Showing papers in "Global Biogeochemical Cycles in 1988"
TL;DR: In this paper, the authors identify and evaluate several constraints on the budget of atmospheric methane, its sources, sinks and residence time, and construct a list of sources and sinks, identities, and sizes.
Abstract: Methane is the most abundant organic chemical in Earth's atmosphere, and its concentration is increasing with time, as a variety of independent measurements have shown. Photochemical reactions oxidize methane in the atmosphere; through these reactions, methane exerts strong influence over the chemistry of the troposphere and the stratosphere and many species including ozone, hydroxyl radicals, and carbon monoxide. Also, through its infrared absorption spectrum, methane is an important greenhouse gas in the climate system. We describe and enumerate key roles and reactions. Then we focus on two kinds of methane production: microbial and thermogenic. Microbial methanogenesis is described, and key organisms and substrates are identified along with their properties and habitats. Microbial methane oxidation limits the release of methane from certain methanogenic areas. Both aerobic and anaerobic oxidation are described here along with methods to measure rates of methane production and oxidation experimentally. Indicators of the origin of methane, including C and H isotopes, are reviewed. We identify and evaluate several constraints on the budget of atmospheric methane, its sources, sinks and residence time. From these constraints and other data on sources and sinks we construct a list of sources and sinks, identities, and sizes. The quasi-steady state (defined in the text) annual source (or sink) totals about 310(±60) × 1012 mol (500(±95) × 1012 g), but there are many remaining uncertainties in source and sink sizes and several types of data that could lead to stronger constraints and revised estimates in the future. It is particularly difficult to identify enough sources of radiocarbon-free methane.
1,513 citations
TL;DR: In this paper, a variety of Minnesota peatlands were measured during May, June, and August 1986, including forested and unforested ombrotrophic bogs and minerotrophic fens in and near the U.S. Department of Agriculture Marcell Experimental Forest.
Abstract: Northern (>40°N) wetlands have been suggested as the largest natural source of methane (CH4) to the troposphere. To refine our estimates of source strengths from this region and to investigate climatic controls on the process, fluxes were measured from a variety of Minnesota peatlands during May, June, and August 1986. Sites included forested and unforested ombrotrophic bogs and minerotrophic fens in and near the U.S. Department of Agriculture Marcell Experimental Forest and the Red Lake peatlands. Late spring and summer fluxes ranged from 11 to 866 mg CH4 m−2 d−1, averaging 207 mg CH4 m−2 d−1 overall. At Marcell Forest, forested bogs and fen sites had lower fluxes (averages of 77 ± 21 mg CH4 m−2 d−1 and 142 ± 19 mg CH4 m−2 d−1) than open bogs (average of 294 ± 30 mg CH4 m−2 d−1). In the Red Lake peatland, circumneutral fens, with standing water above the peat surface, produced more methane than acid bog sites in which the water table was beneath the moss surface (325 ± 31 and 102 ± 13 mg CH4 m−2 d−1, respectively). Peat temperature was an important control. Methane flux increased in response to increasing soil temperature. For example, the open bog in the Marcell Forest with the highest CH4 flux exhibited a 74-fold increase in flux over a three-fold increase in temperature. We estimate that the methane flux from all peatlands north of 40° may be on the order of 70 to 90 Tg/yr though estimates of this sort are plagued by uncertainties in the areal extent of peatlands, length of the CH4 producing season, and the spatial and temporal variability of the flux.
404 citations
TL;DR: In this article, the carbon and hydrogen isotope fractionation factors were estimated by fitting methane concentration, delta C{sup 13-CH{sub 4} and delta-D-CH-sub 4 data with depth distributions predicted by an open system, steady state model.
Abstract: Methane oxidation in the anoxic sediments of Skan Bay, Alaska resulted in fractionation of carbon and hydrogen isotopes in methane. Isotope fractionation factors were estimated by fitting methane concentration, delta C{sup 13}-CH{sub 4} and delta-D-CH{sub 4} data with depth distributions predicted by an open system, steady state model. Assuming that molecular diffusion coefficients for C{sup 12}-CH{sub 4}, C{sup 13}-CH{sub 4}, and C{sup 12}-CH{sub 4}D are identical, the predicted fractionation factors were 0.0088 + or{minus}0.0013 and 1.157 + or{minus}0.023 for carbon and hydrogen isotopes, respectively. If aqueous diffusion coefficients for the different isotopic species of methane differ significantly, the predicted fractionation factors are larger by an amount proportional to the diffusion isotope effect. 50 refs., 5 figs.
339 citations
279 citations
TL;DR: In this article, seasonal measurements of net methane flux were made at permanent sites representing important components of arctic tundra, including Eriophorum tussocks, intertussock depressions, moss-covered areas, and Carex stands.
Abstract: Seasonal measurements of net methane flux were made at permanent sites representing important components of arctic tundra. The sites include Eriophorum tussocks, intertussock depressions, moss-covered areas, and Carex stands. Methane fluxes showed high diel, seasonal, intra site, and between site variability. Eriophorum tussocks and Carex dominated methane release to the atmosphere, with mean annual net methane fluxes of 8.05 + or{minus}2.50 g CH{sub 4}/sq m and 4.88 + or{minus}0.73 g CH{sub 4}/sq m, respectively. Methane fluxes form the moss sites and intertussock depressions were much lower. Over 90% of the mean annual methane flux from the Eriophorum, intertussock depressions, and Carex sites occurred between thaw and freeze-up. Some 40% of the mean annual methane flux from the moss sites occurred during winter. Composite methane fluxes for tussock tundra and Carex-dominated wet meadow tundra environments were produced by weighting measured component fluxes according to areal coverage. Tussock and wet meadow tundra account for an estimated global methane emission of 19-33 Tg/yr. 39 refs., 7 figs., 2 tabs.
239 citations
TL;DR: Esaias et al. as mentioned in this paper solved the equations describing marine plankton dynamics for the climatological oceanographic conditions during the month of May in the North Atlantic, and predicted the geographical distribution of phytoplankton, zooplankston and limiting nutrient (nitrate) concentration in the surface mixed layer of the ocean from historical mixed layer depth and total nutrient made locally available to the plankton ecosystem by convective mixing.
Abstract: Mathematical equations describing marine plankton dynamics are solved for the climatological oceanographic conditions during the month of May in the North Atlantic. Geographical distributions of phytoplankton, zooplankton and limiting nutrient (nitrate) concentration in the surface mixed layer of the ocean are predicted from historical mixed layer depth and the total nutrient made locally available to the plankton ecosystem by convective mixing. The effects of major ocean currents are parameterized in the model through the geographic distribution of nitrate and its vertical gradient. Major upwelling and downwelling circulations control the proximity of high nutrient concentrations to the surface. Model solution of the phytoplankton field with 1° longitude and latitude grid resolution is compared to a recently produced composite of Coastal Zone Color Scanner images of surface chlorophyll in the North Atlantic during May 1979 [W.E. Esaias et al., 1986]. Large-scale chlorophyll patterns seen in the CZCS composite can be explained as transition zones in the supply of plant nutrients to the surface layer by vertical mixing or localities of light limitation of phytoplankton growth by a deep mixed layer.
145 citations
TL;DR: In this paper, the authors examined the causes of anoxia in regions such as the Eastern Mediterranean, which have exchange over sills with adjacent basins, and showed that the concentration of the limiting nutrient is the major determinant of deep oxygen levels.
Abstract: We examine the causes of anoxia in regions such as the Eastern Mediterranean, which have exchange over sills with adjacent basins. Box models show that the concentration of the limiting nutrient is the major determinant of deep oxygen levels. The most effective way of increasing nutrient concentrations to the point where anoxia occurs is to change the flow pattern across the sills ventilating the basins. With a sill exchange pattern such as that in the present Strait of Sicily, it is difficult to obtain anoxia in the Eastern Mediterranean without also driving the Western Mediterranean to low oxygen and high nutrient levels. Episodes of anoxia in the Eastern Mediterranean are associated with a freshening of surface waters. A reversal in flow directions, presumably resulting from the observed freshening, will inevitably lead to anoxia associated with increased sediment burial rates of the limiting nutrient and will leave the Western Mediterranean largely unaffected, in keeping with the observational evidence.
138 citations
TL;DR: Sediment traps deployed at two sites in the equatorial Pacific during and following the 1982-1983 El Nino southern oscillation demonstrate the biological effects of this event as mentioned in this paper.
Abstract: Sediment traps deployed at two sites in the equatorial Pacific during and following the 1982-1983 El Nino southern oscillation (ENSO) demonstrate the biological effects of this event. Biogenic particle fluxes for a site 1° north of the equator were at least a factor of 2 lower during a 3 month period of intense ENSO influence compared to fluxes recorded at any other time during a 28-month period beginning in December 1982. These low particle fluxes reflect the expected decrease in primary production in response to the ENSO event. Surprisingly, the biogenic particle fluxes measured at the second site, 11°N, were anomalously high during this same ENSO-affected period. The apparent increase in productivity north of the equator seems to be a consequence of enhanced flow of the North Equatorial Countercurrent (NECC) and the associated doming of the shallow thermocline. The observed temporal variability in magnitude of the biogenic particle flux was accompanied by compositional changes in the biogenic components. The period of high carbon flux at the 11°N site was a time of exceptional opal flux, while the particle flux during the period of low carbon flux observed at 1°N during the ENSO was depleted in opal. These patterns appear to reflect the dominance of diatom productivity relative to coccolithophorid productivity during conditions of greater nutrient availability.
136 citations
TL;DR: In this paper, the authors examined the hypothesis that global scale episodes of anoxia such as occurred in the Cretaceous are due to global scale events such as hurricanes and floods.
Abstract: We examine the hypothesis that global scale episodes of anoxia such as occurred in the Cretaceous are due to
135 citations
TL;DR: The measurement of dissolved rare earth elements (REE) in the surface waters, water column of anoxic basins, and pore waters in Chesapeake Bay has provided new insights to the biogeochemistry and estuarine chemistry of REE as mentioned in this paper.
Abstract: The measurement of dissolved rare earth elements (REE) in the surface waters, water column of anoxic basins, and pore waters in Chesapeake Bay has provided new insights to the biogeochemistry and estuarine chemistry of REE. All dissolved REE from the riverine source show large-scale removal in the lower salinity zone (0-10‰). The shale-normalized pattern of dissolved Susquehanna River water is opposite in form to that of surface sediments in the Bay. The former is enriched in heavy REE (HREE) while the latter are enriched in light REE (LREE). Neither component has a flat pattern normally assumed for river- transported REE to the ocean. The dissolved LREE (i.e., La, Ce, Nd, Sm, and Eu) are enriched 3 to 9 times) in the oxygen-depleted deep waters over their concentrations in the oxic surface waters. In contrast, HREE (Er, Yb, and Lu) are slightly depleted. All REE concentrations in the two surface (0-2 cm) pore waters are greatly enriched (8-17 times; 43 times for Ce) relative to oxygen-depleted bottom waters and have relative abundances opposite to those of their sediments. While Ce has a positive anomaly in the pore waters, negative anomalies exist in the oxygen-depleted bottom waters. The REE are participating in a set of complex biogeochemical cycles within the water column and surface sediments. Fractionation of REE during these cycles leads to the preferential enrichment of LREE in the seasonally oxygen-depleted bottom waters. It is proposed that this fractionation is coupled to redox cycles of Mn and Fe and the interaction of dissolved REE with suspended particles and surficial sediments.
126 citations
TL;DR: In this article, the potential rates of methane production and carbon dioxide production were measured on 11 dates in 1986 in peat from six plant communities typical of moss-dominated peatlands in the Appalachian Mountains.
Abstract: Potential rates of methane production and carbon dioxide production were measured on 11 dates in 1986 in peat from six plant communities typical of moss-dominated peatlands in the Appalachian Mountains. Annual methane production ranged from 2.7 to 17.5 mol/sq m, and annual carbon dioxide production ranged from 30.6 to 79.0 mol/sq m. The wide range in methane production values among the communities found within a single peatland indicates that obtaining one production value for a peatland may not be appropriate. Low temperature constrained the potential for methane production in winter, while the chemical quality of the peat substrate appears to control methane production in the summer. Methane oxidation was measured throughout the peat profile to a depth of 30 cm. Values for methane oxidation ranged from 0.08 to 18.7 microM/hr among the six plant communities. Aerobic methane-oxidizing bacteria probably mediated most of the activity. On a daily basis during the summer, between 11 and 100% of the methane produced is susceptible to oxidation within the peat column. Pools of dissolved methane and dissolved carbon dioxide in pore waters were less than 0.2 and less than 1.0 mol/sq m, respectively, indicating that methane does not accumulate in the pore waters. Peatlandsmore » have been considered as an important source of biologically produced methane. Despite the high rates of methane production, the high rates of methane oxidation dampen the potential emission of methane to the atmosphere. 41 refs., 7 figs., 4 tabs.« less
TL;DR: In this article, it was shown that ebullitive methane fluxes are depleted in C{sup 13}-CH{sub 4} relative to fluxes transported via molecular diffusion or through plants, as zones of Csup 13-enriching microbial methane oxidation are bypassed.
Abstract: Methane carbon isotopic composition ranged from {minus}76.9 to {minus}62.6{per thousand} in a tidal freshwater estuary (the White Oak River, North Carolina, US) with the site specific seasonal variations ranging from 6 to 10{per thousand}. During warmer months, tidally induced bubble ebullition actively transported this methane to the atmosphere. At two sites, these seasonally varying fluxes ranged from 1.2 + or{minus}0.3 to 1.3 + or{minus}0.3 mol CH{sub 4}/sq m/yr with flux-weighted average isotopic compositions at two sites of {minus}66.3 + or{minus}0.4 and {minus}69.5 + or{minus}0.6{per thousand}. The carbon isotopic composition of naturally released bubbles was shown to be indistinguishable from the sedimentary methane bubble reservoir at three sites, leading to the conclusion that isotopic fractionation did not occur during the ebullition of methane. The hypothesis was developed that ebullitive methane fluxes are depleted in C{sup 13}-CH{sub 4} relative to fluxes transported via molecular diffusion or through plants, as zones of C{sup 13}-enriching microbial methane oxidation are bypassed.
TL;DR: In this article, a high-resolution global data base of animal population densities and associated methane emission is presented, which includes cattle and dairy cows, water buffalo, sheep, goats, camels, pigs, horses and caribou.
Abstract: We present a high-resolution global data base of animal population densities and associated methane emission. Statistics on animal populations from the Food and Agriculture Organization and other sources have been compiled. Animals were distributed using a 1° resolution data base of countries of the world and a 1° resolution data base of land use. The animals included are cattle and dairy cows, water buffalo, sheep, goats, camels, pigs, horses and caribou. Published estimates of methane production from each type of animal have been applied to the animal populations to yield a global distribution of annual methane emission by animals. There is large spatial variability in the distribution of animal populations and their methane emissions. Emission rates greater than 5000 kg CH4 km−2 yr−1 are found in small regions such as Bangladesh, the Benelux countries, parts of northern India, and New Zealand. Of the global annual emission of 75.8 Tg CH4 for 1984, about 55% is concentrated between 25°N and 55°N, a significant contribution to the observed north-south gradient of atmospheric methane concentration. A magnetic tape of the global data bases is available from the authors.
TL;DR: In this paper, the mean delta C{sup 13} values for peat bogs and Alaskan tundra are reported, with a flux-weighted global average delta-C{sup13} value of {minus}59 + or{minus}6{per thousand} for methane released from wetlands, a major natural methane source.
Abstract: Measurements of the delta-C{sup 13} of methane released from tropical, temperate, and arctic wetland sites are reported. The mean delta C{sup 13} values (relative to PDB carbonate standard) for peat bogs and Alaskan tundra are {minus}53 + or{minus}8, {minus}66 + or{minus}5 and {minus}64 + or{minus}5{per thousand}, respectively. These measurements combined with methane flux estimates yield a flux-weighted global average delta-C{sup 13} value of {minus}59 + or{minus}6{per thousand} for methane released from wetlands, a major natural methane source. The agreement between the measured delta-C{sup 13} for methane emitted from wetlands and the calculated steady state value of approximately {minus}6{per thousand} for the delta-C{sup 13} of preindustrial methane sources suggests that methane was predominantly produced biogenically in the preindustrial era. The industrial era time rate of change of the delta-C{sup 13} of the global methane flux is calculated from estimates of the growth rate of the major anthropogenically derived methane sources and the C{sup 13} composition of these sources, and compared to the measured change in the delta-C{sup 13} of methane during the last 300 years. Based on these results, it is estimated that 13 + or{minus}8% of the current global methane flux is derived abiogenically from natural gas and biomass burning,more » whereas the remainder is derived biogenically primarily from wetlands, rice paddies, and livestock. 40 refs., 5 figs., 2 tabs.« less
TL;DR: In this article, the stable isotopic composition of sedimentary methane was measured at four locations in the Florida Everglades system and individual estimates of methane flux ranged over more than 3 orders of magnitude, from about 0.001 to 2.6 g CH4 m−2 d−1.
Abstract: Methane flux and the stable isotopic composition of sedimentary methane were measured at four locations in the Florida Everglades system. Individual estimates of methane flux ranged over more than 3 orders of magnitude, from about 0.001 to 2.6 g CH4 m−2 d−1. Significant interstation differences in total methane flux were also observed and are judged most likely attributable to differences in the size and spacing of emergent aquatic vegetation, and possibly differences in the type (i.e., vascular plant versus algal) of organic matter incorporated into the sediments. On the basis of measurements presented here and by other investigators, the Everglades system appears to be a relatively weak source of atmospheric methane, probably contributing less than 0.5 Tg CH4 yr−1. Emergent aquatic plants appear to be capable of indirectly affecting the stable isotopic composition of sedimentary methane by stimulating methane oxidation via root aeration. A significant positive correlation between δD-CH4 and δ13C-CH4 was observed for samples collected from sediments covered by tall, dense stands of emergent plants. In contrast, a significant negative correlation between the δD and δ13C of sedimentary methane was observed for samples collected at an open water site where ebullition dominated methane transfer to the atmosphere. The mean δ13C of sedimentary methane samples measured in the Everglades system (mean δ13C =−61.7‰, s.d. = 3.6‰, n = 51) is not significantly different from the estimated average δ13C of all natural sources (−58.3‰). The mean δD of Everglades sedimentary methane (mean δ D = −293‰, s.d. = 14‰, n = 50) appears to be slightly less D-depleted than the estimated average methane (δD =−360 ± 30‰) from all sources.
TL;DR: In this article, a dynamical model of the Pleistocene ice ages is presented, which incorporates many of the qualitative ideas advanced recently regarding the possible role of ocean circulation, chemistry, temperature, and productivity in regulating long-term atmospheric carbon dioxide variations.
Abstract: A dynamical model of the Pleistocene ice ages is presented, which incorporates many of the qualitative ideas advanced recently regarding the possible role of ocean circulation, chemistry, temperature, and productivity in regulating long-term atmospheric carbon dioxide variations. This model involves one additional term (and free parameter) beyond that included in a previous model (Saltzman and Sutera, 1987), providing the capacity for an asymmetric response. It is shown that many of the main features exhibited by the delta(O-18)-derived ice record and the Vostok core/delta(C-13)-derived carbon dioxide record in the late Pleistocene can be deduced as a free oscillatory solution of the model.
TL;DR: In this article, a direct measurement of CH4 flux from wetland ecosystems of south Florida demonstrates that freshwater wet prairies and inundated sawgrass marsh are the dominant sources of atmospheric CH4 in the region.
Abstract: Direct measurement of methane (CH4) flux from wetland ecosystems of south Florida demonstrates that freshwater wet prairies and inundated sawgrass marsh are the dominant sources of atmospheric CH4 in the region. Fluctuations in soil moisture are an important environmental factor controlling both seasonal and interannual fluctuations in CH4 emissions from undisturbed wetlands. Land use estimates for 1900 and 1973 were used to calculate regional CH4 flux. Human settlement in south Florida has modified wetland sources of CH4, reducing the natural prairies and marsh sources by 37%. During the same period, impoundments and disturbed wetlands were created which produce CH4 at rates approximately 50% higher than the natural wetlands they replaced. Preliminary estimates of urban and ruminant sources of CH4 based on extrapolation from literature data indicate these sources may now contribute approximately 23% of the total regional source. We estimate that the integrated effects of urban and agricultural development in south Florida between 1900 and 1973 resulted in a 26% enhancement in CH4 flux to the troposphere.
TL;DR: In this paper, the average dissolved methane concentration for an organic-rich forested swamp was the highest of any site at 12.6 microM; however, the calculated diffusive flux from this location, 2.88 mol CH{sub 4}/sq m/yr, was diminished by an extensive plant canopy that sheltered the air-water interface from the wind.
Abstract: Diffusion of methane across the air-water interface from several wetland environments in south Florida was estimated from measured surface water concentrations using an empirically derived gas exchange model. The flux from the Everglades sawgrass marsh system varied widely, ranging from 0.18 + or{minus}0.21 mol CH{sub 4}/sq m/yr for densely vegetated regions to 2.01 + or{minus}0.88 for sparsely vegetated, calcitic mud areas. Despite brackish salinities, a strong methane flux, 1.87 + or{minus}0.63 mol CH{sub 4}/sq m/yr, was estimated for an organic-rich mangrove pond near Florida Bay. The diffusive flux accounted for 23, 36, and 13% of the total amount of CH{sub 4} emitted to the atmosphere from these environments, respectively. The average dissolved methane concentration for an organic-rich forested swamp was the highest of any site at 12.6 microM; however, the calculated diffusive flux from this location, 2.57 + or{minus}1.88 mol CH{sub 4}/sq m/yr, was diminished by an extensive plant canopy that sheltered the air-water interface from the wind. The mean diffusive flux from four freshwater lakes, 0.77 + or{minus}0.73 mol CH{sub 4}/sq m/yr, demonstrated little temperature dependence. The mean diffusive flux for an urbanized, subtropical estuary was 0.06 + or{minus}0.05 mol CH{sub 4}/sq m/yr.
TL;DR: In this paper, the authors measured the ratio of C{sup 13}/C{sup 12} in CH{sub 4} for termites from a variety of sources in tropical Kenya.
Abstract: Ratios of C{sup 13}/C{sup 12} have been measured in methane from a variety of sources in tropical Kenya. Ranges of delta-C{sup 13} in CH{sub 4} for termites (most values range from {minus}56 to {minus}64{per thousand}, one is at {minus}44{per thousand}), one is at approximately {minus}73{per thousand}, rice paddies (range {minus}57 to {minus}63{per thousand}), and wetlands (range-45 to {minus}50{per thousand} for Lake Baringo, approximately {minus}55{per thousand} in the Moloi River, approximately {minus}62{per thousand} and approximately {minus}31{per thousand} in two swamp areas) are presented. The data are interpreted with the help of additional measurements of delta-C{sup 13} of CO{sub 2} gas, and organic carbon in plant material, termite bodies, and termite fungus combs. The implications of these findings are related to the problem of studying the atmospheric methane budget. 40 refs., 2 figs. 5 tabs.
TL;DR: A comprehensive water balance study in a New England salt marsh reveals that evapotranspiration and infiltration during tidal inundation and precipitation are the dominant hydrological processes in the sediment on a marsh-wide scale as mentioned in this paper.
Abstract: Rates of gas emissions and solute fluxes from salt marsh sediments are influenced by sediment hydrology. A comprehensive water balance study in a New England salt marsh reveals that evapotranspiration and infiltration during tidal inundation and precipitation are the dominant hydrological processes in the sediment on a marsh-wide scale. Water loss by drainage through the sediment into tidal creeks is effectively limited to within 10 m to 15 m of the creek bank; however, drainage is responsible for 40% of the water loss within 10 m of the creek during nonflooding, neap tide periods. The rate and extent of advective transport by pore water drainage is controlled by the topography of the marsh surface. Tidal fluctuations in creek level drive larger, oscillating water fluxes across the creek bank, which results in a dispersive transport of the solutes in the sediment, but these fluxes are attenuated in the first meter. Convexities in the marsh surface, for example, the crests of the creek banks, are the location of maximum water loss by drainage and probably the highest degree of desaturation and aeration, which can, in turn, increase gas emissions locally. The spring-neap tide cycle modulates wetting and drying of the sediment and, by inference, gas emissions in the interior of the marsh. The limited extent of solute transport by drainage implies that an as yet undescribed mechanism is responsible for controlling the concentration of conservative solutes in salt marshes.
TL;DR: In this paper, the authors measured biogenic soil emissions of nitric oxide (NO) and nitrous oxide (N2O) before and after a controlled burn conducted in a chaparral ecosystem on June 22, 1987.
Abstract: Measurements of biogenic soil emissions of nitric oxide (NO) and nitrous oxide (N2O) before and after a controlled burn conducted in a chaparral ecosystem on June 22, 1987, showed significantly enhanced emissions of both gases after the burn. Mean NO emissions from heavily burned and wetted (to simulate rainfall) sites exceeded 40 ng N/sq m s, and increase of 2 to 3 compared to preburn wetted site measurements. N2O emissions from burned and wetted sites ranged from 9 to 22 ng N/sq m s. Preburn N2O emissions from these wetted sites were all below the detection level of the instrumentation, indicating a flux below 2 ng N/sq m s. The flux of NO exceeded the N2O flux from burned wetted sites by factors ranging from 2.7 to 3.4. These measurements, coupled with preburn and postburn measurements of ammonium and nitrate in the soil of this chaparral ecosystem and measurements of NO and N2O emissions obtained under controlled laboratory conditions, suggest that the postfire enhancement of NO and N2O emissions is due to production of these gases by nitrifying bacteria.
TL;DR: In this article, the authors studied the emission of methane in the central central regions of one freshwater and three meromictic, alkaline saline lakes, and the range of emissions was 0.004 to 2.916 mmol/sq m/hr (n=41).
Abstract: Methane emission to the atmosphere was studied in the deepest, central (pelagic) regions of one freshwater and three meromictic, alkaline saline lakes. The range of methane emissions was 0.004 to 2.916 mmol/sq m/hr (n=41). Outward flux was dominated by bubble ebullition only in the freshwater lake. Diffusive gas exchange was the sole mechanism of transfer in the meromictic lakes, and flux from these lakes was equivalent to or lower than that from the freshwater lake during its periods of ebullition. A comparison of measured flux with flux calculated using a model of gas exchange in Mono Lake suggested that floating chambers provide reasonable estimates of the magnitude of methane emissions from diffusion-dominated systems. 43 refs., 4 figs., 2 tabs.
TL;DR: In this paper, the delta-C{sup 13} stable carbon isotopic composition of methane collected in bubbles from the submerged soils of specific environments within the Everglades wetland in southern Florida was analyzed.
Abstract: The delta-C{sup 13} stable carbon isotopic composition of methane collected in bubbles from the submerged soils of specific environments within the Everglades wetland in southern Florida varied from {minus}70{per thousand} to {minus}63{per thousand} across the system while organic carbon in the soils and dominant plants varied from {minus}28{per thousand} to {minus}25{per thousand}. A methane isotopic budget based upon the soil bubble isotope data and published methane flux measurements predicted a flux of isotopic composition {minus}65{per thousand}, a value 5-10{per thousand} more depleted in C{sup 13} than the isotopic composition of methane emanating to the atmosphere. Emergent aquatic plants, which are known to be active methane transporters between soil and atmosphere in this ecosystem, were found to transport methane of delta-C{sup 13} content up to 12{per thousand} different from the delta-C{sup 13} content of the soil methane bubble reservoir. Methane C{sup 13} content at one site was determined to be 108.6% modern (delta-C{sup 13} = 83 + or{minus}10{per thousand}). 47 refs., 1 fig., 5 tabs.
TL;DR: In this paper, the relative values of the surface temperature and surface nutrients, the two major contributors to the CO2 source and/or sink properties, are determined using various models in which CO2 does cycle in a steady state at which sources (ocean outgassing) and sinks (ingassing) are in balance.
Abstract: Several regions in the ocean in which disequilibrium persists on an annual avarage between CO2 in the surface water and the overlying atmosphere were examined using various models in which CO2 does cycle in a steady state at which sources (ocean outgassing) and sinks (ingassing) are in balance. The relative values of the surface temperature and surface nutrients, the two major contributors to the CO2 source and/or sink properties, are determined. Results from models with two ocean surfaces indicate that the sink in the north Atlantic and the sources in the equatorial Atlantic and Pacific are all dominated by the global temperature patterns. Results from ocean models with three surface zones show that, in the equatorial Pacific, the temperature control is responsible for over 50 percent (and, possibly, for almost 70 percent) of the CO2 outgassing, with the balance coming from the earth scale surface nutrient structure.
TL;DR: A Beechcraft King Air and a Lockheed WP-3D (P-3) Orion aircraft were flown side by side on January 8, 1986 near Boston, Massachusetts, to compare the scientific measurements being made using the two platforms as discussed by the authors.
Abstract: A Beechcraft King Air and a Lockheed WP-3D (P-3) Orion aircraft were flown side by side on January 8, 1986 near Boston, Massachusetts, to compare the scientific measurements being made using the two platforms. The King Air was also flown in formation with a Beechcraft Queen Air and Douglas DC-3 on March 1, 1986 near Raleigh, North Carolina, for the same purpose. This paper summarizes the results of these comparison flights and discusses the scientific measurements made by the aircraft. The accuracies and response times of the aircraft instrumentation are estimated.
TL;DR: The first airborne real-time H2O2 measurements made in winter were made on all Western Atlantic Ocean Experiment 1986 (WATOX-86) flights aboard the National Oceanic and Atmospheric Administration (NOAA) WP-3D aircraft as mentioned in this paper.
Abstract: Measurements of gas phase H2O2 were made on all Western Atlantic Ocean Experiment 1986 (WATOX-86) flights aboard the National Oceanic and Atmospheric Administration (NOAA) WP-3D aircraft. These were some of the first airborne real-time H2O2 measurements made in winter. Operation of the instru- ment was limited to altitude < 3.1 km with a detection limit, determined by interference considerations, of 0.05 parts per billion by volume (ppbv), 10% calibration accuracy and 0.03-ppbv precision. Experimental measurements showed the mean H2O2 to be 0.12 ppbv (standard deviation = 0.07, maximum = 1.2 ppbv). Vertical structure was observed with maximum H2O2 above the cloud-capped marine boundary layer. Boundary layer H2O2 was typically at or below the detection limit.
TL;DR: The Western Atlantic Ocean Experiment (WATOX) as discussed by the authors was used to collect 80 air samples on four aircraft flights over a horizontal surface parallel to the east coast of the United States spanning latitudes from 30°N to 46°N and altitudes from near the Earth's surface to about 6 km above.
Abstract: During January 1986 we took about 80 air samples on four aircraft flights over a horizontal surface parallel to the east coast of the United States spanning latitudes from 30°N to 46°N and altitudes from near the Earth's surface to about 6 km above. These measurements were part of the Western Atlantic Ocean Experiment (WATOX). The prevailing winds carry man-made pollutants from the densely populated and industrialized eastern United States to regions over the western Atlantic. The measurements taken over the vertical surface intercept the pollutants. By calculating the fluxes of gases through this surface we obtained estimates of emissions from the eastern United States during winter. We estimate that every day about 165 tons of man-made chlorine-containing gases passed through the region of measurements. Some 3,200 tons/day of light hydrocarbons (C2 and C3) , 25,300 tons of methane, and nearly 40,000 tons of carbon monoxide were also transported every day from the east coast to the western Atlantic. These estimates can probably be extended to the entire winter; however, the fluxes can change dramatically during other seasons.
TL;DR: In this article, the optically absorbing carbonaceous component of the ambient aerosol was measured in real-time during the Western Atlantic Ocean Experiment (WATOX) program conducted in 1986 off the eastern seaboard of the United States.
Abstract: During the aircraft operations phase of the Western Atlantic Ocean Experiment (WATOX) program conducted in January 1986 off the eastern seaboard of the United States, we performed measurements of the optically absorbing carbonaceous component of the ambient aerosol. We collected the aerosol on filters that were exposed for several hours; we also operated the aethalo meter to measure the concentration of aerosol black carbon in real time. The filter analyses represent averages over the altitude range and time span during which the filter was collecting. The real-time results were sorted by altitude to calculate vertical profiles of black carbon concentration. Values typically ranged from 200 to 500 ng/m3 in the boundary layer, decreasing to 50 to 100 ng/m3 at higher altitudes. By multiplying the mean concentration profile by the offshore air flux, we may estimate the export of aerosol black carbon from the coast to be of the order of 5 × 1010 g/yr.