David J. Large

A Database and Synthesis of Northern Peatland Soil Properties and Holocene Carbon and Nitrogen Accumulation

Here, we present results from the most comprehensive compilation of Holocene peat soil properties with associated carbon and nitrogen accumulation rates for northern peatlands. Our database consists of 268 peat cores from 215 sites located north of 45°N. It encompasses regions within which peat carbon data have only recently become available, such as the West Siberia Lowlands, the Hudson Bay Lowlands, Kamchatka in Far East Russia, and the Tibetan Plateau. For all northern peatlands, carbon content in organic matter was estimated at 42 ± 3% (standard deviation) for Sphagnum peat, 51 ± 2% for non-Sphagnum peat, and at 49 ± 2% overall. Dry bulk density averaged 0.12 ± 0.07 g/cm3, organic matter bulk density averaged 0.11 ± 0.05 g/cm3, and total carbon content in peat averaged 47 ± 6%. In general, large differences were found between Sphagnum and non-Sphagnum peat types in terms of peat properties. Time-weighted peat carbon accumulation rates averaged 23 ± 2 (standard error of mean) g C/m2/yr during the Holocene on the basis of 151 peat cores from 127 sites, with the highest rates of carbon accumulation (25–28 g C/m2/yr) recorded during the early Holocene when the climate was warmer than the present. Furthermore, we estimate the northern peatland carbon and nitrogen pools at 436 and 10 gigatons, respectively. The database is publicly available at https://peatlands.lehigh.edu.

Silica−Volatile Interaction and the Geological Cause of the Xuan Wei Lung Cancer Epidemic

Parts of Xuan Wei County, Yunnan Province, China have the highest known lung cancer mortality in nonsmoking women. This high mortality displays a clear spatial relationship to the mines producing coal from the uppermost Permian. Geochemical, petrographic, and grainsize analyses were undertaken on a set of coal samples from Xuan Wei. Results demonstrate that the single geochemical property that makes this coal unusual is its high concentration of quartz (13.5 wt %) of which 35-55% occurs as <10 microm grains. We propose the potential for silica-volatile interaction (PSVI) as a new method for assessing the combined influence of silica and volatile organic matter and use this as a basis for re-evaluating existing ecological data. Published lung cancer mortality values are more strongly correlated with PSVI values for Xuan Wei coal than with volatiles or silica alone and the PSVI values measured are distinct from those of other coals. Finally we propose that the localization of this epidemic to Xuan Wei results from enhanced weathering of the local Emeishan basalts as a consequence of geochemical perturbations at the Permo-Triassic Boundary.

Hydropyrolysis: Implications for radiocarbon pretreatment and characterization of black carbon

Charcoal is the result of natural and anthropogenic burning events, when biomass is exposed to elevated temperatures under conditions of restricted oxygen. This process produces a range of materials, collectively known as pyrogenic carbon, the most inert fraction of which is known as black carbon (BC). BC degrades extremely slowly and is resistant to diagenetic alteration involving the addition of exogenous carbon, making it a useful target substance for radiocarbon dating particularly of more ancient samples, where contamination issues are critical. We present results of tests using a new method for the quantification and isolation of BC, known as hydropyrolysis (hypy). Results show controlled reductive removal of non-BC organic components in charcoal samples, including lignocellulosic and humic material. The process is reproducible and rapid, making hypy a promising new approach not only for isolation of purified BC for 14C measurement but also in quantification of different labile and resistant sample C fractions.

A Petrographic Investigation of two Sequential Extraction Techniques Applied to Anaerobic Canal Bed Mud

The application of sequential extraction procedures to determine metal speciation in sediments is fraught with uncertainty regarding what is actually dissolving or re-precipitating at each stage. In order to choose an appropriate scheme for the investigation of contaminated anaerobic mud two different sequential extraction procedures (Kersten and Förstner, 1986; Quevauviller, 1998) were investigated using a Cryogenic SEM (CryoSEM) technique coupled with energy dispersive X-ray analysis (EDXA). This enabled assessment of the degree of reagent selectivity and any re-precipitation associated with the respective methods. Analysis of the non-leached sediment revealed the most abundant authigenic minerals in order of decreasing abundance to be Fe2+-phosphate vivianite (Fe3(PO4)2·8H2O), mixed Fe, Zn, Cu sulphides, pyrite and calcite. After each stage of the sequential extraction the sediment residue was examined using CryoSEM. After extraction of the exchangeable fraction no obvious evidence of mineral dissolution was observed. Calcite was not completely dissolved during the carbonate extraction stage of either procedure. Vivianite began to dissolve in the carbonate extraction stage of both procedures and was completely dissolved by oxide extraction stage of both procedures. The sediment leached by acidified ammonium oxalate, contained abundant Fe oxalate crystals, suggesting that a large proportion of the Fe released from the vivianite has been re-precipitated. The Fe oxalate was then dissolved with the subsequent sulphide fraction. The technique used to extract the sulphide and organic fraction is the same in both schemes and no sulphide or metal rich organic matter was found in either residue.

Petrographic Observations of Iron, Copper, and Zinc Sulfides in Freshwater Canal Sediment

ABSTRACT Sulfide minerals are known to be important hosts for metals in many freshwater and marine sediments, but little is known about their petrography, particularly in fine-grained recent freshwater sediments. In this paper the results of a Cryogenic SEM investigation of sulfide textures in two fine-grained anaerobic canal-bed muds are reported. The technique allows direct observation of the undisrupted mineral and organic textures in the canal-bed mud. Iron sulfides occur in two forms: coatings on biofilms and framboids. Iron sulfide-coated biofilms have iron sulfur ratios in the range FeS to Fe3S4. Framboid structures display a continuum of textures from greigite proto-framboids with a poorly developed crystallite texture to pyrite framboids with well developed crystallites. Proto-framboids tend to be smaller than framboids. A positive correlation was observed between crystallite diameter and framboid diameter. By dividing the framboid diameter by the crystallite diameter it was deduced that framboids tend not to have single crystallites at their centers. Copper occurs as a discrete sulfide with a composition similar to chalcopyrite. Zinc occurs as a zinc iron sulfide with metal-to-sulfur ratios in the range 0.59 to 0.87. Copper sulfides tend to nucleate on surfaces whereas the zinc sulfides occur both on surfaces and as floccular precipitates in open pore space.

Pristane/phytane ratios in the mineralized Kupferschiefer of the Fore-Sudetic Monocline, southwest Poland

The interaction of organic matter with fluids is important in geochemical processes in surface and diagenetic environments. In the Kupferschiefer copper deposits of southwestern Poland organic-fluid interactions are inferred to have been important in the genesis of the ore deposits. Previous organic geochemical studies of the Kupferschiefer report evidence of a late diagenetic oxidation event that altered the organic geochemistry. This study uses the saturated hydrocarbons as indicators of the biological input and the earliest diagenetic processes to affect the organic geochemistry of the Kupferschiefer. The normal alkane distributions are lithofacies controlled indicating that they reflect biological input. The ratio of the saturated isoprenoids pristane/phytane are potential indicators of the redox conditions during sedimentation and diagenesis. Very low PrPh ratios are associated with lithofacies that were deposited in hypersaline environments. Increases in the PrPh ratio within individual traverses are interpreted as indicating increasing oxidation of organic matter during deposition and early diagenesis. Trends of increasing pristane/phytane ratios are observed at the base of the Kupferschiefer and at the transition, within the Kupferschiefer, from the clay-rich to the carbonate-rich Kupferschiefer which corresponds approximately to the transition from Cu-zone to the Pb-zone. Early diagenetic, copper-depleted Cu- and CuFe-sulfides have also been reported form the top of the Weissliegendes and the Cu-zone/Pb-zone transition, and it is conceivable that both could be related to the same processes.

High-resolution terrestrial record of orbital climate forcing in coal

Pre-Quaternary terrestrial climate records in which time has been calibrated using astronomical cycles are, with the exception of lacustrine proxies, poorly represented in the geological record. This omission is a significant gap in our knowledge of ancient climate systems. Here we present new evidence of orbital periodicities in an 18.3-m-thick late Paleocene coal and conclude that coal has the potential to provide continuous time-calibrated terrestrial climate data. Spectral analysis of changes in the relative proportions of vitrinite to inertinite, two environmentally sensitive coal macerals, reveals several characteristic frequencies, some of which display evidence of amplitude modulation every five to six cycles. Combining this observation with depositional time limitations derived from present-day rates of carbon accumulation in mires, we interpret the characteristic frequencies as resulting from precession and obliquity and their influence on oxidation and decay. Using the inferred precession component of the data to derive an internal time scale, we estimate that the Wyodak coal was deposited over a period of ∼414 k.y. with a long-term carbon sequestration rate of 29 g m−2 yr−1. The identification of an internal astronomical time scale in coal is an important step toward realizing the potential for coal to extend our high-resolution knowledge of Earths terrestrial climate back to the formation of the first peat deposits at 360 Ma.

A cobaltite-framboidal pyrite association from the Kupferschiefer; possible implications for trace element behaviour during the earliest stages of diagenesis

Abstract Cobaltite-cemented pyrite framboids are reported from the base of the Kupferschiefer in the Lubin- Sieroszowice mining district in southern Poland. In the framboids, cobaltite occurs interstitial to the pyrite crystals. The cobaltite-cemented framboids are confined to within a few cm either side of the boundary between the Weissliegendes sandstone and the Kupferschiefer laminated organic-rich shales. Textural relations and distribution of the cobaltite is interpreted as indicating that the framboids acted as a site of preferred cobaltite precipitation and that the cobaltite precipitated in response to the changing chemical environment at the Weissliegendes/Kupferschiefer contact. It is proposed that the texture may have formed as a result of desorption of Co and/or As which had been adsorbed onto the monosulphide precursors to the framboidal pyrite. Desorption during the transition to pyrite resulted in cobaltite saturation within the framboid and subsequent precipitation. The source of the Co and As was probably oxyhydroxides which exist in the upper oxic part of the Weissliegendes.

Orbital tuning and correlation of 1.7 m.y. of continuous carbon storage in an early Miocene peatland

Peatland is an important terrestrial carbon reservoir that contains >25% of soil carbon and accounts for 25%-38% of natural methane emissions. Most of this carbon is contained in postglacial boreal peat. Our understandingof the carbon cycle within this reservoir and its links to the atmosphere is therefore restricted to periods of 1 m.y. Spectral analysis of varying lignite color reveals that 120 m of early Miocene lignite from the Gippsland Basin, Australia, contains a 1.7 m.y. record of orbitally paced climate oscillations dominated by the response to obliquity. Use of the regular orbital signal indicates that the average long-term rate of peatland carbon accumulation recorded in the lignite is 27.5 g.m - 2 .yr - 1 . This rate is constant over periods of >100 k.y. and is independent of shorter-term, <10 k.y., fluctuations in climate and hydrology. Matching the lignite record to the theoretical insolation curve indicates that the lignite formed between 22.5 and 20.8 Ma. Contemporaneous long-term changes in lignite color and the 1 3 C/ 1 2 C ratios of marine foraminifera may relate to changing peatland methane flux and thus point to a link between terrestrial and marine carbon dynamics.

Geochemistry and petrography of phosphorus in urban canal bed sediment

Abstract Urban canal sediment provides an opportunity to investigate the processes controlling P geochemistry in a system dominated by anthropogenic input. To achieve this a combined study was undertaken of pore water geochemistry and petrology of the top 25 cm canal bed sediment from two urban canals in the English West Midland conurbation. Processes in the sediment are dominated by the geochemistry of Fe, P and organic matter. Results indicate that sediment re-suspension by boat traffic has a major influence on pore water chemistry. In addition to the sediment water interface an additional interface at 6–7 cm depth was identified and corresponds to the maximum depth of sediment re-suspension by boat traffic. Phosphorus in the sediment occurs predominantly as vivianite. Low PO4 concentrations occur close to the sediment water interface in summer due to frequent re-suspension and Fe oxidation. High PO4 concentrations occur close to the sediment water interface in winter when boat traffic is infrequent. The greatest potential to exchange phosphate between sediment and water column will therefore occur during infrequent boat traffic regimes.