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1.
The evolution of the atmospheric CO 2 content is partly a response to the lack of balance between oceanic sedimentation and continental weathering, because the oceanic C reservoir tends to balance net inputs or losses from slow processes by rapid exchanges with the atmospheric reservoir. This response strongly depends on both amplitudes and time scales of the related processes. At Milankovitch or lower time scales, global models generally do neglect organic matter fossilisation, but such an assumption is only valid for oligotrophic systems. In eutrophic or mesotrophic systems, organic matter is not negligible and should be considered relatively to the carbonate sedimentation in order to know whether the impact of the sedimentation was a source or a sink for atmospheric CO 2. To cite this article: P. Bertrand, C. R. Geoscience 334 (2002) 521–528. 相似文献
2.
To stabilize the atmospheric concentration of greenhouse gases (GHG), a huge reduction of carbon dioxide (CO 2) emissions is required. Although some people believe that this necessitates a considerable reduction in the use of fossil fuels or fuel switching, other options are available that allow the use of fossil fuels and reduce atmospheric emissions of CO 2. Sequestration of CO 2 from fossil fuel combustion in the subsurface could prevent the CO 2 from reaching the surface for millions of years. Geological sequestration of CO 2 in deep aquifers or in depleted oil and gas reservoirs is a mature technology. Despite the huge quantities of CO 2 that can be sequestered in this way, this approach does not provide any economic benefit. This paper discusses a third option, which consists of injecting CO 2 in deep coal seams to sequester the carbon and enhance the recovery of coalbed methane (CBM). Waste CO 2 from CBM-fueled power plants could be injected into CBM reservoirs to produce more methane (CH 4) for the power plant. The 2:1 coal-sorption selectivity for CO 2 over CH 4 supports the feasibility of operating fossil-fueled power plants without atmospheric CO 2 emissions. Other CO 2 sequestration technologies, such as ocean disposal and biofixation, are briefly discussed and the suitability of these approaches is evaluated for use in Alberta, Canada. 相似文献
3.
米兰科维奇理论认为,北半球高纬夏季太阳辐射变化是驱动第四纪冰期旋回的主因。这个理论的核心是单一敏感区的触发驱动机制,即北半球高纬气候变化信号被放大、传输进而影响全球。最近,由于大量高分辨率及精确定年的气候变化记录的获得,从以下4个方面构成了对米氏理论的挑战:1)一些低纬地区并没有明显的10万年冰量周期,而是以2万年岁差周期为主,表明北半球冰盖的扩张、收缩变化并没有完全控制低纬区的气候变化;2)在最近几次冰消期时,南半球和低纬区的温度增高,要早于北半球冰盖的融化,表明冰消期的触发机制并非是北半球高纬夏季太阳辐射;3)大气CO 2浓度在第2冰消期的增加同南极升温相一致,表明该时大气CO 2浓度增加亦有可能早于北半球冰盖消融;4)南半球的末次冰盛期有可能早于北半球。这就说明单一敏感区触发驱动机制已难以圆满解释所有观察事实,天文因素控制下轨道尺度气候变化机制研究正面临理论突破的新需求和新机遇。 相似文献
4.
米兰科维奇旋回理论是古环境研究中重要的时间“度量”工具.文中以贵州普安糯东17号煤层和云南富源天佑10号煤层为例,对晚二叠世煤层的地球物理测井信号进行频谱分析,以获得其中的米兰科维奇轨道周期参数.研究发现,测井信号所反映出的煤层灰分含量变化受泥炭地发育时期的米兰科维奇轨道周期(123 ka(偏心率):35.6 ka(斜... 相似文献
5.
The Carnian Raibl group of the Eastern Alps consists of three 50–100 m thick, alternating carbonate and clastic third-order cycles, each of which can be traced for hundreds of kilometers. Tectono-eustatic sea-level fluctuations of a few tens of metres, spanning a few millions of years, are the driving mechanism of this cyclicity. The carbonate intervals represent restricted marginal marine, tidal and evaporitic environments. The clastic intervals represent inner and outer shelf facies, and are related to the fluviatile “Schilfsandstein” of the Germanic facies belt. In the Raibl group, contrary to other carbonate/clastic depositional settings, relative sea-level lowstands are dominated by carbonate production, and highstands are dominated by clastic deposition. Each of the three Raibl cycles corresponds to a type-2 sequence, containing shelf margin, transgressive and highstand systems tracts. During sea-level lowstands, deltaic point sources were near the shelf margin, allowing clastics to bypass the carbonate platform. This setting corresponds to a shelf margin systems tract. Transgressive and highstand systems tracts developed during the subsequent sea-level rise, as deltaic clastics were reworked and redistributed over the carbonate platform, and the deltas retrograded to the inner shelf. The highstand systems tracts are capped by a type 2 sequence boundary, which is conformable in the study area. The systems tracts can be further subdivided into shallowing upward subcycles, caused by fourth-order sea-level fluctuations, believed to represent Milankovitch rhythms. The middle Raibl cycle is consistently thinner, and may represent a shorter termed, third-order sea-level fluctuation. Our data also corroborate a second-order transgressive trend for the Carnian. 相似文献
6.
The rise of large vascular plants during the mid-Paleozoic brought about a major increase in the rates of weathering of silicate minerals that induced a drop in the level of atmospheric CO 2 and contributed, via the atmospheric greenhouse effect, to global cooling and the initiation of the most long lived and a really extensive glaciation of the past 550 million years. Sedimentary burial of the microbiologically resistant remains of the plants resulted during the Permo-Carboniferous in both further lowering of CO 2 and in elevation of atmospheric O 2. Evidence of changes in CO 2 and O 2 are provided by mathematical models, studies of paleosols, fossil plants, fossil insects, and the effects of modern plants on silicate weathering, and by laboratory studies of the effects of changes in O 2 on plants and insects. To cite this article: R.A. Berner, C. R. Geoscience 335 (2003). 相似文献
7.
Past global mean ocean temperature may be reconstructed from measurements of atmospheric noble gas concentrations in ice core bubbles. Assuming conservation of noble gases in the atmosphere-ocean system, the total concentration within the ocean mostly depends on solubility which itself is temperature dependent. Therefore, the colder the ocean, the more gas can be dissolved and the less remains in the atmosphere. Here, the characteristics of this novel paleoclimatic proxy are explored by implementing krypton, xenon, argon, and N 2 into a reduced-complexity climate model. The relationship between noble gas concentrations and global mean ocean temperature is investigated and their sensitivities to changes in ocean volume, ocean salinity, sea-level pressure and geothermal heat flux are quantified. We conclude that atmospheric noble gas concentrations are suitable proxies of global mean ocean temperature. Changes in ocean volume need to be considered when reconstructing ocean temperatures from noble gases. Calibration curves are provided to translate ice-core measurements of krypton, xenon, and argon into a global mean ocean temperature change. Simulated noble gas-to-nitrogen ratios for the last glacial maximum are δKr atm = ?1.10‰, δXe atm = ?3.25‰, and δAr atm = ?0.29‰. The uncertainty of the krypton calibration curve due to uncertainties of the ocean saturation concentrations is estimated to be ±0.3 °C. An additional ±0.3 °C uncertainty must be added for the last deglaciation and up to ±0.4 °C for earlier transitions due to age-scale uncertainties in the sea-level reconstructions. Finally, the fingerprint of idealized Dansgaard-Oeschger events in the atmospheric krypton-to-nitrogen ratio is presented. A δKr atm change of up to 0.34‰ is simulated for a 2 kyr Dansgaard-Oeschger event, and a change of up to 0.48‰ is simulated for a 4 kyr event. 相似文献
8.
Over geological timescales, CO 2 levels are determined by the operation of the long term carbon cycle, and it is generally thought that changes in atmospheric CO 2 concentration have controlled variations in Earth's surface temperature over the Phanerozoic Eon. Here we compile independent estimates for global average surface temperature and atmospheric CO 2 concentration, and compare these to the predictions of box models of the long term carbon cycle COPSE and GEOCARBSULF.We find a strong relationship between CO 2 forcing and temperature from the proxy data, for times where data is available, and we find that current published models reproduce many aspects of CO 2 change, but compare poorly to temperature estimates. Models are then modified in line with recent advances in understanding the tectonic controls on carbon cycle source and sink processes, with these changes constrained by modelling 87Sr/ 86Sr ratios. We estimate CO 2 degassing rates from the lengths of subduction zones and rifts, add differential effects of erosion rates on the weathering of silicates and carbonates, and revise the relationship between global average temperature changes and the temperature change in key weathering zones.Under these modifications, models produce combined records of CO 2 and temperature change that are reasonably in line with geological and geochemical proxies (e.g. central model predictions are within the proxy windows for >~75% of the time covered by data). However, whilst broad long-term changes are reconstructed, the models still do not adequately predict the timing of glacial periods. We show that the 87Sr/ 86Sr record is largely influenced by the weathering contributions of different lithologies, and is strongly controlled by erosion rates, rather than being a good indicator of overall silicate chemical weathering rates. We also confirm that a combination of increasing erosion rates and decreasing degassing rates over the Neogene can cause the observed cooling and Sr isotope changes without requiring an overall increase in silicate weathering rates.On the question of a source or sink dominated carbon cycle, we find that neither alone can adequately reconstruct the combination of CO 2, temperature and strontium isotope dynamics over Phanerozoic time, necessitating a combination of changes to sources and sinks. Further progress in this field relies on >10 8 year dynamic spatial reconstructions of ancient tectonics, paleogeography and hydrology. Whilst this is a significant challenge, the latest reconstruction techniques, proxy records and modelling advances make this an achievable target. 相似文献
9.
新生代以来,全球气候在持续不断的变冷,从两极无冰的"温室地球"变为现今两极终年有冰的"冰室地球",经历了多次冰盖扩张的变冷事件。始新世-渐新世界线(E/O)附近,δ 18O值大幅度正偏,在短期内由 1.2‰迅速增加到 3.0‰,底层海水温度从12 ℃降低为 4.5 ℃。保存在大洋和大陆中的记录表明:E/O界线附近,全球气温大幅降低,海陆生物均有不同程度的灭绝,指示了气候变冷、变干的趋势。始新世-渐新世转换期间,南极洲与澳大利亚之间的塔斯曼尼亚海道和南极洲与南美洲之间的德雷克海峡(DrakeStrait)相继打开,形成环南极洋流,从而阻止赤道地区的热量向南极传送,导致南极大陆"热隔绝",使南极大陆东部为冰川所覆盖。最近的研究显示,E/O事件是与大气CO 2含量快速变化密切相关的瞬时气候变化,其变化速率类似于现今地球由于人类活动引起大气CO 2的变化,表明大气CO 2浓度的变化在这一事件中起了极为重要的作用。 相似文献
10.
Release of CO 2 from surface ocean water owing to precipitation of CaCO 3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface
water to sedimentary storage was studied by means of a quotient θ = (CO 2 flux to the atmosphere)/(CaCO 3 precipitated). θ depends not only on water temperature and atmospheric CO 2 concentration but also on the CaCO 3 and organic carbon masses formed. In CO 2 generation by CaCO 3 precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric
CO 2 concentration (195–375 ppmv), and increasing CaCO 3 precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic
carbon counteracts the CO 2 production by carbonate precipitation and it results in lower CO 2 emissions from the surface layer. When atmospheric CO 2 increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO 2 transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric
CO 2. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon
from land, the calculated CO 2 flux to the atmosphere is a function of the CaCO 3 and C org net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO 2 flux near the Last Glacial Maximum is 17 to 7×10 12 mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time
it is 38–42×10 12 mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic
emissions of CO 2 to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total
alkalinity owing to the CaCO 3 storage and consequent emission of CO 2. These results are in agreement with the conclusions of a number of other investigators. As the CO 2 uptake in mineral weathering is a major flux in the global carbon cycle, the CO 2 weathering pathway that originates in the CO 2 produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large
imbalances of the atmosphere and land organic reservoir at 10 2–10 4-year time scales. 相似文献
11.
We evaluate whether the global weathering budget is near steady state for the pre-anthropogenic modern environment by assessing the magnitude of acidity-generating volcanic exhalations. The weathering rate induced by volcanic acid fluxes, of which the CO 2 flux is the most important, can be expressed as an average release rate of dissolved silica, based on a model feldspar-weathering scheme, and the ratio of carbonate-to-silicate rock weathering. The theoretically predicted flux of silica from chemical weathering is slightly smaller than the estimated global riverine silica flux. After adjustment for carbonate weathering, the riverine dissolved bicarbonate flux is larger than the volcanic carbon degassing rate by a factor of about three. There are substantial uncertainties associated with the calculated and observed flux values, but the modern system may either not be in steady state, or additional, “unknown” carbon sources may exist. The closure errors in the predicted budgets and observed riverine fluxes suggest that continental weathering rates might have had an impact on atmospheric CO 2 levels at a time scale of 10 3-10 4 years, and that enhanced weathering rates during glacial periods might have been a factor in the reduced glacial atmospheric CO 2 levels. Recent anthropogenic emissions of carbon and sulfur have a much larger acid-generating capacity than the natural fluxes. Estimated potential weathering budgets to neutralize these fluxes are far in excess of observed values. A theoretical scenario for a return to steady state at the current anthropogenic acidity emissions (disregarding the temporary buffering action of the ocean reservoir) requires either significantly lower pH values in continental surface waters as a result of storage of strong acids, and/or higher temperatures as a result of enhanced atmospheric CO 2 levels in order to create weathering rates that can neutralize the total flux of anthropogenic and natural background acidity. 相似文献
12.
对采自浙江西天目山地区的3株柳杉树盘,交叉定年后,测定了3株树轮 δ13C的年序列,分析了3株树轮 δ13C序列中所含的共同环境变化信息。用二项式拟合法去除气候因素引起的3个 δ13C序列的高频变化,得到3个低频变化序列。分析了theLowDome冰芯记录的大气CO 2浓度与树轮 δ13C序列低频变化趋势的关系,建立了相应的转移函数,重建了天目山地区1685年以来大气CO 2浓度变化。结果表明:用3株树轮 δ13C序列重建的结果有较好的一致性,并与南极冰芯的记录及前人研究结果有很好的吻合。这一结果表明用同一地区不同树木个体的树轮 δ13C序列的低频变化序列可以重建出基本一致的大气CO 2浓度变化历史。 相似文献
13.
To accurately predict future CO 2 levels in the atmosphere, which is crucial in predicting global climate change, the sources and sinks of the atmospheric
CO 2 and their change over time must be determined. In this paper, some typical cases are examined using published and unpublished
data. Firstly, the sensitivity of carbonate rock weathering (including the effects by both dissolution and reprecipitation
of carbonate) to the change of soil CO 2 and runoff will be discussed, and then the net amount of CO 2 removed from the atmosphere in the carbonate rock areas of mainland China and the world will be determined by the hydrochem-discharge
and carbonate-rock-tablet methods, to obtain an estimate of the contribution of carbonate rock weathering to the atmospheric
CO 2 sink. These contributions are about 0.018 billion metric tons of carbon/a and 0.11 billion metric tons of carbon/a for China
and the world, respectively. Further, by the DBL (Diffusion Boundary Layer)-model calculation, the potential CO 2 sink by carbonate rock dissolution is estimated to be 0.41 billion metric tons of carbon/a for the world. Therefore, the
potential CO 2 source by carbonate reprecipitation is 0.3 billion metric tons of carbon/a.
Received: 12 May 1999 · Accepted: 16 August 1999 相似文献
14.
A recent high‐resolution record of Late‐glacial CO 2 change from Dome Concordia in Antarctica reveals a trend of increasing CO 2 across the Younger Dryas stadial (GS‐1). These results are in good agreement with previous Antarctic ice‐core records. However, they contrast markedly with a proxy CO 2 record based on the stomatal approach to CO 2 reconstruction, which records a ca. 70 ppm mean CO 2 decline at the onset of GS‐1. To address these apparent discrepancies we tested the validity of the stomatal‐based CO 2 reconstructions from Kråkenes by obtaining further proxy CO 2 records based on a similar approach using fossil leaves from two independent lakes in Atlantic Canada. Our Late‐glacial CO 2 reconstructions reveal an abrupt ca. 77 ppm decrease in atmospheric CO 2 at the onset of the Younger Dryas stadial, which lagged climatic cooling by ca. 130 yr. Furthermore, the trends recorded in the most accurate high‐resolution ice‐core record of CO 2, from Dome Concordia, can be reproduced from our stomatal‐based CO 2 records, when time‐averaged by the mean age distribution of air contained within Dome Concordia ice (200 to 550 yr). If correct, our results indicate an abrupt drawdown of atmospheric CO 2 within two centuries at the onset of GS‐1, suggesting that some re‐evaluation of the behaviour of atmospheric CO 2 sinks and sources during times of rapid climatic change, such as the Late‐glacial, may be required. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
15.
We propose that humans significantly altered atmospheric CH 4 levels after 5000 years BP and that anthropogenic inputs just prior to the industrial revolution accounted for up to 25% of the CH 4 level of 725 ppb (parts per billion). We base this hypothesis on three arguments: (1) the 100 ppb increase in atmospheric CH 4 that occurred after 5000 years BP follows a pattern unprecedented in any prior orbitally driven change in the ice-core record; (2) non-anthropogenic explanations for this increase (expansion of boreal peat lands or tropical wetlands) are inconsistent with existing evidence; and (3) inefficient early rice farming is a quantitatively plausible means of producing anomalously large CH 4 inputs to the atmosphere prior to the industrial revolution. If the areas flooded for farming harbored abundant CH 4-producing weeds, disproportionately large amounts of CH 4 would have been produced in feeding relatively small pre-industrial populations. 相似文献
16.
由于广泛而强烈的岩浆作用,我国东部的松辽、渤海湾、莺歌海以及西部的塔里木等盆地中都有富CO 2深部流体的活动。富CO 2深部流体与碳酸盐岩相互作用可用Duan and Li(2008)所建立的CO 2-H 2O-CaCO 3-NaCl体系的热力学模型来进行模拟计算。计算结果表明,富CO 2深部流体在自深部向浅部运移过程中对CaCO 3的溶解度会逐渐增加,到达一定深度后溶解度达到最大值,再向浅部溶解度开始逐渐降低; 也就是深部流体具有深部溶蚀碳酸盐岩-浅部沉淀碳酸盐矿物的规律。与浅部地层中的流体发生混合会使流体的CO 2含量和盐度降低,会导致CaCO 3的沉淀充填; 深部流体进入开启性断裂/裂缝体系中时,由于压力的降低,也会发生CaCO 3的沉淀充填。深部流体的CO 2含量、盐度、温度和压力的变化影响着实际的溶蚀-充填过程。塔中地区钻井也揭示了深部下奥陶统碳酸盐岩中发育有丰富的溶蚀孔隙,而在相对浅部的奥陶系灰岩和志留系砂岩中见有大量方解石的充填,这是富CO 2流体深部溶蚀-浅部充填的一个较好的实例。基于理论和实际分析,本文认为在岩浆火山作用广泛发育的塔里木等盆地中下古生界深部优质碳酸盐岩储层存在的可能性。 相似文献
17.
Seismic surveys successfully imaged a small scale CO 2 injection (1,600 ton) conducted in a brine aquifer of the Frio Formation near Houston, Texas. These time-lapse borehole seismic
surveys, crosswell and vertical seismic profile (VSP), were acquired to monitor the CO 2 distribution using two boreholes (the new injection well and a pre-existing well used for monitoring) which are 30 m apart
at a depth of 1,500 m. The crosswell survey provided a high-resolution image of the CO 2 distribution between the wells via tomographic imaging of the P-wave velocity decrease (up to 500 m/s). The simultaneously
acquired S-wave tomography showed little change in S-wave velocity, as expected for fluid substitution. A rock physics model
was used to estimate CO 2 saturations of 10–20% from the P-wave velocity change. The VSP survey resolved a large (∼70%) change in reflection amplitude
for the Frio horizon. This CO 2 induced reflection amplitude change allowed estimation of the CO 2 extent beyond the monitor well and on three azimuths. The VSP result is compared with numerical modeling of CO 2 saturations and is seismically modeled using the velocity change estimated in the crosswell survey. 相似文献
18.
Carbonate-rich sediments at shoal to shelf depths (<200 m) represent a major CaCO 3 reservoir that can rapidly react to the decreasing saturation state of seawater with respect to carbonate minerals, produced by the increasing partial pressure of atmospheric carbon dioxide ( pCO 2) and “acidification” of ocean waters. Aragonite is usually the most abundant carbonate mineral in these sediments. However, the second most abundant (typically ∼24 wt%) carbonate mineral is high Mg-calcite (Mg-calcite) whose solubility can exceed that of aragonite making it the “first responder” to the decreasing saturation state of seawater. For the naturally occurring biogenic Mg-calcites, dissolution experiments have been used to predict their “stoichiometric solubilities” as a function of mol% MgCO 3. The only valid relationship that one can provisionally use for the metastable stabilities for Mg-calcite based on composition is that for the synthetically produced phases where metastable equilibrium has been achieved from both under- and over-saturation. Biogenic Mg-calcites exhibit a large offset in solubility from that of abiotic Mg-calcite and can also exhibit a wide range of solubilities for biogenic Mg-calcites of similar Mg content. This indicates that factors other than the Mg content can influence the solubility of these mineral phases. Thus, it is necessary to turn to observations of natural sediments where changes in the saturation state of surrounding waters occur in order to determine their likely responses to the changing saturation state in upper oceanic waters brought on by increasing pCO 2. In the present study, we investigate the responses of Mg-calcites to rising pCO 2 and “ocean acidification” by means of a simple numerical model based on the experimental range of biogenic Mg-calcite solubilities as a function of Mg content in order to bracket the behavior of the most abundant Mg-calcite phases in the natural environment. In addition, observational data from Bermuda and the Great Bahama Bank are also presented in order to project future responses of these minerals. The numerical simulations suggest that Mg-calcite minerals will respond to rising pCO 2 by sequential dissolution according to mineral stability, progressively leading to removal of the more soluble phases until the least soluble phases remain. These results are confirmed by laboratory experiments and observations from Bermuda. As a consequence of continuous increases in atmospheric CO 2 from burning of fossil fuels, the average composition of contemporary carbonate sediments could change, i.e., the average Mg content in the sediments may slowly decrease. Furthermore, evidence from the Great Bahama Bank indicates that the amount of abiotic carbonate production is likely to decline as pCO 2 continues to rise. 相似文献
19.
The marine shelf areas in subtropical and tropical regions represent only 35% of the total shelf areas globally, but receive a disproportionately large amount of water (65%) and sediment (58%) discharges that enter such environments. Small rivers and/or streams that drain the mountainous areas in these climatic zones deliver the majority of the sediment and nutrient inputs to these narrow shelf environments; such inputs often occur as discrete, episodic introductions associated with storm events. To gain insight into the linked biogeochemical behavior of subtropical/tropical mountainous watershed-coastal ocean ecosystems, this work describes the use of a buoy system to monitor autonomously water quality responses to land-derived nutrient inputs and physical forcing associated with local storm events in the coastal ocean of southern Kaneohe Bay, Oahu, Hawaii, USA. The data represent 2.5 years of near-real time observations at a fixed station, collected concurrently with spatially distributed synoptic sampling over larger sections of Kaneohe Bay. Storm events cause most of the fluvial nutrient, particulate, and dissolved organic carbon inputs to Kaneohe Bay. Nutrient loadings from direct rainfall and/or terrestrial runoff produce an immediate increase in the N:P ratio of bay waters up to values of 48 and drive phytoplankton biomass growth. Rapid uptake of such nutrient subsidies by phytoplankton causes rapid declines of N levels, return to N-limited conditions, and subsequent decline of phytoplankton biomass over timescales ranging from a few days to several weeks, depending on conditions and proximity to the sources of runoff. The enhanced productivity may promote the drawing down of pCO 2 and lowering of surface water column carbonate saturation states, and in some events, a temporary shift from N to P limitation. The productivity-driven CO 2 drawdown may temporarily lead to air-to-sea transfer of atmospheric CO 2 in a system that is on an annual basis a source of CO 2 to the atmosphere due to calcification and perhaps heterotrophy. Storms may also strongly affect proximal coastal zone pCO 2 and hence carbonate saturation state due to river runoff flushing out high pCO 2 soil and ground waters. Mixing of the CO 2-charged water with seawater causes a salting out effect that releases CO 2 to the atmosphere. Many subtropical and tropical systems throughout the Pacific region are similar to Kaneohe Bay, and our work provides an important indication of the variability and range of CO 2 dynamics that are likely to exist elsewhere. Such variability must be taken into account in any analysis of the direction and magnitude of the air?Csea CO 2 exchange for the integrated coastal ocean, proximal and distal. It cannot be overemphasized that this research illustrates several examples of how high frequency sampling by a moored autonomous system can provide details about ecosystem responses to stochastic atmospheric forcing that are commonly missed by traditional synoptic observational approaches. Finally, the work exemplifies the utility of combining synoptic sampling and real-time autonomous observations to elucidate the biogeochemical and physical responses of coastal subtropical/tropical coral reef ecosystems to climatic perturbations. 相似文献
20.
The history of life on Earth is critically dependent on the carbon, sulfur and oxygen cycles of the lithosphere – hydrosphere – atmosphere – biosphere system. An Archean oxygen-poor greenhouse atmosphere developed through: (i) accumulation of CO 2 and CH 4 from episodic injections of CO 2 from volcanic activity, volatilised crust impacted by asteroids and comets, metamorphic devolatilisation processes and release of methane from sediments; and (ii) little CO 2 weathering-capture due to both high temperatures of the hydrosphere (low CO 2 solubility) and a low ratio of exposed continents to oceans. In the wake of the Sturtian glaciation, enrichment in oxygen and appearance of multicellular eukaryotes heralded the onset of the Phanerozoic where greenhouse conditions were interrupted by periods of strong CO 2-sequestration through intensified capture of CO 2 by marine plants, onset of land plants and burial of carbonaceous shale and coal (Late Ordovician; Carboniferous – Permian; Late Jurassic; Late Tertiary – Quaternary). The progression from Late Mesozoic and Early Tertiary greenhouse conditions to Late Tertiary – Quaternary ice ages was related to the sequestration of CO 2 by rapid weathering of the emerging Alpine and Himalayan mountain chains. A number of peak warming and sea-level-rise events include the Late Oligocene, mid-Miocene, mid-Pliocene and Pleistocene glacial terminations. The Late Tertiary – Quaternary ice ages were dominated by cyclic orbital-forcing-triggered terminations which involved CO 2-feedback effects from warming seas and the biosphere and albedo flips due to ice-sheet melting. Since ca AD 1750 human emissions were ~305 Gt of carbon, as compared with ~750 Gt C in the atmosphere. The emissions constitute ~12% of the terrestrial biosphere and ~10% of the known global fossil fuel reserve of ~4000 Gt C, whose combustion would compare to the ~ 4600 Gt C released to the atmosphere during the K – T impact event 65 million years ago, with associated ~65% mass extinction of species. The current growth rate of atmospheric greenhouse gases and global mean temperatures exceed those of Pleistocene glacial terminations by one to two orders of magnitude. The relationship between temperatures and sea-levels for the last few million years project future sea-level rises toward time-averaged values of at least 5 m per 1°C. The instability of ice sheets suggested by the Dansgaard – Oeschinger glacial cycles during 50 – 20 ka, observed ice melt lag effects of glacial terminations, spring ice collapse dynamics and the doubling per-decade of Greenland and west Antarctic ice melt suggest that the Intergovernmental Panel on Climate Change's projected sea-level rises (<59 cm) for the 21st century may be exceeded. The biological and philosophical rationale underlying climate change and mass extinction perpetrated by an intelligent carbon-emitting mammal species may never be known. 相似文献
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