摘要:

Methane emissions from Philippine rice paddies, fertilized with either urea or green manure, were monitored for several weeks after harvesting the dry and the wet season crops of 1992. The fields were still flooded during harvest but irrigation was stopped after harvest and the fields were allowed to evaporatively dry while CH4emissions were monitored with a closed chamber technique. In all plots we observed a sudden, strong increase of CH4emissions to the atmosphere for 2 to 4 days just after the soil fell dry. As soil drying continued, the soils began to crack and CH4emissions decreased to nil. The release of CH4during soil drying was observed for fields on three different soil types and both for urea or organically manured rice fields in both seasons. The absolute amounts of CH4emitted during soil drying differed greatly depending on fertilizer treatment. However, the ratio between the amount of CH4released upon soil drying and CH4emitted during the growing season was quite constant (0.10 ±0.04). This suggests that about 10% of the CH4emitted during a full rice crop cycle is released during drying of the fields and thus needs to be included in estimates of the total CH4emission from rice agriculture

ISSN:0886-6236    

DOI:10.1029/95GB03460

年代:1996

数据来源: WILEY

摘要:

We present a record of variations in the O2/N2ratio of air at 41°S latitude from 1991–1994 based on the mass spectrometric analysis of flask samples from Cape Grim, Tasmania, and Baring Head, New Zealand. Results for Cape Grim for the period from June 1991 to February 1992 are in good agreement with previously published data ofKeeling and Shertz[1992]. Plotted versus time, O2/N2ratios show the expected annual cycles. O2/N2increases in austral spring and summer (caused mainly by net oceanic production) and decreases in fall and winter (caused by ventilation of the seasonal and main thermoclines). The average amplitude of the seasonal cycle implies net oceanic production of about 5 mol C m−2yr−1with considerable interannual variability. The O2/N2ratio of air decreased at the rate of 12±4 per meg/yr (0.012 ‰/yr) between winter 1991 and winter 1993. This value is considerably less than the O2consumption rate associated with fossil fuel burning (about 20 per meg/yr), suggesting that the land biosphere was an O2source and an important CO2sink during this period. Alternatively, the oceans may have been a transient O2sink during 1991–1993, most likely caused by an enhanced rate of thermocline ventilation with respect to the steady

ISSN:0886-6236    

DOI:10.1029/95GB03295

年代:1996

数据来源: WILEY

摘要:

For a large set of major world rivers we established the empirical relations existing between the observed organic carbon fluxes and the climatic, biologic, and geomorphologic patterns characterizing the river basins. These characteristics were extracted from various ecological databases. The corresponding carbon fluxes were taken from the literature. Dissolved organic carbon fluxes are mainly related to drainage intensity, basin slope, and the amount of carbon stored in soils. Particulate organic carbon fluxes are calculated as a function of sediment fluxes, which depend principally upon drainage intensity, rainfall intensity, and basin slope. Although the drainage intensity is mainly related to the amount of precipitation and to mean temperature in the basin, slope is also retained as one of the controlling factors. Our empirical models result in a total organic carbon flux to the oceans of about 0.38 Gt per year globally. About 0.21 Gt carbon (Gt C) enter the oceans in dissolved form and about 0.17 Gt C in particulate form. We further regionalize fluxes with respect to major climates, different continents, and different ocean basins. About 45 % of the organic carbon is discharged from tropical wet regions. The major part of the dissolved organic carbon is discharged into the Atlantic Ocean, while the bulk of the particulate organic carbon is discharged into the Indian and Pacific Oceans.

ISSN:0886-6236    

DOI:10.1029/95GB02925

年代:1996

数据来源: WILEY

摘要:

A global equation, designed to estimate the column‐integrated oceanic primary production realized by a given phytoplankton biomass under various environmental conditions, is used to develop a practical method to assess the primary production (P) from the chlorophyll concentration as provided by satellite imagery. This basic equation combines three terms, namely the photosynthetically available radiation impinging at the sea surface, PAR(0+), the column‐integrated chlorophyll content,tot, and the cross section for photosynthesis per unit of chlorophyll, Ψ*. Global monitoring of incident irradiance and near‐surface algal biomass is now achievable from space, and thus the next step toward a monitoring of oceanic primary production would be to dispose in parallel of a “climatological field” of the Ψ* quantity. Actually, Ψ* depends on the two other terms of the equation (PAR(0+) andtot,), and, in addition, on temperature (also detectable from satellite). Therefore such a “climatological field” is variable and complex and it can be conveniently replaced by lookup tables allowing easy interpolation. The entries are date, latitude, cloudiness, temperature, and remotely sensed chlorophyll concentration. This upper layer concentration is extended downward owing to previous results of a statistical analysis of the chlorophyll vertical distribution; accordingly, two parallel tables, corresponding to well‐mixed or stratified upper layers with uniform or non uniform chlorophyll vertical profiles, respectively, are constructed. These tables are produced by systematically using a previously published spectral light‐photosynthesis model. For such extensive computations, the model necessarily relies on, and is operated with, a standard set of ecological and physiological parameters. Therefore sensitivity analyses have been carried out in view of assessing the impact on Ψ*, and on the resulting production of deviations in these parameters or parameterizations, vis‐a‐vis the standard values or formulations which were adopted when building the tables. The effects of the biomass vertical structure, of possible light and temperature adaptation, and of the presence of degraded pigments are among the sensitivity studies which have been performed. The method as proposed can accomodate any improvement and complexity in parameterization to the extent that additional computation time is faced only when generating the lookup tables, not when using them in conjun

ISSN:0886-6236    

DOI:10.1029/95GB02831

年代:1996

数据来源: WILEY

摘要:

A fast method has been proposed [Antoine and Morel, this issue] to compute the oceanic primary production from the upper ocean chlorophyll‐like pigment concentration, as it can be routinely detected by a spaceborne ocean color sensor. This method is applied here to the monthly global maps of the photosynthetic pigments that were derived from the coastal zone color scanner (CZCS) data archive [Feldman et al., 1989]. The photosynthetically active radiation (PAR) field is computed from the astronomical constant and by using an atmospheric model, thereafter combined with averaged cloud information, derived from the International Satellite Cloud Climatology Project (ISCCP). The aim is to assess the seasonal evolution, as well as the spatial distribution of the photosynthetic carbon fixation within the world ocean and for a “climatological year”, to the extent that both the chlorophyll information and the cloud coverage statistics actually are averages obtained over several years. The computed global annual production actually ranges between 36.5 and 45.6 Gt C yr−1according to the assumption which is made (0.8 or 1) about the ratio of active‐to‐total pigments (recall that chlorophyll and pheopigments are not radiometrically resolved by CZCS). The relative contributions to the global productivity of the various oceans and zonal belts are examined. By considering the hypotheses needed in such computations, the nature of the data used as inputs, and the results of the sensitivity studies, the global numbers have to be cautiously considered. Improving the reliability of the primary production estimates implies (1) new global data sets allowing a higher temporal resolution and a better coverage, (2) progress in the knowledge of physiological responses of phytoplankton and therefore refinements of the time and space dependent parameterizations of thes

ISSN:0886-6236    

DOI:10.1029/95GB02832

年代:1996

数据来源: WILEY

摘要:

The magnitude and distribution of the particulate organic carbon (POC) rain rate to the seafloor in the Atlantic, Pacific and Indian Ocean basins between 61°N and 61°S has been estimated from benthic oxygen flux estimates (for water depths ≥ 1000 m only). The calculation utilizes the extensive data sets of sedimentary organic carbon, CaCO3, and accumulation rate to extrapolate between individual benthic flux measurement sites using an empirically‐derived correlation between the seafloor oxygen flux and these parameters. The POC flux through the 1000 m depth horizon was then estimated from published correlations between sediment trap‐determined fluxes and water depth. Total oxygen utilization in the deep ocean is estimated to be 1.2×1014mol O2yr−1, a value that agrees well with previous estimates which were based on surface water primary productivity, sediment trap, and depth relationships and with deep water respiration rates estimated from apparant oxygen utilization (AOU)‐14C relationships. On the basis of the derived global ocean flux distribution, it is concluded that (1) dissolved organic carbon (DOC) inputs are not required to account for estimated deep water respiration rates; (2) the majority of the POC input to the deep ocean occurs within 30° of the equator; (3) the proportion of primary production that reaches the deep sea does not vary greatly with latitude; (4) gyre and continental margin regions contribute roughly equally to the deep POC flux with a relatively minor contribution from the equatorial divergence region; (5) of the estimated 7.2×1013mol C yr−1of POC that sinks below the 1000 m depth horizon, 45% (3.3×1013mol C yr−1) reaches the seafloor where it is oxidized; (6) when normalized to basin area, average deep flux rates in the Atlantic and Pacific are similar while highest rates are observed in the Indian Ocean; and (7) the results can be fully reconciled only if the benthic flux of DOC is significantly less than

ISSN:0886-6236    

DOI:10.1029/95GB03525

年代:1996

数据来源: WILEY

摘要:

The recent proposals to estimate the oceanic uptake of CO2by monitoring the oceanic change in13C/12C isotope ratio [Quay et al., 1992] or the air‐sea13C/12C isotopic disequilibrium [Tans et al., 1993] is reviewed. Because the history of atmospheric CO2and13CO2since preindustrial times is almost the same and increasing in an almost exponential fashion, the oceanic penetration depth of both tracers must be the same. This dynamic constraint permits the establishment of yet a third method to estimate the global ocean uptake of CO2from13C measurements. Using available observations in conjunction with canonical values for global carbon cycle parameters, the three methods yield inconsistent oceanic CO2uptake rates for the time period 1970–1990, ranging from 0.6 to 3.1 GtC yr−1. However, uncertainties in the available carbon cycle data must be taken into account. Using a nonlinear estimation procedure, a consistent scenario with an oceanic CO2uptake rate of 2.1±0.9 GtC yr−1can be established. The method also permits an investigation of the sensitivities of the different approaches. An analysis of the results of two three‐dimensional simulations with the Hamburg model of the oceanic carbon cycle shows that the13C isotope indeed tracks the oceanic penetration of anthropogenic CO2. Because of its different time history, bomb produced radiocarbon, as measured at the time of the Geochemical Ocean Sections Study (GEOSECS), correlates not as well to exc

ISSN:0886-6236    

DOI:10.1029/95GB03191

年代:1996

数据来源: WILEY

摘要:

A new method to transform satellite ocean color data into estimates of primary production and carbon fluxes is presented. A one‐dimensional coupled physical‐bio‐geochemical model of the surface ocean is constrained to reproduce the seasonal evolution of surface chlorophyll concentration by adjusting the parameters of the 10‐compartment trophic system using a variational technique. The method is applied to in situ surface chlorophyll data from station Papa, but averaged over the characteristic depth of ocean color measurements, and affected by errors compatible with those of satellite values. Using 35 measurements for the year 1976, it is found that five linear combinations of the trophic parameters can be adjusted. This adjustment is also valid for 1975 chlorophyll data. In general, the adjusted values of the trophic parameters are sensitive to their a priori values, but consistent results are found for the grazing rate (0.35 to 0.6 d−1), the phytoplankton mortality rate (very small), and the minimum concentration of zooplankton in winter (less than 0.16 mmolC m−3). Some carbon fluxes, namely photosynthetic carbon production in the euphotic layer (95 to 110 gC m−2yr−1), its regeneration by grazing (60 % of the latter), and the recycling efficiency of nitrogen (60%) seem to be robustly constrained, though primary production is apparently underestimated compared to the most recent ones. The export flux amounts to 35 to 40% of primary production, but its value depends on the particle sinking rate, which is not adjustable from chlorophyll data. This study suggests that simplified biological models, compared to the model used here, would be sufficient to ac

ISSN:0886-6236    

DOI:10.1029/95GB03436

年代:1996

数据来源: WILEY

摘要:

A one‐dimensional coupled physical bio‐geochemical model of the surface ocean was constrained to reproduce the seasonal evolution of surface chlorophyll, temperature and nitrate concentration by adjusting the parameters of a simple trophic system using a variational technique. It is found that assimilation of surface chlorophyll data only not allow a robust constraint of the simulated trophic cycle. When surface chlorophyll, temperature and nitrate data are used simultaneously, seven linear combinations of the model parameters can be adjusted. While temperature values are useful to constrain vertical diffusion below the mixed layer, the seasonal nitrate evolution (2 values/year) is a strong constraint on the balance between vertical diffusion and particle sinking rate. The three types of surface information provide robust constraints on the model parameters and on the main carbon fluxes within the euphotic layer. For the model to reproduce observed surface pCO2concentrations, it is found as necessary to adjust the C/N ratios. An example is given, where the C/N ratio for net organic matter export from euphotic zone is increased to 12±1 and the C/N ratio for detritus remineralization is decreased to 3.3±2, rather than the canonical value

ISSN:0886-6236    

DOI:10.1029/95GB03435

年代:1996

数据来源: WILEY

摘要:

Historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater CO3=concentration to reveal regional variations in the calcite lysocline. The most obvious mode of variability of the calcite lysocline is the thickness of the lysocline (defined here as the difference in overlying water carbonate saturation, ΔCO3=, between high and low calcite sediments) with a thicker lysocline in the Atlantic than in the Pacific. I attribute this variation to differences in the delivery rate of terriginous material. A recent model for the lower glacial atmospheric pCO2proposed to change the relationship between the depth of the lysocline and the ΔCO3=of the water column by changing the rain rate ratio of organic carbon to calcite production (the “rain ratio model”: Archer and Maier‐Reimer, 1994). I search the data set for analogs to the proposed glacial world, by looking for a link between the regional climate at the sea surface and the depth of the lysocline below. The ΔCO3=at the carbonate compensation depth (CCD) in the tropics appears to be 10–20 μmol kg−1ΔCO3=more undersaturated than in high latitudes, but this is smaller than the ∼40 μmol kg−1shift required by the model. In addition, the general resemblance of the glacial lysocline to the present day requires that the proposed shift in ΔCO3=at the CCD be globally uniform rather than locally variable, as climate forcing would probably generate. I conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time, such as a change in ocean Si content, if it is to explain the entire pCO2decrease observed in the glacial atmosphere. Finally, I grid the sedimentary data to estimate that the inventory CaCO3which is available to neutralize fossil fuel CO2is approximately 1600 Gt carbon, a quantity which may be exceeded by fossil fuel release in the ne

ISSN:0886-6236    

DOI:10.1029/95GB03016

年代:1996

数据来源: WILEY