Julianna Eileen Fessenden
California Institute of Technology
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Global Biogeochemical Cycles | 2002
James T. Randerson; G. J. Collatz; Julianna Eileen Fessenden; A. D. Munoz; Christopher J. Still; Joseph A. Berry; Inez Y. Fung; Neil S. Suits; A. S. Denning
the potential to influence the 13 C budget of the atmosphere because these changes scale with the relatively large one-way gross primary production (GPP) flux. Over a period of days to years, this atmospheric isotopic forcing is damped by the return flux consisting mostly of respiration, Fire, and volatile organic carbon losses. Here we explore the magnitude of this class of isotopic disequilibria with an ecophysiological model (SiB2) and a double deconvolution inversion framework that includes timevarying discrimination for the period of 1981–1994. If the net land carbon sink and plant 13 C discrimination covary on interannual timescales at the global scale, consistent with
Geophysical Research Letters | 2002
Thom Rahn; John M. Eiler; Nami Kitchen; Julianna Eileen Fessenden; James T. Randerson
We examined the concentration and δD of atmospheric H2 in a boreal forest in interior Alaska to investigate the systematics of high latitude soil uptake at ecosystem scale. Samples collected during nighttime inversions exhibited vigorous H_2 uptake, with concentration negatively correlated with the concentration of CO_2 (−0.8 to −1.2 ppb H_2 per ppm CO_2) and negatively correlated with δD of H_2. We derived H_2 deposition rates of between 2 to 12 nmol m^(−2) s^(−1). These rates are comparable to those observed in lower latitude ecosystems. We also derive an average fractionation factor, α = D:H_(residual)/D:H_(consumed) = 0.94 ± 0.01 and suggestive evidence that α depends on forest maturity. Our results show that high northern latitude soils are a significant sink of molecular hydrogen indicating that the record of atmospheric H_2 may be sensitive to changes in climate and land use.
Global Biogeochemical Cycles | 2003
Alon Angert; Eugeni Barkan; Bruce Barnett; Enrico Brugnoli; Eric A. Davidson; Julianna Eileen Fessenden; Somsak Maneepong; Nipa Panapitukkul; James T. Randerson; Kathleen Savage; Dan Yakir; Boaz Luz
[1] The 18 O content of atmospheric O2 is an important tracer for past changes in the biosphere. Its quantitative use depends on knowledge of the discrimination against 18 O associated with the various O2 consumption processes. Here we evaluated, for the first time, the in situ 18 O discrimination associated with soil respiration in natural ecosystems. The discrimination was estimated from the measured [O2] and d 18 Oo f O2 in the soilair. The discriminations that were found are 10.1 ± 1.5%, 17.8 ± 1.0%, and 22.5 ± 3.6%, for tropical, temperate, and boreal forests, respectively, 17.9 ± 2.5% for Mediterranean woodland, and 15.4 ± 1.6% for tropical shrub land. Current understanding of the isotopic composition of atmospheric O2 is based on the assumption that the magnitude of the fractionation in soil respiration is identical to that of dark respiration through the cytochrome pathway alone (� 18%). The discrimination we found in the tropical sites is significantly lower, and is explained by slow diffusion in soil aggregates and root tissues that limits the O2 concentration in the consumption sites. The high discrimination in the boreal sites may be the result of high engagement of the alternative oxidase pathway (AOX), which has high discrimination associated with it (� 27%). The intermediate discrimination (� 18%) in the temperate and Mediterranean sites can be explained by the opposing effects of AOX and diffusion limitation that cancel out. Since soil respiration is a major component of the global oxygen uptake, the contribution of large variations in the discrimination, observed here, to the global Dole Effect should be considered in global scale studies. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/ atmosphere interactions; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 1040 Geochemistry: Isotopic composition/chemistry; 1615 Global Change: Biogeochemical processes (4805); KEYWORDS: Dole Effect, oxygen isotopes, soil respiration Citation: Angert, A., et al., Contribution of soil respiration in tropical, temperate, and boreal forests to the 18 O enrichment of
Rapid Communications in Mass Spectrometry | 2002
Julianna Eileen Fessenden; Craig S. Cook; Michael J. Lott; James R. Ehleringer
Archive | 2010
Seth David Humphries; Samuel Michael Clegg; Thomas A. Rahn; Julianna Eileen Fessenden; Laura M. Dobeck; Lee H. Spangler; Travis L. McLing
Archive | 2002
Julianna Eileen Fessenden; James T. Randerson; Edward A. G. Schuur; Sergey Zimov
Global Biogeochemical Cycles | 2002
James T. Randerson; G. J. Collatz; Julianna Eileen Fessenden; A. D. Munoz; Christopher J. Still; Joseph A. Berry; Inez Y. Fung; Neil S. Suits; A. S. Denning
Geophysical Research Letters | 2002
Thom Rahn; John M. Eiler; Nami Kitchen; Julianna Eileen Fessenden; James T. Randerson
Archive | 2001
Julianna Eileen Fessenden; Hengfeng Li; Michelle C. Mack; Terry James Schuur; Stephen J. Warren; James T. Randerson
Archive | 2001
James T. Randerson; Neil S. Suits; Christopher J. Still; Julianna Eileen Fessenden; A. Scott Denning; James Berry; Inez Y. Fung