ALBERT

Beschreibung: ABSTRACT Variations in the Holocene circulation of the West Greenland Current (WGC) in the Disko Bugt region have been reconstructed from a suite of sediment cores. Palaeoceanographic proxies include magnetic susceptibility (MS) and X-ray fluorescence titanium counts, which document a major shift in circulation at c . 6000 cal a BP. Before this date, sediments in southern Disko Bugt were characterized by high terrigeneous and basaltic input, suggesting widespread influence of meltwater plumes. Our data show that the WGC re-circulated in the southern Disko Bugt area because a potential northern pathway, the narrow Vaigat Strait, was blocked by icebergs that calved from marine outlet glaciers in eastern Disko Bugt. Sediments in southern Disko Bugt deposited after c . 6000 cal a BP have significantly lower terrestrial and basaltic sediment input, which coincides with minimum Holocene ice sheet extent. The reduced meltwater and iceberg discharge to the embayment caused the Vaigat Strait to become free of blocking icebergs and terrigenous input was partly diverted to the outer shelf. Thus, the modern circulation pattern of the WGC was established in the Disko Bugt region through the opening of the Vaigat Strait c . 6000 cal a BP.

Beschreibung: ABSTRACT Debate concerning the environmental impact of human arrival in Australia has continued for more than a century. Here we review the evidence for human impact and the mechanisms by which humans may have affected the environment of tropical Australia. We limit our review to tropical Australia because, over three decades ago, it was proposed that the imposition of an anthropogenic fire regime upon human occupation of the Australian continent may have resulted in profound changes in regional vegetation and climate across this region. We conclude that ecological processes and vegetation–fire–climate–human feedbacks do exist that could have driven a significant shift in boundary conditions and ecosystem state at the sub-continental scale through the sustained imposition of an anthropogenic fire regime over tens of millennia. These potential feedbacks operate through the inhibition of forest expansion both directly, by targeted burning at established forest edges and newly irrupted forest patches, and indirectly, through lengthening of the dry season because of changes to the timing of burning. However, the impact of any such anthropogenic forcing may have been entirely overshadowed by the effects of natural climate change and variability, as well as the generally low nutrient status of Australian soils. A robust assessment of the degree to which the environment of tropical Australia at the large scale has been modified from its ‘natural’ state because of human occupation will require new, coordinated collaborations between indigenous traditional landowners, archaeologists, anthropologists, geochronologists, geoscientists, ecologists, climatologists and modellers.

Beschreibung: ABSTRACT During the last deglaciation, the ventilation of the subarctic Pacific is hypothesized to have changed dramatically, including the rejuvenation of a poorly-ventilated abyssal water mass that filled the deep ocean, and fluctuations in the strength of North Pacific intermediate and deep water formation at millennial timescales. Foraminiferal radiocarbon reconstructions of past ventilation changes in the Pacific are valuable, but are hampered by poor carbonate preservation, low sediment accumulation rates, bias from bioturbation, and poorly constrained past surface reservoir age. In this study, we present paired benthic-planktonic radiocarbon measurements from the Okhotsk Sea and Emperor Seamounts. We take advantage of large contemporaneous peaks in benthic abundances from the glacial maximum, Bolling-Allerod (BA) and early Holocene to produce time slices of radiocarbon from 1–4 km water depth. We explore the impact of uncertain surface reservoir age, and evaluate several approaches to quantifying past ocean radiocarbon distribution using our NW Pacific data and a compilation of published data from the North Pacific. Both the calendar age and the absolute value of an ocean radiocarbon estimate depend on the assumed surface reservoir age. But for a time slice from a small geographical area, the shape of a water-column profile is independent of surface reservoir age. The NW Pacific profiles are similar in shape to the compilation profiles for the entire North Pacific, which suggests that deglacial surface reservoir age changes across the N Pacific did not diverge dramatically across the areas sampled. The LGM profile 〉2 km spans a wide range of values, which when compared to values 〈2 km encompass a profile similar in shape to today to one with decreasing radiocarbon with depth. However, by the BA the profile has a similar shape to today. Ultimately, local surface reservoir ages, end-member water mass composition and mixing ratios must each be constrained before a radiocarbon activity reconstruction can be used to confidently infer ventilation changes.

Beschreibung: The multispecies analysis of daily air samples collected at the NOAA Boulder Atmospheric Observatory (BAO) in Weld County in northeastern Colorado since 2007 shows highly correlated alkane enhancements caused by a regionally distributed mix of sources in the Denver-Julesburg Basin. To further characterize the emissions of methane and non-methane hydrocarbons (propane, n-butane, i-pentane, n-pentane and benzene) around BAO, a pilot study involving automobile-based surveys was carried out during the summer of 2008. A mix of venting emissions (leaks) of raw natural gas and flashing emissions from condensate storage tanks can explain the alkane ratios we observe in air masses impacted by oil and gas operations in northeastern Colorado. Using the WRAP Phase III inventory of total volatile organic compound (VOC) emissions from oil and gas exploration, production and processing, together with flashing and venting emission speciation profiles provided by State agencies or the oil and gas industry, we derive a range of bottom-up speciated emissions for Weld County in 2008. We use the observed ambient molar ratios and flashing and venting emissions data to calculate top-down scenarios for the amount of natural gas leaked to the atmosphere and the associated methane and non-methane emissions. Our analysis suggests that the emissions of the species we measured are most likely underestimated in current inventories and that the uncertainties attached to these estimates can be as high as a factor of two.

Beschreibung: [1]  [1] The Gamburtsev Subglacial Mountains (GSM), located near the center of East Antarctica, are the highest feature within the East Antarctic highlands and have been investigated seismically for the first time during the 2007/2008 International Polar Year by the Gamburtsev Mountains Seismic Experiment. Using data from a network of 26 broadband seismic stations and body wave tomography, the P and S wave velocity structure of the upper mantle beneath the GSM and adjacent regions has been examined. Tomographic images produced from teleseismic P and S phases reveal several large-scale, small amplitude anomalies (δV p  = 1.0%, δV s  = 2.0%) in the upper 250 km of the mantle. The lateral distributions of these large-scale anomalies are similar in both the P and S wave velocity models and resolution tests show that they are well resolved. Velocity anomalies indicate slower, thinner lithosphere beneath the likely Meso- or Neoproterozoic Polar Subglacial Basin and faster, thicker lithosphere beneath the likely Archean/Paleoproterozoic East Antarctic highlands. Within the region of faster, thicker lithosphere, a lower amplitude (δV p  = 0.5%, δV s  = 1.0%) slow to fast velocity pattern is observed beneath the western flank of the GSM, suggesting a suture between two lithospheric blocks possibly of similar age. These findings point to a Precambrian origin for the high topography of the GSM, corroborating other studies invoking a long-lived highland landscape in central East Antarctica, as opposed to uplift caused by Permian/Cretaceous rifting or Cenozoic magmatism. The longevity of the GSM makes them geologically unusual, however, plausible analogues exist, such as the 550 Ma Petermann Ranges in central Australia. Additional uplift may have occurred by the reactivation of pre-existing faults, for example during the Carboniferous-Permian collision of Gondwana and Laurussia.

Beschreibung: Although climate change is predicted to place mountain-top and other narrowly endemic species at severe risk of extinction, the ecological processes involved in such extinctions are still poorly resolved. In addition, much of this biodiversity loss will likely go unobserved, and therefore largely unappreciated. The Haleakalā silversword is restricted to a single volcano summit in Hawaiʻi, but is a highly charismatic giant rosette plant that is viewed by 1-2 million visitors annually. We link detailed local climate data to a lengthy demographic record, and combine both with a population-wide assessment of recent plant mortality and recruitment, to show that after decades of strong recovery following successful management, this iconic species has entered a period of substantial climate-associated decline. Mortality has been highest at the lower end of the distributional range, where most silverswords occur, and the strong association of annual population growth rates with patterns of precipitation suggests an increasing frequency of lethal water stress. Local climate data confirm trends towards warmer and drier conditions on the mountain, and signify a bleak outlook for silverswords if these trends continue. The silversword example foreshadows trouble for diversity in other biological hotspots, and illustrates how even well-protected and relatively abundant species may succumb to climate-induced stresses. © 2012 Blackwell Publishing Ltd

Beschreibung: The combination of global and local stressors is leading to a decline in coral reef health globally. In the case of eutrophication, increased concentrations of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) are largely attributed to local land use changes. From the global perspective, increased atmospheric CO 2 levels are not only contributing to global warming but also ocean acidification (OA). Both eutrophication and OA have serious implications for calcium carbonate production and dissolution among calcifying organisms. In particular, benthic foraminifera precipitate the most soluble form of mineral calcium carbonate (high-Mg calcite), potentially making them more sensitive to dissolution. In the present study a manipulative orthogonal two-factor experiment was conducted to test the effects of dissolved inorganic nutrients and OA on the growth, respiration and photophysiology of the large photosymbiont-bearing benthic foraminifer, Marginopora rossi . This study found the growth rate of M. rossi was inhibited by the interaction of eutrophication and acidification. The relationship between M. rossi and its photosymbionts became destabilised due to the photosymbiont's release from nutrient limitation in the nitrate-enriched treatment, as shown by an increase in zooxanthellae cells per host surface area. Foraminifers from the OA treatments had an increased amount of Chl a per cell, suggesting a greater potential to harvest light energy, however there was no net benefit to foraminifer growth. Overall, this study demonstrates that the impacts of OA and eutrophication are dose-dependant and interactive. This research indicates an OA threshold at pH 7.6, alone or in combination with eutrophication, will lead to a decline in M. rossi calcification. The decline in foraminifera calcification associated with pollution and OA will have broad ecological implications across their ubiquitous range and suggests that without mitigation it could have serious implications for the future of coral reefs. © 2012 Blackwell Publishing Ltd

Beschreibung: We compare the characteristics of synthetic European droughts generated by the HiGEM 1 coupled climate model run with present day atmospheric composition with observed drought events extracted from the CRU TS3 data set. The results demonstrate consistency in both the rate of drought occurrence and the spatiotemporal structure of the events. Estimates of the probability density functions for event area, duration and severity are shown to be similar with confidence 〉 90%. Encouragingly, HiGEM is shown to replicate the extreme tails of the observed distributions and thus the most damaging European drought events. The soil moisture state is shown to play an important role in drought development. Once a large-scale drought has been initiated it is found to be 50% more likely to continue if the local soil moisture is below the 40 th percentile . In response to increased concentrations of atmospheric CO 2 , the modelled droughts are found to increase in duration, area and severity. The drought response can be largely attributed to temperature driven changes in relative humidity. Copyright © 2012 Royal Meteorological Society

Beschreibung: It is important to demonstrate that replacing fossil fuel with bioenergy crops can reduce the national greenhouse gas (GHG) footprint. We compared field emissions of nitrous oxide (N 2 O), methane (CH 4 ) and soil respiration rates from the C 4 grass Miscanthus × giganteus and willow ( salix) with emissions from annual arable crops grown for food production. The study was carried out in NE England on adjacent fields of willow , Miscanthus , wheat ( Triticum aetivum ) and oilseed rape ( Brassica napus ). N 2 O, CH 4 fluxes and soil respiration rates were measured monthly using static chambers from June 2008 to November 2010. Net ecosystem exchange (NEE) of carbon dioxide (CO 2 ) was measured by eddy covariance on Miscanthus from May 2008 and on willow from October 2009 until November 2010. The N 2 O fluxes were significantly smaller from the bioenergy crops than that of the annual crops. Average fluxes were 8 and 32 μg m −2  h −1 N 2 O-N from wheat and oilseed rape, and 4 and 0.2 μg m −2  h −1 N 2 O-N from Miscanthus and willow, respectively. Soil CH 4 fluxes were negligible for all crops and soil respiration rates were similar for all crops. NEE of CO 2 was larger for Miscanthus (−770 g C m −2  h −1 ) than willow (−602 g C m −2  h −1 ) in the growing season of 2010. N 2 O emissions from Miscanthus and willow were lower than for the wheat and oilseed rape which is most likely a result of regular fertilizer application and tillage in the annual arable cropping systems. Application of 15 N-labelled fertilizer to Miscanthus and oil seed rape resulted in a fertilizer-induced increase in N 2 O emission in both crops. Denitrification rates (N 2 O + N 2 ) were similar for soil under Miscanthus and oilseed rape. Thus, perennial bioenergy crops only emit less GHGs than annual crops when they receive no or very low rates of N fertilizer.

Beschreibung: We examine the influence of climate, soil properties and vegetation characteristics on soil organic carbon (SOC) along a transect of West African ecosystems sampled across a precipitation gradient on contrasting soil types stretching from Ghana (15°N) to Mali (7°N). Our findings derive from a total of 1108 soil cores sampled over 14 permanent plots. The observed pattern in SOC stocks reflects the very different climatic conditions and contrasting soil properties existing along the latitudinal transect. The combined effects of these factors strongly influence vegetation structure. SOC stocks in the first 2 m of soil ranged from 20 Mg C ha −1 for a Sahelian savanna in Mali to over 120 Mg C ha −1 for a transitional forest in Ghana. The degree of interdependence between soil bulk density (SBD) and soil properties is highlighted by the strong negative relationships observed between SBD and SOC ( r 2  〉 0.84). A simple predictive function capable of encompassing the effect of climate, soil properties and vegetation type on SOC stocks showed that available water and sand content taken together could explain 0.84 and 0.86 of the total variability in SOC stocks observed to 0.3 and 1.0 m depth respectively. Used in combination with a suitable climatic parameter, sand content is a good predictor of SOC stored in highly weathered dry tropical ecosystems with arguably less confounding effects than provided by clay content. There was an increased contribution of resistant SOC to the total SOC pool for lower rainfall soils, this likely being the result of more frequent fire events in the grassier savannas of the more arid regions. This work provides new insights into the mechanisms determining the distribution of carbon storage in tropical soils and should contribute significantly to the development of robust predictive models of biogeochemical cycling and vegetation dynamics in tropical regions.