Global Biogeochemical Cycles (GLOBAL BIOGEOCHEM CY )

Publisher: American Geophysical Union, American Geophysical Union


Global Biogeochemical Cycles includes papers in the broad areas of global change involving the geosphere and biosphere. Marine, hydrologic, atmospheric, extraterrestrial, geologic, biologic, and human causes of and response to environmental change on timescales of tens, thousands, and millions of years are the purview of the journal.

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    Global Biogeochemical Cycles website
  • Other titles
    Global biogeochemical cycles
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    Periodical, Internet resource
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    Journal / Magazine / Newspaper, Internet Resource

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American Geophysical Union

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    • Preprints and Authors final version on Authors own or departmental website
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    • Publisher's version/PDF must be used in Institutional Repository 6 months after publication.
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Publications in this journal

  • [Show abstract] [Hide abstract]
    ABSTRACT: Carbon sequestration and storage in peatlands rely on consistently high water tables. Anthropogenic pressures including drainage, burning, land conversion for agriculture, timber and biofuel production, cause loss of peat-forming vegetation and exposure of previously anaerobic peat to aerobic decomposition. This can shift peatlands from net CO2 sinks to large CO2 sources, releasing carbon held for millennia. Peatlands also export significant quantities of carbon via fluvial pathways, mainly as dissolved organic carbon (DOC). We analysed radiocarbon (14C) levels of DOC in drainage water from multiple peatlands in Europe and Southeast Asia, to infer differences in the age of carbon lost from intact and drained systems. In most cases, drainage led to increased release of older carbon from the peat profile, but with marked differences related to peat type. Very low DOC-14C levels in runoff from drained tropical peatlands indicate loss of very old (centuries to millennia) stored peat carbon. High latitude peatlands appear more resilient to drainage; 14C measurements from UK blanket bogs suggest that exported DOC remains young (<50 years) despite drainage. Boreal and temperate fens and raised bogs in Finland and the Czech Republic showed intermediate sensitivity. We attribute observed differences to physical and climatic differences between peatlands, in particular hydraulic conductivity and temperature, as well as the extent of disturbance associated with drainage, notably land-use changes in the tropics. Data from the UK Peak District, an area where air pollution and intensive land-management have triggered Sphagnum loss and peat erosion, suggest that additional anthropogenic pressures may trigger fluvial loss of much older (>500 year) carbon in high-latitude systems. Re-wetting at least partially offsets drainage effects on DOC age.
    Global Biogeochemical Cycles 09/2014;
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    ABSTRACT: We compared carbon (C), nitrogen (N), and phosphorus (P) concentrations in atmospheric deposition, runoff, and soils with microbial respiration [dehydrogenase (DHA)] and ecoenzyme activity (EEA) in an ombrotrophic bog and a minerotrophic fen to investigate the environmental drivers of biogeochemical cycling in peatlands at the Marcell Experimental Forest in northern Minnesota, USA. Ecoenzymatic stoichiometry was used to construct models for C use efficiency (CUE) and decomposition (M), and these were used to model respiration (Rm). Our goals were to determine the relative C, N, and P limitations on microbial processes and organic matter decomposition, and to identify environmental constraints on ecoenzymatic processes. Mean annual water, C, and P yields were greater in the fen, while N yields were similar in both the bog and fen. Soil chemistry differed between the bog and fen, and both watersheds exhibited significant differences among soil horizons. DHA and EEA differed by watersheds and soil horizons, CUE, M, and Rm differed only by soil horizons. C, N, or P limitations indicated by EEA stoichiometry were confirmed with orthogonal regressions of ecoenzyme pairs and enzyme vector analyses, and indicated greater N and P limitation in the bog than in the fen, with an overall tendency toward P-limitation in both the bog and fen. Ecoenzymatic stoichiometry, microbial respiration, and organic matter decomposition were responsive to resource availability and the environmental drivers of microbial metabolism, including those related to global climate changes.
    Global Biogeochemical Cycles 08/2014; 120(1-3):203-224.
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    ABSTRACT: The emissions of carbon dioxide (CO2) from inland waters are substantial on a global scale. Yet, the fundamental question remains open which proportion of these CO2 emissions is induced by sunlight via photochemical mineralization of dissolved organic carbon (DOC), rather than by microbial respiration during DOC decomposition. Also, it is unknown on larger spatial and temporal scales how photochemical mineralization compares to other C fluxes in the inland water C cycle. We combined field and laboratory data with atmospheric radiative transfer modeling to parameterize a photochemical rate model for each day of the year 2009, for 1086 lakes situated between latitudes from 55 to 69°N in Sweden. The sunlight-induced production of dissolved inorganic carbon (DIC) averaged 3.8 ± 0.04 g C m-2 yr-1, which is a flux comparable in size to the organic carbon burial in the lake sediments. Countrywide, 151 ± 1 kt C yr-1 was produced by photochemical mineralization, corresponding to about 12% of total annual mean CO2 emissions from Swedish lakes. With a median depth of 3.2 m, the lakes were generally deep enough that incoming, photochemically active photons were absorbed in the water column. This resulted in a linear positive relationship between DIC photoproduction and the incoming photon flux, which correspond to the absorbed photons. Therefore, the slope of the regression line represents the wavelength- and depth-integrated apparent quantum yield of DIC photoproduction. We used this relationship to obtain a first estimate of DIC photoproduction in lakes and reservoirs worldwide. Global DIC photoproduction amounted to 13 and 35 Mt C yr-1 under overcast and clear sky, respectively. Consequently, these directly sunlight-induced CO2 emissions contribute up to about one tenth to the global CO2 emissions from lakes and reservoirs, corroborating that microbial respiration contributes a substantially larger share than formerly thought, and generate annual C fluxes similar in magnitude to the C burial in natural lake sediments worldwide.
    Global Biogeochemical Cycles 01/2014;
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    ABSTRACT: [1] Temperature-dependent remineralization of organic matter is, in general, not included in marine biogeochemistry models currently used for Coupled Model Intercomparison Project Phase 5 (CMIP5) climate projections. Associated feedbacks have therefore not been quantified. In this study we aim at investigating how temperature-dependent remineralization rates (Q10 = 2) in a warming ocean impact on the marine carbon cycle, and if this may weaken the oceanic sink for anthropogenic CO2. We perturb an Earth system model used for CMIP5 with temperature-dependent remineralization rates of organic matter using representative concentration pathway (RCP)8.5-derived temperature anomalies for 2100. The result is a modest change of organic carbon export but also derived effects associated with feedback processes between changed nutrient concentrations and ecosystem structure. As more nutrients are recycled in the euphotic layer, increased primary production causes a depletion of silicate in the surface layer as opal is exported to depth more efficiently than particulate organic carbon. Shifts in the ecosystem occur as diatoms find less favorable conditions. Export production of calcite shells increases causing a decrease in alkalinity and higher surface pCO2. With regard to future climate projections, the results indicate a reduction of oceanic uptake of anthropogenic CO2 of about 0.2 PgC yr−1 toward the end of the 21st century in addition to reductions caused by already identified climate-carbon cycle feedbacks. Similar shifts in the ecosystem as identified here, but driven by external forcing, have been proposed to drive glacial/interglacial changes in atmospheric pCO2. We propose a similar positive feedback between climate perturbations and the global carbon cycle but driven solely by internal biogeochemical processes.
    Global Biogeochemical Cycles 12/2013; 27:1214-1225.
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    ABSTRACT: Major transformation processes of reactive nitrogen occur in the upper oxygen‐deficient zone (ODZ)Nitrate reduction and reoxidation of nitrite are closely coupledThe availability of organic substrate limits denitrification in the lower ODZMajor transformation processes of reactive nitrogen occur in the upper oxygen‐deficient zone (ODZ)Nitrate reduction and reoxidation of nitrite are closely coupledThe availability of organic substrate limits denitrification in the lower ODZ
    Global Biogeochemical Cycles 12/2013; 27:1-13.