Observational climatology and characteristics of wintertime atmospheric blocking over Ural–Siberia     

Ho Nam Cheung  Wen Zhou  Yaping Shao  Wen Chen  Hing Yim Mok  Man Chi Wu 《Climate Dynamics》2013,41(1):63-79

This study investigates the climatological aspects and temporal characteristics of wintertime Ural-Siberian blocking (USB, centered over 30°–100°E), for the period 1980/1981–2009/2010. Sixty-eight events are identified and their physical structure is diagnosed using thermodynamic and geostrophic vorticity tendency equations. In climatology, horizontal advections play a fundamental role in constructing a USB event, in which the anticyclonic center is a warm core in the troposphere and a cold core in the lower stratosphere. The decay of the thermal structure is related to diabatic cooling along the vertical structure and warm advection in the lower stratosphere. Meanwhile, the collapse of the height structure is caused primarily by cyclonic vorticity advection. A strong interrelationship exists between the intensity and extension of USB events. The temporal characteristics of USB events are analyzed by examining strong and weak events, which are of high and low intensity. The strong events are probably preceded by an open ridge over Europe and a cyclogenesis over the Mediterranean Sea, and their formation is followed by the stronger amplification of a Rossby wave packet across Eurasia. On the other hand, the weak events are likely to be triggered by surface cold anomalies over Siberia. Overall, the evolution of a USB event forms a dynamic linkage with the Siberian high, in which the decay stage of the USB event is accompanied by a southeastward migration of the Siberian high and a subsequent cold air outbreak in East Asia. These results advance our understanding of USB and its relationship with East Asian winter monsoon activities.  相似文献   

Impact of hypoxia on the structure and function of benthic epifauna in Tolo Harbour, Hong Kong   总被引：1，自引：0，他引：1  

Fleddum A  Cheung SG  Hodgson P  Shin PK 《Marine pollution bulletin》2011,63(5-12):221-229

In Tolo Harbour, Hong Kong, where hypoxia occurs periodically, a large amount of benthic epifauna was found to be absent in the summer but become abundant again in the winter. This observation may indicate that some species are sensitive in detecting low dissolved oxygen (DO) levels and are able to escape from the harbour to more oxygenated, open waters when conditions deteriorate and return when DO levels are improved. Analysis of biological traits of these animals showed that 58% of the categories showed significant differences between the community structure in summer and winter. The significant biological traits of the few species, which remained in the harbour under the summer's hypoxic conditions suggested adaptation rather than opportunism to the low DO levels. Our data also showed that trawling can increase DO at the bottom and may benefit the less sensitive species that remained in the habitat during the summer.  相似文献   

Respiration rate and swimming activity of larvae of two sub-tidal nassariid gastropods under reduced oxygen levels: implications for their distributions in Hong Kong waters     

Liu CC  Chiu JM  Li L  Shin PK  Cheung SG 《Marine pollution bulletin》2011,63(5-12):230-236

The effects of hypoxia on the larvae of two sub-tidal nassariid gastropods, Nassarius siquijorensis and N. conoidalis were compared so as to understand how the species-specific tolerance to hypoxia might have resulted in changes in the abundance and distribution of these two species in the hypoxic Tolo Harbour, Hong Kong, since the 1980s. Respiration rates of N. siquijorensis and N. conoidalis larvae were reduced at 4.5 mg O2 l(-1), or below, as compared with the normoxic control. Significant reduction in swimming velocity was also observed for 10-day old larvae which were exposed to <2.0 mg O2 l(-1) for N. siquijorensis and <1.0 mg O2 l(-1) for N. conoidalis. The 48 h LC50 values of N. siquijorensis and N. conoidalis larvae were 0.7 and 1.7 mg O2 l(-1), respectively. The results suggested that N. siquijorensis are more tolerant to hypoxia than N. conoidalis.  相似文献   

Differences in leaf construction cost between alien and native mangrove species in Futian, Shenzhen, China: implications for invasiveness of alien species   总被引：1，自引：0，他引：1  

Li F  Yang Q  Zan Q  Tam NF  Shin PK  Vrijmoed LL  Cheung SG 《Marine pollution bulletin》2011,62(9):1957-1962

Construction cost (CC) is a quantifiable measure of energy demand for biomass production, and low CC is hypothesized to give an alien plant growth advantages and increase its potential to be an invader. Comparison of leaf CC and growth traits between alien and native mangroves in Shenzhen Futian Nature Reserve showed CC per unit mass (CC_mass), carbon concentration and gross and ash-free caloric values of alien mangroves were significantly lower than those of native species, while the height and chest circumference were just the opposite. Alien species Sonneratia apetala had the lowest CC_mass while Sonneratia caseolaris had the lowest CC_area, and were 8.99% and 32.17% lower than those of native species, respectively. Conversely, specific leaf area (SLA) of these two Sonneratia species was significantly higher than native species. Lower CC and higher SLA make the two Sonneratia species grow and spread faster than other mangroves and enhance their invasive potential.  相似文献   

Tracing iron-fueled microbial carbon production within the hydrothermal plume at the Loihi seamount     

Sarah A. Bennett  Alex L. Sessions  Katrina J. Edwards 《Geochimica et cosmochimica acta》2011,75(19):5526-5539

The Loihi hydrothermal plume provides an opportunity to investigate iron (Fe) oxidation and microbial processes in a system that is truly Fe dominated and distinct from mid-ocean ridge spreading centers. The lack of hydrogen sulfide within the Loihi hydrothermal fluids and the presence of an oxygen minimum zone at this submarine volcano’s summit, results in a prolonged presence of reduced Fe within the dispersing non-buoyant plume. In this study, we have investigated the potential for microbial carbon fixation within the Loihi plume. We sampled for both particulate and dissolved organic carbon in hydrothermal fluids, microbial mats growing around vents, and the dispersing plume, and carried out stable carbon isotope analysis on the particulate fraction. The δ¹³C values of the microbial mats ranged from −23‰ to −28‰, and are distinct from those of deep-ocean particulate organic carbon (POC). The mats and hydrothermal fluids were also elevated in dissolved organic carbon (DOC) compared to background seawater. Within the hydrothermal plume, DOC and POC concentrations were elevated and the isotopic composition of POC within the plume suggests mixing between background seawater POC and a ¹³C-depleted hydrothermal component. The combination of both DOC and POC increasing in the dispersing plume that cannot solely be the result of entrainment and DOC adsorption, provides strong evidence for in-situ microbial productivity by chemolithoautotrophs, including a likelihood for iron-oxidizing microorganisms.  相似文献   

AFLP analysis of genetic variation among three natural populations of horseshoe crab Tachypleus tridentatus along Chinese coast     

����  �·�  ������  ���ؼ�  ����  �²Ż� 《中国海洋湖沼学报》2011,29(2):284-289

The AFLP(amplified fragment length polymorphism) technique was used to analyze and compare the genetic diversity of Tachypleus tridentatus from three south-eastern coastal sites of China(Pingtan,Hong Kong and Beihai).Eight pairs of primers generated 361 loci,including 285 polymorphic loci.The ratio of polymorphic loci was 96.97%.Nei's genetic diversity index was 0.420 8 and the Shannon information index was 0.607 5,both of which were higher than that reported for many other arthropods.These results show tha...  相似文献   

Response of meiofaunal and nematode communities to sewage pollution abatement: a field transplantation experiment   总被引：1，自引：0，他引：1  

������  ���ؼ�  ������ 《中国海洋湖沼学报》2011,29(6):1174-1185

To assess the recovery rate of meiofaunal and nematode communities upon abatement of sewage pollution, a field transplantation experiment was conducted in Tai Tam, which is a non-polluted, shallow subtidal habitat on the southern portion of Hong Kong Island. The sediments used were from one site located in Victoria Harbour that was heavily influenced by sewage pollution, and one site in the outside-harbor area, which was relatively clean. In addition, sediments from Tai Tam were used as a control. Fresh sediments with meiofauna were collected from the aforementioned sites, placed in plastic trays and transplanted to Tai Tam. Sediments were retrieved at the beginning of the experiment and at 1-, 3-, and 8-weeks after transplantation for analysis of the meiofaunal and nematode communities as well as the sediment characteristics. The results showed that the meiofaunal and nematode communities in the control sediments were consistent at the four sampling periods, while it took three and eight weeks, respectively, for the nematode communities from the outside-harbor and inside-harbor sites to become similar to the control. These findings indicated that the relatively poor habitat quality and the nematode community composition in the sewage polluted inside-harbor sediments required a longer time for recovery than samples from the better habitat quality and the nematode community composition in the outside-harbor sediments.  相似文献   

Vertical response of single piles: transient analysis by time-domain BEM     

Z.X. Lei  Y.K. Cheung  L.G. Tham 《Soil Dynamics and Earthquake Engineering》1993,12(1)

The transient dynamic response of single piles in a layered half-space under a time-dependent vertical force is analyzed by an FEM-BEM coupling approach. The pile is modeled by FEM and the layered half-space is modeled by a general cylindrical coordinates time-domain BEM. Only one-dimensional discretization is necessary on the boundaries of the three-dimensional layered half-space by virtue of the Fourier theory, while the pile shaft can be discretized as a one-dimensional elastic beam. The compatibility and equilibrium conditions between pile shaft and soil layers are employed to assemble respective equations into one. Fairly good agreement between two unknown solutions and the current approach is found. Parametric studies reveal the influences of several dimensionless factors, such as E_p/E_s, l/r₀, _p/_s and ν_s. The effect of soil layering and the support condition of the pile tip is also reported by numerical examples.  相似文献   

Perceptions of Environmental Change and Climate Concern Among Idaho’s Farmers     

Katrina Running  Jordan Burke  Kathleen Shipley 《社会与自然资源》2017,30(6):659-673

Climate change public opinion research has identified conservative political ideology as the primary predictor of skepticism about climate change’s anthropogenic causes. Most farmers in Idaho are politically conservative, but they are also a unique group for whom observing their environment is part of daily life and work. We use data from in-depth interviews with 30 Idaho farmers to examine the relationship between observations of specific environmental changes and climate concern. We find that while most farmers report noticing changes in precipitation patterns, growing season length, and winter temperatures, few farmers connect these with long-term global climate change. These findings have two important implications: 1) direct experience, even in the form of disruption to an individual’s economic security, is not enough to overcome the influence of political ideology on climate change beliefs, and 2) acknowledging climate variation is not sufficient to convince individuals that the changes are produced by human activities.  相似文献   

Catchment and in-stream influences on metal concentration and ochre deposit density in upland streams, Northern Ireland     

Katrina Ann Macintosh  David Griffiths 《Environmental Earth Sciences》2013,70(7):3023-3030

Metal concentrations from stream waters in two geological blocks in Northern Ireland were compared to determine the contributions of catchment characteristics and in-stream conditions. One block is composed of metamorphosed schist and unconsolidated glacial drift with peat or peaty podzol (mainly humic) soils, while the other block consists of tertiary basalt with brown earth and gley soils. Water samples were collected from 52 stream sites and analysed for iron (Fe), manganese (Mn) and aluminium (Al) as well as a range of other chemical determinands known to affect metal solubility. Densities of metal-rich ochre deposit were determined for stream bed stone samples. Higher conductivities and concentrations of bicarbonate, alkalinity, calcium and magnesium occurred on basalt than on schist. Despite higher Fe and Mn oxide concentrations in basalt-derived non-humic soils, stream water concentrations were much lower and ochre deposit densities only one-third of those on schist overlain by humic soils. Neither rock nor soil type predicted Al concentrations, but pH and dissolved oxygen did. Peat-generated acidity and the limited acid neutralising capacity of base-poor metamorphosed schist have resulted in elevated concentrations of metals and ochre deposit in surface waters.  相似文献