Miracle-dz/UniFAR-FTUs huggingface dataset:
The carbonate-silicate geochemical cycle and its effect on atmospheric carbon dioxide over the past 100 million years

A computer model has been constructed that considers the effects on the CO/sub 2/ level of the atmosphere, and the Ca, Mg, and HCO/sub 3/ levels of the ocean, of the following processes: weathering on the continents of calcite, dolomite, and calcium-and-magnesium-containing silicates; biogenic precipitation and removal of CaCO/sub 3/ from the ocean; removal of Mg from the ocean via volcanic-seawater reaction; and the metamorphic-magmatic decarbonation of calcite and dolomite (and resulting CO/sub 2/ degassing) as a consequence of plate subduction. Assuming steady state, values for fluxes to and from the atmosphere and oceans are first derived for the modern ocean-atmosphere system. Then the consequences of perturbing steady state are examined by deriving rate expressions for all transfer reactions. These rate expressions are constructed so as to reflect changes over the past 100 my. Results indicate that the CO/sub 2/ content of the atmosphere is highly sensitive to changes in seafloor spreading rate and continental land area, and, to a much lesser extent, to changes in the relative masses of calcite and dolomite. Consideration of a number of alternative seafloor spreading rate formulations shows that in all cases a several-fold higher CO/sub 2/ level for the Cretaceous atmosphere (65-100 mymore » BP) is obtained via the model. Assuming that CO/sub 2/ level and surface air temperature are positively correlated via an atmospheric greenhouse model, they authors predict Cretaceous paleotemperatures which are in rough general agreement with independent published data. Consequently, their results point to plate tectonics, as it affects both metamorphic-magmatic decarbonation and changes in continental land area, as a major control of world climate. « less
Response of soil nitrous oxide flux to nitrogen fertiliser application and legume rotation in a semi-arid climate, identified by smoothing spline models

Although large areas of semi-arid land are extensively cropped, few studies have investigated the effect of nitrogen (N) fertiliser on nitrous oxide (N2O) emissions in these regions (Galbally et al. 2010). These emissions need to be measured in order to estimate N losses and calculate national greenhouse gas inventories. We examined the effect of different agronomic management practices applied to wheat (Triticum aestivum) grown on an alkaline Vertosol in south-eastern Australia on N2O emissions. In 2007, N2O emissions were measured over 12 months, during which N fertiliser (urea) was applied at sowing or N fertiliser plus supplementary irrigation (50 mm) was applied during the vegetative stage and compared with a treatment of no N fertiliser or irrigation. In a second experiment (2008), the effect of source of N on N2O emissions was examined. Wheat was grown on plots where either a pulse (field peas, Pisum sativum) or pasture legume (barrel medic, Medicago truncatula) crop had been sown in the previous season compared with a non-legume crop (canola, Brassica napus). To account for the N supplied by the legume phase, N fertiliser (50 kg N ha–1 as urea) was applied only to the wheat in the plots previously sown to canola. Fluxes of N2O were measured on a sub-daily basis (up to 16 measurements per chamber) by using automated chamber enclosures and a tuneable diode laser, and treatment differences were evaluated by a linear mixed model including cubic smoothing splines. Fluxes were low and highly variable, ranging from –3 to 28 ng N2O-N m–2 s–1. The application of N fertiliser at sowing increased N2O emissions for ~2 months after the fertiliser was applied. Applying irrigation (50 mm) during the vegetative growth stage produced a temporary (~1-week) but non-significant increase in N2O emissions compared with plots that received N fertiliser at sowing but were not irrigated. Including a legume in the rotation significantly increased soil inorganic N at sowing of the following wheat crop by 38 kg N ha–1 (field peas) or 57 kg ha–1 (barrel medic) compared with a canola crop. However, N2O emissions were greater in wheat plots where N fertiliser was applied than where wheat was sown into legume plots where no N fertiliser was applied. Over the 2 years of the field study, N2O emissions attributed to fertiliser ranged from 41 to 111 g N2O-N ha–1, and averaged of 75 g N2O-N ha–1 or 0.15% of the applied N fertiliser. Our findings confirm that the proportion of N fertiliser emitted as N2O from rainfed grain crops grown in Australian semi-arid regions is less than the international average of 1.0%.
Charts of joint Kelvin‐Helmholtz and Rayleigh‐Taylor instabilites at the dayside magnetopause for strongly northward interplanetary magnetic field

We present maximum growth rate charts of the Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) instabilities at the dayside magnetopause (MP), considering two orientations of the interplanetary magnetic field (IMF) (due north and 30° west of north). We input parameters in the plasma depletion layer calculated from an MHD code. We study both a sharp MP transition and an MP with an attached boundary layer (“thin” and “thick” approximations, respectively). Our analysis applies to wavelengths (λ) from ∼2 × 103 km to ≤9 RE. Thin model results are as follows: For a stationary MP and due north IMF, the off-noon, low-latitude MP is very low shear (≤10°) and is substantially KH active. With an IMF inclined to north, extremely low shear, KH-active regions are confined to two strips, one in each hemisphere, where short λ perturbations are generated, which propagate as surface ripples on the high-latitude, duskside MP. For a sunward accelerating magnetopause and IMF north, a large part of the MP is unstable. With an inclined IMF, the KH+RT unstable strips are broader and growth rates are higher. Thick model results are as follows: For IMF due north and a stationary MP, the middle- to high-latitude MP is stable. At middle to low latitudes, the inner edge of the boundary layer (IEBL) is active, except for a 2-hour local time band on either side of noon. For the inclined IMF, the MP is stable for long λ, with activity for short λ confined to two strips, as before, with slightly reduced growth rates. For the IEBL, a clear dawn-dusk asymmetry in KH activity is evident. When the MP accelerates sunward and the IMF points north, we have to consider also the λ of the perturbation. For short λ, growth rates are enhanced with respect to stationarity at both the MP and the IEBL. While there are extensive regions of negligible growth at the MP, the entire IEBL is RT+KH unstable. We give an example of a long λ perturbation where both interfaces are coupled and oscillate together. Finally, for an inclined IMF, we have at the MP unstable strips which are wider and have higher growth rates. The IEBL, by contrast, is completely destabilized, with larger growth rates than under stationary conditions.
The relationship between aerosol backscatter coefficient and atmospheric relative humidity in an urban area over Athens, Greece, using Raman lidar and radiosonde data

In this article a statistical assessment concerning the relationship between the aerosol backscatter coefficient (βaer) and the relative humidity (RH) in the lower and middle troposphere, over Athens (Greece), is presented. For the purpose of this study, correlative radiosonde and aerosol backscatter lidar data were analysed for a period of 4 years (January 2003–December 2006), as obtained in the framework of the European Aerosol Lidar Network (EARLINET) project. The vertical profiles of the aerosol backscatter coefficients were measured by a combined Raman/elastic lidar system at ultraviolet (355 nm) and visible (532 nm) wavelengths. The correlation coefficient (R) of the vertical profiles of the RH against the backscatter coefficient of aerosols was investigated in altitudes within the free troposphere (0–6000 m). The altitude range was divided into three areas: 0 m up to the top of the planetary boundary layer (PBL); PBL up to PBL + 2000 m; and PBL + 2000 m up to 6000 m. The properties and seasonal variations of the height of the PBL were also studied. The annual mean PBL height over Athens was found to be (1320 ± 480) m, while during the warm period of the year (spring–summer) the PBL was higher than during the cold period (autumn–winter). Regarding the correlation coefficient (R), low (0–0.5) and medium (0.5–0.8) R values were mostly observed during the warm months of the year. For the aerosols originating from the Balkan area the highest correlation was observed at both wavelengths (R = 0.71 at 355 nm and R = 0.41 at 532 nm), especially during the years 2003 and 2005 (R = 0.61 at 355 nm and R = 0.93 at 532 nm). The almost linear correlation of this type of aerosols can be attributed to the fact that these remained for a longer time in a coherently alternating atmosphere, therefore having the tendency to become homogenized.
Turner Valley, Canada — A case history in contemporary airborne gravity

E-44 TURNER VALLEY CANADA – A CASE HISTORY IN CONTEMPORARY AIRBORNE GRAVITY J.W. PEIRCE 1 S. SANDER 2 R.A. CHARTERS 1 and V. LAVOIE 2 Abstract 1 In the summer of 2001 GEDCO and Sander Geophysics (SGL) carried out an airborne gravity survey using Sander’s AIRGrav system in the overthrust belt in the Turner Valley area near Calgary Alberta. The final results image all of the structures known from older ground surveys and reveal more complex details. This comparison demonstrates the exploration value of high quality airborne gravity surveys flown in severe foothills environments. Geological Setting The Turner Valley region
A fundamental probability distribution for heavy rainfall

There is currently no physical understanding of the statistics of heavy precipitation. These statistics are, however, central to diagnosing climate change and making weather risk assessments. This work derives a fundamental rainfall distribution. Interpretation of the water balance equation gives a simple expression for precipitation as the product of mass flux or advected mass, specific humidity and precipitation efficiency. Statistical theory predicts that the tail of the distribution of the product of these three random variables will have a stretched exponential form with a shape parameter of 2/3. This is verified for a global daily precipitation data set. The stretched exponential tail explains the apparent ‘heavy’ tailed behaviour of precipitation under standard assumptions used in extreme value theory. The novel implications for climate change are that the stretched exponential shape is unlikely to change, although the scale may, and precipitation efficiency is important in understanding future changes in heavy precipitation.
Giant bed from a sustained catastrophic density current flowing over topography: Acatlán ignimbrite, Mexico

A giant bed of ash and pumice (≤ 80 m thick and covering >300 km 2 ) in central Mexico demonstrates that thick clastic beds lacking sedimentary structures can aggrade incrementally from the base of sustained density currents. Like similar giant beds with matrix-supported clasts elsewhere, it had been interpreted as having formed en masse from a giant flow with high yield strength. However, intergradational compositional zones within the bed record changes in the material supplied at the source over time; the zones show that the density current was initially topographically restricted and that valleys progressively filled with deposit so that later parts of same density current were able to pass over and bury successively higher ground. This example provides a key to understanding the origin of massive parts of ignimbrites, megaturbidites, lahar deposits, and some debris-flow deposits. It shows that (1) an absence of sedimentary structures cannot be used to infer near-instantaneous deposition by en masse “freezing” or “collapse” of a giant flow, and (2) the thickness and vertical organization of a giant bed tell us little about thickness, vertical organization, and rheology of the current that produced it.
Effects of oblique subduction on the 3‐D pattern of small‐scale convection within the mantle wedge

We have developed a 3‐D numerical model of obliquely subducting slab and mantle flow above. Using this model, we explore the effects of oblique subduction on the small‐scale convection within the mantle wedge. We find that the spatial pattern and time dependent characteristics of oblique subduction are similar to those of non‐oblique cases whose subduction speed is the same as the subduction velocity component normal to the strike of subducting slab. This also implies that the axes of rolls of small‐scale convection are nearly normal to the plate boundary, assuming that the plate boundary represents the strike of subducting plate. Only when the back‐arc lithosphere overlying the small‐scale convection moves along the strike of subduction, a significant change of the orientation of roll axes is observed.
Multispectral polarization active imager in the visible band

We present the concept of a Multispectral Polarization Active Imager operating in the visible range. The acquisition of three degree of polarization (0% < Dp < 100%) images and three intensity images at different wavelengths (RGB) enables to get information about the spectral signature of targets as well as their polarization properties. A theoretical analysis and an experimental validation of this technique are presented. The device is operating in a monostatic configuration, using a white light source to illuminate the target. The reception system consists of a liquid crystal achromatic polarization rotator followed by a liquid crystal color filter and a CCD camera, all driven by a computer. The three polarization images can be merged in one by using a RGB coding in order to visualize the whole polarization information. Results with different targets will be presented, emphasizing polarization effects about backscattering. In particular the degree of polarization is found to be highly correlated to the reflectance of diffuse materials like paints, papers and other coatings. A first interpretation is given to explain this phenomenon. Application to identification of targets with low sensitivity to irradiance can be envisaged thanks to multispectral polarization signature.
Cretaceous–Tertiary palynofloral perturbations and extinctions within the Aquilapollenites Phytogeographic Province

A combination of detailed, intermediate and large scale stratigraphic perspectives is necessary to understand the driving mechanisms for floral change across the Cretaceous–Tertiary (K–T) boundary, because short-term physical and biotic events occur within longer term trends. Most Maastrichtian palynofloral extinctions have been identified within the northern circumpolar, supra-continental, Aquilapollenites Province. In mid-continental North America, the presence of a physically defined K–T boundary provides opportunities to examine contemporaneous terrestrial palynofloras over a latitudinal (also approximately paleolatitudinal) distance of 3200 km. Seventy-five percent of last appearances occur before the K–T boundary at high latitudes and must have been caused by ongoing terrestrial processes. Palynofloral events directly associated with the K–T boundary include both local last appearances, and inferred extinctions, and synchronous and diachronous changes in relative abundances. Two different styles of factors are reflected in these events. The first, possibly attributable to chemical or other profound atmospheric perturbations associated with the worldwide distribution of the “fireball” layer of the K–T claystone, resulted in extinctions of angiosperm with a zoophilous pollination strategy. The second factor, possibly reflecting energy released during the deposition of ballistically transported impact debris or hackly (ejecta) layer of the boundary claystone, resulted in the selective, northward-attenuating removal of the canopy vegetation, best documented for southwestern Canada, which was succeeded by a fern-dominated vegetation in mid-continental North America. These consequences of the boundary event were mediated by independent, preexisting circumstances: climate (regional and through time), local depositional environment, and ongoing background extinctions and origins.
Current state of glaciers in the tropical Andes: a multi-century perspective on glacier evolution and climate change

Abstract. The aim of this paper is to provide the community with a comprehensive overview of the studies of glaciers in the tropical Andes conducted in recent decades leading to the current status of the glaciers in the context of climate change. In terms of changes in surface area and length, we show that the glacier retreat in the tropical Andes over the last three decades is unprecedented since the maximum extension of the Little Ice Age (LIA, mid-17th–early 18th century). In terms of changes in mass balance, although there have been some sporadic gains on several glaciers, we show that the trend has been quite negative over the past 50 yr, with a mean mass balance deficit for glaciers in the tropical Andes that is slightly more negative than the one computed on a global scale. A break point in the trend appeared in the late 1970s with mean annual mass balance per year decreasing from −0.2 m w.e. in the period 1964–1975 to −0.76 m w.e. in the period 1976–2010. In addition, even if glaciers are currently retreating everywhere in the tropical Andes, it should be noted that this is much more pronounced on small glaciers at low altitudes that do not have a permanent accumulation zone, and which could disappear in the coming years/decades. Monthly mass balance measurements performed in Bolivia, Ecuador and Colombia show that variability of the surface temperature of the Pacific Ocean is the main factor governing variability of the mass balance at the decadal timescale. Precipitation did not display a significant trend in the tropical Andes in the 20th century, and consequently cannot explain the glacier recession. On the other hand, temperature increased at a significant rate of 0.10 °C decade−1 in the last 70 yr. The higher frequency of El Nino events and changes in its spatial and temporal occurrence since the late 1970s together with a warming troposphere over the tropical Andes may thus explain much of the recent dramatic shrinkage of glaciers in this part of the world.
Mountain Hydroclimatology and Snow Seasonality—Perspectives on climate impacts, snow seasonality and hydrological change in mountain environments

Mountain environments are extremely important to the world’s water resources, weather systems and populations. This Special Issue of Hydrological Processes on ‘Mountain hydroclimatology and snow seasonality’ is a follow-up of the last Special Issue on Mountain Hydrology in Hydrological Processes (de Jong et al., 2005b). It is largely based on mountain and snow hydrology sessions at successive European Geosciences Union (EGU) General Assembly meetings in Vienna in 2005 and 2006, supported by some invited papers. These sessions dealt with the theme of ‘Mountain hydrology and climatology: present state and future scenarios’. This introductory paper provides an overview of the hydrological importance of mountain regions, outlines some recent developments in the field and introduces the other 11 papers which comprise this timely Special Issue.
Mantle peridotites from the Bouvet Triple Junction Region, South Atlantic

ABSTRACT The Bouvet Triple Junction (BTJ) region in the South Atlantic, where the African, South American and Antarctica plates meet, is affected by several topographic/melting anomalies. Causes of these anomalies were investigated through a study of mantle‐derived serpentinized peridotites sampled from three sites in the BTJ region: (1) the Inner Corner High at the intersection of the America Antarctic Ridge (AAR) with the Conrad transform; (2) the south wall of the Bouvet transform (South West Indian Ridge, SWIR); and (3) the eastern Bouvet SWIR Transform Intersection. The degree of melting undergone by these rocks was estimated from relic mineral major‐ and trace‐element composition. Geochemical profiles from residual peridotites and associated basalts show a > 1000‐km‐wide melting anomaly centred on the Bouvet and Spiess topographic anomalies.
A 1000‐year record of dry conditions in the eastern Canadian prairies reconstructed from oxygen and carbon isotope measurements on Lake Winnipeg sediment organics

A short sediment core (162 cm), covering the period AD 920–1999, was sampled from the south basin of Lake Winnipeg for a suite of multi‐proxy analyses leading towards a detailed characterisation of the recent millennial lake environment and hydroclimate of southern Manitoba, Canada. Information on the frequency and duration of major dry periods in southern Manitoba, in light of the changes that are likely to occur as a result of an increasingly warming atmosphere, is of specific interest in this study. Intervals of relatively enriched lake sediment cellulose oxygen isotope values (δ18Ocellulose) were found to occur from AD 1180 to 1230 (error range: AD 1104–1231 to 1160–1280), 1610–1640 (error range: AD 1571–1634 to 1603–1662), 1670–1720 (error range: AD 1643–1697 to 1692–1738) and 1750–1780 (error range: AD 1724–1766 to 1756–1794). Regional water balance, inferred from calculated Lake Winnipeg water oxygen isotope values (δ18Oinf‐lw), suggest that the ratio of lake evaporation to catchment input may have been 25–40% higher during these isotopically distinct periods. Associated with the enriched δ18Ocellulose intervals are some depleted carbon isotope values associated with more abundantly preserved sediment organic matter (δ13COM). These suggest reduced microbial oxidation of terrestrially derived organic matter and/or subdued lake productivity during periods of minimised input of nutrients from the catchment area. With reference to other corroborating evidence, it is suggested that the AD 1180–1230, 1610–1640, 1670–1720 and 1750–1780 intervals represent four distinctly drier periods (droughts) in southern Manitoba, Canada. Additionally, lower‐magnitude and duration dry periods may have also occurred from 1320 to 1340 (error range: AD 1257–1363), 1530–1540 (error range: AD 1490–1565 to 1498–1572) and 1570–1580 (error range: AD 1531–1599 to 1539–1606). Copyright © 2009 John Wiley & Sons, Ltd.
Chemistry of the sea surface microlayer 1. Fabrication and testing of the sampler

A screen sampler fabricated to study the sea surface microlayer (SML) has been described. The screen sampler was tested in the Mandovi estuary and adjacent waters. Physico-chemical parameters of the subsurface waters from a depth of 25 cm was also studied for comparison with that of the SML