ISSN:0886-6236    

DOI:10.1029/GB004i001p00001

年代:1990

数据来源: WILEY

ISSN:0886-6236    

DOI:10.1029/GB004i001p00003

年代:1990

数据来源: WILEY

摘要:

Enrichment experiments were performed in the Ross Sea to test the hypothesis that iron deficiency is responsible for the phytoplankton's failure to use up the luxuriant major nutrient supplies found in these and all other offshore Antarctic ocean waters . Nitrate uptake rates in the controls without added trace elements ranged from 0.58 to 1.22 μmol kg−1d−1; the addition of 1 to 5 nmol of unchelated Fe per liter resulted in rates that were 2 to 10 times higher (2.54 to 6.00 μmol NO3kg−1d−1). Rates in bottles with 2 nmol Mn added were identical to those in the controls (0.57 to 1.04 μmol NO3kg−1d−1). Total decreases in NO3were balanced by increases in particulate organic N. These results suggest that Fe deficiency is the primary reason that the present‐day southern ocean biological pump is shut off. In contrast, iron was 50 times more abundant during the last glacial maximum; greater Fe availability may have stimulated the biological pump and contributed to the ice age drawdown of atmospheric C02. These results also imply that large‐scale southern ocean Fe fertilization is feasible, at least in terms of the total amounts of Fe required; i.e., 100,000 to

ISSN:0886-6236    

DOI:10.1029/GB004i001p00005

年代:1990

数据来源: WILEY

摘要:

In an accompanying paper, Martin et al. [this issue] interpret the results of four iron enrichment experiments using Antarctic seawater to indicate iron limitation of phytoplankton growth and nitrate uptake and suggest that Fe additions may contribute to reducing atmospheric CO2and the greenhouse problem. We have published a review [Dugdale and Wilkerson, 1989] of nitrogen uptake measurements using15N in Antarctic waters and here reanalyze the nitrate depletion data of Martin et al. [this issue], reported as absolute uptake rates (ρ with units of concentration per unit time), in the context of previous investigations by converting the data to nitrogen‐specific uptake rates (V, in reciprocal time units). We conclude that Fe addition to the enclosed water does not affect the algal growth terms due to nitrate uptake per se, but apparently influences loss terms enabling phytoplankton biomass to accumulate in the experimental bottl

ISSN:0886-6236    

DOI:10.1029/GB004i001p00013

年代:1990

数据来源: WILEY

摘要:

Laboratory and in situ measurements of soil methane consumption in a moist forest area of central Panama indicate that the conversion of forests to agricultural lands diminishes the soil sink for atmospheric methane. Rates of microbial methane consumption in agricultural soils were one fourth those of undisturbed forest soils. This reduction in soil methane consumption may partially account for past and future increases in atmospheric methane concentrations.

ISSN:0886-6236    

DOI:10.1029/GB004i001p00021

年代:1990

数据来源: WILEY

摘要:

Emissions of CH4were measured by a static chamber technique (five chambers/site) at 23 sites in four fens near Schefferville, subarctic Quebec. At three intensively‐monitored sites along a transect from fen margin to central and flooded sites, mean CH4fluxes from June to August, 1989 were 65, 125, and 36 mg m−2d−1, respectively. Pore water CH4concentrations in the peat profiles to a depth of l m averaged 125 to 200 μM, with lower concentrations (generally<50 μM) at 0.1 m. Total, depth‐integrated storage of CH4in the peat profiles ranged from 3.5 to 4.3 g m−2. Although CH4flux was only weakly correlated with either peat temperature at 0.1 m or water table position within each site, there was a strong association of flux and these variables among the three sites, indicating the value of ecological attributes in identifying patterns of CH4flux. A pulse of CH4was recorded at two of the three sites in mid‐August, associated with a degassing of the peat profile, based on pore water CH4concentrations. This pulse appeared to be initiated by the lowering of the water table by between 5 and 10 cm during a 3‐week period of low rainfall and is estimated to have contributed 18 to 65% of the seasonal CH4emission, depending on the location of the site. An estimate of the regional CH4flux from 130 km2of the Schefferville area was based on CH4flux measurements at 23 sites in the area, stratified by fen type (forested margin, margin, central, flooded, ridge, and pool). June to August regional CH4flux was 18 mg m−2d−1, for an area in which fen coverage was 29%. When extrapolated to the global scale, these results indicate that northern fens may contribute about 14 Tg yr−1, somewhat lower than o

ISSN:0886-6236    

DOI:10.1029/GB004i001p00029

年代:1990

数据来源: WILEY

摘要:

To refine estimates of source strengths from agricultural wetlands and to study the process of methane production and emission, this study was carried out in rice fields at the Texas A&M University Agricultural Research and Extension Center, Beaumont, Texas, during the summer of 1989. It focussed on two fields on different soil types (Lake Charles clay and Beaumont clay) and spanned a period from shortly after permanent field flooding (June 6, 1989) until field draining prior to harvest (August 28, 1989). Integrated methane emission over 75 days ranged from 4.5 to 15.9 g m−2. Aboveground biomass, net primary production, and root biomass were determined. Methane emission was strongly related to aboveground biomass in one of two fields studied. Laboratory incubations of soil cores show that methane production by soil bacteria is highest near the soil surface in the rice row and decreases with depth and distance from the plant. Much of the seasonal increase in total methane production is due to increasing activity at intermediate depths and distances from the plants. The temporal and spatial distribution of methane production was found to be related to root biomass. Seasonally integrated emission was 42% of methane production in both fields. Soil pore water methane and plant stem gas composition are related to the distribution in the soil of methane production and root biomass. Methane production ceased with field draining prior to harvest, even following prolonged anaerobic incubation. Methanogenesis rapidly resumed with added acetate substrat

ISSN:0886-6236    

DOI:10.1029/GB004i001p00047

年代:1990

数据来源: WILEY

摘要:

The exchange of CO2between the atmosphere and tropical forest ecosystem of American Samoa was continuously monitored for 3 days in December 1988. The island was modeled as a simple wind‐ventilated respiration chamber with CO2input concentration, CO2output concentration, and residence time as measured variables. Net ecosystem production rates were calculated by incorporating Gaussian vertical diffusion into the model. Nighttime respiration averaged 0.34 (±0.06) g C m−2h−1; peak midday uptake was 0.85 (±0.23) g C m−2h−1. Thirty‐nine percent (±30%) more carbon was assimilated by the ecosystem during the day than was released at night. The diurnal net ecosystem production averaged 1.5 g C m−2d−1. The daytime CO2exchange rate varied as the logarithm of incident solar radiation over a range of 30 W/m2to 900 W/m2, with r2= 0.87. Total ecosystem respiration equaled photosynthesis at a radiation intensity of 72 (±14) W/m2. The saturation int

ISSN:0886-6236    

DOI:10.1029/GB004i001p00069

年代:1990

数据来源: WILEY

摘要:

Particulate Ba profiles were measured in the Indian sector of the southern ocean. The largest fraction (>80%) of this barium is present as barite microcrystals. The profiles of total barium are characterized by a subsurface maximum between 200 and 500 m depth in the vicinity of the oxygen minimum. Highest barium values are found just south of the Polar Front, while lowest values occur close to the Antarctic Divergence. Between the divergence and the Polar Front a tight inverse relationship is observed between oxygen in the oxygen minimum and barium in the barium maximum. This relationship disappears north of the Polar Front. Since suspended barite is known to be of biological origin, the correlation of barite with oxygen suggests that the observed decrease of oxygen in the oxygen minimum, between the divergence and the Polar Front is due to local consumption of oxygen. It is proposed that deep low oxygen water is advected towards the Divergence where upwelling occurs and where this water subsequently partly spreads out to the north, north‐east, as entrained by the Antarctic Circumpolar Current. Oxidation of locally produced organic matter, with which barite crystals are associated, consumes oxygen and sets free individual discrete barites. As a result, oxygen decreases and barite increases away from the divergence, with barite integrating former biological processe

ISSN:0886-6236    

DOI:10.1029/GB004i001p00085

年代:1990

数据来源: WILEY

摘要:

Accelerator mass spectrometric radiocarbon measurements on benthic foraminifera shells, picked from samples on which concordant ages were obtained on the shells of two species of planktonic foraminifera, reveal that the age of deep water in the equatorial Atlantic during glacial time was 675±80 years (compared to today's age of 350 years) and that the age of deep water in the South China Sea was 1670±105 years (compared to today's value of 1600 years). These results demonstrate that the 1.3 to 1.5 times higher radiocarbon content of carbon in glacial surface waters of the Caribbean Sea reconstructed by Bard et al. [1990] was primarily the result of a higher global inventory of radiocarbon rather than a decrease in rate of mixing between surface and deep waters of the ocean. The results are also consistent with the conclusion by Boyle and Keigwin [1987]that the flow of North Atlantic Deep Water was considerably weakened during glacial time, allowing deep waters of Antarctic origin to push much further north into the Atlantic than they do toda

ISSN:0886-6236    

DOI:10.1029/GB004i001p00103

年代:1990

数据来源: WILEY