摘要:

The interdependence of tropospheric CH4, CO and OH is explored using a simple analytic three‐component box model. The steady state solution for this model places constraints on the relative strengths of the source fluxes of CH4and CO and the production rate for OH. It is demonstrated that if these quantities vary independently the system can only remain stable for a narrow range of conditions. In order for the system to remain stable and well‐behaved for a wide range of fluxes, the fluxes of CO and CH4and the production rate for OH must be covariant, either due to internal feedback processes or to coordinated response to external conditions. The observed steady state abundances of methane in ice records representing preindustrial and glacial times, although sparse, suggest covariant fluxes and OH production. Otherwise the global flux of methane must have varied by less than about 20% during deglaciation and emergence of the boreal wetlands, a period of major change in global hydrology, climate, and biome distributi

ISSN:0886-6236    

DOI:10.1029/GB003i004p00287

年代:1989

数据来源: WILEY

摘要:

Simultaneous measurements of oceanic dimethylsulfide (DMS), atmospheric aerosol sulfate and the size‐resolved physical properties of the aerosol were made aboard a ship in the equatorial Pacific during July 1987. Under light and variable winds, in an area essentially free of continental and anthropogenic air masses, an observed increase in oceanic DMS concentrations preceded simultaneous increases in non‐sea salt sulfate aerosol, the fraction of volatile submicrometer (sub‐μm) aerosol, the condensation nuclei population, and the mean particle diameter of the sub‐μm aerosol. Although the increase in oceanic DMS can qualitatively account for the corresponding changes in the atmospheric aerosol particles, there are numerous difficulties in quantifying the relationship between the sea‐to‐air flux of DMS and the formation and growth of atmospheric aero

ISSN:0886-6236    

DOI:10.1029/GB003i004p00299

年代:1989

数据来源: WILEY

摘要:

The global ocean to atmosphere flux of carbon monoxide (CO) is simulated with 4.5° × 7.5° latitude‐longitude spatial resolution using global data fields derived from an atmospheric general circulation model. The cloud and radiation package in the National Center for Atmospheric Research Community Climate Model is used to estimate the solar energy at the Earth's surface. This quantity is empirically related to photochemical interaction with dissolved organic matter, and the global concentration field of CO in surface seawater is estimated. Areas associated with the Intertropical Convergence Zone and mid‐ to high‐latitude winter hemisphere regions have relatively low climatological CO surface ocean concentrations on a local scale. The global surface wind and temperature fields are simultaneously used to calculate the global transfer velocity field of CO. Coupling these two computed fields, a global ocean to atmosphere CO flux of 165± 80 Tg yr−1is proposed. The CO flux rates vary globally from 0.1 to 12 ug cm−2month−1. The fluxes are largest in the mid‐latitude summer hemispheres, with a maximum at 40° S during the austral summer that is 40% larger on a zonal average than at any northern hemisphere latitude. Relatively small continental sources of CO to the southern hemisphere atmosphere and the short atmospheric residence time of this trace gas indicate that ocean‐derived CO may influence the local photochemical dynamics in the remote marine boundary layer of this region. A possible climate feedback scenario involving UV radiation, ozone, OH, and the air‐sea exchange of CO is proposed. The global ocean to atmosphere CO flux proposed here is at the high end of those used in previous atmospheric CO budgets. This estimate however must be considered a lower limit because no explicit simulation of global oceanic primary productivity is

ISSN:0886-6236    

DOI:10.1029/GB003i004p00305

年代:1989

数据来源: WILEY

摘要:

The supply and utilization of organic carbon in the deep western Mediterranean Sea was investigated based on measured electron transport system (ETS) activities of the nanoplankton and microplankton. The total carbon oxidation rate between 200 and 3000 m, as calculated from ETS activity, was 15.0 g C m−2yr−1. This represents 21% of the primary production and is similar to published estimates of the annual new production. A vertical advection ‐ diffusion ‐ reaction model based on profiles of salinity, oxygen, and the carbon oxidation rate converted to oxygen consumption yielded a deepwater residence time of about 7 years, in close agreement with a published estimate based on bomb‐produced tritium profiles. This suggested that the ETS‐based rates in the deep waters were reasonably accurate. These deep rates were much greater than ETS‐based rates from the same depths in the Atlantic and equatorial Pacific Oceans. In the western Mediterranean, ETS‐based rates also greatly exceeded the rate predicted from the primary production rate and sediment trap relationships. The rapid rates observed in the deep western Mediterranean are not consistent with the supply of organic matter via rapidly sinking particulate material. Instead, rates may be supported by dissolved organic carbon (DOC) transported to depth by wintertime deepwater convection. In order to account for the portion of the ETS‐based rate which was not explained by the sediment trap flux, DOC concentrations in the surface waters entrained during deepwater formation would need to be only 11 μmol C L−1greater than those in the deep waters exiting the basin. ETS activities from the equatorial Pacific (Packard et al., 1988) may also implicate DOC in supporting deep‐sea metabolism. There, ETS‐based carbon oxidation rates between 200 and 5000 m greatly exceeded rates calculated from sediment trap data in the same region. The source of the organic matter being respired may ultimately be the high rates of new production in the equatorial Pacific region, but the mechanism by which this material is transported to depth cannot be determined from these data. The ETS data from both the Mediterranean and the Pacific indicate much greater rates of carbon oxidation in the deep sea than expected from existing sediment trap results. Globally, transport of DOC into the deep sea possibly could rival the sinking particulate flux in importance

ISSN:0886-6236    

DOI:10.1029/GB003i004p00315

年代:1989

数据来源: WILEY

摘要:

Ecologically sound models of the terrestrial biosphere are needed in the investigation of the Earth system and global change. Traditional ecosystem models simulate many processes and dynamics relevant to the functioning of the Earth system, but their application is limited by their local, small‐scale, often site‐specific nature. We address this limitation by deriving a method for predicting regional biosphere dynamics by extrapolation from smaller‐scale ecosystem models. We use models of local ecosystem carbon dynamics to predict the seasonal exchange of CO2between the atmosphere and terrestrial ecosystems of 64°N to 90°N latitude. Monte Carlo simulation is used to integrate solutions of a tundra model and a coniferous forest model across within‐biome heterogeneity in the models' climatic driving variables. The product of the expected value of each model's output and the area of the region occupied by that biome or ecosystem type is an estimate of biome‐scale CO2exchange. Regional CO2exchange is the sum of the biome exchanges. Comparisons of the extrapolation's results with independent estimates of seasonal CO2exchange and annual net primary production support the proposition that extrapolation of ecosystem models can be used to simulate regional biosphe

ISSN:0886-6236    

DOI:10.1029/GB003i004p00337

年代:1989

数据来源: WILEY

摘要:

Natural wetlands are presumed to be major sources of atmospheric methane, but current estimates of the global wetland emission vary by almost a factor of 20. Estimates of global source strengths are based on extrapolation of in situ flux measurements to large areas occupied by broad classes of wetland environments, and recent efforts at refinement of these estimates have concentrated on improving inventories of the global distribution of major wetland types. An additional potential source of uncertainty which has not been quantified is regional scale variability in emission rates within the major wetland types. We conducted an experiment which examined the spatial variability of methane flux within a large regional wetland system, the Florida Everglades. We also investigated the association of flux variability with relevant surface characteristics such as soil thickness, water depth, soil temperature, and vegetative community distribution. Unit area methane flux to the atmosphere from water‐saturated Everglades environments, measured in situ, varied over more than an order of magnitude (4.2 to 81.9 mg CH4/m2/d), depending on which habitat component of the ecosystem was sampled. Observed physical characteristics of the surface (water and soil depth, soil temperature) were not quantitatively associated with the variability in flux rates. However, the distribution of vegetative community types provided an empirical indicator of flux, permitting an inventory of emissions to be based on mapping of regional vegetation patterns. Use of high‐resolution, orbital remote sensing data helped reduce uncertainty in the emission inventory of the Everglades by directing in situ sampling efforts to important habitat types and by providing a means for calculating area‐weighted mean flux for the system as a whole. The results indicated that spatial variability in flux within a major wetland ecosystem can introduce significant uncertainty in extrapolations to larger areas, even if the extent of the major ecosystem itself is well known. The results also suggested that the response of total ecosystem flux to changing water level is not a linear function of flooded area, but is damped, with regional flux at lowered water levels decreasing proportionally less than flooded area. Both sources of variability can be addressed by the combination of remote sensing and in situ techniques we have employed in the Everg

ISSN:0886-6236    

DOI:10.1029/GB003i004p00363

年代:1989

数据来源: WILEY

摘要:

Fluxes of nitrous oxide were determined in several sites in drought‐deciduous tropical forest, an extensive but little‐studied biome. N2O‐N fluxes from eight sites within intact Mexican forest averaged 0.91 ng cm−2h−1during the wet season; they were virtually absent in the dry season. Two subsistence maize fields yielded increased soil N2O‐N fluxes, while five pastures were more variable. Watering during the dry season caused a substantial but short‐lived pulse of N2O. Similar fluxes were observed in less‐intensive sampling of dry‐forest sites in Hawaii and Costa Rica. Overall, N2O fluxes from soils of dry tropical forests appear to be similar to those from moist tropical forests during the wet season and very low duri

ISSN:0886-6236    

DOI:10.1029/GB003i004p00375

年代:1989

数据来源: WILEY

摘要:

Samples from several major world rivers were analyzed for their particulate nitrogen (PN) contents, C/N ratios, and total particulate amino acid (TPAA) contents. The results show a global PN transport of 33 × 1012g N yr−1, more than 80% of which occurs in rivers carrying high suspended matter concentrations such as the Ganges, Brahmaputra, Mekong, and Huanghe. Quantitatively, nitrogen transported in the particulate fraction exceeds that reported for dissolved inorganic nitrogen. The bulk of the PN transport is associated with material having relatively low C/N ratios and low TPAA contents. TPAA accounted for about 20% of the total PN transport. Although natural processes leading to high rates of erosion in Asian rivers might have partly contributed to the observed PN transport pattern, our results suggest that human activities such as deforestation and increased use of nitrogen fertilizer in their drainage basins are also an important factor. The biogeochemical nature of the remaining 80% is only poorly known, but should be of relevance in studying the response of estuaries and coastal seas to human activities in the terrestrial environme

ISSN:0886-6236    

DOI:10.1029/GB003i004p00383

年代:1989

数据来源: WILEY

摘要:

Surface air temperatures of the Arctic rose 1.2° −1.5°C from 1880 to 1980, in contrast to a global warming of only 0.4° −0.5°C; since 1980, six of the warmest years in the past century have been observed. Polar enhancement of a temperature rise, induced possibly by anthropogenic release of “greenhouse” gases, CO2, N2O, CH4, and freons, to the atmosphere, is attributed to altered ice/snow albedo at sea level, i.e., melting of sea ice. A 5% decline of sea ice extent in the Arctic and Antarctic from 1979 to 1987 may have resulted in increased light availability within previously ice‐covered polar regions. If such a short‐term trend were to continue, it might lead to a negative biogeochemical feedback, i.e., enhanced extraction of atmospheric CO2during marine photosynthesis. As a consequence of deep vertical mixing in the Antarctic Ocean, however, primary production during the austral summer may have actually declined in response to a reduction in extent of meltwater regions, where stratified water columns allow carbon fixation tenfold that of open water. In contrast, within shallow adjacent seas of the Arctic Ocean, where shelf regions are tenfold larger than those of the Antarctic, the positive global consequences of greenhouse warming at polar latitudes will probably be felt first. Specifically, the Pacific‐influenced regions of the Chukchi and East Siberian Seas, where sufficient nutrients and shallow depths prevail, now have annual primary productions of>200 g C m−2yr−1, tenfold that of other high Arctic shelves, and may supply 50% of the carbon respiration demands within the halocline of the deep Canadian and Eurasian basins via brine‐mediated runoff. Continued melting of ice in the Arctic could increase by an order of magnitude the present CO2sin

ISSN:0886-6236    

DOI:10.1029/GB003i004p00393

年代:1989

数据来源: WILEY