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Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 30, SJR: 2.439, h-index: 91)
Geophysical Research Letters     Full-text available via subscription   (Followers: 131, SJR: 3.323, h-index: 185)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 15, SJR: 3.22, h-index: 136)
J. of Advances in Modeling Earth Systems     Open Access   (Followers: 5, SJR: 4.444, h-index: 18)
J. of Geophysical Research : Atmospheres     Partially Free   (Followers: 130)
J. of Geophysical Research : Biogeosciences     Full-text available via subscription   (Followers: 29)
J. of Geophysical Research : Earth Surface     Partially Free   (Followers: 54)
J. of Geophysical Research : Oceans     Partially Free   (Followers: 52)
J. of Geophysical Research : Planets     Full-text available via subscription   (Followers: 112)
J. of Geophysical Research : Solid Earth     Full-text available via subscription   (Followers: 46)
J. of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 133)
Paleoceanography     Full-text available via subscription   (Followers: 5, SJR: 3.067, h-index: 100)
Radio Science     Full-text available via subscription   (Followers: 38, SJR: 1.072, h-index: 59)
Reviews of Geophysics     Full-text available via subscription   (Followers: 36, SJR: 8.833, h-index: 107)
Space Weather     Full-text available via subscription   (Followers: 17, SJR: 1.341, h-index: 26)
Tectonics     Full-text available via subscription   (Followers: 16, SJR: 2.628, h-index: 96)
Water Resources Research     Full-text available via subscription   (Followers: 80, SJR: 2.661, h-index: 144)
Journal Cover Global Biogeochemical Cycles
  [SJR: 3.22]   [H-I: 136]   [15 followers]  Follow
   Full-text available via subscription Subscription journal
   ISSN (Print) 0886-6236 - ISSN (Online) 1944-9224
   Published by AGU Homepage  [17 journals]
  • Elemental composition of natural nanoparticles and fine colloids in
           European forest stream waters and their role as phosphorus carriers
    • Authors: N. Gottselig; W. Amelung, J. W. Kirchner, R. Bol, W. Eugster, S. J. Granger, C. Hernández-Crespo, F. Herrmann, J. J. Keizer, M. Korkiakoski, H. Laudon, I. Lehner, S. Löfgren, A. Lohila, C. J. A. Macleod, M. Mölder, C. Müller, P. Nasta, V. Nischwitz, E. Paul-Limoges, M. C. Pierret, K. Pilegaard, N. Romano, M. T. Sebastià, M. Stähli, M. Voltz, H. Vereecken, J. Siemens, E. Klumpp
      Abstract: Biogeochemical cycling of elements largely occurs in dissolved state, but many elements may also be bound to natural nanoparticles (NNP, 1–100 nm) and fine colloids (100-450 nm). We examined the hypothesis that the size and composition of stream water NNP and colloids vary systematically across Europe. To test this hypothesis, 96 stream water samples were simultaneously collected in 26 forested headwater catchments along two transects across Europe. Three size fractions (~1–20 nm,>20–60 nm,>60 nm) of NNP and fine colloids were identified with Field Flow Fractionation coupled to inductively coupled plasma mass-spectrometry and an organic carbon detector. The results showed that NNP and fine colloids constituted between 2±5% (Si) and 53±21% (Fe; mean ± SD) of total element concentrations, indicating a substantial contribution of particles to element transport in these European streams, especially for P and Fe. The particulate contents of Fe, Al and organic C were correlated to their total element concentrations, but those of particulate Si, Mn, P and Ca were not. The fine colloidal fractions>60 nm were dominated by clay minerals across all sites. The resulting element patterns of NNP
      PubDate: 2017-10-05T20:25:29.664278-05:
      DOI: 10.1002/2017GB005657
  • Buffering of ocean export production by flexible elemental stoichiometry
           of particulate organic matter
    • Authors: Tatsuro Tanioka; Katsumi Matsumoto
      Abstract: One of the most important factors that determine the ocean-atmosphere carbon partitioning is the sinking of particulate organic matter (POM) from the surface ocean to the deep ocean. The amount of carbon (C) removed from the surface ocean by this POM export production depends critically on the elemental ratio in POM of C to nitrogen (N) and phosphorus (P), two essential elements that limit productivity. Recent observations indicate that P:N:C in marine POM varies both spatially and temporally due to chemical, physical, and ecological dynamics. In a new approach for predicting a flexible P:C ratio, we developed a power law model with a stoichiometry sensitivity factor, which is able to relate P:C of POM to ambient phosphate concentration. The new factor is robust, measurable, and biogeochemically meaningful. Using the new stoichiometry sensitivity factor, we present a first-order estimate that P:C plasticity could buffer against a generally expected future reduction in global carbon export production by up to 5% under a future warming scenario compared to a fixed, Redfield P:C. Further, we demonstrate that our new stoichiometry model can be implemented successfully and easily in a global model to reproduce the large scale P:N:C variability in the ocean.
      PubDate: 2017-10-05T17:16:00.90392-05:0
      DOI: 10.1002/2017GB005670
  • Widespread increases in iron concentration in European and North American
    • Authors: Caroline Björnerås; Gesa A. Weyhenmeyer, Chris D. Evans, Mark O. Gessner, Hans-Peter Grossart, Külli Kangur, Ilga Kokorite, Pirkko Kortelainen, Hjalmar Laudon, Jouni Lehtoranta, Noah Lottig, Don T. Monteith, Peeter Nõges, Tiina Nõges, Filip Oulehle, Gunnhild Riise, James A. Rusak, Antti Räike, Janis Sire, Shannon Sterling, Emma S. Kritzberg
      Abstract: Recent reports of increasing iron (Fe) concentrations in freshwaters are of concern, given the fundamental role of Fe in biogeochemical processes. Still, little is known about the frequency and geographical distribution of Fe trends, or about the underlying drivers. We analyzed temporal trends of Fe concentrations across 340 water bodies distributed over 10 countries in northern Europe and North America in order to gain a clearer understanding of where, to what extent, and why Fe concentrations are on the rise. We found that Fe concentrations have significantly increased in 28% of sites, and decreased in 4%, with most positive trends located in northern Europe. Regions with rising Fe concentrations tend to coincide with those with organic carbon (OC) increases. Hence, Fe and OC increases may not be directly mechanistically linked, but may nevertheless be responding to common regional-scale drivers such as declining sulfur deposition or hydrological changes. A role of hydrological factors was supported by covarying trends in Fe and dissolved silica, as these elements tend to stem from similar soil depths. A positive relationship between Fe increases and conifer cover suggests that changing land-use and expanded forestry could have contributed to enhanced Fe export, although increases were also observed in non-forested areas. We conclude that the phenomenon of increasing Fe concentrations is widespread, especially in northern Europe, with potentially significant implications for wider ecosystem biogeochemistry, and for the current browning of freshwaters.
      PubDate: 2017-10-05T06:05:26.11961-05:0
      DOI: 10.1002/2017GB005749
  • On the role of dust‚Äźdeposited lithogenic particles for iron cycling in
           the tropical and subtropical Atlantic
    • Authors: Y. Ye; C. Völker
      Abstract: Lithogenic material deposited as dust is one of the major sources of trace metals to the ocean, particularly in the tropical and subtropical Atlantic. On the other hand, it can also act as a scavenging surface for iron. Here we studied this double role of lithogenic material in the marine iron cycle by adding a new scheme for describing particle dynamics into a global biogeochemistry and ecosystem model including particle aggregation and disaggregation of two particle size classes as well as scavenging on both organic and lithogenic particles. Considering the additional scavenging of iron on lithogenic particles, the modelled dissolved iron concentration is reduced significantly in the tropical and subtropical Atlantic, bringing the model much closer to observations. This underlines the necessity to consider the double role of dust particles as iron source and sink in studies on the marine iron cycle in high dust regions and with changing dust fluxes.
      PubDate: 2017-10-03T08:35:28.878689-05:
      DOI: 10.1002/2017GB005663
  • Oceanic uptake of oxygen during deep convection events through diffusive
           and bubble mediated gas exchange
    • Authors: Daoxun Sun; Takamitsu Ito, Annalisa Bracco
      Abstract: The concentration of dissolved oxygen (O2) plays fundamental roles in diverse chemical and biological processes throughout the oceans. The balance between the physical supply and the biological consumption controls the O2 level of the interior ocean, and the O2 supply to the deep waters can only occur through deep convection in the polar oceans. We develop a theoretical framework describing the oceanic O2 uptake during open‐ocean deep convection events and test it against a suite of numerical sensitivity experiments. Our framework allows for two predictions, confirmed by the numerical simulations. First, both the duration and the intensity of the winter‐time cooling contribute to the total O2 uptake for a given buoyancy loss. Stronger cooling leads to deeper convection and the oxygenation can reach down to deeper depths. Longer duration of the cooling period increases the total amount of O2 uptake over the convective season. Second, the bubble‐mediated influx of O2 tends to weaken the diffusive influx by shifting the air‐sea disequilibrium of O2 towards supersaturation. The degree of compensation between the diffusive and bubble‐mediated gas exchange depends on the dimensionless number measuring the relative strength of oceanic vertical mixing and the gas transfer velocity. Strong convective mixing, which may occur under strong cooling, reduces the degree of compensation so that the two components of gas exchange together drive exceptionally strong oceanic O2 uptake.
      PubDate: 2017-10-03T07:00:38.887534-05:
      DOI: 10.1002/2017GB005716
  • Controls on the Cadmium‐Phosphate Relationship in the Tropical South
    • Authors: Saeed Roshan; Jingfeng Wu, Timothy DeVries
      Abstract: The relationship between dissolved cadmium (Cd) and phosphate (PO4‐3) can elucidate a biological role for Cd in the ocean, and help to evaluate the usefulness of Cd as a tracer of past ocean circulation and nutrient distributions. Here we determine and analyze this relationship in the poorly‐studied region of the tropical South Pacific. The dissolved Cd distribution is generally similar to PO43‐, but a plot of Cd vs. PO43‐ shows a clear concavity resulting from distinct Cd:PO43‐ ratios in waters local to our transect, and in waters formed distally in higher latitudes. To determine the factors affecting the subsurface Cd:PO43‐ ratio along our transect, we used an ocean circulation model and a multi‐linear regression model to determine the preformed and regenerated components of dissolved Cd and PO43‐. We found that both the preformed and regenerated Cd:PO43‐ ratios are low in the shallow, locally‐formed water masses along the transect, and significantly higher in the deeper and older water‐masses. Overall, the regenerated:preformed Cd:PO43‐ ratio in the deep waters (>1000 m) along our transect is ~1.8:1, reflecting the basin‐wide average Cd:PO43‐ “fractionation factor” during biological uptake. However, we find a lower fractionation factor in local waters of 1.1 (± 0.6). We suggest that this locally lower biological fractionation factor is due to either the chemical speciation of Cd, or to a lower efficiency of Cd assimilation by the pico‐ and nano‐plankton species found in our study region.
      PubDate: 2017-10-03T07:00:26.885445-05:
      DOI: 10.1002/2016GB005556
  • Release of Black Carbon from Thawing Permafrost Estimated by Sequestration
           Fluxes in the East Siberian Arctic Shelf Recipient
    • Authors: Joan A. Salvadó; Lisa Bröder, August Andersson, Igor P. Semiletov, Örjan Gustafsson
      Abstract: Black carbon (BC) plays an important role in carbon burial in marine sediments globally. Yet, the sequestration of BC in the Arctic Ocean is poorly understood. Here, we assess the concentrations, fluxes and sources of soot BC (SBC) ‐the most refractory component of BC‐ in sediments from the East Siberian Arctic Shelf (ESAS), the World's largest shelf sea system. SBC concentrations in the contemporary shelf sediments range from 0.1‐2.1 mg·g‐1·dw, corresponding to 2‐12% of total organic carbon. The 210Pb‐derived fluxes of SBC (0.42‐11 g·m‐2·yr‐1) are higher or in the same range as fluxes reported for marine surface sediments closer to anthropogenic emissions. The total burial flux of SBC in the ESAS (~4,000 Gg·yr‐1) illustrates the great importance of this Arctic shelf in marine sequestration of SBC. The radiocarbon signal of the SBC shows more depleted yet also more uniform signatures (‐721 to ‐896‰; average of ‐774±62‰) than of the non‐SBC pool (‐304 to ‐728‰; average of ‐491±163‰), suggesting that SBC is coming from an, on average, 5900±300 years older and more specific source than the non‐SBC pool. We estimate that the atmospheric BC input to the ESAS is negligible (~0.6% of the SBC burial flux). Statistical source apportionment modeling suggests that the ESAS sedimentary SBC is remobilized by thawing of two permafrost carbon (PF/C) systems: surface soil permafrost (topsoil/PF; 25±8%) and Pleistocene ice complex deposits (ICD/PF; 75±8%). The SBC contribution to the total mobilized permafrost carbon (PF/C) increases with increasing distance from the coast (from 5 to 14%), indicating that the SBC is more recalcitrant than other forms of translocated PF/C. These results elucidate for the first time the key role of permafrost thaw in the transport of SBC to the Arctic Ocean. With ongoing global warming, these findings have implications for the biogeochemical carbon cycle, increasing the size of this refractory carbon pool in the Arctic Ocean.
      PubDate: 2017-10-02T06:55:20.363192-05:
      DOI: 10.1002/2017GB005693
  • ENSO driven variability of denitrification and suboxia in the Eastern
           Tropical Pacific Ocean
    • Authors: Simon Yang; Nicolas Gruber, Matt C. Long, Meike Vogt
      Abstract: The Eastern Tropical Pacific (ETP) hosts two of the world's three Oxygen Deficient Zones (ODZs), large bodies of suboxic water that are subject to high rates of water column denitrification (WCD). In the mean, these two ODZs are responsible for about 15 to 40% of all fixed N loss in the ocean, but little is known about how this loss varies in time. Here, we use a hindcast simulation with the ocean component of the NCAR Community Earth System Model over the period 1948 to 2009 to show that the El Niño‐Southern Oscillation (ENSO) drives large variations in the rates of WCD in this region. During mature La Niña (El Niño) conditions, peak denitrification rates are up to 70% higher (lower) than the mean rates. This large variability is the result of wind‐driven changes in circulation and isopycnal structure concurrently modifying the thermocline distribution of O2 and organic matter export in such a way that WCD is strongly amplified. During average La Niña (El Niño) conditions, the overall changes in ODZ structure and primarily the shoaling (deepening) of the upper boundary of both ODZs by 40 to 100 m explains 50% of the changes in WCD in the North Pacific and 94% in the South Pacific. Such a large variability of WCD in the ETP has strong implications for the assessments of trends, the balance of the marine N‐cycle and the emission of the greenhouse gas N2O.
      PubDate: 2017-09-15T16:00:58.058609-05:
      DOI: 10.1002/2016GB005596
  • Tropical dominance of N2 fixation in the North Atlantic Ocean
    • Authors: Dario Marconi; Daniel M. Sigman, Karen L. Casciotti, Ethan C. Campbell, M. Alexandra Weigand, Sarah E. Fawcett, Angela N. Knapp, Patrick A. Rafter, Bess B. Ward, Gerald H. Haug
      Abstract: To investigate the controls on N2 fixation and the role of the Atlantic in the ocean fixed nitrogen (N) budget, Atlantic N2 fixation is calculated by combining meridional nitrate fluxes across World Ocean Circulation Experiment sections with observed nitrate 15N/14N differences between northward‐ and southward‐transported nitrate. N2 fixation inputs of 27.1±4.3 Tg N/yr and 3.0±0.5 Tg N/yr are estimated north of 11°S and 24°N, respectively. That is, ~90% of the N2 fixation in the Atlantic north of 11°S occurs south of 24°N, in a region with upwelling that imports phosphorus (P) in excess of N relative to phytoplankton requirements. This suggests that, under the modern iron‐rich conditions of the equatorial and North Atlantic, N2 fixation occurs predominantly in response to P‐bearing, N‐poor conditions. We estimate a N2 fixation rate of 30.5±4.9 Tg N/yr north of 30°S, implying only 3 Tg N/yr between 30° and 11°S, despite evidence of P‐bearing, N‐poor surface waters in this region as well; this is consistent with iron limitation of N2 fixation in the South Atlantic. Since the ocean flows through the Atlantic surface in
      PubDate: 2017-09-15T16:00:39.303147-05:
      DOI: 10.1002/2016GB005613
  • The missing silica sink: revisiting the marine sedimentary Si cycle using
           cosmogenic 32Si†
    • Authors: S. Rahman; R. C. Aller, J. K. Cochran
      Abstract: Burial of biogenic silica (bSitotal) in high sedimentation rate continental margins remains highly uncertain. Cosmogenic 32Si (t1/2~140y) can be used to trace the fates of bSitotal post deposition, including as opal (bSiopal) and diagenetically altered opal (bSialtered); the latter dominantly authigenic clay (bSiclay). To determine the magnitude and form of bSitotal storage in coastal sediments, conventional operational leaches targeting bSiopal and bSialtered (including bSiclay) were modified for large scale samples necessary for measurement of 32Si. 32Si activity was used to estimate total biogenic silica burial (bSitotal = bSiopal+bSialtered) in several depositional settings:Gulf of Papua, Gulf of Mexico, Long Island Sound, and in the previously studied Amazon‐Guianas deltaic system. In subtropical and temperate regions, 32Si was detected in both traditional biogenic silica leaches (bSiopal) and residual authigenic clays. Traditional bSiopal and modified operational leaches designed to target the most reactive authigenic silicates (~bSialtered) consistently underestimate authigenic clay formation (bSiclay) and thus the magnitude of bSitotal burial in temperate coastal zones and subtropical deltas by 2–4 fold. In tropical deltas, 32Si activities in the residua≳l fraction after removal of bSiopal demonstrate rapid and almost complete alteration of initial bSiopal to new forms, most likely bSiclay. Globally, 4.5–4.9 Tmol/y Si may be trapped in marine nearshore deposits as rapidly formed clay (bSiclay), ≳100% of the “missing silica sink” in the marine silica budget.
      PubDate: 2017-09-15T16:00:34.491331-05:
      DOI: 10.1002/2017GB005746
  • Issue Information
    • Pages: 1367 - 1367
      Abstract: No abstract is available for this article.
      PubDate: 2017-10-10T21:38:42.992614-05:
      DOI: 10.1002/gbc.20457
  • Eddy-induced carbon transport across the Antarctic Circumpolar Current
    • Authors: Sébastien Moreau; Alice Della Penna, Joan Llort, Ramkrushnbhai Patel, Clothilde Langlais, Philip W. Boyd, Richard J. Matear, Helen E. Phillips, Thomas W. Trull, Bronte Tilbrook, Andrew Lenton, Peter G. Strutton
      First page: 1368
      Abstract: The implications of a mesoscale eddy for relevant properties of the Southern Ocean carbon cycle is examined with in situ observations. We explored carbon properties inside a large (~190 km diameter) cyclonic eddy that detached from the Subantarctic Front (SAF) south of Tasmania in March 2016. Based on remote sensing, the eddy was present for ~2 months in the Subantarctic Zone (SAZ), an important region of oceanic carbon dioxide (CO2) uptake throughout the annual cycle and carbon subduction (i.e., where mode and intermediate waters form), before it was re-absorbed into the SAF. The eddy was sampled during the middle of its life, 1 month after it spawned. Comparatively, the eddy was ~3°C colder, 0.5 PSU fresher and less biologically productive than surrounding SAZ waters. The eddy was also richer in dissolved inorganic carbon (DIC) and had lower saturation states of aragonite and calcite than the surrounding SAZ waters. As a consequence, it was a strong source of CO2 to the atmosphere (with fluxes up to +25 mmol C m-2 d-1). Compared to the SAF waters, from which it originated, DIC concentration in the eddy was ~20 μmol kg-1 lower, indicating lateral mixing, small-scale recirculation or eddy stirring with lower-DIC SAZ waters by the time the eddy was observed. As they are commonly spawned from the Antarctic Circumpolar Current (ACC), and as 50% of them decay in the SAZ (the rest being re-absorbed by the SAF-N), these types of eddies may represent a significant south-north transport pathway for carbon across the ACC and may alter the carbon properties of SAZ waters.
      PubDate: 2017-09-07T18:47:09.386915-05:
      DOI: 10.1002/2017GB005669
  • A Model for CH2D2 and 13CH3D as Complementary Tracers for the Budget of
           Atmospheric CH4
    • Authors: Mojhgan A. Haghnegahdar; Edwin A. Schauble, Edward D. Young
      First page: 1387
      Abstract: We present a theoretical model to investigate the potential of 13CH3D and 12CH2D2, the doubly substituted mass-18 isotopologues of methane, as tools for tracking atmospheric methane sources and sinks. We use electronic structure methods to estimate kinetic isotope fractionations associated with the major sink reactions of methane in air (reactions with OH and Cl radicals), and combine literature data with reconnaissance measurements of the relative abundances of 13CH3D and 12CH2D2 to estimate the compositions of the largest atmospheric sources. This model atmospheric budget is investigated with a simplified box model in which we explore both steady state and dynamical (non-steady state) conditions triggered by changes in emission or sink fluxes. The steady-state model predicts that sink reactions will generate a marked (>100‰) clumped isotope excess in atmospheric Δ12CH2D2 relative to the net source composition. 12CH2D2 measurements may thus be useful for tracing both atmospheric source and sink fluxes. The effect of sinks on Δ13CH3D is much less pronounced, indicating that 13CH3D in air will give a more focused picture of the source composition.
      PubDate: 2017-07-27T10:15:27.482409-05:
      DOI: 10.1002/2017GB005655
  • Isotopic ratios of tropical methane emissions by atmospheric measurement.
    • Authors: R. Brownlow; D. Lowry, R.E. Fisher, J.L. France, M. Lanoisellé, B. White, M.J. Wooster, T. Zhang, E.G. Nisbet
      First page: 1408
      Abstract: Tropical methane sources are an important part of the global methane budget and include natural wetlands, rice agriculture, biomass burning, ruminants, fossil fuels and waste. δ13CCH4 can provide strong constraints on methane source apportionment. For example, tropical wetlands in this study give δ13CCH4 values between -61.5 ±2.9 ‰ and -53.0 ±0.4 ‰ and in general are more enriched in 13C than temperate and boreal wetlands. However, thus far, relatively few measurements of δ13CCH4 in methane-enriched air have been made in the tropics. In this study samples have been collected from tropical wetland, rice, ruminant, and biomass burning emissions to the atmosphere. Regional isotopic signatures vary greatly as different processes and source material affect methane signatures. Measurements were made to determine bulk source inputs to the atmosphere, rather than to study individual processes. These measurements provide inputs for regional methane budget models, to constrain emissions with better source apportionment.
      PubDate: 2017-09-04T04:55:25.081605-05:
      DOI: 10.1002/2017GB005689
  • Stirring up the biological pump: Vertical mixing and carbon export in the
           Southern Ocean
    • Authors: Michael R. Stukel; Hugh W. Ducklow
      First page: 1420
      Abstract: The biological carbon pump (BCP) transports organic carbon from the surface to the ocean's interior via sinking particles, vertically migrating organisms, and passive transport of organic matter by advection and diffusion. While many studies have quantified sinking particles, the magnitude of passive transport remains poorly constrained. In the Southern Ocean weak thermal stratification, strong vertical gradients in particulate organic matter, and weak vertical nitrate gradients suggest that passive transport from the euphotic zone may be particularly important. We compile data from seasonal time-series at a coastal site near Palmer Station, annual regional cruises in the Western Antarctic Peninsula (WAP), cruises throughout the broader Southern Ocean, and SOCCOM autonomous profiling floats to estimate spatial and temporal patterns in vertical gradients of nitrate, particulate nitrogen (PN), and dissolved organic carbon (DOC). Under a steady-state approximation, the ratio of ∂PN/∂z to ∂NO3-/∂z suggests that passive transport of PN may be responsible for removing 46% (37%-58%) of the nitrate introduced into the surface ocean of the WAP (with DOM contributing an additional 3-6%) and for 23% (19%-28%) of the BCP in the broader Southern Ocean. A simple model parameterized with in situ nitrate, PN, and primary production data suggested that passive transport was responsible for 54% of the magnitude of the BCP in the WAP. Our results highlight the potential importance of passive transport (by advection and diffusion) of organic matter in the Southern Ocean, but should only be considered indicative of high passive transport (rather than conclusive evidence) due to our steady-state assumptions.
      PubDate: 2017-08-31T05:16:30.18627-05:0
      DOI: 10.1002/2017GB005652
  • Evaluating the classical versus an emerging conceptual model of peatland
           methane dynamics
    • Authors: Wendy H. Yang; Gavin McNicol, Yit Arn Teh, Katerina Estera, Tana E. Wood, Whendee L. Silver
      First page: 1435
      Abstract: Methane (CH4) is a potent greenhouse gas that is both produced and consumed in soils by microbially mediated processes sensitive to soil redox. We evaluated the classical conceptual model of peatland CH4 dynamics—in which the water-table position determines the vertical distribution of methanogenesis and methanotrophy—versus an emerging model in which methanogenesis and methanotrophy can both occur throughout the soil profile due to spatially heterogeneous redox and anaerobic CH4 oxidation. We simultaneously measured gross CH4 production and oxidation in situ across a microtopographical gradient in a drained temperate peatland and ex situ along the soil profile, giving us novel insight into the component fluxes of landscape-level net CH4 fluxes. Net CH4 fluxes varied among landforms (p< 0.001), ranging from 180.3 ± 81.2 mg-C m-2 d-1 in drainage ditches to -0.7 ± 1.2 mg-C m-2 d-1 in the highest landform. Contrary to prediction by the classical conceptual model, variability in methanogenesis alone drove the landscape-level net CH4 flux patterns. Consistent with the emerging model, freshly-collected soils from above the water table produced CH4 within anaerobic microsites. Even in soil from beneath the water table, gross CH4 production was best predicted by the methanogenic fraction of carbon mineralization, an index of highly reducing microsites. We measured low rates of anaerobic CH4 oxidation, which may have been limited by relatively low in situ CH4 concentrations in the hummock/hollow soil profile. Our study revealed complex CH4 dynamics better represented by the emerging heterogeneous conceptual model than the classical model based on redox strata.
      PubDate: 2017-08-30T02:06:32.171312-05:
      DOI: 10.1002/2017GB005622
  • Distribution of dissolved zinc in the western and central subarctic North
    • Authors: T. Kim; H. Obata, J. Nishioka, T. Gamo
      First page: 1454
      Abstract: We investigated the biogeochemical cycling of dissolved zinc (Zn) in the western and central subarctic North Pacific during the GEOTRACES GP 02 cruise. The relationship between dissolved Zn and silicate in the subarctic North Pacific plotted as a concave curve. Values of Zn* were strongly positive in the intermediate waters (26.6–27.5 σθ) of both the western and the central subarctic North Pacific. There was a distinct kink in the relationship between dissolved Zn and soluble reactive phosphorus (SRP) at the transition from shallow to intermediate water, which is similar to what has been reported for other open oceans. The high Zn:SRP ratio and high Zn* in the intermediate water suggests that intermediate water masses play an important role in the decoupling of dissolved Zn and silicate in the subarctic North Pacific, which implies that the biogeochemical processes that control dissolved Zn and silicate in the intermediate water are different from those in other oceanic regions.
      PubDate: 2017-09-09T06:20:22.818823-05:
      DOI: 10.1002/2017GB005711
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