Climate sensitivity to wetlands and wetland vegetation in mid-Holocene North Africa

 Wetland regions are important components of the local climate, with their own characteristic surface energy and moisture budgets. Realistic representation of wetlands, including the important vegetation component, may therefore be necessary for more accurate simulations of climate and climate change. However, many land-atmosphere coupled models either ignore wetlands or treat wetlands as bare, water-saturated soil, neglecting the vegetation present within wetland environments. This study investigates the possible response of the mid-Holocene climate of North Africa to changes in orbital forcing, both with and without the presence of wetlands. The location of these wetlands is guided by analysis of paleovegetation and wetland distribution. In this study, the wetland regime in the land surface component of a climate model was modified to incorporate vegetation. Field measurements have shown that vegetation affects water loss associated with evaporation (including transpiration) within a wetland area. Comparisons between non-vegetated wetland and vegetated wetland revealed an increase in local albedo that produced an associated decrease in net radiation, evaporation and precipitation in the vicinity of the wetlands regions. Based on an analysis of the model surface water balance, the calculated area of mid-Holocene wetland coverage for North Africa closely matches the observed. For the North African region as a whole, the effects of adding vegetation to the wetland produced relatively small changes in climate, but local recycling of water may have served to help maintain paleo wetland communities. Received: 16 March 1999 / Accepted: 17 May 2000     

A Direct Image of the Inner Torus of NGC 1068

We present the first VLBI observations of the compact source S1 in the radio jet of NGC 1068. Roughly 1 pc in length and 0.2 pc wide, S1 resolves into clumps aligned perpendicular to the local radio jet axis. The radio continuum emission arises from a hot (Te ~ 106 K), dense (ne ~ 106 cm-3) plasma, and the source of the radio emission is either thermal free-free emission or Thomson-reflected synchrotron emission. The clouds comprising S1 are opaque to soft X-radiation, and we therefore propose that S1 is the inner, ionized region, or ‘hot zone,’ of the obscuring medium surrounding the active nucleus. The covering fraction of the hot zone is small, Cf ⋦ 10%. Since the covering fraction of the dusty, obscuring medium is probably much larger, the obscuring disk must either flare or warp outside of the hot zone. That the radio jet and hot zone axes are perpendicular also suggests that the hot zone may be considered to trace the outermost extent of the accretion disk. This revised version was published online in July 2006 with corrections to the Cover Date.     

Neutral hydrogen absorption observations of the central region of NGC 5929

We present 0.15-arcsec (25-pc) resolution MERLIN observations of neutral hydrogen absorption detected towards the nuclear region of the type 2 Seyfert galaxy NGC 5929. Absorption is detected only towards the north-eastern radio component with a column density of (6.5 ± 0.6) × 10²¹ cm⁻². Based on comparison with an HST WFPC2 continuum image, we propose that the absorption is caused by a 1.5-arcsec structure of neutral gas and dust offset 0.3 arcsec south-east of the nucleus and running NE–SW. A separate cloud of dust is apparent 1.5 arcsec to the south-west of the nucleus in the HST image. A comparison of the centroid velocity (2358 ± 5 km s⁻¹) and full width at half-maximum (43 ± 6 km s⁻¹) of the absorbing gas with previous [O  III ] observations suggests that both the neutral and ionized gas are undergoing galactic rotation towards the observer in the north-east and away from the observer in the south-west. The main structure is consistent with an inclined ring of gas and dust encircling the active galactic nucleus (AGN); alternatively it may be a bar or inner spiral arm. We do not detect neutral hydrogen absorption or dust obscuration against the radio nucleus (column density < 3.1 × 10²¹ cm⁻²) expected by a torus of neutral gas and dust in unified models of AGNs for a type 2 Seyfert galaxy.     

Effects of soil moisture on the sensitivity of a climate model to earth orbital forcing at 9000 yr BP

The sensitivity of climate to orbitally-related changes in solar radiation at 9000 yr BP (before present) is examined using fixed and interactive soil moisture versions of a low resolution general circulation model. In both versions of the model increased solar radiation for June–August at 9000 yr BP (compared to present) produced enhanced northern monsoons and warmer continental interiors in comparison to present whereas decreased solar radiation at 9000 yr BP in December–February produced weaker southern monsoons. The increased rainfall in the northern tropics in summer increased soil moisture and runoff at 9000 yr BP in the interactive model; in the southern hemisphere decreased rainfall in summer led to decreased soil moisture and runoff. Conditions in summer became drier (decreased soil moisture and runoff) at 9000 yr BP in the northern extratropics.The experiments showed that the magnitude (but not the sign) of model sensitivity to 9000 yr BP radiation is altered by the effects of interactive soil moisture. Decreased soil moisture (about 20%) over northern Eurasia in the interactive model led to smaller evaporative increases, greater temperature increases and greater reduction of precipitation than for the model with fixed soil moisture. Over northern tropical lands, slightly smaller temperature increases and greater evaporation and precipitation increases in the interactive model are linked to the simulation of increased soil moisture at 9000 yr BP. The differences in sensitivity between the two versions of the model over northern Eurasia are statistically significant at the 95% level whereas those for the tropics are not.Overall, the results of the simulations are generally supported by the geologic evidence for 9000 yr BP; however, the evidence lacks sufficient precision and the model resolution is too coarse for detailed model/data comparisons and for assessment of the relative accuracy of the two 9000 yr BP experiments.The computed sensitivities of temperature and soil moisture to 9000 yr BP radiation differ from those simulated under equilibrium conditions in the various general circulation model experiments for increased atmospheric concentration of CO₂. In contrast to the effects of the enhanced seasonal cycle of solar radiation at 9000 yr BP, a CO₂ increase causes a broad warming of both the ocean and land with little modification of land/ocean temperature difference. The experiments for 9000 yr BP indicate a clearer signal for summer drying than is obtained in the experiments for increased CO₂. The results suggest that the 9000 yr BP climate may be of limited utility as an analog to future warm climates.     

Spatial variation of nutrients and primary productivity in the Rufiji Delta mangroves,Tanzania

Determinations of spatial and temporal variations in organic matter and nutrient dynamics in water and sediments are crucial for understanding changes in aquatic bodies. In this study, we (i) determine the spatial dynamics of dissolved inorganic nutrients, during the transition from the dry to the rainy season, and (ii) provide future productivity predictions for the Rufiji Delta mangroves, Tanzania, based on the input of various nutrients. Water samples were collected from six locations, three times per year between April 2012 and January 2014, and analysed for dissolved nutrients, total organic and inorganic carbon, chlorophyll a, chlorophyll b and total carotenoids. The prediction of future net primary productivity in the Rufiji mangroves was undertaken using the software STELLA. The mean nutrient concentrations were of the order: nitrate > phosphate > ammonium > silica > dissolved organic carbon. The study revealed that high nutrient concentrations occurred in the northern part of the Rufiji Delta as a result of anthropogenic influence in the watershed. Modelling of nutrient inputs into the delta indicated enhanced primary productivity, which is expected to increase the vulnerability of water quality in the near future due to eutrophication.     

Molecular gas distribution and dynamics in the luminous merger NGC 6240

We present the results of our subarcsecond resolution interferometricobservations of the 1.3 mm CO J = 21 line in the luminous merger NGC6240. Roughly half of the CO flux is contained in a rotating and highlyturbulent thick disk centered between the two radio and near-infrarednuclei. In this disk the molecular gas has velocity widths which reachFWZP line widths of up to 1000 km s^-1. The mass of this gasconcentration makes up between 30%–70% of the dynamical mass in thisregion. NGC 6240 may be in an earlier merging stage than typical ULIRGssuch as Arp 220. We compare these results from NGC 6240 with thoseof other luminous, gas-rich interacting galaxies and mergers.     

湖北铜绿山矿床石英闪长岩的矿物学及Sr-Nd-Pb同位素特征

铜绿山是长江中下游鄂东南矿集区最重要的、大型夕卡岩型Cu-Fe(Au)矿床。本文对该矿区中与成矿密切的石英闪长岩进行了详细的矿物成分、地球化学及Sr-Nd-Pb同位素研究。结果表明:岩石中斜长石主要为更长石(An=21～31);角闪石贫Ti(0.2),高Mg/(Mg+Fe)(0.5),属于富镁角闪石;而黑云母为镁质黑云母。岩石的地球化学具有高硅(58.86%～67.71%),富碱(Na2O+K2O=5.67%～9.63%),富集轻稀土元素(LREE)和大离子亲石元素(LILE),并强亏损元素Nb、Ta、Ti等特征。岩石的(87Sr/86Sr)i为0.7055～0.7069,εNd(t)为-7.65～-3.44;(206Pb/204Pb)i=17.66～18.00,(207Pb/204Pb)i=15.49～15.56,(208Pb/204Pb)i=37.73～38.19。矿物成分、地球化学和同位素特征说明,铜绿山岩体与阳新岩体为同源岩浆的产物,源区为深度大于40km的富集地幔,经下地壳的混染及分离结晶作用形成。岩浆熔体形成的温度应大于889℃。角闪石和黑云母的温度计估算岩浆结晶温度分别为650～800℃和500～630℃,黑云母开始结晶温度略低于角闪石结晶结束温度,压力为1.49kbar,对应侵位深度约4.9km。岩浆具有利于Cu、Fe、Au等成矿元素进入熔体的条件,可能与板块俯冲作用相关。     

Pigmenting agents in Martian soils: inferences from spectral, Mossbauer, and magnetic properties of nanophase and other iron oxides in Hawaiian palagonitic soil PN-9

We have examined a Hawaiian palagonitic tephra sample (PN-9) that has spectroscopic similarities to Martian bright regions using a number of analytical techniques, including Mossbauer and reflectance spectroscopy, X-ray diffraction, instrumental neutron activation analysis, electron probe microanalysis, transmission electron microscopy, and dithionite-citrate-bicarbonate extraction. Chemically, PN-9 has a Hawaiitic composition with alkali (and presumably silica) loss resulting from leaching by meteoric water during palagonitization; no Ce anomaly is present in the REE pattern. Mineralogically, our results show that nanophase ferric oxide (np-Ox) particles (either nanophase hematite (np-Hm) or a mixture of ferrihydrite and np-Hm) are responsible for the distinctive ferric doublet and visible-wavelength ferric absorption edge observed in Mossbauer and reflectivity spectra, respectively, for this and other spectrally similar palagonitic samples. The np-Ox particles appear to be imbedded in a hydrated aluminosilicate matrix material; no evidence was found for phyllosilicates. Other iron-bearing phases observed are titanomagnetite, which accounts for the magnetic nature of the sample; olivine; pyroxene; and glass. By analogy, np-Ox is likely the primary pigmenting agent of the bright soils and dust of Mars.     

敦煌三危山地区白垩纪OIB型基性岩墙的特征及地质意义

本文首次报道甘肃敦煌三危山地区早白垩世玄武质岩浆活动的记录。在三危山附近,基性岩墙侵入于敦煌群TTG和表壳岩大理岩和片岩中。全岩的K-Ar年龄为136.00±11.56Ma到99.11±6.35Ma,形成时代属于早白垩世。基性岩墙SiO₂含量变化范围较小,集中在47.95%~50.65%之间,以富TiO₂ (2.07%~2.35%,平均为2.21%)、MgO(6.03 %~6.51%,平均为6.32%)、贫K₂O(<1.29%),Na₂O>K₂O, Mg^#值中等且比较稳定(48.9~53.1,平均为51.7)为特征。基性岩相容元素含量相对较低,Ni含量变化相对较小,分布在112.7×10^-6~182.7×10^-6之间。而V含量变化较大,介于184×10^-6~267×10^-6之间,表明岩浆早期可能发生了一定的以橄榄石和单斜辉石为主的分离结晶作用。基性岩富集LREE((La/Yb)_N ＝3.97~4.66)和LILE,无Eu负异常,较高的Fe/Mn比值等,具有与洋岛玄武岩(OIB)相似的特征。微量元素比值等特征表明其来源与富集地幔关系密切,玄武质岩浆的形成可能与岩石圈的减薄和软流圈的上涌有关。