摘要:

Elevated carbon dioxide throughout the lifespan of soybean causes an increase in photosynthesis, biomass, and seed yield. A rectangular hyperbola model predicts a 32% increase in soybean seed yield with a doubling of carbon dioxide from 315 to 630 ppm and shows that yields may have increased by 13% from about 1800 A.D. to the present due to global carbon dioxide increases. Several other sets of data indicate that photosynthetic and growth response to rising carbon dioxide of many species, including woody plants, is similar to that of soybean. Calculations suggest that enough carbon could be sequestered annually from increased photosynthesis and biomass production due to the rise in atmospheric carbon dioxide from 315 ppm in 1958 to about 345 ppm in 1986 to reduce the impact of deforestation in the tropics on the putative current flux of carbon from the biosphere to the atmosphere.

ISSN:0886-6236    

DOI:10.1029/GB001i001p00001

年代:1987

数据来源: WILEY

摘要:

The only viable explanations put forth to date for the glacial to interglacial change in atmospheric CO2content suggested from measurements of the CO2content of gas extracted from ice cores involve changes in the ocean's nutrient cycles. Any nutrient change capable of creating the 80 µatm changes in atmosphere CO2pressure suggested by the ice core results also creates significant change in the deep ocean's CO3=content. Evidence from deep sea sediments suggests that these CO3=changes are compensated on the time scale of a few thousand years by reductions or increases in amount of CaCO3accumulating in deep sea sediments. This compensation process has two important consequences. First, it significantly increases the magnitude of the CO2change per unit of nutrient forcing. Second, it causes a delay in the response of the atmospheric CO2change. While the first of these consequences is a boon to those seeking to explain the CO2change, the second may prove to be a curse. The ice core CO2record shows no evidence of a significant lag between the CO2response and the polar warming. In any case it is important that we improve our knowledge of the magnitude and timing of the CaCO3preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

ISSN:0886-6236    

DOI:10.1029/GB001i001p00015

年代:1987

数据来源: WILEY

摘要:

Fecal pellets produced by suspension‐feeding crustacean zooplankton, specifically copepods and euphausids, have frequently been cited as an important mode of large particle transport in the open ocean. The objectives of the present study were to determine the various biogeochemical fluxes provided by pelagic crustacean fecal pellets, to examine such fluxes as a function of depth and variable levels of surface water productivity, and to assess the overall fecal pellet contribution to oceanic particle fluxes as measured with sediment traps. Pellet subsamples were obtained from particulate samples collected at depths between 389 and 5068 m by moored PARFLUX sediment traps deployed for up to 12 months at three tropical‐subtropical open ocean localities. The sites were located over the East Hawaii Abyssal Plain (P site), over the Demerara Abyssal Plain (E site), and in the Pacific Panama Basin (PB site). Fecal pellet flux and chemical composition were found to vary significantly on a geographic scale as a function of productivity levels in the surface waters. The total carbonate, organic carbon, opaline silica, and lithogenic fluxes provided by pellets at the oligotrophic P1site were 1–2 orders of magnitude less than that measured at the eutrophic station in Panama Basin. The pellet data show that contrary to previous assumptions, these biogenic aggregates are responsible for no more than 5% of the total mass flux of oceanic particulate material. Despite the fact that at all trap depths, large numbers of intact pellets were collected which displayed minimal effects of dissolution and microbial degradation, fecal pellets contributed an average of only 1–10%, 0.5–5%, 1–3%, and 0.5–4% to the total measured mass fluxes of organic, carbonate, opaline silica, and lithogenic material, respectively. However, the pellets showed elevated C/N ratios (9–14) as well as high organic content (representing up to 50% of the individual pellet weight), suggesting that they constitute an important source of organic carbon for the deep‐sea benthos. Rapid remineralization of the organic‐rich pellets must occur at the deep‐sea sediment/water interface, as these biogenic aggregates were completely absent fr

ISSN:0886-6236    

DOI:10.1029/GB001i001p00031

年代:1987

数据来源: WILEY

摘要:

The isotopic composition (or18O/16O ratio) of O2produced by photosynthesis and the isotopic composition of O2consumed during respiration are different from each other as well as from the isotopic composition of ambient dissolved O2. In a closed body of water in which photosynthesis and respiration are co‐occurring, the18O/16O of dissolved O2will be a function of both the rate of respiration and the gross rate of photosynthesis. Therefore gross primary production can be calculated if one determines both net O2production and the18O/16O of dissolved O2. As a test of the feasibility of this approach, we present data on the18O/16O ratio of dissolved O2, along with ancillary parameters, in the top 200 m of waters in the North Pacific gyre in August and September 1985. The results are shown to reflect isotope fractionation during photosynthesis and respiration. We outline the additional information needed before natural18O/16O variations can be used to constrain quantitatively the gross productio

ISSN:0886-6236    

DOI:10.1029/GB001i001p00049

年代:1987

数据来源: WILEY

摘要:

A global data base of wetlands at 1° resolution has been developed from the integration of three independent global, digital sources: (1) vegetation, (2) soil properties and (3) fractional inundation in each 1° cell. The integration yielded a global distribution of wetland sites identified with in situ ecological and environmental characteristics. The wetland sites have been classed into five major wetland groups on the basis of environmental characteristics governing methane emissions. The global wetland area derived in this study is ∼5.3 × 1012m2, approximately twice the wetland area previously used in methane‐emission studies. Methane emission was calculated using methane fluxes for the major wetland groups, and simple assumptions about the duration of the methane production season. The annual methane emission from wetlands is ∼110 Tg, well within the range of previous estimates (11‐300 Tg). Tropical/subtropical peat‐poor swamps from 20°N‐30°S account from ∼30% of the global wetland area and ∼25% of the total methane emission. About 60% of the total emission comes from peat‐rich bogs concentrated from 50°‐7O°N, suggesting that the highly seasonal emission from these ecosystems is the major contributor to the large annual oscillations observed in atmospheric methane concent

ISSN:0886-6236    

DOI:10.1029/GB001i001p00061

年代:1987

数据来源: WILEY