共查询到20条相似文献，搜索用时 31 毫秒
1.
Johnston DT Wing BA Farquhar J Kaufman AJ Strauss H Lyons TW Kah LC Canfield DE 《Science (New York, N.Y.)》2005,310(5753):1477-1479
The environmental expression of sulfur compound disproportionation has been placed between 640 and 1050 million years ago (Ma) and linked to increases in atmospheric oxygen. These arguments have their basis in temporal changes in the magnitude of 34S/32S fractionations between sulfate and sulfide. Here, we present a Proterozoic seawater sulfate isotope record that includes the less abundant sulfur isotope 33S. These measurements imply that sulfur compound disproportionation was an active part of the sulfur cycle by 1300 Ma and that progressive Earth surface oxygenation may have characterized the Mesoproterozoic. 相似文献
2.
The composition of sulfur isotopes in sedimentary sulfides and sulfates traces the sulfur cycle throughout Earth's history. In particular, depletions of sulfur-34 ((34)S) in sulfide relative to sulfate exceeding 47 per mil (‰) often serve as a proxy for the disproportionation of intermediate sulfur species in addition to sulfate reduction. Here, we demonstrate that a pure, actively growing culture of a marine sulfate-reducing bacterium can deplete (34)S by up to 66‰ during sulfate reduction alone and in the absence of an extracellular oxidative sulfur cycle. Therefore, similar magnitudes of sulfur isotope fractionation in sedimentary rocks do not unambiguously record the presence of other sulfur-based metabolisms or the stepwise oxygenation of Earth's surface environment during the Proterozoic. 相似文献
3.
A whiff of oxygen before the great oxidation event? 总被引：1，自引：0，他引：1
Anbar AD Duan Y Lyons TW Arnold GL Kendall B Creaser RA Kaufman AJ Gordon GW Scott C Garvin J Buick R 《Science (New York, N.Y.)》2007,317(5846):1903-1906
High-resolution chemostratigraphy reveals an episode of enrichment of the redox-sensitive transition metals molybdenum and rhenium in the late Archean Mount McRae Shale in Western Australia. Correlations with organic carbon indicate that these metals were derived from contemporaneous seawater. Rhenium/osmium geochronology demonstrates that the enrichment is a primary sedimentary feature dating to 2501 +/- 8 million years ago (Ma). Molybdenum and rhenium were probably supplied to Archean oceans by oxidative weathering of crustal sulfide minerals. These findings point to the presence of small amounts of O2 in the environment more than 50 million years before the start of the Great Oxidation Event. 相似文献
4.
The exogenic sulfur cycle is tightly coupled with the carbon and oxygen cycles, and therefore a central component of Earth's biogeochemistry. Here we present a high-resolution record of the sulfur isotopic composition of seawater sulfate for the Cretaceous. The general enrichment of isotopically light sulfur that prevailed during the Cretaceous may have been due to increased volcanic and hydrothermal activity. Two excursions toward isotopically lighter sulfur represent periods of lower rates of pyrite burial, implying a shift in the location of organic carbon burial to terrestrial or open-ocean settings. The concurrent changes in seawater sulfur and inorganic carbon isotopic compositions imply short-term variability in atmospheric oxygen partial pressure. 相似文献
5.
Graham NE 《Science (New York, N.Y.)》1995,267(5198):666-671
Observations show that global average tropospheric temperatures have been rising during the past century, with the most recent portion of record showing a sharp rise since the mid-1970s. This study shows that the most recent portion of the global temperature record (1970 to 1992) can be closely reproduced by atmospheric models forced only with observed ocean surface temperatures. In agreement with a diverse suite of controversial observational evidence from the past 40 years, the upward trend in simulated tropospheric temperatures is caused by an enhancement of the tropical hydrologic cycle driven by increasing tropical ocean temperatures. Although it is possible that the observed behavior is due to natural climate variability, there is disquieting similarity between these model results, observed climate trends in recent decades, and the early expressions of the climatic response to increased atmospheric carbon dioxide in numerical simulations. 相似文献
6.
Fluid inclusion data suggest that the composition of major elements in seawater changes slowly over geological time scales. This view contrasts with high-resolution isotope data that imply more rapid fluctuations of seawater chemistry. We used a non-steady-state box model of the global sulfur cycle to show that the global δ(34)S record can be explained by variable marine sulfate concentrations triggered by basin-scale evaporite precipitation and dissolution. The record is characterized by long phases of stasis, punctuated by short intervals of rapid change. Sulfate concentrations affect several important biological processes, including carbonate mineralogy, microbially mediated organic matter remineralization, sedimentary phosphorous regeneration, nitrogen fixation, and sulfate aerosol formation. These changes are likely to affect ocean productivity, the global carbon cycle, and climate. 相似文献
7.
The injection into the stratosphere of large quantities of sulfur during the June 1991 eruption of Mount Pinatubo (Philippines) and the subsequent formation of sulfate aerosol particles have generated a number of perturbations in the atmosphere with potential effects on the Earth's climate. Changes in the solar and infrared radiation budget caused by the eruption should produce a cooling of the troposphere and a warming of the lower stratosphere. These changes could affect atmospheric circulation. In addition, heterogeneous chemical reactions on the surface of sulfate aerosol particles render the ozone molecules more vulnerable to atmospheric chlorine and hence to man-made chlorofluorocarbons. 相似文献
8.
Joos F Plattner GK Stocker TF Marchal O Schmittner A 《Science (New York, N.Y.)》1999,284(5413):464-467
A low-order physical-biogeochemical climate model was used to project atmospheric carbon dioxide and global warming for scenarios developed by the Intergovernmental Panel on Climate Change. The North Atlantic thermohaline circulation weakens in all global warming simulations and collapses at high levels of carbon dioxide. Projected changes in the marine carbon cycle have a modest impact on atmospheric carbon dioxide. Compared with the control, atmospheric carbon dioxide increased by 4 percent at year 2100 and 20 percent at year 2500. The reduction in ocean carbon uptake can be mainly explained by sea surface warming. The projected changes of the marine biological cycle compensate the reduction in downward mixing of anthropogenic carbon, except when the North Atlantic thermohaline circulation collapses. 相似文献
9.
Schmitt J Schneider R Elsig J Leuenberger D Lourantou A Chappellaz J Köhler P Joos F Stocker TF Leuenberger M Fischer H 《Science (New York, N.Y.)》2012,336(6082):711-714
The stable carbon isotope ratio of atmospheric CO(2) (δ(13)C(atm)) is a key parameter in deciphering past carbon cycle changes. Here we present δ(13)C(atm) data for the past 24,000 years derived from three independent records from two Antarctic ice cores. We conclude that a pronounced 0.3 per mil decrease in δ(13)C(atm) during the early deglaciation can be best explained by upwelling of old, carbon-enriched waters in the Southern Ocean. Later in the deglaciation, regrowth of the terrestrial biosphere, changes in sea surface temperature, and ocean circulation governed the δ(13)C(atm) evolution. During the Last Glacial Maximum, δ(13)C(atm) and atmospheric CO(2) concentration were essentially constant, which suggests that the carbon cycle was in dynamic equilibrium and that the net transfer of carbon to the deep ocean had occurred before then. 相似文献
10.
Changes in the upwelling and degassing of carbon from the Southern Ocean form one of the leading hypotheses for the cause of glacial-interglacial changes in atmospheric carbon dioxide. We present a 25,000-year-long Southern Ocean radiocarbon record reconstructed from deep-sea corals, which shows radiocarbon-depleted waters during the glacial period and through the early deglaciation. This depletion and associated deep stratification disappeared by ~14.6 ka (thousand years ago), consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a Southern Ocean ventilation event. Given this evidence for carbon exchange in the Southern Ocean, we show that existing deep-ocean radiocarbon records from the glacial period are sufficiently depleted to explain the ~190 per mil drop in atmospheric radiocarbon between ~17 and 14.5 ka. 相似文献
11.
Anthropogenic increases of atmospheric carbon dioxide lead to warmer sea surface temperatures and altered ocean chemistry. Experimental evidence suggests that coral calcification decreases as aragonite saturation drops but increases as temperatures rise toward thresholds optimal for coral growth. In situ studies have documented alarming recent declines in calcification rates on several tropical coral reef ecosystems. We show there is no widespread pattern of consistent decline in calcification rates of massive Porites during the 20th century on reefs spanning an 11° latitudinal range in the southeast Indian Ocean off Western Australia. Increasing calcification rates on the high-latitude reefs contrast with the downward trajectory reported for corals on Australia's Great Barrier Reef and provide additional evidence that recent changes in coral calcification are responses to temperature rather than ocean acidification. 相似文献
12.
The large burden of sulfate aerosols injected into the stratosphere by the eruption of Mount Pinatubo in 1991 cooled Earth and enhanced the destruction of polar ozone in the subsequent few years. The continuous injection of sulfur into the stratosphere has been suggested as a "geoengineering" scheme to counteract global warming. We use an empirical relationship between ozone depletion and chlorine activation to estimate how this approach might influence polar ozone. An injection of sulfur large enough to compensate for surface warming caused by the doubling of atmospheric CO2 would strongly increase the extent of Arctic ozone depletion during the present century for cold winters and would cause a considerable delay, between 30 and 70 years, in the expected recovery of the Antarctic ozone hole. 相似文献
13.
A theory for el nino and the southern oscillation 总被引：1，自引：0，他引：1
A coupled atmosphere-ocean model is presented for El Ni?o and the Southern Oscillation that reproduces its major features, including its recurrence at irregular intervals. The interannual El Ni?o-Southern Oscillation cycle is maintained by deterministic interactions in the tropical Pacific region. Ocean dynamics alter sea-surface temperature, changing the atmospheric heating; the resulting changes in surface wind alter the ocean dynamics. Annually varying mean conditions largely determine the spatial pattern and temporal evolution of El Ni?o events. 相似文献
14.
The Eocene greenhouse climate state has been linked to a more vigorous hydrologic cycle at mid- and high latitudes; similar information on precipitation levels at low latitudes is, however, limited. Oxygen isotopic fluxes track moisture fluxes and, thus, the δ(18)O values of ocean surface waters can provide insight into hydrologic cycle changes. The offset between tropical δ(18)O values from sampled Eocene sirenian tooth enamel and modern surface waters is greater than the expected 1.0 per mil increase due to increased continental ice volume. This increased offset could result from suppression of surface-water δ(18)O values by a tropical, annual moisture balance substantially wetter than that of today. Results from an atmospheric general circulation model support this interpretation and suggest that Eocene low latitudes were extremely wet. 相似文献
15.
Atmospheric influence of Earth's earliest sulfur cycle 总被引：1，自引：0，他引：1
Mass-independent isotopic signatures for delta(33)S, delta(34)S, and delta(36)S from sulfide and sulfate in Precambrian rocks indicate that a change occurred in the sulfur cycle between 2090 and 2450 million years ago (Ma). Before 2450 Ma, the cycle was influenced by gas-phase atmospheric reactions. These atmospheric reactions also played a role in determining the oxidation state of sulfur, implying that atmospheric oxygen partial pressures were low and that the roles of oxidative weathering and of microbial oxidation and reduction of sulfur were minimal. Atmospheric fractionation processes should be considered in the use of sulfur isotopes to study the onset and consequences of microbial fractionation processes in Earth's early history. 相似文献
16.
A record of foraminiferal shell weight across glacial-interglacial Termination I shows a response related to seawater carbonate ion concentration and allows reconstruction of a record of carbon dioxide in surface seawater that matches the atmospheric record. The results support suggestions that higher atmospheric carbon dioxide directly affects marine calcification, an effect that may be of global importance to past and future changes in atmospheric CO2. The process provides negative feedback to the influence of marine calcification on atmospheric carbon dioxide and is of practical importance to the application of paleoceanographic proxies. 相似文献
17.
Shackleton NJ 《Science (New York, N.Y.)》2000,289(5486):1897-1902
The deep-sea sediment oxygen isotopic composition (delta(18)O) record is dominated by a 100,000-year cyclicity that is universally interpreted as the main ice-age rhythm. Here, the ice volume component of this delta(18)O signal was extracted by using the record of delta(18)O in atmospheric oxygen trapped in Antarctic ice at Vostok, precisely orbitally tuned. The benthic marine delta(18)O record is heavily contaminated by the effect of deep-water temperature variability, but by using the Vostok record, the delta(18)O signals of ice volume, deep-water temperature, and additional processes affecting air delta(18)O (that is, a varying Dole effect) were separated. At the 100,000-year period, atmospheric carbon dioxide, Vostok air temperature, and deep-water temperature are in phase with orbital eccentricity, whereas ice volume lags these three variables. Hence, the 100,000-year cycle does not arise from ice sheet dynamics; instead, it is probably the response of the global carbon cycle that generates the eccentricity signal by causing changes in atmospheric carbon dioxide concentration. 相似文献
18.
How much dissolved oxygen was present in the mid-Proterozoic oceans between 1.8 and 1.0 billion years ago is debated vigorously. One model argues for oxygenation of the oceans soon after the initial rise of atmospheric oxygen approximately 2.3 billion years ago. Recent evidence for H(2)S in some mid-Proterozoic marine basins suggests, however, that the deep ocean remained anoxic until much later. New molybdenum isotope data from modern and ancient sediments indicate expanded anoxia during the mid-Proterozoic compared to the present-day ocean. Consequently, oxygenation of the deep oceans may have lagged that of the atmosphere by over a billion years. 相似文献
19.
An unresolved issue in ocean and climate sciences is whether changes to the surface ocean input of the micronutrient iron can alter the flux of carbon to the deep ocean. During the Southern Ocean Iron Experiment, we measured an increase in the flux of particulate carbon from the surface mixed layer, as well as changes in particle cycling below the iron-fertilized patch. The flux of carbon was similar in magnitude to that of natural blooms in the Southern Ocean and thus small relative to global carbon budgets and proposed geoengineering plans to sequester atmospheric carbon dioxide in the deep sea. 相似文献
20.
Tropical origins for recent North Atlantic climate change 总被引：3，自引：0，他引：3
Evidence is presented that North Atlantic climate change since 1950 is linked to a progressive warming of tropical sea surface temperatures, especially over the Indian and Pacific Oceans. The ocean changes alter the pattern and magnitude of tropical rainfall and atmospheric heating, the atmospheric response to which includes the spatial structure of the North Atlantic Oscillation (NAO). The slow, tropical ocean warming has thus forced a commensurate trend toward one extreme phase of the NAO during the past half-century. 相似文献