Holocene freshwater diatoms: palaeoenvironmental implications from south Kamchatka,Russia     

Ulrike Hoff  Oleg Dirksen  Veronika Dirksen  Gerhard Kuhn  Hanno Meyer  Bernhard Diekmann 《Boreas: An International Journal of Quaternary Research》2014,43(1):22-41

Holocene palaeolimnological conditions were reconstructed by analysing fossil diatom assemblages within a lacustrine sediment core from Lake Sokoch, southern Kamchatka (Russia). Sediments of this proglacial lake cover the past 9400 years and hence represent almost the whole Holocene history. The biosiliceous muddy sample material was analysed for several geochemical and biological parameters, such as the total organic carbon and biogenic silica content, and the diatom community (quantitative and qualitative changes). Based on changes in the relative abundances of the most frequent species Aulacoseira subarctica, Staurosira martyi and Stephanodiscus alpinus and a depth‐constrained cluster analyses (CONISS), five diatom assemblage zones could be identified. The oldest stage recovered lies between 9400 and 9000 cal. a BP and reflects the initial lake stage after the retreat of local glaciers, with a high detrital sediment supply, shallow‐water conditions and a high diatom diversity. The next zone (9000–6200 cal. a BP) shows a more mature lake system with accumulating biogenic remains and higher water levels during climate amelioration. This is followed by the most obvious change in the diatom assemblage, delineated by an occurrence of S. alpinus, between 6200 and 2700 cal. a BP. Wet conditions in spring probably led to an enhanced fluvial runoff and eutrophic to hypertrophic conditions. The end of this period might reflect climate deterioration related to the Neoglacial epoch of the Holocene. Between 2700 and 1600 cal. a BP the sediments of Lake Sokoch reveal oligotrophic water conditions in a windy high‐energy environment. The youngest interval, between 1600 cal. a BP and the Present, indicates shallow‐water conditions and a very short growing season, which might reflect the Little Ice Age. The results may offer a baseline for the interpretation of Holocene palaeoenvironmental changes in Kamchatka and their relation to regional climate change from a palaeoecological perspective.  相似文献   

Forecast of the key parameters of the 24-th solar cycle     

Oleg Vasilievich Chumak  Tatiana Viktorovna Matveychuk 《中国天文和天体物理学报》2010,10(9)

To predict the key parameters of the solar cycle,a new method is proposed based on the empirical law describing the correlation between the maximum height of the preceding solar cycle and the entropy of the forthcoming one.The entropy of the forthcoming cycle may be estimated using this empirical law,if the maximum height of the current cycle is known.The cycle entropy is shown to correlate well with the cycle's maximum height and,as a consequence,the height of the forthcoming maximum can be estimated.In turn,the correlation found between the height of the maximum and the duration of the ascending branch(the Waldmeier rule)allows the epoch of the maximum,Tmax,to be estimated,if the date of the minimum is known.Moreover,using the law discovered,one can find out the analogous cycles which are similar to the cycle being forecasted,and hence,obtain the synoptic forecast of all main features of the forthcoming cycle.The estimates have shown the accuracy level of this technique to be 86%.The new regularities discovered are also interesting because they are fundamental in the theory of solar cycles and may provide new empirical data.The main parameters of the future solar cycle 24 are as follows: the height of the maximum is Wmax = 95±20,the duration of the ascending branch is Ta = 4.5±0.5 yr,the total cycle duration according to the synoptic forecast is 11.3 yr.  相似文献   

Wind Farm Support Vessel Extreme Roll Assessment While Docking in the Bohai Sea     

XU Xiao-sen  Oleg Gaidai  Oleh Karpa  WANG Jun-lei  YE Ren-chuan  CHENG Yong 《中国海洋工程》2021,35(2):308-316

Robust prediction of extreme motions during wind farm support vessel(WFSV)operation is an important safety concern that requires further extensive research as offshore wind energy industry sector widens.In particular,it is important to study the safety of operation in random sea conditions during WFSV docking against the wind tower,while workers are able to get on the tower.Docking is performed by thrusting vessel fender against wind tower(an alternative docking way by hinging is not studied here).In this paper,the finite element software AQWA has been used to analyze vessel response due to hydrodynamic wave loads,acting on a specific maintenance ship under actual sea conditions.Excessive roll may occur during certain sea conditions,especially in the beam sea,posing a risk to the crew transfer operation.The Bohai Sea is the area of diverse industrial activities such as offshore oil production,wave and wind power generation,etc.This paper advocates a novel method for estimating extreme roll statistics,based on Monte Carlo simulations(or measurements).The ACER(averaged conditional exceedance rate)method and its modification are presented in brief detail in Appendix.The proposed methodology provides an accurate extreme value prediction,utilizing available data efficiently.In this study the estimated return level values,obtained by ACER method,are compared with the corresponding return level values obtained by Gumbel method.Based on the overall performance of the proposed method,it is concluded that the ACER method can provide more robust and accurate prediction of the extreme vessel roll.The described approach may be well used at the vessel design stage,while defining optimal boat parameters would minimize potential roll.  相似文献   

CO2 threshold for millennial-scale oscillations in the climate system: implications for global warming scenarios     

Katrin J. Meissner  Michael Eby  Andrew J. Weaver  Oleg A. Saenko 《Climate Dynamics》2008,30(2-3):161-174

We present several equilibrium runs under varying atmospheric CO₂ concentrations using the University of Victoria Earth System Climate Model (UVic ESCM). The model shows two very different responses: for CO₂ concentrations of 400 ppm or lower, the system evolves into an equilibrium state. For CO₂ concentrations of 440 ppm or higher, the system starts oscillating between a state with vigorous deep water formation in the Southern Ocean and a state with no deep water formation in the Southern Ocean. The flushing events result in a rapid increase in atmospheric temperatures, degassing of CO₂ and therefore an increase in atmospheric CO₂ concentrations, and a reduction of sea ice cover in the Southern Ocean. They also cool the deep ocean worldwide. After the flush, the deep ocean warms slowly again and CO₂ is taken up by the ocean until the stratification becomes unstable again at high latitudes thousands of years later. The existence of a threshold in CO₂ concentration which places the UVic ESCM in either an oscillating or non-oscillating state makes our results intriguing. If the UVic ESCM captures a mechanism that is present and important in the real climate system, the consequences would comprise a rapid increase in atmospheric carbon dioxide concentrations of several tens of ppm, an increase in global surface temperature of the order of 1–2°C, local temperature changes of the order of 6°C and a profound change in ocean stratification, deep water temperature and sea ice cover.  相似文献   

中国东北与俄罗斯远东富CO_2矿泉水化学对比     

毛绪美  王焰新  Oleg V.Chudaev 《地质科技情报》2009,28(6)

中国东北与俄罗斯远东富CO2矿泉是宝贵的饮用、医用矿水资源。五大连池、长白山天池、俄罗斯远东Primorye地区各泉水水化学特征对比显示,中国东北五大连池与俄罗斯远东Primorye地区出露泉水为低温、微酸、HCO3型、富含Si、Fe、Sr和CO2气体的综合优质饮用矿泉水;长白山天池出露泉水为高温、中性-微碱、HCO3型、富含Si和CO2气体的优质热矿泉水。五大连池和俄罗斯远东富CO2冷矿泉与长白山天池富CO2热矿泉具有相似而不同的形成过程,CO2气体对水化学的形成起了决定性的作用,广泛发育的花岗岩提供了富CO2热泉的物质来源,断层破碎带增加了CO2气体-地下水-花岗岩之间的反应程度,温度仅对可溶性Si有影响。  相似文献   

Finite element modeling of net panels using a consistent net element   总被引：3，自引：0，他引：3  

Igor Tsukrov  Oleg Eroshkin  David Fredriksson  M. Robinson Swift  Barbaros Celikkol 《Ocean Engineering》2003,30(2):251-270

A consistent finite element is proposed to model the hydrodynamic response of net panels to environmental loading. This equivalent net element is constructed to reproduce the drag, buoyancy, inertial and elastic forces exerted on the netting by current and waves. To evaluate the accuracy of the proposed finite element modeling, numerical predictions have been compared with the experimental observations and (simplified) analytical results of other authors. This new modeling technique has been applied to evaluate the performance of a tension leg fish cage in the open ocean environment.  相似文献   

Radiation shielding study for the joint European X-ray Telescope focal plane Detectors     

Alan Owens  Michael Denby  Mark R. Sims  Oleg Terekhov  Alan A. Wells 《Experimental Astronomy》1997,7(3):161-189

The requirements, philosophy and implementation of inorbit radiation shielding for the Charge Coupled Devices (CCDs) on-board the Joint European X-ray Telescope (JET-X) are described in detail. Relevant trade-offs between displacement damage, spectral degradation, instrument mass and mission lifetime are examined and a maximum permissible fluence at the CCDs derived. The calculations show that for the ambient JET-X radiation environment no benefit is obtained by increasing the shield thickness above 30 mm of aluminum due to the local production of cascade nucleons. However, a large flare of the August 1972 type will exceed the required maximum fluence by a factor of 2. In order to survive such a flare, a thicker shield is required. Because of mass constraints, JET-X will fly a composite shield composed of 20 mm of aluminum on the outside and 5 mm of tungsten on the inside. Such a shield is designed to ensure that the degradation in the CCD FWHM energy resolution is no more than 40% around the Fe line over the nominal two year mission lifetime (a factor of 2 x the intrinsic line broadening). The predicted degradation in energy resolution and the efficacy of the shield design has been recently verified by experiment (Owens et al., Nucl. Instr. and Meth., A361 (1995) 602).  相似文献   

On an instability mechanism in a stably stratified atmospheric layer over a moistened surface     

Oleg V. Perestenko  Lev Kh. Ingel 《Boundary-Layer Meteorology》1996,78(3-4):383-398

In air stratified by a specific humidity gradient, the vertical motions result in variations in specific humidity (mixing ratio) near the underlying surface. This, in turn, causes a variation of evaporation from the surface, resulting in horizontal thermal inhomogeneities on the surface, which under certain conditions can strengthen the initial vertical motions. The linear problem of the stability of the system under consideration is solved in this paper, boundaries of the unstable region are defined, and specific values of growth rates of disturbances are investigated. The estimates show that even in a density-stratified atmospheric layer over a moist surface, rapid development of disturbances with horizontal scales of several hundred metres is possible. The horizontal sizes of the most rapidly growing modes, as a rule, are an order of magnitude larger than the vertical sizes. The possibility of observing this instability under natural conditions is discussed.  相似文献   

800-yr-long records of annual air temperature and precipitation over southern Siberia inferred from Teletskoye Lake sediments   总被引：2，自引：0，他引：2  

Ivan Kalugin  Andrei Daryin  Lyubov Smolyaninova  Andrei Andreev  Bernhard Diekmann  Oleg Khlystov 《Quaternary Research》2007,67(3):400-410

A unique 800-yr-long record of annual temperatures and precipitation over the south of western Siberia has been reconstructed from the bottom sediments of Teletskoye Lake, Altai Mountains using an X-ray fluorescence scanner (XRF) providing 0.1-mm resolution timeseries of elemental composition and X-ray density (XRD). Br content appears to be broadly correlative with mean annual temperature variations because of changes in catchment vegetation productivity. Sr/Rb ratio reflects the proportion of the unweathered terrestrial fraction. XRD appears to reflect water yield regime and sediment flux. Sedimentation is rather continuous because annual clastic supply and deposited mass are the same. The artificial neural networks method was applied to convert annual sedimentary time-series of XRD, Br content, and Sr/Rb ratio to annual records of temperature and precipitation using a transfer function. Comparison of these reconstructed Siberian records with the annual record of air temperature for the Northern Hemisphere shows similar trends in climatic variability over the past 800 yr. Estimated harmonic oscillations of temperature and precipitation values for both historical and reconstructed periods reveal subdecadal cyclicity.  相似文献   

Active hydrate destabilization in Lake Baikal,Siberia?   总被引：1，自引：0，他引：1  

Marc De Batist  Jan Klerkx  Pieter Van Rensbergen  Maarten Vanneste  Jeffrey Poort  Alexander Y. Golmshtok  rei A. Kremlev  Oleg M. Khlystov  Petr Krinitsky 《地学学报》2002,14(6):436-442

ABSTRACT In this paper, we present new seismic and heat-flow data that show the base of the hydrate stability zone (BHSZ) in Lake Baikal to be locally characterized by abnormal variations in depth, with distinct regions of deeper-than-normal and regions of shallower-than-normal BHSZ. These variations are related to strong lateral variations in heat flow, and occur in close association with important rift-basin faults. Areas of shallow BHSZ are also characterized by the presence of several methane seeps and mud volcanoes at the lake floor. We infer that the seeps are the surface expression of escape pathways for overpressured fluids generated by the dissociation of pre-existing hydrates, in response to a thermal pulse caused by an upward flow of hydrothermal fluids towards the BHSZ. It thus seems that present-day hydrate dissociation in Lake Baikal is modulated by the tectonic activity in the rift rather than by – climatically controlled – changes in lake level or water temperature.  相似文献