The effect of methanogenesis on the geochemistry of low temperature water–Fe0–basalt reactions     

Lisa E. Mayhew  Graham E. Lau  Tom M. McCollom  Sam Webb  Alexis S. Templeton 《Applied Geochemistry》2011

Hydrogen gas produced in the subsurface from the hydration of mafic rocks is known to be a major energy source for chemolithotrophic life in extreme environments such as hydrothermal vents. The possibility that in situ anaerobic microorganisms present in the deep subsurface are sustained by low temperature H₂-generating water–rock reactions taking place around them is being investigated. Whether the growth and activity of H₂-utilizing microbes directly influences aqueous geochemistry, rates of mineral dissolution, and the chemical composition of the alteration products is also being quantitatively evaluated.To explore how microorganisms are affected by water–rock reactions, and how their activity may in turn affect reaction progress, laboratory experiments have been conducted to monitor the growth of a methanogenic Archaea in the presence of H_2(g) produced from low temperature water–Fe⁰–basalt reactions. In these systems, the conversion of Fe(II) to Fe(III) and subsequent hydrolysis of water is responsible for the production of H_2(g). To characterize key components of the geochemical system, time series measurements of H₂ and CH₄ gas concentrations, Fe and Si aqueous concentrations, and spatially resolved synchrotron-based analyses of microscale Fe distribution and speciation were conducted. Culture experiments were compared with an abiotic control to document changes in the geochemistry both in the presence and absence of the methanogen.In the control abiotic batch experiment, H₂ was continuously produced, until the headspace became saturated, while in the biotic experiments, microbial consumption of H₂ for methanogenesis draws H₂ down and produces CH₄. Purging the headspace gas reinitiates H₂ and CH₄ production in abiotic and culture experiments, respectively. Mass balance analysis of the amount of CH₄ produced suggests that the total H₂ production in microbial experiments does not exceed the abiotic experiment. Soluble Si concentrations, while buffered to relatively constant values, were higher in culture experiments than the abiotic control.Iron_(aq) concentrations appear to respond to perturbations of H₂ and CH₄ gas concentrations in both culture experiments and the abiotic control. A pulse of Fe preceded the rise in either H₂ or CH₄ production, and as the gas concentrations increased the Fe_(aq) decreased. Iron-bearing mineral assemblages change with increasing reaction time and mineral assemblages vary between culture experiments and the abiotic control. These geochemical trends suggest that there are different reaction paths between the culture experiments and the abiotic control.The hydration of mafic rocks is a common geologic reaction and one that has taken place on Earth for the majority of its history and is postulated to occur on Mars. These reactions are important because of their effect on the rheology and geochemistry of the ocean crust. While most often studied at temperatures of ～250 °C, this work suggests that at lower temperatures microorganisms may have a profound effect on what has long been thought to be solely an abiotic reaction, and may produce diagnostic mineral assemblages that will be preserved in the geological record.  相似文献   

What constrained disaster management capacity in the township level of China? Case studies of Wenchuan and Lushan earthquakes   总被引：1，自引：1，他引：0  

Qiang Zhang  Qibin Lu  Yameng Hu  Jocelyn Lau 《Natural Hazards》2015,77(3):1915-1938

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Numerical simulation of the genesis of typhoon Durian (2001) over the South China Sea: The effect of sea surface temperature   总被引：1，自引：1，他引：0  

Lei Wang  Kai-Hon Lau  Chi-Hung Fung 《中国海洋大学学报(英文版)》2010,9(2):99-115

Typhoon Durian (2001),which formed over the South China Sea (SCS),was simulated by using the Weather Research and Forecasting (WRF) model. The genesis of typhoon Durian which formed in the monsoon trough was reproduced by numerical simulations. The simulated results agree reasonably well with observations. Two numerical experiments in which the sea surface temperature (SST) was either decreased or increased were performed to investigate the impact of the SST on the genesis of the ty-phoon. When the SST was decreased by 5℃ uniformly for all grids in the model,the winds calculated became divergent in the lower troposphere and convergent in the upper troposphere,creating conditions in which the amount of total latent heat release (TLHR) was low and the tropical cyclone (TC) could not be formed. This simulation shows the importance of the convergence in the lower tropo-sphere and the divergence in the upper troposphere for the genesis of the initial vortex. When the SST was increased by 1℃ uni-formly for all grids,a stronger typhoon was generated in the results with an increase of about 10 m s-1 in the maximum surface wind speed. Only minor differences in intensity were noted during the first 54 h in the simulation with the warmer SST,but apparent dif-ferences in intensity occurred after 54 h when the vortex began to strengthen to typhoon strength. This experiment shows that warmer SST will speed the strengthening from tropical storm strength to typhoon strength and increase the maximum intensity reached,while only minor impact can be seen during the earlier stage of genesis before the TC reaches the tropical storm strength. The results sug-gest that the amount of TLHR may be the dominant factor in determining the formation and the intensification of the TC.  相似文献   

Mechanisms of monsoon-Southern Oscillation coupling: insights from GCM experiments   总被引：1，自引：0，他引：1  

K.-M. Lau  W. Bua 《Climate Dynamics》1998,14(11):759-779

 The relative roles of internal atmospheric dynamics, land surface evaporation and sea surface temperature (SST) forcings on the coupling between the Asian monsoon (AM) and the Southern Oscillation (SO) are investigated in a series of GCM experiments. Results confirm previous studies indicating that the characteristic large-scale pattern of the SO is due primarily to SST anomaly (SSTA) forcing. The AM circulation anomalies are coupled to the SO via a characteristic upper level circulation couplet over the equatorial central Pacific. This couplet acts as a radiating node for teleconnection signals originating from the AM region to the extratropics. Generally, a weak AM is associated with warm SST over the eastern equatorial Pacific, concomitant with the negative phase of the SO, i.e., low (high) surface pressure over Tahiti (Darwin). The reverse holds for strong AM. Two wavetrains associated with the AM fluctuation have been identified: one arcing over northeastern Asia via the Aleutians to North American, and another emanating from northwestern Europe, via Siberia to northern India. Internal dynamics appear to underpin the origin of these wavetrains, which are strongly tempered by SSTA forcing and to a lesser degree by interactive land processes. Regionally, land-atmosphere interaction seems to have the strongest impact over East Asia/Indochina and the adjacent oceanic region of the South China Sea. Here, land-atmosphere interaction is responsible for the enhancement of a subseasonal scale see-saw oscillation in precipitation between land and the adjacent oceans. A local land-atmosphere feedback mechanism involving strong coupling between the hydrologic and energy cycles is identified. It is suggested that the interaction among precipitation, moisture convergence and land surface turbulent heat fluxes and radiation processes play key roles in determining the fast (subseasonal and shorter scales) response of the AM. On these time scales, the occurrences of cool/wet and hot/dry states associated with the precipitation seesaw appear to be chaotic. However, the preferred occurrence of a given state and the abrupt transition between states are dependent on the large-scale circulation and radiation forcings induced by the SO. One of the more provocative findings here is that effects of land-atmosphere interaction do not seem to alter the basic planetary scale features of the AM-SO system. As a result, the interannual variability of the coupled AM-SO is relatively small in the absence of anomalous SST forcing. Yet, the local effect of land-atmosphere interaction on AM is quite pronounced and dependent upon the large-scale forcings related to SO. Received: 18 November 1997 / Accepted: 07 April 1998  相似文献   

Second order wave diffraction forces and runup by finite—infinite element method     

B.Y. Li  S.L. Lau  C.O. Ng 《Applied Ocean Research》1991,13(6):270-286

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Dynamics of an elastically moored floating body by the three-dimensional infinite element method     

S. L. Lau  Z. Ji  C. O. Ng 《Ocean Engineering》1990,17(5)

The three-dimensional problem of the dynamics of a moored floating object under the action of regular waves is solved numerically as a boundary value problem by use of the finite-infinite element method. The cross-sectional shape of the floating body and the mooring arrangements may all be arbitrary. The mathematical formulations of the problem and procedures of the numerical method are presented in this paper. A corresponding computer program WALOAD has been developed, which is capable of computing wave forces on fixed and floating structures. Numerical computations using this program could give very accurate results, even though rather coarse meshes were used. The program is easy to use and is readily applicable in many practical situations.  相似文献   

Gamma-ray emissions from active galaxies     

M. M. Lau  E. C. M. Young  K. N. Yu 《Astrophysics and Space Science》1989,158(1):117-121

Recently, gamma rays (>100 MeV) have been detected from some active galaxies (Young and Yu, 1988). These gamma-ray data together with data in other wavebands give severe constraints to the emission mechanisms of radiations from these objects. The synchrotron self-Compton (SSC) model will be applied to these objects in the present work. It will be seen that the predictions from the SSC model agree excellently with the observations.  相似文献   

Advance and prospectus of seasonal prediction: assessment of the APCC/CliPAS 14-model ensemble retrospective seasonal prediction (1980–2004)     

Bin Wang  June-Yi Lee  In-Sik Kang  J. Shukla  C.-K. Park  A. Kumar  J. Schemm  S. Cocke  J.-S. Kug  J.-J. Luo  T. Zhou  B. Wang  X. Fu  W.-T. Yun  O. Alves  E. K. Jin  J. Kinter  B. Kirtman  T. Krishnamurti  N. C. Lau  W. Lau  P. Liu  P. Pegion  T. Rosati  S. Schubert  W. Stern  M. Suarez  T. Yamagata 《Climate Dynamics》2009,33(1):93-117

We assessed current status of multi-model ensemble (MME) deterministic and probabilistic seasonal prediction based on 25-year (1980–2004) retrospective forecasts performed by 14 climate model systems (7 one-tier and 7 two-tier systems) that participate in the Climate Prediction and its Application to Society (CliPAS) project sponsored by the Asian-Pacific Economic Cooperation Climate Center (APCC). We also evaluated seven DEMETER models’ MME for the period of 1981–2001 for comparison. Based on the assessment, future direction for improvement of seasonal prediction is discussed. We found that two measures of probabilistic forecast skill, the Brier Skill Score (BSS) and Area under the Relative Operating Characteristic curve (AROC), display similar spatial patterns as those represented by temporal correlation coefficient (TCC) score of deterministic MME forecast. A TCC score of 0.6 corresponds approximately to a BSS of 0.1 and an AROC of 0.7 and beyond these critical threshold values, they are almost linearly correlated. The MME method is demonstrated to be a valuable approach for reducing errors and quantifying forecast uncertainty due to model formulation. The MME prediction skill is substantially better than the averaged skill of all individual models. For instance, the TCC score of CliPAS one-tier MME forecast of Niño 3.4 index at a 6-month lead initiated from 1 May is 0.77, which is significantly higher than the corresponding averaged skill of seven individual coupled models (0.63). The MME made by using 14 coupled models from both DEMETER and CliPAS shows an even higher TCC score of 0.87. Effectiveness of MME depends on the averaged skill of individual models and their mutual independency. For probabilistic forecast the CliPAS MME gains considerable skill from increased forecast reliability as the number of model being used increases; the forecast resolution also increases for 2 m temperature but slightly decreases for precipitation. Equatorial Sea Surface Temperature (SST) anomalies are primary sources of atmospheric climate variability worldwide. The MME 1-month lead hindcast can predict, with high fidelity, the spatial–temporal structures of the first two leading empirical orthogonal modes of the equatorial SST anomalies for both boreal summer (JJA) and winter (DJF), which account for about 80–90% of the total variance. The major bias is a westward shift of SST anomaly between the dateline and 120°E, which may potentially degrade global teleconnection associated with it. The TCC score for SST predictions over the equatorial eastern Indian Ocean reaches about 0.68 with a 6-month lead forecast. However, the TCC score for Indian Ocean Dipole (IOD) index drops below 0.40 at a 3-month lead for both the May and November initial conditions due to the prediction barriers across July, and January, respectively. The MME prediction skills are well correlated with the amplitude of Niño 3.4 SST variation. The forecasts for 2 m air temperature are better in El Niño years than in La Niña years. The precipitation and circulation are predicted better in ENSO-decaying JJA than in ENSO-developing JJA. There is virtually no skill in ENSO-neutral years. Continuing improvement of the one-tier climate model’s slow coupled dynamics in reproducing realistic amplitude, spatial patterns, and temporal evolution of ENSO cycle is a key for long-lead seasonal forecast. Forecast of monsoon precipitation remains a major challenge. The seasonal rainfall predictions over land and during local summer have little skill, especially over tropical Africa. The differences in forecast skills over land areas between the CliPAS and DEMETER MMEs indicate potentials for further improvement of prediction over land. There is an urgent need to assess impacts of land surface initialization on the skill of seasonal and monthly forecast using a multi-model framework.  相似文献   

Effect of size, tissue parts and location on six biochemical markers in the green-lipped mussel, Perna viridis     

Lau PS  Wong HL 《Marine pollution bulletin》2003,46(12):1563-1572

The effect of size and tissue parts as well as site locations on a suite of six anti-oxidative biochemical markers, viz. the enzyme degrading neural transmitters acetylcholinesterase (AChE), the Phase II transforming enzyme glutathione-S-transferase (GST), the anti-oxidative enzymes superoxide dismutase (SOD) and catalase (CAT), the lipid metabolite malondialdehyde (MDA) and the ratio of CAT/MDA, in the bivalve mollusc, Perna viridis, was studied. Field mussels were collected from the piers of University of Science and Technology (UST), Pak Sha Wan or Hebe Haven (PS) and Sai Kung (SK) in Port Shelter, Hong Kong. Statistically, ANOVA showed that the activity of all six biochemical markers were generally tissue dependent, size independent and location dependent. Tukey multi comparison test indicated that the biochemical activities fell into two groups, with SK the highest activity group in most cases. The significance of these findings in relation to long-term coastal water biomonitoring is discussed.  相似文献   

Chemical Composition of Ancient Celadon Material （1127-1279 A.D.） from Zhejiang, China and Its Implication     

PENG Zicheng LEUNG Po Lau YU Peter CHENG Peikai LI Mai 《《地质学报》英文版》2006,80(5):759-762

The microprobe EDXRF equipment was used for analysis of the major and trace elements in glaze layer-transitive layer-body layer of the celadon from the Altar Yao （Kiln） and Laohudong Yao in the Southern Song Dynasty （1127-1279 A.D.）, Zhejiang, China. The K values of the discriminant factor for the celadon wares are larger than 8, which means the celadon of the Altar Yao and Laohudong Yao are different from that of the Longquan Yao. The former two belong to the Guan Yao system （the Chinese imperial kilns）, but the latter to the Min Yao system （the Chinese popular kilns）. The principle component analysis shows their relationship between the Altar and Laohudong wares with provenance postulation. The thickness of the transitive layer in the Altar and Laohudong wares is obviously different, which reveals the microstructure characteristics of the celadon even though both kinds of wares belong to the imperial kiln system.  相似文献