Laboratory and field studies have demonstrated that fluid motion occurs at two locations in growing sea ice: in a network of brine channels and within the skeletal layer at the ice-water interface. Brine channel fluxes estimated using brine channel areal density from natural sea ice and channel velocities from laboratory studies are compared with recent measurements reported in the literature. Fluxes into the porous skeletal layer of sea ice may be estimated using rates of nutrient uptake by ice algae and adjacent seawater nutrient concentrations. Both approaches indicate fluxes of the order of 10-6 cc cm-2 s-1 (l m-2 h-1), which are about equal to fluxes reported in bioirrigated sediments. Fluxes of this magnitude indicate a very short residence time for the liquid phase in the skeletal layer, suggesting that this fluid motion may be important in maintaining the ice algae community. © 1984 Springer-Verlag.

Methane flux measurements were made during the summer of 1987 at 10 km intervals along a north-south transect from Prudhoe Bay (70°13′N) to the Arctic Circle (66°30′N) in Alaska. A regional comparison showed that the mean CH4 flux from arctic tundra (52 mg m-2 d-1) was significantly greater than the mean from high latitude taiga (11 mg m-2 d-1). Mean CH4 fluxes (mg m-2 d-1) for each category were: wet tundra, 90; low brush-muskeg bog, 45; moist tundra, 31; freshwater ponds, 21; spruce forest, 4.6; and alpine tundra, 0.6. Differences among means were statistically significant. Annual CH4 emission from global tundra and taiga environments of 38 Tg and 15 Tg. -from Authors

Sediment depth distributions and fluxes of dissolved chemical substances have been interpreted as being a result of reaction, diffusion, bioturbation and irrigation1,2. However, several studies suggest that density-driven convection3 can alter the depth distribution and increase the fluxes of dissolved substances when density decreases below the sediment surface 4-7. We present here temperature-time series measurements for a freshwater lake undergoing autumn cooling. These are the first in situ observations of heat transport due to motion of interstitial waters over periods of less than 1 hour. Density, calculated from temperature, decreases with depth at the time and place that this motion occurs. © 1982 Nature Publishing Group.

We used laboratory experiments to evaluate CH4 uptake kinetics and the influence of soil moisture and temperature on rates of CH4-oxidation by boreal soils at in situ CH4 concentrations. Two upland forest site (AS2 and BS2) were atmospheric CH4 sinks; a bog site (LB) was an atmospheric CH4 source characterized by distinct depth zonation of CH4 production and consumption. Apparent half-saturation constants (K(s)) for CH4-oxidation showed relatively well-adapted communities. The K(s) for the high CH4-source soil (LB) was 1.1 μM, about 10-fold higher than values for CH4-sink soils (AS2 and BS2), 37 and 124 nM. Experiments assessing the individual effects of moisture and temperature on CH4-oxidation indicated that moisture was the primary control in CH4-sink soils at AS2 and BS2, while temperature was more important in CH4-source soil at LB. A combination of the highest moisture content and lowest temperature for each soil gave the lowest CH4-oxidation rates in experiments evaluating the interactive effects of these two variables. Conversely, a soil moisture content close to the optimum identified in moisture dependence experiments combined with the highest soil temperature consistently gave the highest CH4-oxidation rate.

We conducted a 14C pulse-labeling experiment under field conditions to estimate the contribution of recent photosynthates to methane (CH4) emission in arctic wet sedge tundra dominated by Carex aquatilis and Eriophorum angustifolium. The average CH4 emission rate from plant-soil mesocosms in this study was 0.45 g C m-2 d-1. Carbon assimilated by plants via photosynthesis during pulse-labeling turned over rapidly and appeared as emitted CH4 within 24 h. Integration of flux measurements made over a 2-week period shows that the contribution of recent photosynthates to mid-season CH4 emission is relatively low. Less than 1% of the 14C-labeled carbon dioxide taken up through photosynthesis was emitted as 14CH4 during this study. © 2002 Elsevier Science Ltd. All rights reserved.

Biological consumption by aerobic soils is an important, but poorly understood sink for carbon monoxide, a chemically active atmospheric trace gas. We used laboratory experiments to characterize CO consumption in representative soils of the northern boreal forest. This ecozone may be important in atmospheric CO consumption because it occupies 13% of the world's landmass. Soils initially showing net CO consumption emitted CO following biocidal treatment (ethylene oxide or γ-irradiation), indicating that CO consumption was biologically mediated. The use of selective inhibitors (cycloheximide, streptomycin) suggested that both prokaryotes and eukaryotes were responsible. Soil profiles generally indicated net consumption of atmospheric CO to a depth of 15 cm (concentrations decreasing from ∼150 to <20 nl l-1 with depth) and a dynamic equilibrium between CO production and consumption in deeper soils (concentrations nearly constant at <20 nl l-1). Soils to a depth of 30 cm showed vigorous CO-consuming activity, suggesting that local CO production provided necessary substrate beneath the 15 cm surface zone of atmospheric influence. Radiotracer experiments demonstrated that only 5-7% of assimilated 14CO was incorporated into biomass in 5 cm core sections taken to 30 cm and that <1% of assimilated 14CO was incorporated into cellular material by a methanotroph isolated from this soil. Collectively, these data point to nonutilitarian oxidation of CO by a diverse microbial community. Carbon monoxide oxidation increased with increasing temperature over the range 4-34°C, with a Q10 of 1.8. Apparent half-saturation constants (8-36 (μl CO l-1), and maximum rates of CO consumption (0.7-2.7 μg g dry soil-1 h-1) were comparable to reports for diverse temperate soil environments, pointing to a fundamental similarity among CO-consuming microbial communities in aerobic soils. © 2001 Elsevier Science Ltd. All rights reserved.

EMISSION of methane from tundra soil contributes about 10% of the global atmospheric methane budget1. Moreover, tundra soils contain 15% of global soil carbon2, so the response of this large carbon reservoir to projected global warming3,4 could be important. Coupled biological models3-6 predict that a warmer climate will increase methane emission through increased rates of methanogenesis. Microbial oxidation of methane is, however, a possible control on emissions that has previously been overlooked. Here we report the results of field and laboratory experiments on methane consumption by tundra soils. For methane concentrations ranging from below to well above ambient, moist soils were found to consume methane rapidly; in non-waterlogged soils, equilibration with atmospheric methane was fast relative to microbial oxidation. We conclude that lowering of the water table in tundra as a result of a warmer, drier climate will decrease methane fluxes and could cause these areas to provide a negative feedback for atmospheric methane. © 1990 Nature Publishing Group.