"Figures, tables and the appendices appear in the volume II". Bibliography: leaves 130-152.

"Figures, tables and the appendices appear in the volume II". / Bibliography: leaves 130-152. / 2 v. (152 leaves, [5] leaves of plates; [75] leaves) : ill. (some col.), col. maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Botany, 2001

Ice cores are considered the gold standard for recording past climate and biogeochemical changes. However, gas records derived from ice core analysis have until now been largely limited to centennial and longer timescales because sufficient temporal resolution and analytical precision have been lacking, except during rare times when atmospheric concentrations changed rapidly. In this thesis I used a newly developed methane measurement line to make high-resolution, high-precision measurements of methane during the late Holocene (2800 years BP to present). This new measurement line is capable of an analytical precision of < 3 ppb using ~120 g samples whereas the previous highest resolution measurements attained a precision of ± 4.1 ppb using 500-1500g samples [MacFarling Meure et al., 2006]. The reduced sample size requirements as well as automation of a significant portion of the analysis process have enabled me to make >1500 discrete ice core methane measurements and construct the highest resolution records of methane available over the late Holocene. Ice core samples came from the recently completed West Antarctic Ice Sheet (WAIS) Divide ice core which has as one of its primary scientific objectives to produce the highest resolution records of greenhouse gases, and from the Greenland Ice Sheet Project (GISP2) ice core which is a proven paleoclimate archive. My thesis has the following three components. I first used a shallow ice core from WAIS Divide (WDC05A) to produce a 1000 year long methane record with a ~9 year temporal resolution. This record confirmed the existence of multidecadal scale variations that were first observed in the Law Dome, Antarctica ice core. I then explored a range of paleoclimate archives for possible mechanistic connections with methane concentrations on multidecadal timescales. In addition, I present a detailed description of the analytical methods used to obtain high-precision measurements of methane including the effects of solubility and a new chronology for the WDC05A ice core. I found that, in general, the correlations with paleoclimate proxies for temperature and precipitation were low over a range of geographic regions. Of these, the highest correlations were found from 1400-1600 C.E. during the onset of the Little Ice Age and with a drought index in the headwater region of the major East Asian rivers. Large population losses in Asia and the Americas are also coincident with methane concentration decreases indicating that anthropogenic activities may have been impacting multidecadal scale methane variability. In the second component I extended the WAIS Divide record back to 2800 years B.P. and also measured methane from GISP2D over this time interval. These records allowed me to examine the methane Inter-Polar Difference (IPD) which is created by greater northern hemispheric sources. The IPD provides an important constraint on changes in the latitudinal distribution of sources. We used this constraint and an 8-box global methane chemical transport model to examine the Early Anthropogenic Hypothesis which posits that humans began influencing climate thousands of years ago by increasing greenhouse gas emissions and preventing the onset of the next ice age. I found that most of the increase in methane sources over this time came from tropical regions with a smaller contribution coming from the extratropical northern hemisphere. Based on previous modeling estimates of natural methane source changes, I found that the increase in the southern hemisphere tropical methane emissions was likely natural and that the northern hemispheric increase in methane emissions was likely due to anthropogenic activities. These results also provide new constraints on the total magnitude of pre-industrial anthropogenic methane emissions, which I found to be between the high and low estimates that have been previously published in the literature. For the final component of my thesis I assembled a coalition of scientists to investigate the effects of layering on the process of air enclosure in ice at WAIS Divide. Air bubbles are trapped in ice 60-100m below the surface of an ice sheet as snow compacts into solid ice in a region that is known as the Lock-In Zone (LIZ). The details of this process are not known and in the absence of direct measurements previous researchers have assumed it to be a smooth process. This project utilized high-resolution methane and air content measurements as well as density of ice, δ¹⁵N of N₂, and bubble number density measurements to show that air entrapment is affected by high frequency (mm scale) layering in the density of ice within the LIZ. I show that previous parameterizations of the bubble closure process in firn models have not accounted for this variability and present a new parameterization which does. This has implications for interpreting rapid changes in trace gases measured in ice cores since variable bubble closure will impact the smoothing of those records. In particular it is essential to understand the details of this process as new high resolution ice core records from Antarctica and Greenland examine the relative timing between greenhouse gases and rapid climate changes. / Graduation date: 2013

Upland soils are a significant sink of atmospheric methane, but the organisms responsible for methane consumption have yet to be identified. The ecology of methanotrophs was investigated in a beech forest soil which exhibited atmospheric-methane-uptake. Maximal methane-oxidation was observed in the upper mineral layer between the organic and inorganic horizons at a rate of 3.1 +/- 0.3 nmoles CH 4 g [fresh wt soil]-1 d-1. A clone bank of the methanotroph pmoA gene was constructed by PCR amplification from soil DNA extracts. The PCR primers used coamplify the related amoA gene of ammonia-oxidizers. The clones recovered grouped into three clusters: Nitrosospira-like sequences, a group somewhat related to alpha-Proteobacteria methanotrophs and previously referred to as the RA14 group, and a cluster which could not be characterized as either amoA or pmoA sequences. No pmoA genes closely related to genera of cultured methanotrophs were obtained. The 16S rDNA was also targeted using eubacterial and methanotroph-specific primers. 16S rDNA sequence analysis revealed the presence of organisms distantly related to known methanotrophs. Methanotroph enrichment cultures were established by inoculating mineral salts medium with soil and incubating under an atmosphere of 10% methane in air. Gene sequencing from the enrichments indicated the presence of organisms belonging to the genera Methylosinus and Methylocystis. The results suggest that the dominant methanotrophs in the forest soil are not related to known organisms and do not grow under conditions typically used to isolate methanotrophs.

Net ecosystem exchange of CO$ sb2$ (NEE) and CH$ sb4$ flux were measured at five sites within a boreal peatland near Thompson, Manitoba, from June through September, 1994. Sites were chosen to represent the different plant communities present along a productivity gradient where the water table was at or near the peat surface. Methane emissions, water table depth, and peat temperature were measured on weekly basis, while the relationship between photosynthetically active radiation (PAR) and net ecosystem exchange of CO$ sb2$ was determined three times during the field season, and then used to develop net ecosystem production (NEP) models at each site. Porewater methane was sampled for $ rm delta sp{13}C/ sp{12}C$ isotopic analysis once a month. / Among the sites, after PAR, light CO$ sb2$ flux was primarily controlled by sedge biomass and water table position, while dark CO$ sb2$ flux was controlled by peat temperature. From early June to late August, the five sites consumed approximately 1 to 2 g $ rm CO sb2$-C m$ rm sp{-2}d sp{-1}$. Seasonal CH$ sb4$ fluxes ranged between 16 and 456 mg $ rm CH sb4 m sp{-2}d sp{-1}$, and were higher than fluxes measured at other boreal sites in the same latitude. Seasonal average NEP was a good predictor of seasonal CH$ sb4$ fluxes from the sites (r$ sp2$ = 0.50), providing a model which estimates CH$ sb4$ flux based on site productivity alone. Stable carbon isotope analysis indicates root exudates that stimulate methanogenesis are an important control on this relationship, as is a high water table, particularly in its influence on the depth of the CH$ sb4$ oxidizing layer in the peat. These results suggest NEP measurements have the potential to be used in remote sensing applications to estimate CH$ sb4$ flux from wetlands, but that their use may be restricted to inundated sites.

Methane (CH$ sb4$) fluxes were measured in a range of peatland sites by a static chamber method in two regions of northern Canada, the Clay Belt of boreal Ontario and the Labrador Trough of subarctic Quebec. In both regions, seasonal mean water table position was the best predictor of mean CH$ sb4$ flux when microtopography was included in the analysis (r$ sp2$ = 0.73; p $<$ 0.01). The regression coefficients (slopes) were similar in both regions, suggesting a similar functional relationship between water table position and CH$ sb4$ flux; but the constants (intercepts) were different, implying a regional difference in climate or other biogeochemical factors. Broad-scale wetland classifications that do not account for microtopography and regional differences are inadequate for predicting CH$ sb4$ flux. / Vegetation and a suite of environmental variables in both regions were analyzed with multivariate statistics. Canonical correspondence analysis (CCA) showed that hydrology (water table position) explains most of the variability in bryophyte distribution, with chemistry (pore-water pH, Ca, Mg) as the second most important factor. The relative importance of the variables is reversed for vascular species in the Clay Belt; variables correlating with bryophyte and vascular species distribution are more similar in the Labrador Trough. Hydrology and chemistry are independent variables in both regions. CH$ sb4$ flux correlated strongly with hydrology in both regions, but not with chemistry. / Because of the strong correlation between bryophytes and CH$ sb4$ flux in the CCA analyses, a predictive model was developed using weighted averaging (WA) calibration. Optimum CH$ sb4$ flux values are highest for carpet/pool species and lowest for hummock species. No overlap in WA tolerances occurs between hummock and pool species, suggesting species at either end of the moisture gradient are the best predictors of CH$ sb4$ flux. Although the model works best within and not among regions, it has potential application in remote sensing of bryophytes for regional CH$ sb4$ budgets, paleoenvironmental reconstructions of CH$ sb4$ flux, and biological monitoring of future changes in CH$ sb4$ flux from climate-induced changes in peatland hydrology.

Emissions of methane were measured by a static chamber technique at 9 sites on 5 wetlands in the Eastern Temperate Wetland Region, north of Montreal. Mean daily methane fluxes measured from May to October ranged from 0.18 to 1071 mg/m$ sp2$/d, and estimated annual flux ranged from 0.02 to 186 g/m$ sp2$/y. Laboratory incubations of peat samples showed potential anaerobic methane production rates which ranged from 0.00 to 9.12 $ mu$g/g/d, and potential aerobic consumption rates from 0.55 to 3.75 $ mu$g/g/d. Seasonal methane emission patterns are related to water table level and CH$ sb4$ production and consumption potentials in the peat profile. Episodic fluxes were found to be important at several sites, contributing a significant portion of the total emissions. / Analysis of spectral reflectance data from 20 sites on 2 subarctic fens was carried out to address the issue of scaling up CH$ sb4$ emissions using satellite imagery. Hummocks, lawns and pools were found to be spectrally distinct enough to be differentiated by band 5 of Landsat MSS and band 3 of Landsat TM sensors. The averaging of spectral information in mixed pixels proved unlikely to be able to distinguish between wet lawn and string and pool communities. Such weaknesses can be overcome with the use of higher resolution data.

Thesis (M.S.)--University of North Carolina at Greensboro, 2007. / Title from PDF t.p. (viewed Mar. 11, 2008). Directed by : Anne E. Hershey; submitted to the Dept. of Biology. Includes bibliographical references (p. 29-34).

Thesis (M. Sc.)--University of Hong Kong, 1999. / Includes bibliographical references.

The work presented here represents a number of independent studies that investigated various components of the CH4 budget, namely the sources and sinks. We used a chemical-tracer model and created unique long-term time series of atmospheric CH4, carbon monoxide (CO), molecular hydrogen (H2), and methylchloroform (CH3CCl3) measurements at marine background air to derive histories of atmospheric hydroxyl radical (OH) - the main chemical oxidant of CH4, biomass burning - an important source of CH4 in the tropics, and emissions of CH4 from rice paddies - one of the largest anthropogenic sources of CH4, over decadal scales. Globally gridded inventories of CH4 emissions from rice paddies and terrestrial vegetation were created by synthesizing greenhouse and field CH4 fluxes, satellite-derived biophysical data, and terrestrial geospatial information.