Seismic image of a CO2 reservoir beneath a seismically active volcano

Mammoth Mountain is a seismically active volcano 200 000 to 50 000 years old, situated on the southwestern rim of Long Valley caldera, California. Since 1989 it has shown evidence of unrest in the form of earthquake swarms (Hill et al. 1990), volcanic 'long-period' earthquakes (Pitt & Hill 1994), increased output of magmatic ³He (Sorey et al. 1993) and the emission of about 500 tonnes day ⁻¹ of CO₂ (Farrar et al. 1995; Hill 1996; M. Sorey, personal communication, 1997), which has killed trees and poses a threat to human safety. Local-earthquake tomography shows that in mid-1989 areas of subsequent tree-kill were underlain by extensive regions where the ratio of the compressional and shear elastic-wave speeds V_P/V_S was about 9 per cent lower than in the surrounding rocks. Theory (Mavko & Mukerji 1995), experiment (Ito, DeVilbiss & Nur 1979), and experience at other geothermal/volcanic areas (Julian et al. 1996) and at petroleum reservoirs (Harris et al. 1996) indicate that V_P/V_S is sensitive to pore-fluid compressibility, through its effect on V_P . The observed V_P/V_S anomaly is probably caused directly by CO₂, and seismic V_P/V_S tomography is thus a promising tool for monitoring gas concentration and movement in volcanoes, which may in turn be related to volcanic activity.     

Stacking for the frequencies and Qs of 0S0 and 1S0

Summary. Using nine IDA records for the Indonesian earthquake of 1977 August 19, we have formed an optimal linear combination of the records and have measured the frequency and Q of ₀ S ₀ and ₁ S ₀. The frequency was measured using the moment ratio method. The attenuation was measured by the minimum width method and by the time-lapse method. The frequency and attenuation were measured simultaneously by varying them to obtain a best fit to the data. A 2000-hr stack, the sum of nine individual records, for ₀ S ₀ gave a frequency of 0.814664 mHz±4 ppm. The values for the Q of ₀ S ₀ for the three different methods of measurement were 5600,5833 and 5700, respectively. The error in the estimates of Q ^-1 is about 5 per cent for the minimum power method. For ₁ S ₀ a 300-hr stack yielded a frequency of 1.63151 mHz±30 ppm. The values of Q for this mode were 1960, 1800 and 1850, respectively, with an error in Q ^-1 of about 12 per cent for the minimum power method.     

Influence of vascular plant photosynthetic rate on CH4 emission from peat monoliths from southern boreal Sweden

Peat monoliths taken from a boreal peatland system were incubated at two different light intensities to investigate the effect of the photosynthetic rate of vascular plants ( Eriophorum angustifolium ) on net CH₄ emission. The experimental set-up consisted of six replicate monoliths as controls and six where the photosynthetic active radiation (PAR) was reduced by 60%. NEP and total system respiration decreased significantly in response to reduced PAR. No significant changes in CH₄ emission were found, but two different trends were noted. Methane emissions from the shaded monoliths initially seemed to be higher than emissions from the controls. After approximately four weeks the trend was reversed. The pattern may have been caused by "leakage" of organic compounds from inactivated roots that fueled CH₄ production. It is suggested that a new balanced exchange of potential substrate carbon between the plants and the surrounding peat was established. Comparably less easily degradable carbon compounds would then become available for CH₄ production. The fact that there appeared to be an effect of decreased carbon flow on CH₄ emission is further supported by a tendency for lower concentrations of organic acids in porewater in the shaded monoliths at the end of the experiment. These results indicate a possible lagtime on the order of weeks before changes in photosynthesis rates and NEP have an effect onCH₄ emission rates. Nevertheless it confirms the linkage between CO₂ and CH₄ cycling in wetland ecosystems.     

A comparison of annual and seasonal carbon dioxide effluxes between sub-Arctic Sweden and High-Arctic Svalbard

Recent climate change predictions suggest altered patterns of winter precipitation across the Arctic. It has been suggested that the presence, timing and quantity of snow all affect microbial activity, thus influencing CO₂ production in soil. In this study annual and seasonal emissions of CO₂ were estimated in High-Arctic Adventdalen, Svalbard, and sub-Arctic Latnjajaure, Sweden, using a new trace gas-based method to track real-time diffusion rates through the snow. Summer measurements from snow-free soils were made using a chamber-based method. Measurements were obtained from different snow regimes in order to evaluate the effect of snow depth on winter CO₂ effluxes. Total annual emissions of CO₂ from the sub-Arctic site (0.662–1.487 kg CO₂ m^–2 yr^–1) were found to be more than double the emissions from the High-Arctic site (0.369–0.591 kg CO₂ m^–2 yr^–1). There were no significant differences in winter effluxes between snow regimes or vegetation types, indicating that spatial variability in winter soil CO₂ effluxes are not directly linked to snow cover thickness or soil temperatures. Total winter emissions (0.004–0.248 kg CO₂ m^–2) were found to be in the lower range of those previously described in the literature. Winter emissions varied in their contribution to total annual production between 1 and 18%. Artificial snow drifts shortened the snow-free period by 2 weeks and decreased the annual CO₂ emission by up to 20%. This study suggests that future shifts in vegetation zones may increase soil respiration from Arctic tundra regions.     

Three-dimensional VP and VP /VS models of the upper crust in the Friuli area (northeastern Italy)

3-D images of P velocity and P - to S -velocity ratio have been produced for the upper crust of the Friuli area (northeastern Italy) using local earthquake tomography. The data consist of 2565 P and 930 S arrival times of high quality. The best-fitting V _P and V _P / V _S 1-D models were computed before the 3-D inversion. V _P was measured on two rock samples representative of the investigated upper layers of the Friuli crust. The tomographic V _P model was used for modelling the gravity anomalies, by converting the velocity values into densities along three vertical cross-sections. The computed gravity anomalies were optimized with respect to the observed gravity anomalies. The crust investigated is characterized by sharp lateral and deep V _P and V _P / V _S anomalies that are associated with the complex geological structure. High V _P / V _S values are associated with highly fractured zones related to the main faulting pattern. The relocated seismicity is generally associated with sharp variations in the V _P / V _S anomalies. The V _P images show a high-velocity body below 6 km depth in the central part of the Friuli area, marked also by strong V _P / V _S heterogeneities, and this is interpreted as a tectonic wedge. Comparison with the distribution of earthquakes supports the hypothesis that the tectonic wedge controls most of the seismicity and can be considered to be the main seismogenic zone in the Friuli area.     

222Rn and 226Ra: indicators of sea-ice effects on air-sea gas exchange

²²² Rn and ²²⁶Ra distributions beneath the sea ice of the Barents Sea revealed that ice cover has varied effects on air-sea gas exchange. Twice, once in late summer and once in late winter, seawater samples from the top meter below drill holes had ²²²Rn activities that were not lower than their ^226,Ra activities, indicating the existence of secular equilibrium and a negligible net exchange of ²²²Rn and other gases with the atmosphere. However, seawater in the upper 20-85 m usually exhibited at least some ²²²Rn depletion; ²²²Rn-to-²²⁶Ra activity ratios tended to have 'ice-free' values (0.3-0.9) in the summer and values between 0.9 and 1.0 in the winter. Integrated ²²²Rn depletions and piston velocities in both seasons typically fell in the lower 25% of the ranges for ice-free seawater, suggesting that a moderate but far from total reduction in gas exchange is normally caused by ice cover and/or meltwater. The results demonstrate that sea-ice interference with the oceanic uptake of atmospheric gases such as CO, is not well understood and needs further investigation.     

On the linear relation between mb and Ms for discrimination between explosions and earthquakes

Summary. The statistical capability of the m _b: M _s discriminant for the discrimination of earthquake and explosion populations is examined by application of discriminant functions to a group of 83 explosions and 72 earthquakes in Eurasia. Equations are derived for the probability that an event is an earthquake or an explosion. The positive sign of DIS in the decision index equation, DIS _i = 34.3383 – 11.9569 mb _t + 7.1161 M _si , indicates that the event i is an earthquake. Its negative sign indicates that event i is an explosion. The probability of correct classification for an event, P _i , is related to its DIS _i value, by P _i = [1-exp (DIS _i )]⁻¹, where a large, positive DIS indicates a high probability that an event is an earthquake and a large, negative DIS indicates a high probability that an event is an explosion. The discrimination line M _s = 1.680 m _b– 4.825, or m _b= 0.595 M _s+ 2.872 very successfully separates the explosion population from the earthquake population. The points on this line have an equal chance of being an earthquake or an explosion; moreover, for any event, the distance parallel to the M _s-axis from the point representing that event in the m _b: M _s plane to this line is a measure of the probability for the correct classification of that event.     

大兴安岭多年冻土区森林土壤温室气体通量

多年冻土温室气体排放对全球气候变化有重要影响。采用静态暗箱—气相色谱法,于2016—2017年生长季（5—9月）,对大兴安岭多年冻土区兴安落叶松林、樟子松林和白桦林土壤二氧化碳（CO₂）、甲烷（CH₄）和氧化亚氮（N₂O）通量进行野外原位观测,对比分析温室气体通量的动态变化特征及其关键影响因子。结果表明：3种林型土壤CO₂通量范围为65.88~883.59 mg·m^-2·h^-1;CH₄通量范围为-93.29~-2.82 μg·m^-2·h^-1;N₂O通量范围为-5.31~45.22 μg·m^-2·h^-1。整个生长季兴安落叶松林、樟子松林和白桦林土壤均表现为CO₂、N₂O的排放源、CH₄的吸收汇,土壤CO₂和CH₄通量在不同林型和年际间差异显著。3种林型土壤CO₂通量与5 cm、10 cm和15 cm土壤温度呈极显著正相关（P < 0.01）;CH₄通量受土壤含水量和10 cm、15 cm土壤温度的影响较大（P < 0.05）;兴安落叶松林和樟子松林土壤N₂O通量与气温呈显著正相关（P < 0.05）,而白桦林土壤N₂O则与15 cm土壤温度呈显著负相关（P < 0.05）。基于100 a时间尺度计算温室气体全球综合增温潜势,3种林型土壤温室气体的排放对气候变暖具有正反馈作用。     

Core–mantle boundary deformations and J2 variations resulting from the 2004 Sumatra earthquake

The deformation at the core–mantle boundary produced by the 2004 Sumatra earthquake is investigated by means of a semi-analytic theoretical model of global coseismic and postseismic deformation, predicting a millimetric coseismic perturbation over a large portion of the core–mantle boundary. Spectral features of such deformations are analysed and discussed. The time-dependent postseismic evolution of the elliptical part of the gravity field ( J ₂) is also computed for different asthenosphere viscosity models. Our results show that, for asthenospheric viscosities smaller than 10¹⁸ Pa s, the postseismic J ₂ variation in the next years is expected to leave a detectable signal in geodetic observations.     

三江平原湿地CH4、N2O的地-气交换特征

利用暗箱-气相色谱法对三江平原3种具有代表性的湿地类型（常年积水的毛果苔草沼泽、季节性积水的小叶章湿草甸和灌丛湿地）进行了为期两年的CH⁴和N²O现场同步观测。结果表明,湿地全年CH⁴和N²O通量有明显的季节和年际变化,与温度和土壤水分条件密切相关。在发生季节性干旱的年份,生长季（5月¹0月）CH⁴排放通量峰值出现在6月和8月,呈双峰型;而在降水充沛的年份,CH⁴排放通量峰值出现在6、7月份,呈单峰型。冰冻期（11月到次年4月）CH⁴排放通量十分的微弱,其中灌丛湿地表现为负排放。3种类型湿地N²O通量一般在非冰冻期表现为排放,呈双峰型,5月份融化期为第一个高峰期,7、8月为第二个高峰期,冰雪覆盖期表现为吸收。湿地CH⁴和N²O通量在春季的融冻期,存在此消彼长的现象。     

南极大气CO_2、CH_4和N_2O本底趋势特征分析

对南极大气温室气体CO_2(含δ~(13)C-CO_2和δ~(18)O-CO_2)、CH_4和N_2O长期测值进行比较分析。结果表明,南极是全球大气温室气体浓度(CO_2稳定同位素丰度值)随纬度分布变化中的最低(高)区域。南极大气温室气体浓度值变化趋势、年增长率与全球整体上一致,但在具体数值上存在差异。南极CO_2平均年增长率(1958—2014年)为(1.43±0.59)mg·L~(–1)·a~(–1),低于同期赤道(1.51±0.72)mg·L~(–1)·a~(–1),但1980—2014年和2000—2014年年增长率均高于南半球中纬度地区。δ~(13)C-CO_2和δ~(18)O-CO_2丰度趋势揭示了化石燃料排放和全球尺度过程对CO_2的影响,但南极是受影响最小的区域。1983—2014年南极CH_4平均增长率为(6.2±4.9)μg·L~(–1)·a~(–1),低于北半球中纬度(6.5±5.6)μg·L~(–1)·a~(–1)而高于赤道(5.6±5.3)μg·L~(–1)·a~(–1)和南半球中纬度(6.1±4.9)μg·L~(–1)·a~(–1),这与CH_4人为排放增强主要在北半球中纬度地区而显著被OH氧化在赤道和中纬度地区的事实是吻合的。南极N_2O平均年增长率为(0.87±0.15)μg·L~(–1)·a~(–1)(2005—2013年),与南半球中纬度地区接近但低于北半球而高于赤道地区。     

A new derivation of the ratio Q(wobble)/Qμ (mantle)

Summary An extension of the Love-Larmor theory to a low-loss unelastic earth model, leads to the surprisingly simple approximation
   
where τ_s= 447.4 sidereal day is the static wobble period, τ_R= 306 sidereal day is the rigid-earth wobble period and τ_w= 433 sidereal day is the observed Chandler period. Q _W, Q _μ are the respective average Q values of the wobble and the Earth's mantle at τ_W. The known numerical factor F is only slightly dependent on the Earth structure.     

The detection of single-domain greigite (Fe3S4) using rotational remanent magnetization (RRM) and the effective gyro field (Bg): mineral magnetic and palaeomagnetic applications

The intensity of rotational remanent magnetization (RRM) acquired by single-domain greigite at a rotation frequency of 5 rps was combined with measurements of anhysteretic remanent magnetization (ARM) to calculate the effective biasing field ( Bg ) that produced the RRM. Samples of single-domain greigite had Bg values between -137 and -84 μT, and a MDF_RRM of c. 80 mT. By contrast, a suite of natural and synthetic ferrimagnetic iron oxide samples, including single-domain magnetite and y Fe₃O₄ tape particles, acquired Bg values between -3 and -14 μT, and MDF_RRM ranged between 43 and 68 mT (when RRM was acquired). Multidomain magnetite did not acquire a RRM. Bg values at 5 rps were calculated from previously published data for magnetite particles of different grain sizes, which revealed a minimum Bg value of -24 μT and a MDF_RRM of 57 mT for the finest fraction (0.2-0.8 μm in diameter). In a geological example, measurements of Bg and MDF_RRM were used to detect the presence of greigite in a 4 m long Late Weichselian sediment core. Variations in inclination, declination and the intensity of the natural remanent magnetization (NRM) correlate with changes in magnetic mineralogy.     

Carbon dioxide and methane dynamics in a sub-Arctic peatland in northern Finland

We studied carbon dynamics on various surface parts of a highly patterned fen, typical in northern Finland, to examine the importance of different microsites to the areal carbon fluxes. The studies were carried out in June-September 1995 on a mesotrophic flark fen (an aapa mire) in Kaamanen (69°08'N, 27° 17'E). Wet flarks, moist lawns and dry strings accounted for 60%, 10% and 30% of the surface area, respectively. A static chamber technique was applied to measure the CH₄ exchange, the instantaneous net ecosystem exchange (NEE, transparent chamber) and the ecosystem respiration (R_tot' opaque chamber) in several microsites. The static chamber results were compared with those obtained by the eddy covariance technique. The mean daytime areal net ecosystem CO₂ exchange rate measurement in conditions where photosynthesis was light saturated (PAR>400 μmol m_-2 s_-1) varied during the measurement period from −59 mg CO₂-C m⁻²h⁻¹ (release) to 250 (uptake). The mean CH₄ emission during the measuring period was 78 mg CH_4-Cm⁻² d⁻¹ on the flarks, 68 mg on the lawn and 6.0 mg on the strings. The strings without shrubs (mainly Betula nana ) were in general net sources of CO₂, even during the middle of the growing season, whereas the lawns, flarks and also strings growing B. nana showed a daytime net uptake of CO₂. Areally integrated chamber results showed lower CO₂ and higher CH₄ fluxes than predicted from the eddy covariance measurements.     

The effect of disturbance on the day-to-day variability of Sq

Summary. Other workers have recently shown that the apparent day-to-day variability of S_q is appreciably reduced when days with bay-like disturbances are removed from the analysis.
In this paper, it is shown that when these days are removed, there is only a small effect on the scale of the spatial coherence of S_q-ranges and therefore the regional scale of the correlation must be a real feature of S_q range variability rather than an effect due to disturbance.     

湿地土壤气体排放对水位变化响应的持续性动态特征

为探索湿地水位变化与土壤气体排放之间的关系,对黄河中游芦苇湿地进行了半注水和满注水样地处理后的动态监测,对比了7 d水位变化过程中土壤气体排放差异。结果表明：注水造成了土壤CO₂排放速率的显著差异;随土壤温度上升,H₂O、CO₂、H₂S排放速率都有上升趋势（满注水样地的H₂O除外）;半注水和满注水造成的影响,H₂O排放速率表现为趋同-异步-消失的特征,在注水前期（63.73 h）半注水和满注水差异基本一致,后期差异较大,直至125.64 h后注水的影响才消失,总体分别造成H₂O排放总量76.3%和31.3%的增加;CO₂排放速率表现为异步-趋同的特征,注水初期环境的改变造成CO₂排放的一致减少,37.69~68.66 h二者出现明显差异,68.66~125.64 h水位虽然恢复,但差异仍然存在,注水分别造成CO₂排放总量50.1%和43.2%的减少;H₂S排放速率表现为无变化-异步-无变化的特征,总体造成H₂S排放总量42.3%和32.3%的增加。研究追踪了水位上升后土壤H₂O、CO₂和H₂S排放速率变化的动态过程,其影响具有异步性和持续性的特点,CO₂排放速率表现出较长的响应周期。研究结果对于河流湿地生态功能研究具有重要意义,湿地土壤气体排放对水位变化的响应滞后意味着对湿地生态功能的重要影响,其波动过程需要更长时段的精准研究。     

Travel times of Pn -waves in the Aegean and surrounding area

Summary. Based on accurately located 23 very shallow earthquakes ( h = 1–14 km) in northern and central Greece by portable networks of seismic stations and by the joint epicentre method, the travel times of the P_n -waves from the foci of these earthquakes to the sites of 54 permanent stations in the Balkan region have been determined. The travel times of P_n -waves in the central and eastern part of the area (eastern Greece, south-eastern Yugoslavia, the Aegean Sea, Bulgaria, southern Romania, western Turkey) fit a straight line very well with the P_n velocity equal to 7.9 ± 0.1 km s^-1. On the contrary, the travel times of P_n -waves to stations in the western part of the area (Albania, western Greece) do not fit this curve because the P_n -waves travelling to these stations are delayed by more than 1 s due to the thicker crust under the Dinarides–Hellenides mountain range. Time delays for P_n -waves have been calculated for each permanent station in the Balkan area with respect to the mean travel-time curve of these waves in the central and eastern part of the area. Corrections of the travel times for these delays contribute very much to the improvement of the accuracy in the location of the shallow earthquakes in the Aegean and surrounding area.     

铵态氮沉降对内蒙古呼伦贝尔草地CO_2通量的影响（英文）

大气氮沉降可能会影响陆地生态系统的碳通量。本文主要目的是探讨在氮素缺乏的草地生态系统中,氮素添加是否会增加CO2通量。本研究于2008和2009生长季进行,采用静态箱-气相色谱法研究CO2通量对氮沉降增加的响应。结果表明,2年的氮素添加并没有显著影响土壤NH4+含量,NO3-含量只是在2009年生长季后期有所增加。高氮处理增加了CO2通量,而低氮处理在2008年抑制了CO2通量,2009年后期增加了CO2通量。而且氮素添加显著增加了地上生物量和根系的生物量。CO2通量与土壤水分、土壤温度的关系并没有因为氮素的添加而改变,但是氮素添加增加了CO2通量对土壤水分和土壤温度的敏感性。这些结果表明,在未来大气氮沉降增加的背景下,呼伦贝尔草甸草原CO2通量有可能会增加。     

大、小潮日闽江口短叶茳芏+芦苇沼泽甲烷排放通量日变化特征

利用"静态箱-悬浮箱-气相色谱法",分别在小潮日(2010年4月4～5日和9月2～3日)和大潮日(2010年4月14～15日和9月9～10日),在闽江口鳝鱼滩湿地的中高潮滩过渡区短叶茳芏(Cyperus malaccensis)+芦苇(Phragmites australis)沼泽中,取样并测定了该沼泽24h的甲烷排放通量,并同步对潮水水位、温度等环境因子进行了观测。研究结果表明,不论大、小潮日,总体上,沼泽是甲烷排放源,白天的甲烷排放通量大于夜间;4月、9月的2个小潮日的甲烷排放通量分别为4.43mg/(m2·h)和8.13mg/(m2·h),2个大潮日的甲烷排放通量分别为1.39mg/(m2·h)和3.25mg/(m2·h),小潮日甲烷排放通量明显大于大潮日;大潮日,涨落潮阶段的沼泽水-气界面甲烷排放通量低于非涨落潮阶段;温度和潮水水位是控制甲烷排放通量日变化的重要环境因子。     

40Ar/39Ar dates of eastern Iceland lavas

Summary. Twenty-two plateau ages obtained by the ⁴⁰Ar/³⁹Ar step-heating method span most of the time of formation of eastern Iceland. With one exception the dates are consistent with the stratigraphy, the exception having a very unusual argon release pattern. It is concluded that the ⁴⁰Ar/³⁹Ar step-heating method can give correct dates on hydrothermally altered samples the total fusion ages of which are not correct; however, it is not possible to conclude from the results obtained that the method is inherently more accurate than the conventional method using carefully selected samples.
Though it is known from geological evidence that minor irregularities of spreading have occurred the results show that, within the resolution of the dates, spreading has been steady and symmetrical; in particular, neither a large eastward jump nor repetitive westward jumps can have occurred. The average half spreading rate for the period 2Myr to 12 Myr ago was 0.78 ± 0.16 cm yr-¹.