.9 ± 0.9, Mo 1.2 ± 0.2, Cd 0.12 ± 0.01, Hg 0.05 ± 0.01, Pb 3.3 ± 0.2, Th 0.47 ± 0.05, U 1.3 ± 0.2 μg g^− 1 and S 0.25 ± 0.02%. Statistical analyses on these large database showed that Co has the highest positive correlations with many elements and ash content. As, Ni, Mo, ash content and pH are also significantly correlated. The lowest abundance of most trace elements was recorded in mires fed only by precipitation (ombrotrophic), and the highest in mires fed by groundwater and springs (minerotrophic), which are situated in the flood plains of river valleys. Concentrations usually differ between the superficial, middle and bottom peat layers, but the significance decreases depending on the type of mire in the following order: transitional mires – raised bogs – fens. Differences among mire types are highest for the superficial but not significant for the basal peat layers.The use of peat with high concentrations of trace elements in agriculture, horticulture, as fuel, for water purification etc., may pose a risk for humans: via the food chain, through inhalation, drinking water etc.     

Cryospheric change in China

This paper provides an overview of the current status of the cryosphere in China and its changes. Up-to-date statistics of the cryosphere in China are summarized based on the latest available data. There are 46,377 glaciers in China, covering an area of 59,425 km². The glacier ice reserve is estimated to be about 5600 km³ and the annual glacier runoff is about 61.6 × 10⁹ m³. The continuous snow cover extent (> 60 days) in China is about 3.4 × 10⁶ km² and the maximum water equivalent is 95.9 × 10⁹ m³ yr^− 1. The permafrost area in China is about 1.72 × 10⁶ km². The total ground ice reserve on the Qinghai–Tibetan Plateau is estimated to be about 10,923 km³. Recent investigations indicated that glacier areas in China have shrunk about 2–10% over the past 45 yr. Total glacier area has receded by about 5.5%. Snow mass has increased slightly. Permafrost is clearly degrading, as indicated by shrinking areas of permafrost, increasing depth of the active layer, rising of lower limit of permafrost, and thinning of the seasonal frost depth. Some models predict that glacier area shrinkage could be as high as 26.7% in 2050, with glacier runoff increasing until its maximum in about 2030. Although snow mass shows an increasing trend in western China, in eastern China the trend is toward decreasing snow mass, with increasing interannual fluctuations. Permafrost degradation is likely to continue, with one-third to one-half of the permafrost on the Qinghai–Tibetan Plateau anticipated to degrade by 2100. Most of the high-temperature permafrost will disappear by then. The permafrost in northeastern China will retreat further northward.     

Use of Pb/Pb ratios to investigate the surface integrity of peat cores used to study the recent depositional history and geochemical behaviour of inorganic elements in peat bogs

The well characterised temporal trend in the ²⁰⁶Pb/²⁰⁷Pb atom ratio of atmospheric lead deposition in Scotland during the 20th century was used to investigate the surface integrity of several cores collected by different methods from Flanders Moss ombrotrophic peat bog, central Scotland, during 1996–2001. Based on ²⁰⁶Pb/²⁰⁷Pb profile comparisons, in conjunction with identified ²¹⁰Pb radionuclide inventory deficits for two of the cores, it was deduced that 25 ± 7 yrs worth of material was missing from the more seriously affected core. After allowing for an appropriate vertical offset based on ²⁰⁶Pb/²⁰⁷Pb profile matching, the subsequent matching of profiles of titanium, lead, sulfur, arsenic, iron, phosphorus and manganese in three cores for which total concentration data were available was excellent. Without such offset correction, erroneous conclusions could have been drawn concerning the recent historical record of anthropogenic lead and arsenic deposition, the position of the redox boundary, which controls geochemical cycling and enrichment of iron, and the nutrient recycling status of manganese and phosphorus in the near-surface vegetation. Topographic, vegetative and coring (both device and operator) influences may have been responsible, thus endorsing the use of reliable, multiple core sampling and the use of lead isotope ratio profiles, supplemented by appropriate radionuclide data, in both assessing and ensuring the surface integrity of peat cores.     

Airborne laser altimetry survey of Glaciar Tyndall, Patagonia

The first airborne laser altimetry measurements of a glacier in South America are presented. Data were collected in November of 2001 over Glaciar Tyndall, Torres del Paine National Park, Chilean Patagonia, onboard a Twin Otter airplane of the Chilean Air Force. A laser scanner with a rotating polygon-mirror system together with an Inertial Navigation System (INS) were fixed to the floor of the aircraft, and used in combination with two dual-frequency GPS receivers. Together, the laser–INS–GPS system had a nominal accuracy of 30 cm after data processing. On November 23rd, a total of 235 km were flown over the ablation area of Glaciar Tyndall, with 5 longitudinal tracks with a mean swath width of 300 m, which results in a point spacing of approximately 2 m both along and across track. A digital elevation model (DEM) generated using the laser altimetry data was compared with a DEM produced from a 1975 map (1:50,000 scale — Instituto Geográfico Militar (IGM), Chile). A mean thinning of − 3.1 ± 1.0 m a^− 1 was calculated for the ablation area of Glaciar Tyndall, with a maximum value of − 7.7 ± 1.0 m a^− 1 at the calving front at 50 m a.s.l. and minimum values of between − 1.0 and − 2.0 ± 1.0 m a^− 1 at altitudes close to the equilibrium line altitude (900 m a.s.l.). The thinning rates derived from the airborne survey were similar to the results obtained by means of ground survey carried out at  600 m of altitude on Glaciar Tyndall between 1975 and 2002, yielding a mean thinning of − 3.2 m a^− 1 [Raymond, C., Neumann, T.A., Rignot, E., Echelmeyer, K.A., Rivera, A., Casassa, G., 2005. Retreat of Tyndall Glacier, Patagonia, over the last half century. Journal of Glaciology 173 (51), 239–247.]. A good agreement was also found between ice elevation changes measured with laser data and previous results obtained with Shuttle Radar Topography Mission (SRTM) data. We conclude that airborne laser altimetry is an effective means for accurately detecting glacier elevation changes in Patagonia, where an ice thinning acceleration trend has been observed during recent years, presumably in response to warming and possibly also drier conditions.     

Ice elevation and areal changes of glaciers from the Northern Patagonia Icefield, Chile

High thinning rates (up to − 4.0 ± 0.97 m a^− 1) have been measured at Campo de Hielo Patagónico Norte (CHN) or Northern Patagonia Icefield, Chile between 1975 and 2001. Results have been obtained by comparing a Digital Elevation Model (DEM) derived from regular cartography compiled by Instituto Geográfico Militar of Chile (IGM) based upon 1974/1975 aerial photographs and a DEM generated from Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) satellite images acquired in September 2001. A complete cloud-free Landsat ETM+ satellite image mosaic acquired in March 2001 was used to update the available glacier inventory of the CHN, including all glaciers larger than 0.5 km² (48 new glaciers). A new delineation of ice divides was also performed over the accumulation areas of glaciers sharing the high plateau where the existing regular cartography exhibits poor coverage of topographic information. This updated glacier inventory produced a total ice area for 2001 of 3953 km², which represents a decrease of 3.4 ± 1.5% (140 ± 61 km² of ice) with respect to the total ice area of the CHN in 1979 calculated from a Landsat MSS satellite image. Almost 62% of the total area change between 1979 and 2001 took place in glaciers located at the western margin of the CHN, where the maximum area loss was experienced by Glaciar San Quintín with 33 km². At the southern margin, Glaciar Steffen underwent the largest ice-area loss (12 km² or 2.6% of the 1979 area), whilst at the eastern margin the greatest area loss took place in Glaciares Nef (7.9 km², 5.7% of the 1979 area) and Colonia (9.1 km², 2.7% of the 1979 area). At the northern margin of the CHN the lower debris-covered ablation area of Glaciar Grosse collapsed into a new freshwater lake formed during the late 1990s. The areal changes measured at the CHN are much larger than previously estimated due to the inclusion of changes experienced in the accumulation areas. The CHN as a whole is contributing melt water to global sea level rise at rates  25% higher than previous estimates.     

Climate changes and recent glacier behaviour in the Chilean Lake District

Atmospheric temperatures measured at the Chilean Lake District (38°–42°S) showed contrasting trends during the second half of the 20th century. The surface cooling detected at several meteorological stations ranged from − 0.014 to − 0.021 °C a^− 1, whilst upper troposphere (850–300 gpm) records at radiosonde of Puerto Montt (41°26′S/73°07′W) revealed warming between 0.019 and 0.031 °C a^− 1. Regional rainfall data collected from 1961 to 2000 showed the overall decrease with a maximum rate of − 15 mm a^− 2 at Valdivia st. (39°38′S/73°05′W). These ongoing climatic changes, especially the precipitation reduction, seem to be related to El Niño–Southern Oscillation (ENSO) phenomena which has been more frequent after 1976. Glaciers within the Chilean Lake District have significantly retreated during recent decades, in an apparent out-of-phase response to the regional surface cooling. Moreover, very little is known about upper troposphere changes and how they can enhance the glacier responses. In order to analyse their behaviour in the context of the observed climate changes, Casa Pangue glacier (41°08′S/71°52′W) has been selected and studied by comparing Digital Elevation Models (DEMs) computed at three different dates throughout the last four decades. This approach allowed the determination of ice elevation changes between 1961 and 1998, yielding a mean thinning rate of − 2.3 ± 0.6 m a^− 1. Strikingly, when ice thinning is computed for the period between 1981 and 1998, the resulting rate is 50% higher (− 3.6 ± 0.6 m a^− 1). This enhanced trend and the related area loss and frontal retreat suggests that Casa Pangue might currently be suffering negative mass balances in response to the upper troposphere warming and decreased precipitation of the last 25–30 yr, as well as debris cover would not prevent the glacier from a fast reaction to climate forcing. Most of recent glaciological studies regarding Andean glaciers have concentrated on low altitude changes, namely frontal variations, however, in order to better understand the regional glacier changes, new data are necessary, especially from the accumulation areas.     

Morphological and ice-dynamical changes on the Tasman Glacier, New Zealand, 1990–2007

This paper presents data concerning recent (1990–2007) surface morphological and ice-dynamical changes on the Tasman Glacier, New Zealand. We use remote-sensing data to derive rates of lake growth, glacier velocities and rates of glacier surface lowering. Between 1990 and 2007, the glacier terminus receded ~ 3.5 km and a large ice-contact proglacial lake developed behind the outwash head. By 2007 the lake area was ~ 6 km² and had replaced the majority of the lowermost 4 km of the glacier tongue. There is evidence that lake growth is proceeding at increasing rates — the lake area doubled between 2000 and 2007 alone. Measured horizontal glacier velocities decline from 150 m a^− 1 in the upper glacier catchment to almost zero at the glacier terminus and there is a consequent down-glacier increase in surface debris cover. Surface debris mapping shows that a large catastrophic rockfall onto the glacier surface in 1991 is still evident as a series of arcuate debris ridges below the Hochstetter icefall. Calculated glacier surface lowering is most clearly pronounced around the terminal area of the glacier tongue, with down-wasting rates of 4.2 ± 1.4 m a^− 1 in areas adjacent to the lateral moraine ridges outside of the current lake extent. Surface lowering rates of approximately 1.9 ± 1.4 m a^− 1 are common in the upper areas of the glacier. Calculations of future lake expansion are dependent on accurate bathymetric and bed topography surveys, but published data indicate that a further 8–10 km of the glacier is susceptible to calving and further lake development in the future.     

Are sea-level-rise trends along the coasts of the north Indian Ocean consistent with global estimates?

Mean-sea-level data from coastal tide gauges in the north Indian Ocean were used to show that low-frequency variability is consistent among the stations in the basin. Statistically significant trends obtained from records longer than 40 years yielded sea-level-rise estimates between 1.06–1.75 mm yr^− 1, with a regional average of 1.29 mm yr^− 1, when corrected for global isostatic adjustment (GIA) using model data. These estimates are consistent with the 1–2 mm yr^− 1 global sea-level-rise estimates reported by the Intergovernmental Panel on Climate Change.     

Reconstruction of Mediterranean sea level fields for the period 1945–2000

The distribution of sea level in the Mediterranean Sea is recovered for the period 1945–2000 by using a reduced space optimal interpolation analysis. The method involves estimating empirical orthogonal functions from satellite altimeter data spanning the period 1993–2005 that are then combined with tide gauge data to recover sea level fields over the period 1945–2000. The reconstruction technique is discussed and its robustness is checked through different tests. For the altimetric period (1993–2000) the prediction skill is quantified over the whole domain by comparing the reconstructed fields with satellite altimeter observations. For past times the skill can only be tested locally, by validating the reconstruction against independent tide gauge records. The reconstructed distribution of sea level trends for the period 1945–2000 shows a positive peak in the Ionian Sea (up to 1.5 mm yr^− 1) and a negative peak of − 0.5 mm yr^− 1 in a small area to the south-east of Crete. Positive trends are found nearly everywhere, being larger in the western Mediterranean (between 0.5 and 1 mm yr^− 1) than in the eastern Mediterranean (between 0 and 0.5 mm yr^− 1). The estimated rate of mean sea level rise for the period 1945–2000 is 0.7 ± 0.2 mm yr^− 1, i.e. about a half of the rate estimated for global mean sea level. These overall results do not appear to be very sensitive to the distribution of tide gauges. The poorest results are obtained in open-sea regions with intense mesoscale variability not correlated with any tide gauge station, such as the Algerian Basin.     

A Quaternary uplift record for the Auckland region, North Island, New Zealand, based on marine and fluvial terraces

Marine and fluvial terrace sequences near the Waitakere Ranges on the North Island of New Zealand have been surveyed, yielding an inventory of 13 fluvial and 12 marine terrace levels. Based on sparse tephra age control and correlation with the global palaeoclimatic record, rates of regional Quaternary uplift have been reconstructed. Between 1000 ka and 345 ka the time-averaged uplift rate was 0.072 mm a^− 1, between 345 ka and 50 ka it increased to 0.278 mm a^− 1, accelerating to 0.42 mm a^− 1 since 50 ka. The fluvial terrace sequence did not yield clear sedimentary records or other datable material. However, although others have disputed the existence of marine terraces in this study region, a pattern of accelerating regional uplift, superimposed onto glacio-eustatic sea-level changes, is substantiated as the only possible mechanism for maintaining the considerable relief and the active denudation processes inland. The observed uplift is similar to that in other regions where the uplift has been attributed to coupling between surface processes and lower-crustal flow, making this a likely mechanism in the North Island of New Zealand. Regarding the fluvial terrace sequence, the proposed general model is of an actively incising river, carving out on average one strath terrace every ~ 16,000 years. The incision phases are reactivated by sea-level lowering and interrupted by net aggradation events due to landslides triggered by cyclones and/or fires within the catchment; volcanic ash falls also cause transient increases in sediment supply.     

Quaternary uplift of northern England

Upland flats, attributable to erosion, have long been recognised in the landscape of the Lake District region of NW England, at altitudes of up to ~ 800 m O.D. Extrapolation using uplift rates derived from dated Pleistocene sites (karstic caves and other features) in the adjacent Pennine uplands suggests that if this succession of flats formed close to sea-level they date from the Middle Pliocene onwards, indicating a subsequent time-averaged uplift rate of almost 0.3 mm a^− 1. Numerical modelling indicates that erosion of surrounding areas at a typical rate of 0.2 mm a^− 1 since 3.1 Ma could have caused this uplift, as well as constraining the local effective viscosity of the lower crust as ~ 4 × 10¹⁸ Pa s and the typical local Moho temperature as ~ 650 °C. It is thus feasible that most of the topography of northern England has developed since the Middle Pliocene, as a consequence of coupling between erosion and the resulting induced flow in the lower continental crust. The much faster vertical crustal motions indicated in this part of northern England, compared with SE England, are thus mainly a consequence of much greater mobility of the lower crust in the north, due to its younger thermal age and the heating effect of radioactive Palaeozoic granites. Uplift of this magnitude, which has previously gone unrecognised, may have affected post-Pliocene global climate.     

Geochemical and stratigraphic evidence of environmental change at Lynch's Crater, Queensland, Australia

This is one of the first applications of geochemical proxies to define changes in vegetation, hydrology and atmospheric dust influence on a peat deposit in the southern hemisphere. A 6.6 m deep peat record from Lynch's Crater in NE-Queensland, Australia, provides a sensitive  5000 to 30,000 cal years BP archive of environmental change. The deposit consists of 1.5 m of ombrotrophic peat underlain by a minerotrophic peat. Within the minerotrophic section, sponge spicules and diatom fragments offer evidence of prolonged flooding of the peat environment resulting in several layers containing (up to 50%) high inorganic material. The Ca and Mg data display episodes of enhanced dust influx and nutrient recycling and support previous palynological studies that show a Pleistocene to Holocene switch from sclerophyll woodlands to rainforest vegetation.     

Calculation and visualisation of future glacier extent in the Swiss Alps by means of hypsographic modelling

The observed rapid glacier wastage in the European Alps during the past 20 years already has strong impacts on the natural environment (rock fall, lake formation) as well as on human activities (tourism, hydro-power production, etc.) and poses several new challenges also for glacier monitoring. With a further increase of global mean temperature in the future, it is likely that Alpine glaciers and the high-mountain environment as an entire system will further develop into a state of imbalance. Hence, the assessment of future glacier geometries is a valuable prerequisite for various impact studies. In order to calculate and visualize in a consistent manner future glacier extent for a large number of individual glaciers (> 100) according to a given climate change scenario, we have developed an automated and simple but robust approach that is based on an empirical relationship between glacier size and the steady-state accumulation area ratio (AAR₀) in the Alps. The model requires digital glacier outlines and a digital elevation model (DEM) only and calculates new glacier geometries from a given shift of the steady-state equilibrium line altitude (ELA₀) by means of hypsographic modelling. We have calculated changes in number, area and volume for 3062 individual glacier units in Switzerland and applied six step changes in ELA₀ (from + 100 to + 600 m) combined with four different values of the AAR₀ (0.5, 0.6, 0.67, 0.75). For an AAR₀ of 0.6 and an ELA₀ rise of 200 m (400 m) we calculate a total area loss of − 54% (− 80%) and a corresponding volume loss of − 50% (− 78%) compared to the 1973 glacier extent. In combination with a geocoded satellite image, the future glacier outlines are also used for automated rendering of perspective visualisations. This is a very attractive tool for communicating research results to the general public. Our study is illustrated for a test site in the Upper Engadine (Switzerland), where landscape changes above timberline play an important role for the local economy. The model is seen as a first-step approach, where several parts can be (and should be) further developed.     

Late Cenozoic uplift of western Turkey: Improved dating of the Kula Quaternary volcanic field and numerical modelling of the Gediz River terrace staircase

A set of 13 new unspiked K–Ar dates has been obtained for the Quaternary basaltic volcanism in the Kula area of western Turkey, providing improved age control for the fluvial deposits of the Gediz River that underlie these basalt flows. This dating is able, for the first time, to resolve different ages for the oldest basalts, assigned to category β2, that cap the earliest Gediz deposits recognised in this area, at altitudes of 140 to 210 m above present river level. In particular, the β2 basalt capping the Sarnıç Plateau is dated to 1215 ± 16 ka (± 2σ), suggesting that the youngest underlying fluvial deposits, 185 m above present river level, are no younger than marine oxygen isotope stage (MIS) 38. In contrast, the β2 basalt capping the adjacent Burgaz Plateau is dated to 1014 ± 23 ka, suggesting that the youngest underlying fluvial deposits, 140 m above present river level, date from MIS 28. The staircase of 11 high Gediz terraces capping the latter plateau is thus dated to MIS 48-28, assuming they represent consecutive 40 ka Milankovitch cycles, although it is possible that as many as two cycles are missing from this sequence such that the highest terrace is correspondingly older. Basalt flows assigned to the β3 category, capping Gediz terraces 35 and 25 m above the present river level, have been dated to 236 ± 6 ka and 180 ± 5 ka, indicating incision rates of 0.15 mm a^− 1, similar to the time-averaged rates since the eruptions of the β2 basalts. The youngest basalts, assigned to category β4, are Late Holocene; our K–Ar results for them range from zero age to a maximum of 7 ± 2 ka.This fluvial incision is interpreted using numerical modelling as a consequence of uplift caused by a regional-scale increase in spatial average erosion rates to 0.1 mm a^− 1, starting at 3100 ka, caused by climate deterioration, since when a total of 410 m of uplift has occurred. Parameters deduced on this basis from the observed disposition of the Early Pleistocene Gediz terraces include the local effective viscosity of the lower crust, which is 2 × 10¹⁸ Pa s, the Moho temperature of 660 °C, and the depth of the base of the brittle upper crust, which is 13 km. The thin lithosphere in this area results in high heat flow, causing this relatively shallow base of the brittle upper crust and the associated relatively thick lower-crustal layer, situated between depths of 13 and 30 km. It estimated that around 900 ka, at the start of the 100 ka Milankovitch forcing, the spatial average erosion rate increased slightly, to 0.12 mm a^− 1; the associated relatively sluggish variations in uplift rates are as expected given the relatively thick lower-crustal layer.This modelling indicates that the growth of topography since the Pliocene in this study region has not involved a steady state. The landscape was significantly perturbed by the Middle Pliocene increase in erosion rates, and has subsequently adjusted towards—but not reached—a new steady state consistent with these increased erosion rates. It would not be possible to constrain what has been occurring from the Middle to Late Pleistocene or even the Early Pleistocene uplift response alone; information regarding the starting conditions is also essential, this being available in this region from the older geological record of stacked fluvial and lacustrine deposition. This result has major implications for the rigorous modelling of uplift histories in regions of rapid erosion, where preservation of information to constrain the starting conditions is unlikely.     

Biomization and quantitative climate reconstruction techniques in northwestern Mexico—With an application to four Holocene pollen sequences

New paleovegetation and paleoclimatic reconstructions from the Sierra Madre Occidental (SMO) in northwestern Mexico are presented. This work involves climate and biome reconstruction using Plant Functional Types (PFT) assigned to pollen taxa. We used fossil pollen data from four Holocene peat bogs located at different altitudes (1500‑2000 m) at the border region of Sonora and Chihuahua at around 28° N latitude (Ortega-Rosas, C.I. 2003. Palinología de la Ciénega de Camilo: datos para la historia de la vegetación y el clima del Holoceno medio y superior en el NW de la Sierra Madre Occidental, Sonora, Mexico. Master Thesis, Universidad Nacional Autónoma de México, México D.F.; Ortega-Rosas, C.I., Peñalba, M.C., Guiot, J. Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico. Submitted for publication of Palaeobotany and Palynology). The closest modern pollen data come from pollen analysis across an altitudinal transect from the Sonoran Desert towards the highlands of the temperate SMO at the same latitude (Ortega-Rosas, C.I. 2003. Palinología de la Ciénega de Camilo: datos para la historia de la vegetación y el clima del Holoceno medio y superior en el NW de la Sierra Madre Occidental, Sonora, Mexico. Master Thesis, Universidad Nacional Autónoma de México, México D.F.). An additional modern pollen dataset of 400 sites across NW Mexico and the SW United States was compiled from different sources (Davis, O.K., 1995. Climate and vegetation pattern in surface samples from arid western U.S.A.: application to Holocene climatic reconstruction. Palynology 19, 95–119, North American Pollen Database, Latin-American Pollen Database, personal data, and different scientific papers). For the biomization method (Prentice, I.C., Guiot, J., Huntley, B., Jolly, D., Cheddadi, R., 1996. Reconstructing biomes from paleoecological data: a general method and its application to European pollen data at 0 and 6 ka. Climate Dynamics 12, 185–194), we modified the pollen-PFT and PFT-biomes assignation of Thompson and Anderson (Thompson, R.S., Anderson, K.H., 2000. Biomes of western North America at 18,000; 6000 and 0 14C yr BP reconstructed from pollen and packrat midden data. Journal of Biogeography 27, 555–584) for a better representation of the modern vegetation of NW Mexico. The biome reconstruction method was validated with the modern pollen sites and applied to the fossil sites. Our results show that, during the early Holocene, a cool conifer forest extended at least down to 1700 m, while today this biome is present above 2000 m in the Chihuahua state. The Younger Dryas event was recorded in one site with cold and dry conditions. The reconstructed annual temperature for this period was 3°–6 °C colder than today, and annual precipitation was 250 mm lower than at present (900 mm/yr). The middle Holocene after 9200 cal yr BP was marked by a warming trend, reaching temperatures 2 °C warmer than today at 7000 cal yr BP, and by the installation of a warm mixed forest, the present day biome, at 1700 m elevation, while at higher elevations (1900 m) the cool conifer forest was still present. Summer precipitation was 200 mm/yr above the early Holocene values, suggesting that monsoon-like conditions strengthened since 9200 cal yr BP at this region. During the last 4000 yr, the same warm mixed forest was reconstructed below 1700 m and a conifer forest above 1700 m. A great variability of vegetation and climate patterns was recorded for the last 3000 yr particularly at high elevation sites, where warming and cooling trends would be coeval of the Medieval warm period and Little Ice Age, likely related to ENSO variability.