New measurements of the carbon and hydrogen isotopic ratios of methane (δ13C of CH4 and δD of CH4) over the last millennium are presented from the WAIS Divide, Antarctica, ice core (WDC05A), showing ...significant changes that likely were the result of human influences prior to the industrial revolution (at least as early as the 16th century of the common era (CE)). The δ13C of CH4 data corroborate the record from Law Dome, Antarctica, with high fidelity. The new δD of CH4 data set covaries with the δ13C of CH4 record. Both δ13C of CH4 and δD of CH4 were relatively stable and close to the present‐day values from ∼1000 to ∼1500 CE. Both isotopic ratios decreased to minima around 1700 CE, remained low until the late 18th century, and then rose exponentially to present‐day values. Our new δD of CH4 data provide an additional independent constraint for evaluating possible CH4 source histories. We searched a broad range of source scenarios using a simple box model to identify histories consistent with the constraints of the CH4 concentration and isotope data from 990–1730 CE. Results typically show a decrease over time in the biomass‐burning source (found in 85% of acceptable scenarios) and an increase in the agricultural source (found in 77% of acceptable scenarios), indicating preindustrial human influence on atmospheric methane as proposed in previous studies.
The total air content (TAC) of polar ice cores has long been considered a potential proxy for past ice sheet elevation. Recent work, however, has shown that a variety of other factors also influence ...this parameter. In this paper we present a high-resolution TAC record from the South Pole ice core (SPC14) covering the last 54 000 years and discuss the implications of the data for interpreting TAC from ice cores. The SPC14 TAC record shows multiple features of interest, including (1) long-term orbital-scale variability, (2) millennial-scale variability in the Holocene and last glacial period, and (3) a period of stability from 35 to 25 ka. The longer, orbital-scale variations in TAC are highly correlated with integrated summer insolation (ISI), corroborating the potential of TAC to provide an independent dating tool via orbital tuning. Large millennial-scale variability in TAC during the last glacial period is positively correlated with past accumulation rate reconstructions as well as δ15N-N2, a firn thickness proxy. These TAC variations are too large to be controlled by direct effects of temperature and too rapid to be tied to elevation changes. We propose that grain size metamorphism near the firn surface explains these changes. We note, however, that at sites with different climate histories than the South Pole, TAC variations may be dominated by other processes. Our observations of millennial-scale variations in TAC show a different relationship with accumulation rate than observed at sites in Greenland.
Ice cores that were recovered from the summit of Sajama mountain in Bolivia provide carbon-14-dated tropical records and extend to the Late Glacial Stage (LGS). Oxygen isotopic ratios of the ice ...decreased 5.4 per mil between the early Holocene and the Last Glacial Maximum, which is consistent with values from other ice cores. The abrupt onset and termination of a Younger Dryas-type event suggest atmospheric processes as the probable drivers. Regional accumulation increased during the LGS, during deglaciation, and over the past 3000 years, which is concurrent with higher water levels in regional paleolakes. Unlike polar cores, Sajama glacial ice contains eight times less dust than the Holocene ice, which reflects wetter conditions and extensive snow cover.
Isoflavones are naturally occurring selective estrogen receptor modulators, with potential bone protective effects. To study the relation between soy isoflavone intake and bone mineral density (BMD), ...the authors analyzed baseline data from the Study of Women's Health Across the Nation, a US community-based cohort study of women aged 42–52 years. Their 1996–1997 analysis included African-American (n = 497), Caucasian (n = 1,003), Chinese (n = 200), and Japanese (n = 227) participants. Genistein and daidzein intakes were highly correlated (r = 0.98); therefore, analyses were conducted by using genistein. Median intakes of genistein (measured in micrograms/day) by African Americans and Caucasians were too low to pursue relational analyses further. For Chinese and Japanese women, median genistein intakes were 3,511 and 7,151 μg/day, respectively. Ethnic-specific, linear models were used to predict BMD as a function of energy-adjusted tertile of intake, controlled for relevant covariates. For Chinese women, no association between genistein and BMD was found. Premenopausal, but not perimenopausal, Japanese women whose intakes were greater had higher spine and femoral neck BMD. Adjusted mean spinal BMD of those in the highest tertile of intake was 7.7% greater than that of women in the lowest tertile (p = 0.02); femoral neck BMD was 12% greater in the highest versus the lowest tertile (p < 0.0001).
Emerging evidence indicates that impaired mitochondrial fatty acid β-oxidation plays a key role in liver steatosis. We have recently demonstrated that increased angiotensin (ANG) II causes ...progressive hepatic steatosis associated with oxidative stress; however, the underlying mechanisms remain unclear. We hypothesized that ANG II causes hepatic mitochondrial oxidative damage and impairs mitochondrial β-oxidation, thereby leading to hepatic steatosis. We used the Ren2 rat with elevated endogenous ANG II levels to evaluate mitochondrial ultrastructural changes, gene expression levels, and β-oxidation. Compared with Sprague-Dawley littermates, Ren2 livers exhibited mitochondrial damage and reduced β-oxidation, as evidenced by ultrastructural abnormalities, decrease of mitochondrial content, percentage of palmitate oxidation to CO2 , enzymatic activities (β-HAD and citrate synthase), and the expression levels of cytochrome c , cytochrome c oxidase subunit 1, and mitochondrial transcription factor A. These abnormalities were improved with either ANG II receptor blocker valsartan or superoxide dismutase/catalase mimetic tempol treatment. Both valsartan and tempol substantially attenuated mitochondrial lipid peroxidation in Ren2 livers. Interestingly, there was no difference in the expression of key enzymes (ACC1 and FAS) for fatty acid syntheses and their transcription factors (SREBP-1c and ChREBP) between Sprague-Dawley, untreated Ren2, and valsartan- or tempol-treated Ren2 rats. These results document that ANG II induces mitochondrial oxidative damage and impairs mitochondrial β-oxidation, contributing to liver steatosis.
Methanogenesis, the biological production of methane, plays a pivotal role in the global carbon cycle and contributes significantly to global warming. The majority of methane in nature is derived ...from acetate. Here we report the complete genome sequence of an acetate-utilizing methanogen, Methanosarcina acetivorans C2A. Methanosarcineae are the most metabolically diverse methanogens, thrive in a broad range of environments, and are unique among the Archaea in forming complex multicellular structures. This diversity is reflected in the genome of M. acetivorans. At 5,751,492 base pairs it is by far the largest known archaeal genome. The 4524 open reading frames code for a strikingly wide and unanticipated variety of metabolic and cellular capabilities. The presence of novel methyltransferases indicates the likelihood of undiscovered natural energy sources for methanogenesis, whereas the presence of single-subunit carbon monoxide dehydrogenases raises the possibility of nonmethanogenic growth. Although motility has not been observed in any Methanosarcineae, a flagellin gene cluster and two complete chemotaxis gene clusters were identified. The availability of genetic methods, coupled with its physiological and metabolic diversity, makes M. acetivorans a powerful model organism for the study of archaeal biology. Sequence, data, annotations and analyses are available at http://www-genome.wi.mit.edu/.
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