Relating a recruitment shift of Patagonian grenadier (Macruronus magellanicus Lönnberg) to large-scale environmental changes off Southern Chile

The SE Pacific stock of Patagonian grenadier (Macruronus magellanicus) showed evidence of an abrupt reduction in recruitment after 2000. This drop exceeded expectations from changes in the spawning stock biomass (SSB), indicating a change in the stock-recruitment relationship (S-R). We evaluated whether variability in recruitment could be explained by concurrent changes in three environmental indices: sea-surface temperature anomaly (SSTA); southern oscillation index (SOI); and latitudinal position of the west wind drift bifurcation (WWDL). Continuous and discrete effects of these indices were tested as covariates in linear log-log and non-linear Ricker's S-R models. Discrete effects represented regime shifts detected in SSTA (1998), SOI (1998) and WWDL (1995). While SSTA was the only continuous variable found to be significant, the discrete 1998 regime shift supported the most informative model. The best Ricker's model considered a discrete intercept change in the same year: 1998. Although a spurious correlation between SSTA and S-R changes is possible, SSTA may be reflecting major physical or biological changes relevant to M. magellanicus juveniles in the SE Pacific.     

西藏羊八井热田地热流体成因及演化的惰性气体制约

地热流体中惰性气体的相对丰度和同位素组成，不仅可以揭露热田的热源性质，而且还能够揭示深，浅层地热流体的内在联系和演化过程等。在西藏羊八井热田的地热气体中，已检测出大量的^4He组分，3He/^4He值是大气的0．087－0．259倍，表明深部地壳物质的局部熔融为热田提供能量，浅层地热流体的3He/4He 值自西北向东南呈降低趋势，与热储温度的变化相一致，反映出侧向运移时补充了更多的壳源氦，热田北区深层地热流体具有稍高的3He/4He值，是浅层地热流体的母源，气体中氪和氙的相对丰度具有大气降水成因的特征，结合现有的实际资料，建立了热田地热流体的概念模型。     

Amazonian forest dieback under climate-carbon cycle projections for the 21st century

Summary The first GCM climate change projections to include dynamic vegetation and an interactive carbon cycle produced a very significant amplification of global warming over the 21st century. Under the IS92a business as usual emissions scenario CO₂ concentrations reached about 980ppmv by 2100, which is about 280ppmv higher than when these feedbacks were ignored. The major contribution to the increased CO₂ arose from reductions in soil carbon because global warming is assumed to accelerate respiration. However, there was also a lesser contribution from an alarming loss of the Amazonian rainforest. This paper describes the phenomenon of Amazonian forest dieback under elevated CO₂ in the Hadley Centre climate-carbon cycle model.     

The Effect of Orography on Evaporation

The effect of orography on the spatial variability of surface evaporation is studied numerically for two hill heights and two prescribed forms of surface resistance. A numerical model of the planetary boundary layer carrying scalars of temperature and specific humidity, and with a surface energy balance scheme, is employed. It is found that the difference in mean evaporation between model runs with hills and analogous runs for flat terrain may be explained primarily by an increase in surface area and adiabatic cooling at the hill surface.     

Calibration of a land-surface model using data from primary forest sites in Amazonia

Summary A land-surface model (MOSES) was tested against observed fluxes of heat, water vapour and carbon dioxide for two primary forest sites near Manaus, Brazil. Flux data from one site (called C14) were used to calibrate the model, and data from the other site (called K34) were used to validate the calibrated model. Long-term fluxes of water vapour at C14 and K34 simulated by the uncalibrated model were good, whereas modelled net ecosystem exchange (NEE) was poor. The uncalibrated model persistently underpredicted canopy conductance (g _c ) from mid-morning to mid-afternoon due to saturation of the response to solar radiation at low light levels. This in turn caused a poor simulation of the diurnal cycles of water vapour and carbon fluxes. Calibration of the stomatal conductance/photosynthesis sub-model of MOSES improved the simulated diurnal cycle of g _c and increased the diurnal maximum NEE, but at the expense of degrading long-term water vapour fluxes. Seasonality in observed canopy conductance due to soil moisture change was not captured by the model. Introducing realistic depth-dependent soil parameters decreased the amount of moisture available for transpiration at each depth and led to the model experiencing soil moisture limitation on canopy conductance during the dry season. However, this limitation had only a limited effect on the seasonality in modelled NEE.     

The role of ecosystem-atmosphere interactions in simulated Amazonian precipitation decrease and forest dieback under global climate warming

Summary A suite of simulations with the HadCM3LC coupled climate-carbon cycle model is used to examine the various forcings and feedbacks involved in the simulated precipitation decrease and forest dieback. Rising atmospheric CO₂ is found to contribute 20% to the precipitation reduction through the physiological forcing of stomatal closure, with 80% of the reduction being seen when stomatal closure was excluded and only radiative forcing by CO₂ was included. The forest dieback exerts two positive feedbacks on the precipitation reduction; a biogeophysical feedback through reduced forest cover suppressing local evaporative water recycling, and a biogeochemical feedback through the release of CO₂ contributing to an accelerated global warming. The precipitation reduction is enhanced by 20% by the biogeophysical feedback, and 5% by the carbon cycle feedback from the forest dieback. This analysis helps to explain why the Amazonian precipitation reduction simulated by HadCM3LC is more extreme than that simulated in other GCMs; in the fully-coupled, climate-carbon cycle simulation, approximately half of the precipitation reduction in Amazonia is attributable to a combination of physiological forcing and biogeophysical and global carbon cycle feedbacks, which are generally not included in other GCM simulations of future climate change. The analysis also demonstrates the potential contribution of regional-scale climate and ecosystem change to uncertainties in global CO₂ and climate change projections. Moreover, the importance of feedbacks suggests that a human-induced increase in forest vulnerability to climate change may have implications for regional and global scale climate sensitivity.     

The behaviour of a mixed-layer model of the convective boundary layer coupled to a big leaf model of surface energy partitioning

Daily mean values of the Priestley-Taylor coefficient, ¯, are derived from a simple model of the daily growth of a convective boundary layer. For a particular control set of driving environmental variables, ¯ is related to the prescribed bulk surface resistance, r_S by 1/¯ = 1/₀ + mr_S for parameters ₀ and m. The dependence of the parameters ₀ and m on weather is explored and a potential use of this linear relation to provide information about regional values of r_S is indicated.     

An analogue model to derive additional climate change scenarios from existing GCM simulations

 Changes in land surface driving variables, predicted by GCM transient climate change experiments, are confirmed to exhibit linearity in the global mean land temperature anomaly, ΔT _l . The associated constants of proportionality retain spatial and seasonal characteristics of the GCM output, whilst ΔT _l is related to radiative forcing anomalies. The resultant analogue model is shown to be robust between GCM runs and as such provides a computationally efficient technique of extending existing GCM experiments to a large range of climate change scenarios. As an example impacts study, the analogue model is used to drive a terrestrial ecosystem model, and predicted changes in terrestrial carbon are found to be similar to those when using GCM anomalies directly. Received: 4 January 1999 / Accepted: 11 December 1999     

准噶尔盆地南缘新生代构造特征及其与砂岩型铀矿成矿作用初析

准噶尔盆地南缘盆山结合部中新生界沉积巨厚,新生代变形强烈,是研究新盆山耦合的理想场所,也是我国砂岩型铀矿找矿的远景区段。本文在综合前人资料和野外观测分析基础上,根据新生代构造活动特征,将准噶尔盆地南缘划分为博格达山前和西部断褶带两个构造分区,博格达山前以强烈的逆冲推覆为特征,发育多条活动的逆冲推覆断裂; 乌鲁木齐以西至乌苏南的西部断褶带则发育三-四排的褶皱-逆冲断裂构造带。对采自博格达山前逆冲推覆断裂带内的方解石和断层泥,利用电子自旋共振测年手段,推测博格达山前的富康-吉木萨尔断裂带和北三台断裂带分别在0.7~1Ma和0.25Ma期间,经历了一期重要的逆冲推覆作用。结合盆地南缘砂岩型铀矿的展布规律及其成矿条件的分析,探讨了新生代构造运动对砂岩型铀矿成矿的控制作用,认为西部断褶带的第一排构造带具有较好的成矿前景,而博格达山前由于新生代构造活动强烈而相对成矿不利,为此提出了准噶尔盆地南缘砂岩型铀矿成矿“构造优先权”的构造控矿模式,进而指出了区域找矿的优选区段。