Spatio-temporal characteristics of aerosol distribution over Tibetan Plateau and numerical simulation of radiative forcing and climate response

In this paper we have analyzed aerosol distribution over the Tibetan Plateau by using the global monthly mean satellite data of Stratospheric Aerosol and Gas Experiment II (SAGE II). The results are as follows: (1) Stratospheric aerosol optical depth can oscillate in the four seasons. It means that the aerosol optical depth is the thickest in winter and a little thinner in spring and the thinnest in summer and then a little thicker in autumn. We have found that the oscillation is caused by the oscillation of tropopause in different seasons. (2) Stratospheric aerosol comes mainly from sprays of volcano. After eruption of Mount Pinatubo aerosol optical depth in stratosphere over the Tibetan Plateau increases 10 times compared with before. (3) The characteristic of aerosol vertical distribution over the Tibetan Plateau is that there is an extremely high value at the altitude of 70 hPa. The most interesting thing is that the extremely high value can oscillate between 50 hPa and 100 hPa. We have verified that the oscillation is a unique characteristic over the Tibetan Plateau by comparing it with South China and North China. Then the radiative forcing and regional climate response over the Tibetan Plateau of aerosol are investigated. We have discovered such things as followed by: (1) The radiative forcing is positive because the parameterized aerosol optical depth is less than 0.14 which is the optical depth of the uniform background boundary aerosol layer. It is 0–3 W/m² in January and 0–4 W/m² in April and less than 3 W/m² in July and 3–6 W/m² in October. (2) Ground temperature rises 0.1–0.2 K in October which is the biggest increasing magnitude, and 0.01–0.02 in July which is the smallest one. It rises about 0.05-0.01 K in January and April. (3) Air temperature near the earth’s surface and the one at the altitude of 500 hPa rise too, but the increasing magnitude is less than the former one.

     

Analysis of aerosol and carbon monoxide characteristics over Arabian Sea during crop residue burning period in the Indo-Gangetic Plains using multi-satellite remote sensing datasets

In this study, we have used multi-satellite data to retrieve aerosol loadings and carbon monoxide (CO) pollution over the Arabian Sea, caused due to anthropogenic activities over the Indo-Gangetic Plains (IGP) in India. Relatively high aerosol and CO loadings during 9–14 November 2007 over Arabian Sea were attributed to crop residues burning in the IGP and fireworks during Diwali festival. Aerosol index (AI) obtained from ozone monitoring instrument (OMI) and CO from measurements of pollution in the troposphere instrument (MOPITT). CO showed higher values over the Arabian Sea suggesting long-range transport of anthropogenic aerosols and trace gases from the continental to Arabian Sea region.     

Sources of polyfluoroalkyl compounds in the North Sea, Baltic Sea and Norwegian Sea: Evidence from their spatial distribution in surface water

The spatial distribution of 15 polyfluoroalkyl compounds (PFCs) in surface water was investigated in the North Sea, Baltic Sea and Norwegian Sea. In addition, an interlaboratory comparison of the sampling techniques and analysis was conducted. Highest concentration in the North Sea was found near the coast, whereas the ∑PFC concentration decreased rapidly from 18.4 to 0.07 ng l⁻¹ towards the open North Sea. The river Elbe could identify as a local input source for PFCs into the North Sea, whereas perfluorobutanoic acid (PFBA) was transported into the sampling area with the easterly current. In contrast to the North Sea, the distribution of PFCs in the Baltic Sea was relatively homogenous, where diffuse sources dominated. In general, the composition profile was influenced from local sources caused by human activities, whereas atmospheric depositions of here analysed PFCs were negligible, but it could have possibly an influence on low contaminated sites like the open North Sea or Norwegian Sea.     

南海东北部973剖面BSR及其热流特征

对南海东北部973项目采集的地震测线进行了处理,阐明了恒春海脊处天然气水合物似海底反射（BSR）的特征.不同类型剖面的分析表明,单道地震剖面可以揭示南海东北部地区BSR一定的分布,但地震处理对揭示BSR分布全貌起重要作用.南海东北部的BSR具有世界大陆边缘BSR典型的特征,切穿了沉积层理反射,与海底起伏大体平行,为一强振幅的负极性反射.该BSR特征明显,意味着南海东北部地区存在含天然气水合物沉积.利用甲烷水合物与多组分天然气水合物相平衡曲线,计算了稳定带底界的埋深,并与BSR深度进行了对比分析.无论是甲烷水合物稳定带底界还是多组分天然气水合物稳定带的底界,单一地温梯度计算的结果不可能与BSR深度在整个剖面上对应.可知本区横向上地温梯度变化较大.利用BSR资料估算了地温梯度并求得热流值.计算表明,地温梯度与热流值由西向东,随着离海沟距离的增大、离岛弧距离的减小而减小.BSR计算得到的热流值为28～64 mW/m2,与台湾西南实测热流值的结果基本可以对比.     

Oxygen and lead isotope characteristics of granitic rocks from the Nansha block (South China Sea): Implications for their petrogenesis and tectonic affinity

The pre‐Cenozoic history of the South China Sea (SCS) region is the object of continued debate. To trace the evolution of the SCS, a better understanding of the petrogenesis and tectonic affiliation of the granitic rocks that comprise the microblocks within the region is necessary. In this study, we analyzed the whole‐rock oxygen and lead isotope ratios of granitic samples dredged from two locations in the Nansha microblock, one of the microblocks in the SCS. Oxygen isotope data combined with previously published Sr isotope data show that group I rocks (δ¹⁸O = 6.00–7.20‰; average = 6.64‰) originated from a mantle source contaminated by material and/or fluid input from a Mesozoic subduction zone in the southeastern side of the microblock. Group II rocks (δ¹⁸O = 6.86‰–9.13‰; average = 7.75‰) also came from the same source, but they were additionally affected by crustal contamination. The Nansha microblock has high radiogenic lead ratios (²⁰⁶Pb/²⁰⁴Pb_i = 18.602–18.756, ²⁰⁷Pb/²⁰⁴Pb_i = 15.660–15.713, ²⁰⁸Pb/²⁰⁴Pb_i = 38.693–38.893), which indicate that the Nansha microblock is tectonically affiliated with the Nanling–Hainan or South China block. This notion is consistent with the results of a previous Nd isotope study. As a whole, results of our study suggest that some of the other microblocks dispersed in the SCS are also possible fragments of South China block, and thus further studies are needed to better constrain the pre‐Cenozoic evolutionary history of the SCS region.     

Biomarker responses in Atlantic cod (Gadus morhua) exposed to produced water from a North Sea oil field: laboratory and field assessments

Biological markers of produced water (PW) exposure were studied in Atlantic cod (Gadus morhua) in both laboratory and field experiments, using authentic PW from a North Sea oil field. In the laboratory study, the PW exposure yielded significantly elevated levels of metabolites of polycyclic aromatic hydrocarbons (PAHs) and alkylphenols (APs) in bile even at the lowest exposure dose (0.125% PW). Other biomarkers (hepatic CYP1A induction and DNA adduct formation) responded at 0.25% and 0.5% PW concentrations. In the field study, bile metabolite markers and hepatic CYP1A were clearly increased in fish caged close to the PW outfall. Induction of plasma vitellogenin was not found in laboratory or field exposures, suggesting that the levels of oestrogen agonists (such as APs) might not have been sufficient to elicit induction, under the present conditions. The applicability of the biomarkers for use in water column biomonitoring programs is discussed.     

Dioxin-like compounds in sediments from the Daliao River Estuary of Bohai Sea: distribution and their influencing factors

The concentrations, compositional profiles, and potential ecological risk of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs) and polychlorinated naphthalenes (PCNs) in sediments of the Daliao River Estuary were investigated. Total concentrations of PCDD/Fs, PCBs, and PCNs were in the range of 11.3-133.2 ng/kg dry weight (dw), 1 971-37 632 ng/kg dw and 33.1-284.4 ng/kg dw, respectively. The total TEQ values varied from 0.37 to 4.08 ng/kg dw, with the dominant contributions by PCDD/Fs, then by PCBs and PCNs. The spatial distributions of PCDD/Fs, PCBs and PCNs in the river estuary were much related to hydrodynamic conditions. The risk of contamination to the deeper sea was increased in the flood seasons. Moreover, our data confirmed that both organic matter in sediments and molecular properties of dioxin-like compounds were the factors which strongly influenced the partition behavior of these dioxin-like compounds between sediments and water phase in the estuarine zone.     

A geochemical record of environmental changes in sediments from Sishili Bay,northern Yellow Sea,China: Anthropogenic influence on organic matter sources and composition over the last 100 years

Total organic carbon (TOC), total nitrogen (TN), δ¹³C and δ¹⁵N were measured in sediment cores at three sites in Sishili Bay, China, to track the impacts of anthropogenic activities on the coastal environment over the last 100 years. The increased TOC and TN in the upper section of sediment cores indicated a eutrophic process since 1975. In comparison, the TOC and TN in the sediment core near to a scallop aquaculture area displayed a much slower increase, indicating the contribution of scallop aquaculture in mitigating eutrophication. Combined information from δ¹³C, δ¹⁵N and TOC:TN indicated an increased terrestrial signal, although organic matter sources in Sishili Bay featured a mixture of terrestrial and marine sources, with phytoplankton being dominant. Increased fertilizer use since 1970s contributed to the eutrophic process in Sishili Bay since 1975, and increased sewage discharge from 1990s has added to this process.     

PAH body burden and biomarker responses in mussels (Mytilus edulis) exposed to produced water from a North Sea oil field: laboratory and field assessments

In order to study the impact of produced water (PW) from a North Sea oil field on blue mussels (Mytilus edulis), chemical and biological markers were selected. A laboratory exposure (0.125%, 0.25% and 0.5% of PW) and a field study (6 stations 0.2-2 km from a PW discharge point) were conducted. In the laboratory study, PAH bioaccumulation increased in mussel soft tissue even at the lowest exposure dose. Micronuclei frequency demonstrated a dose-response pattern, whereas lysosomal membrane stability showed tendency towards a dose-response pattern. The same markers were assessed in the field study, biomarker analyses were consistent with the contamination level, as evaluated by mussel polycyclic aromatic hydrocarbons body burden. Overall, obtained results confirmed the value of an ecotoxicological approach for a scientifically sound characterisation of biological effects induced by offshore oilfield operational discharges.     

Influence of foraminifera on formation and occurrence characteristics of natural gas hydrates in fine-grained sediments from Shenhu area,South China Sea

Marine gas hydrates accumulate primarily in coarse-grained, high-permeability layers; however, highly saturated natural gas hydrates have been discovered in the fine-grained sediments of Shenhu area, South China Sea (SCS). This may be explained by key factors, such as the great abundance of foraminifera shells. In this paper, by analyzing the SCS foraminifera structure and performing hydrate formation experiments in the foraminifera shells, the contribution of foraminifera to hydrate accumulation in the SCS was investigated from a microscopic point of view. Simulations of hydrate formation were carried out in both pure SCS foraminifera shells and the host sediments. Pore structures in typical foraminifera were studied by use of micro-focus X-ray computed tomography (CT) and scanning electron microscopy (SEM). Hydrate growth and occurrence characteristics in the foraminifera shells were observed in-situ. The results showed that the presence of foraminifera significantly enhanced the effective porosity of the SCS sediments. Moreover, while the hydrates grew preferentially in the chambers of the coarse-grained foraminifera by adhering to the inner walls of the foraminifera shells, no apparent hydrate accumulation was observed in the fine-grained or argillaceous matrix. These findings provide a basis for further studies on the accumulation mechanism of hydrates and physical properties of hydrate reservoir in the South China Sea.     

Bedform characteristics in natural and regulated channels: A comparative field study on the Wilga River,Poland

This paper presents results of a field investigation conducted to examine the bed sediment, riverbed morphology and flow structure over dunes in natural and regulated channels. Field measurements using an acoustic Doppler current profiler (ADCP) have been carried out on two parts of lowland Wilga River in Poland. It is shown that the bedforms with a low angle of lee side develop more frequently than asymmetrical dunes with high lee-side angles, which are mostly associated with the occurrence of local scours and river meanders. Wavenumber analysis of bed elevation confirms the existence of scaling region in the longitudinal wavenumber spectrum, with “?3” scaling exponents for the natural and regulated channels as well. Moreover, the results of flow velocity field are presented in the form of a 2-D streamwise-vertical vector field, showing several similarities to previous laboratory and field investigations conducted on much deeper rivers than the Wilga. The experimental campaign and methods used to obtain the results are also presented briefly. In addition, a short database of fluvial dunes statistics is provided.     

Modelling the effects of changes in the Earth's magnetic field from 1957 to 1997 on the ionospheric hmF2 and foF2 parameters

We have modelled the effects of changes in the Earth's magnetic field on the ionosphere as have occurred from 1957 to 1997 using the NCAR Thermosphere–Ionosphere–Electrodynamics General Circulation Model. Previous studies that attempted to quantify these effects used a constant wind field, so that any electro-dynamical coupling processes could not be accounted for. Using TIE-GCM we can account for these processes. We find substantial changes in the F2 layer peak height hmF2 (up to ±20 km) and critical frequency foF2 (up to ±0.5 MHz) over the Atlantic Ocean and South America, purely due to changes in the Earth's magnetic field (i.e. unrelated to greenhouse gas cooling effects, which are often held responsible for long-term trends in hmf2 and fof2). These would make up a significant contribution to observed long-term trends in these areas and therefore must be taken into account in their interpretation. Modelled trends of hmF2 and foF2 exhibit a strong seasonal and diurnal variation, highlighting the importance of separating data with respect to season and local time. Most of the modelled changes in hmF2 and foF2 can be related to changes in plasma transport up or down magnetic field lines driven by neutral winds, changes, which are mostly caused by changes in the inclination of the field, though changes in declination and neutral wind also play a role. Changes in the vertical component of the E×B drift seem to have little effect on hmF2 and foF2.     

Climate changes and their impacts on water resources in semiarid regions: a case study of the Wei River basin,China

Understanding the impacts of climate change and human activity on the hydrological processes in river basins is important for maintaining ecosystem integrity and sustaining local economic development. The objective of this study was to evaluate the impact of climate variability and human activity on mean annual flow in the Wei River, the largest tributary of the Yellow River. The nonparametric Mann–Kendall test and wavelet transform were applied to detect the variations of hydrometeorological variables in the semiarid Wei River basin in the northwestern China. The identifications were based on streamflow records from 1958 to 2008 at four hydrological stations as well as precipitation and potential evapotranspiration (PET) data from 21 climate stations. A simple method based on Budyko curve was used to evaluate potential impacts of climate change and human activities on mean annual flow. The results show that annual streamflow decreased because of the reduced precipitation and increased PET at most stations. Both annual and seasonal precipitation and PET demonstrated mixed trends of decreasing and increasing, although significant trends (P < 0.05) were consistently detected in spring and autumn at most stations. Significant periodicities of 0.5 and 1 year (P < 0.05) were examined in all the time series. The spectrum of streamflow at the Huaxian station shows insignificant annual cycle during 1971–1975, 1986–1993 and 1996–2008, which is probably resulted from human activities. Climate variability greatly affected water resources in the Beiluo River, whereas human activities (including soil and water conservation, irrigation, reservoirs construction, etc.) accounted more for the changes of streamflow in the area near the Huaxian station during different periods. The results from this article can be used as a reference for water resources planning and management in the semiarid Wei River basin. Copyright © 2012 John Wiley & Sons, Ltd.     

Climate changes and their impacts on water resources in the arid regions: a case study of the Tarim River basin, China

Streamflow series of five hydrological stations were analyzed with aim to indicate variability of water resources in the Tarim River basin. Besides, impacts of climate changes on water resources were investigated by analyzing daily precipitation and temperature data of 23 meteorological stations covering 1960–2005. Some interesting and important results were obtained: (1) the study region is characterized by increasing temperature, however, only temperature in autumn is in significant increasing trend; (2) precipitation changes present different properties. Generally, increasing precipitation can be detected. However, only the precipitation in the Tienshan mountain area is in significant increasing trend. Annual streamflow of major rivers of the Tarim River basin are not in significant trends, except that of the Akesu River which is in significantly increasing trend. Due to the geomorphologic properties of the Tienshan mountain area, precipitation in this area demonstrates significant increasing trend and which in turn leads to increasing streamflow of the Akesu River. Due to the fact that the sources of streamflow of the rivers in the Tarim River basin are precipitation and melting glacial, both increasing precipitation and accelerating melting ice has the potential to cause increasing streamflow. These results are of practical and scientific merits in basin-scale water resource management in the arid regions in China under the changing environment.     

On the synchronism in the events within the core and on the surface of the earth: the changes in the organic world and in the polarity of the geomagnetic field in the phanerozoic

The data on geomagnetic reversals are compared with the changes in the organic world and with the lower-mantle plumes. The times of the formation of plumes and the times of their appearance on the Earth’s surface relate to the intervals characterized by the different frequencies of geomagnetic reversals, i.e., there is no interrelation between the formation of plumes and the frequency of the changes in the geomagnetic field polarity. At the same time, a certain synchronism is observed between the frequency of the geomagnetic reversals and the boundaries of the biostratigraphic ages, i.e., the changes in the organic world in the long-period range. A hypothesis is proposed, which explains the change in the sign of the geomagnetic field by the combined effect of the irregular rotation of the internal core relative to the mantle and the changes in the slope angle of the axis of the Earth’s rotation, which, in turn, results in synchronous events on the Earth’s surface: the rates of changes in the organic world.     

Large wood in central Appalachian headwater streams: controls on and potential changes to wood loads from infestation of hemlock woolly adelgid

Large wood (LW) is an important component of forested headwater streams. The character of LW loads reflects a balance between adjacent valley processes that deliver LW to the channel (herein recruitment processes) and stream channel processes that either retain or transport LW through the reach (herein retention processes). In the central Appalachian Mountains, USA, LW characteristics in headwater streams located in eastern hemlocks (Tsuga candensis) forests are expected to change because of infestation of hemlock woolly adelgid (Adelges tsugae, HWA), an exotic, invasive insect. We examined LW characteristics in 24 headwater streams ranging from un‐infested to severe infestation, as determined by hemlock canopy health. The objectives of this work were to: (i) quantify wood loads; (ii) assess the relative importance of valley recruitment and in‐stream retention mechanisms in controlling reach‐scale wood loads; and (iii) assess if there was a detectable influence of HWA on LW loads. We hypothesized that LW loads would be similar to other forested streams in eastern USA and dominated by recruitment processes. In addition, higher LW loads would correspond with advanced HWA infestation. Mean wood frequency was 38 pieces/100 m ± 17 (standard deviation); mean wood volume was 3.69 m³/100 m ± 2.76. In general, LW load characteristics were influenced by both recruitment and retention parameters; jam (accumulations ≥ 3 pieces) characteristics were dominated by retention parameters. Results suggest that adjacent stand basal area influences LW loads and once LW is recruited to the channel, streams lack sufficient hydraulic driving forces, despite having lower resistance structures, to transport LW out of the reach. Sites in moderate decline had higher proportions of short (1–2 m and 1–4 m) and very long (>10 m) LW with higher frequency of jams that were low in volume. We present a hypothesized conceptual model of expected changes to LW loads associated with HWA infestation and hemlock mortality. Copyright © 2015 John Wiley & Sons, Ltd.     

The impact of rural land management changes on soil hydraulic properties and runoff processes: results from experimental plots in upland UK

To develop an evidence base to help predict the impacts of land management change on flood generation, four experimental sites were established on improved grassland used for sheep grazing at the Pontbren catchment in upland Wales, UK. At each site, three plots were established where surface runoff was measured, supplemented by measurements of soil infiltration rates and soil and vegetation physical properties. Following baseline monitoring, treatments were applied to two of the plots: exclusion of sheep (ungrazed) and exclusion of sheep and planting with native broadleaf tree species (tree planted), with the third plot acting as a control (grazed pasture). Due to a particularly dry summer that occurred pre‐treatment, the soil hydrological responses were initially impacted by the effects of the climate on soil structure. Nevertheless, treatments did have a clear influence on soil hydrological response. On average, post‐treatment runoff volumes were reduced by 48% and 78% in ungrazed and tree‐planted plots relative to the control, although all results varied greatly over the sites. Five years following treatment application, near‐surface soil bulk density was reduced and median soil infiltration rates were 67 times greater in plots planted with trees compared to grazed pasture. The results illustrate the potential use of upland land management for ameliorating local‐scale flood generation but emphasise the need for long‐term monitoring to more clearly separate the effects of land management from those of climatic variability. Copyright © 2013 John Wiley & Sons, Ltd.     

Temporal and spatial changes in grain size on a macro-tidal channel-flat complex: results from Kingsport,Nova Scotia,Bay of Fundy

Ocean Dynamics - Understanding the processes that lead to seasonal changes in grain size on muddy macro-tidal flat and channel complexes will assist efforts to predict future changes caused by...     

Formation and Evolution of the Anaerobic Zone in the Black Sea from the Most Recent Salinization to the Present State: Retrospective Estimation Based on Mathematical Modeling

It is established that the formation and evolution of the anaerobic zone of the Black Sea are associated with the beginning and development of the most recent salinization of the sea and the formation of pycnocline at intermediate depths; a deterioration of deep-water aeration and the formation of anaerobic conditions in deeper layers; the rate of sulfate-reduction first in the near-bed layer and later, as oxygen is depleted, in the water mass. Formalization of these processes based on refined present-day data on water balance enabled the reproduction of profiles of water salinity and vertical-exchange coefficient for different formation stages of salinity regime in the Black Sea. The vertical distribution of oxygen and hydrogen sulfide is reconstructed, and the rates of oxygen consumption in water column and sulfate reduction in the near-bed layer and at the upper boundary of the anaerobic zone are evaluated in numerical experiments. The obtained data show the transformation of the vertical distribution of oxygen and hydrogen sulfide in the Black Sea from the beginning of its most recent salinization to the present-day state. It is shown that the anaerobic zone rises from 2000 to 200 m within 500–600 years (in the period 3.9–4.5 Ka from the beginning of water exchange through the Bosphorus), and next the upper boundary of the anaerobic zone slowly ascends up to its present-day position (130–180 m). Mathematical modeling was used to evaluate the fluxes of oxygen and hydrogen sulfide at different formation stages of the anaerobic zone in the sea.__________Translated from Vodnye Resursy, Vol. 32, No. 3, 2005, pp. 307–321.Original Russian Text Copyright © 2005 by Leonov, Shaporenko.