摘要:

Most scientists are convinced of the importance of their own research subjects. Broecker [1991] has deplored the temptation, if not the tendency, to go overboard and exaggerate this importance once funding enters the mind. In particular, he alleges inflated or even false claims by biological (and other) oceanographers regarding the relevance of their research to the “greenhouse effect,” caused by the anthropogenic enhancement of the atmospheric CO2content. He writes [Broecker, 1991, p. 191]: “In my estimation, on any list of subjects requiring intense study with regard to the prediction of the consequences of CO2buildup in the atmosphere, I would place marine biological cycles near the bo

ISSN:0886-6236    

DOI:10.1029/91GB02690

年代:1991

数据来源: WILEY

摘要:

The recent notes by Broecker [1991] and by Smith and Mackenzie [1991]rightfully point out that many oceanographers do not have a clear grasp of the relationship between the oceanic biological pump and anthropogenic CO2transient. This misunderstanding has unfortunately led some scientists to make misleading claims as to the importance of the biological pump in the anthropogenic transient. It is remarkable that someone who contributed as much to our understanding of the oceanic carbon cycle as Revelle could have incorrectly stated that the biological pump takes up anthropogenic CO2[Revelle, 199O]. However, both notes go too far when they dismiss the biological pump as being of minimal relevance to global change, with a particular indictment by Broecker of the Joint Global Ocean Flux Study (JGOFS) as having been guilty of “tarnishing the integrity of global change research” by “hitching their wagons to the greenhouse

ISSN:0886-6236    

DOI:10.1029/91GB02705

年代:1991

数据来源: WILEY

ISSN:0886-6236    

DOI:10.1029/91GB02738

年代:1991

数据来源: WILEY

ISSN:0886-6236    

DOI:10.1029/91GB02737

年代:1991

数据来源: WILEY

摘要:

Direct measurements of CH4and CO2atmosphere/soil exchange with a drained upland inceptisol were made over a 2‐year period in a mixed hardwood forest in New Hampshire. Soil gas concentrations of CH4and CO2were also monitored over the same period. Soil incubation experiments were used to characterize the depth variation and the temperature response of the consumption and production reactions. CH4was always taken up by the soils after spring thaw in April. Maximum rates of consumption were 4.8 mg CH4m−2d−1in 1989 and 4.9 mg CH4m−2d−1in 1990. CO2efflux was much higher with rates over 25 g CO2m−2d−1measured in July 1990. Annually, about 600 mg CH4were consumed and approximately 2 kg CO2emitted per square meter. There was an apparent negative correlation between soil CH4and CO2concentrations. Gas samples taken in the surface litter layer showed CH4to be depleted and CO2enhanced within 1 cm of the surface. Below the surface, CH4decreased and CO2increased with depth. At 15 cm, CH4was never greater than 0.3 ppm and was usually less than 0.2 ppm. At the same depth, CO2concentrations ranged from 1100 to over 7500 ppm. Incubation experiments indicated that CO2was being produced throughout the top 15 cm of surface soil with a similar temperature response. Significant CH4oxidation was measured only in a zone at the top of the mineral soil layer. Both activities could be stopped by autoclaving. CO2flux from the ground throughout the year was driven by biological activity, mainly soil and root respiration. CH4uptake, on the other hand, was more complicated. Biological activity controlled the establishment of soil concentration gradients, and so in spring, CH4influx was tightly linked to rates of consumption. However, in summer and fall, diffusive supply of CH4to its site of consumption in the soils limit

ISSN:0886-6236    

DOI:10.1029/91GB02466

年代:1991

数据来源: WILEY

摘要:

Since rice fields emit methane, an important contributor to the increasing greenhouse effect, one of our goals is to characterize factors that influence this emission. To create a range in plant and soil temperature, solar radiation, and microbial substrate, rice fields were planted on April 13, May 18 and June 18 of 1990 on silty clay soils near Beaumont, Texas. Immediately prior to planting, one half of each field was supplemented with 6000 kg ha−1of disc‐incorporated grass straw (Paspalum spp.). Methane emission rates were measured throughout the cultivation period. Methane emission rates varied markedly with planting date and straw addition. The highest emission rate originated from the earliest planted straw‐supplemented field. In general, methane emission decreased with the later plantings that received less solar radiation. Annual emission rates of methane and rice grain yield from individual fields were positively correlated with accumulated solar radiation for both straw‐incorporated and control plots. Straw incorporation resulted in decreased grain yield and increased methane emission in all three fields. Diel variation of methane emission strongly correlated with temperature. The activation energies for methane production, obtained from laboratory soil incubations, and methane emission, obtained from diel field measurements, were approximately the same: 88–98 kJ mol−1for production and 87 kJ mol−

ISSN:0886-6236    

DOI:10.1029/91GB02586

年代:1991

数据来源: WILEY

摘要:

Processes that shift nutrients from mid to lower ocean depths may or may not increase the ocean's vertical carbon pump. Redistribution of δ13C produced by these processes is compared in two box models: a vertical three‐box ocean and a thirteen‐box ocean. In the former there is no δ13C fractionation laterally between surface waters, and the ocean nutrient and δ13C distributions are linearly correlated. This correlation is not changed when these tracers become redistributed, and if the model surface ocean is nutrient limited, the surface δ13C cannot change. In the 13‐box ocean there is a transfer of negative δ13C from the cold surface water through the atmosphere into the warm ocean. Its δ13C is therefore lower than it would be as a result of the carbon pump by itself. If a middepth nutrient depletion occurs because of lower nutrients in Antarctic waters, the warm surface δ13C increases. If the vertical nutrient shift occurs because of ocean circulation or biological recycling changes, the warm surface water δ13C change depends on the ratio of its vertical CO2fluxes, i.e., exchange of atmospheric CO2versus upwelling total CO2and net biological production. If this ratio remains about the same, then little change occurs in surface δ13C, and the δ13C of Pacific deep water decreases about 0.3%. In this case, no change in the average ocean δ13C is required to explain observations from sediment data. This would imply that the ice age land biota carbon mass was about the same as that of today. The vertical CO2flux ratio could be an important consideration if greater wind‐driven upwelling is a factor in the nutri

ISSN:0886-6236    

DOI:10.1029/91GB01913

年代:1991

数据来源: WILEY

摘要:

Radiocarbon measurements suggest that14C‐free carbon enters from beneath Mono Lake at a rate of about 1 mol/m2/yr. An input of this magnitude should be manifested in the inorganic carbon budget of the lake and with this in mind we have devised a model to reconstruct the evolution of the partial pressure of CO2(pCO2) over the past 150 years. This encompasses a period (1945 to present) during which major diversions of source waters via the Los Angeles aqueduct have been in effect, significantly increasing the salinity of the lake and hence its pCO2. The model has been constrained by experimental characterization of the carbonate chemistry of the lake water, by the temperature dependence of pCO2for the lake water, and by pCO2measurements made on the lake water in 1966, 1969,1981, and 1989. Our calculations suggest that prior to 1945 the pCO2of Mono Lake water was about 1.3 times the atmospheric value. To produce this excess, an input of CO2of about 3.3 mol/m2/yr is required. Volcanic activity beneath the lake is a probable source of this inpu

ISSN:0886-6236    

DOI:10.1029/91GB02475

年代:1991

数据来源: WILEY

摘要:

The convolution integral form of a carbon cycle model is transformed to a simple first‐order differential equation. This allows one to derive an extremely efficient numerical algorithm for the carbon cycle model. The algorithm can be easily inverted to obtain a practical and efficient inverse carbon cycle model. The model is described and an example is given showing how modelled land‐use‐change emissions over 1765–1990 vary with assumptions made regarding the efficiency of oceanic CO

ISSN:0886-6236    

DOI:10.1029/91GB02279

年代:1991

数据来源: WILEY