摘要:

Can the buildup of anthropogenic CO2 in the atmosphere be reduced significantly by fertilizing the surface southern ocean waters with iron? There aremany issues that need to be addressed in answering this question. Is iron scarcity indeed the dominant process limiting biological uptake of carbon, as hasbeen suggested by Martin [e.g., Martin et al., 199O]?

ISSN:0886-6236    

DOI:10.1029/91GB00276

年代:1991

数据来源: WILEY

摘要:

We present high‐resolution global data bases on the geographic and seasonal distribution of rice cultivation and associated methane emission. The data bases were developed by integrating extensive and eclectic information on the cultivation of rice in all 103 rice‐producing countries of the world. The geographic distribution of rice‐growing locations was developed by combining a 1° resolution land‐use data base identifying rice‐farming regimes, a 1° resolution data base of countries of the world, and country statistics on areas of annual rice harvest available from the U. N. Food and Agriculture Organization. The seasonal distribution of cultivated rice areas was derived via the integration of the data base on rice‐growing locations with information on cultivation activities and rice cropping practices for each rice‐producing country of the world; this information included seasonal rice‐cropping calendars for individual countries and statistics or estimates of the seasonal distribution of annual harvest areas in each crop cycle. Since the causes of the variability in methane fluxes from flooded rice fields have yet to be quantified, we did not attempt a new estimate of the role of rice cultivation in the global emission of methane. We evaluate, instead, the temporal and spatial distribution of emissions from a hypothetical annual source of 100 Tg methane. In 1984, 1475 × 109m2of rice was harvested in 103 countries. Although rice cultivation extends from about 50°N to 50°S, 48% of the harvest area is confined to a narrow subtropical zone from 30°N to 20°N, while another 35% is harvested in the 10° zones directly to the north and south. Globally, about 60% of the harvested rice area is managed under a triple rice crop system, ∼15% is double cropped, and 25% is harvested from fields planted for rice once a year. In China and India, which together account for 52% of the world's harvest area, rice is harvested predominantly under a triple‐crop system. These patterns suggest that much of the potential for multiple rice cropping is currently exploited. In this analysis, methane emission is proportional to the area and duration of each harvest so that the seasonal, zonal and country patterns of annual methane emission mimic the distribution of rice‐harvest areas. Although rice is grown throughout the year, the close coupling of rice cultivation with climate results in the concentration of about 55% of the annual methane emission into four months from July through October and almost half the total emission in la

ISSN:0886-6236    

DOI:10.1029/90GB02311

年代:1991

数据来源: WILEY

摘要:

The13C/12C of atmospheric methane (CH4) was measured at Point Barrow (71°N, 156°W), Olympic Peninsula (48°N, 126°W), Mauna Loa (19°N, 155°W), and Cape Grim (41°S, 144°E) between 1987 and 1989. The global average δ13CPDBfrom these measurements (n = 208) was −47.20 ± 0.13%o. The lowest mean annual δ13C value of‐47.61 ± 0.14‰ was measured at Point Barrow with values increasing to ‐47.03 ± 0.14‰ at Cape Grim. The seasonal cycle in the δ13C of CH4was greatest at Point Barrow, with an amplitude of 0.5‰, and varied inversely with concentration. The isotopic fractionation during CH4oxidation is calculated to be 0.993 ± 0.002 based on the measured CH4concentration and δ13C values. The14C content of atmospheric CH4, measured at monthly intervals at the Olympic Peninsula site between 1987 and 1989, is increasing at 1.4 ± 0.5 pM yr−1, primarily owing to14CH4release from nuclear reactors. The global average14C content of 122 pM for CH4implies a fossil methane source strength that is 16% of the total source. The global mean δ13C of −47.2‰, when coupled with the14C results, implies that ∼11% of the total CH4release rate is derived from biomass burning. These results indicate for a total CH4source of ∼550 Tg yr−1that natural gas release accounts for ∼90 Tg yr−1and biomass burning yields ∼60 Tg yr−1. Preliminary analyses of the δ13C data using a three‐dimensional chemical tracer model indicate that the observed meridional gradients in the annual average δ13C and concentration of CH4are most closely matched with a CH4source scenario i

ISSN:0886-6236    

DOI:10.1029/91GB00003

年代:1991

数据来源: WILEY

摘要:

Distributions of oxygen, argon, nitrogen, and radon in the upper ocean of the subarctic Pacific distinguish the fluxes controlling the oxygen mass balance during the summers of 1987 and 1988. The difference between the net O2flux (in mmol m−2d−1) to the atmosphere via gas exchange (32) and the integrated decrease with time (−14) is balanced by biological production (13‐17), air injection by bubble entrainment (5), and O2flux to the thermocline −(0‐4). Nitrogen/argon and oxygen/argon ratios reveal that ˜15% of the oxygen supersaturation in summer is produced by air injection and ˜40% by biological production, with the rest induced by surface water warming. Our estimate of biologically induced oxygen production when translated stoichiometrically to nitrogen uptake agrees to within error estimates with both the particulate and dissolved nitrogen mass balances for the upper ocean determined in the SUPER program during the same time period. The oxygen mass balance requires a net carbon production in the euphotic zone of ˜140 mg C m−2d−1(PQ=1.5), which is 20–30% of the level of14C primary production determined by

ISSN:0886-6236    

DOI:10.1029/90GB02656

年代:1991

数据来源: WILEY

摘要:

The flux of organic carbon associated with new production has been modeled by advection of dissolved organic carbon in addition to falling particulate organic carbon, in a carbon cycle model that is based on an oceanic general circulation model. Model predictions of chemical species involved in the carbon cycle are compared with observations. Relative to a model in which new production is carried only by falling particulate organic carbon, there is significantly better agreement between predicted and observed oceanic phosphate and oxygen concentrations if a large part of the new production flux is carried by dissolved organic carbon.

ISSN:0886-6236    

DOI:10.1029/91GB00015

年代:1991

数据来源: WILEY

摘要:

A parameter based on the sum of the concentrations of PO4and O2(divided by the Redfield coefficient‐ΔO2/δPO4) is used to separate the contributions of the northern and southern components to deep waters in the Atlantic. This separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep Atlantic to be calculated. Maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary. The O2and14C deficiences are highly correlated, suggesting an O2utilization rate of 12 μm/kg per century. The apparent mean isolation time of water in the deep Atlantic is about 200 y

ISSN:0886-6236    

DOI:10.1029/90GB02279

年代:1991

数据来源: WILEY