珠江流域前汛期降水和旱涝的影响因子与预测方法

利用统计学方法分析了珠江流域前汛期（４～６月）降水和旱涝的影响因子,在此基础上建立了相应的预测方法。     

砂土中吸力式导管架基础沉贯试验研究

吸力式导管架基础具备高承载力、高施工效率、高环境友好度、低造价等特点,使用其作为海上风电底部支撑结构有利于产业的规模化发展,实现上述愿景的前提在于使筒型基础顺利安装以满足设计要求。基于此,在不同初始施加泵压下,对吸力式导管架的沉贯效率特征值、基础内外围渗流变化、筒裙端部土压力特点进行探究。通过抱桩器使吸力式导管架在吸力安装过程中仅具备竖向自由度,从而进行纯沉贯试验。结果表明：初始泵压2 kPa时沉贯效率特征值最高;沉贯过程中基础外围渗流水压小于基础内围渗流水压;筒裙外侧所受土压要大于筒壁内侧所受土压力。     

Absolute Calibration of the Jason-1 Altimeter Using UK Tide Gauges

This article describes an “absolute” calibration of Jason-1 (J-1) altimeter sea surface height bias using a method developed for TOPEX/Poseidon (T/P) bias determination reported previously. The method makes use of U.K. tide gauges equipped with Global Positioning System (GPS) receivers to measure sea surface heights at the same time, and in the same geocentric reference frame, as Jason-1 altimetric heights recorded in the nearby ocean. The main time-dependent components of the observed altimeter-minus-gauge height-difference time series are due to the slightly different ocean tides at the gauge and in the ocean. The main harmonic coefficients of the tide differences are calculated from analysis of the copious TOPEX data set and then applied to the determination of T, P, and J-1 bias in turn. Datum connections between the tide gauge and altimetric sea surface heights are made by means of precise, local geoid differences from the EGG97 model. By these means, we have estimated Jason-1 altimeter bias determined from Geophysical Data Record (GDR) data for cycles 1–61 to be 12.9 cm, with an accuracy estimated to be approximately 3 cm on the basis of our earlier work. This J-1 bias value is in close agreement with those determined by other groups, which provides a further confirmation of the validity of our method and of its potential for application in other parts of the world where suitable tide gauge, GPS, and geoid information exist.     

Community structure of picoplankton abundance and biomass in the southern Huanghai Sea during the spring and autumn of 2006

During spring and autumn of 2006,the investigations on abundance,carbon biomass and distribution of picoplankton were carried out in the southern Huanghai Sea(Yellow Sea,sHS) . Three groups of picoplankton-Synechococcus(Syn) ,Picoeukaryotes(PEuk) and heterotrophic bacteria(BAC) were identified,but Prochlorococcus(Pro) was undetected. The average abundance of Syn and PEuk was lower in spring(5.0 and 1.3 × 10 3 cells/cm 3,respectively) than in autumn(92.4 and 2.7 × 10 3 cells/cm 3,respectively) ,but it was opposite for BAC(1.3 and 0.7 × 10 6 cells/cm 3 in spring and autumn,respectively) . And the total carbon biomass of picoplankton was higher in spring(37.23 ± 11.67) mg/m 3 than in autumn(21.29 ± 13.75) mg/m 3 . The ratios of the three cell abundance were 5:1:1 341 and 30:1:124 in spring and autumn,respectively. And the ratios of carbon biomass of them were 5:7:362 and 9:4:4 in spring and autumn,respectively. Seasonal distribution characteristics of Syn,PEuk,BAC were quite different from each other. In spring,Syn abundance decreased in turn in the central waters(where phytoplankton bloom in spring occurred) ,the southern waters and inshore waters of the Shandong Peninsula(where even Syn was undetected) ;the high values of PEuk abundance appeared in the central and southern waters and the inshore of the Shandong Peninsula;the abundance of BAC was nearly three order of magnitude higher than that of photosynthetic picoplankton,and high values appeared in the central waters. In autumn,Syn abundance in central waters was higher than that in surrounding waters,while for PEuk abundance,it decreased in turn in the inshore waters of the Shandong Peninsula,the southern waters and the central waters;BAC presented a complicated blocky type distribution. Sub-surface maximum of each group of picopalnkton appeared in both spring and autumn. Compared with the available literatures concerning the studied area,the range of Syn abundance was larger,and the abundance of BAC was higher. In addition,the conversion factors for calculating picoplanktonic carbon biomass were discussed,with the conversion factors which are different from previous studies in the same surveyed waters. The result of regression analysis showed that there was distinct positive correlation between BAC and photosynthetic picoplankton in spring(r=0.61,P 0.001) ,but no correlation was found in autumn.     

Assimilation of image sequences in numerical models

Understanding and forecasting the evolution of geophysical fluids is a major scientific and societal challenge. Forecasting algorithms should take into account all the available information on the considered dynamic system. The variational data assimilation (VDA) technique combines all these informations in an optimality system (O.S.) in a consistent way to reconstruct the model inputs. VDA is currently used by the major meteorological centres. During the last two decades about 30 satellites were launched to improve the knowledge of the atmosphere and of the oceans. They continuously provide a huge amount of data that are still underused by numerical forecast systems. In particular, the dynamic evolution of certain meteorological or oceanic features (such as eddies, fronts, etc.) that the human vision may easily detect is not optimally taken into account in realistic applications of VDA. Image Assimilation in VDA framework can be performed using 'pseudo-observation' techniques: they provide apparent velocity fields, which are assimilated as classical observations. These measurements are obtained by certain external procedures, which are decoupled with the considered dynamic system. In this paper, we suggest a more consistent approach, which directly incorporates image sequences into the O.S.     

Origin of stratified basal ice in outlet glaciers of Vatnajökull and Öræfajökull,Iceland

Larson, G.J., Lawson, D.E., Evenson, E.B., Knudsen, Ó., Alley, R.B. & Phanikumar, M.S. 2010: Origin of stratified basal ice in outlet glaciers of Vatnajökull and Öræfajökull, Iceland. Boreas, Vol. 39, pp. 457–470. 10.1111/j.1502‐3885.2009.00134.x. ISSN 0300‐9483. During the period 2000–2005, we collected samples of englacial ice, vent water, frazil/anchor ice and stratified basal ice from warm‐based outlet glaciers of Vatnajökull and Öræfajökull, Iceland, and analysed them for ³H, ¹⁸O and D. Results of ³H analyses show that the stratified basal ice contains ³H from atmospheric thermonuclear testing and is younger than the englacial ice. Results of the ¹⁸O and D analyses show that frazil/anchor and stratified basal ice are both enriched by an average of 2.4‰ in ¹⁸O and 11‰ in D relative to vent water. These values are consistent with fractionation during partial freezing of supercooled subglacial water in an open system, one in which the remaining water is continuously removed and replenished by water of similar composition. The isotopic data and field observations do not support either a regelation or a thermal ad‐freeze‐on origin for the stratified basal ice.     

Sedimentology of subaqueous volcaniclastic sediment gravity flows in the Neogene Santa Maria Basin, California

Subaqueous tuff deposits within the lower Miocene Lospe Formation of the Santa Maria Basin, California, are up to 20 m thick and were deposited by high density turbidity flows after large volumes of ash were supplied to the basin and remobilized. Tuff units in the Lospe Formation include a lower lithofacies assemblage of planar bedded tuff that grades upward into massive tuff, which in turn is overlain by an upper lithofacies assemblage of alternating thin bedded, coarse grained tuff beds and tuffaceous mudstone. The planar bedded tuff ranges from 0.3 to 3 m thick and contains 1-8 cm thick beds that exhibit inverse grading, and low angle and planar laminations. The overlying massive tuff ranges from 1 to 10 m thick and includes large intraclasts of pumiceous tuff and stringers of pumice grains aligned parallel to bedding. The upper lithofacies assemblage of thin bedded tuff ranges from 0.4 to 3 m thick; individual beds are 6-30 cm thick and display planar laminae and dewatering structures. Pumice is generally concentrated in the upper halves of beds in the thin bedded tuff interval. The association of sedimentary structures combined with semi-quantitative analysis for dispersive and hydraulic equivalence of bubble-wall vitric shards and pumice grains reveals that particles in the planar bedded lithofacies are in dispersive, not settling, equivalence. This suggests deposition under dispersive pressures in a tractive flow. Grains in the overlying massive tuff are more closely in settling equivalence as opposed to dispersive equivalence, which suggests rapid deposition from a suspended sediment load. The set of lithofacies that comprises the lower lithofacies assemblage of each of the Lospe Formation tuff units is analogous to those of traction carpets and subsequent suspension sedimentation deposits often attributed to high density turbidity flows. Grain distributions in the upper thin bedded lithofacies do not reveal a clear relation for dispersive or settling equivalence. This information, together with the association of sedimentary features in the thin bedded lithofacies, including dewatering structures, suggests a combination of tractive and liquefied flows. Absence of evidence for elevated emplacement temperatures (e.g. eutaxitic texture or shattered crystàls) suggests emplacement of the Lospe Formation tuff deposits in a cold state closely following pyroclastic eruptions. The tuff deposits are not only a result of primary volcanic processes which supplied the detritus, but also of processes which involved remobilization of unconsolidated ash as subaqueous sediment gravity flows. These deposits provide an opportunity to study the sedimentation processes that may occur during subaqueous volcaniclastic flows and demonstrate similarities with existing models for sediment gravity flow processes.     

Correlations between Holocene flood tidal delta and barrier island inlet fill sequences: Back Sound-Shackleford Banks, North Carolina

Large, well-developed flood tidal deltas on a barrier island coastline generally indicate a wave-dominated, microtidal sedimentary regime. Vibracores in a lagoon behind the barrier island Shackleford Banks, North Carolina contain an upward fining sequence of coarse-medium, very shelly sand, medium-fine laminated sand, fine-very fine cross-laminated sand and marsh mud. This sequence is interpreted as being a flood tidal delta deposit based on analogy with modern flood tidal delta sediments and represents lagoonal deposition in response to a migrating or closing inlet. The sand facies defined in lagoonal vibracores is found to be continuous beneath a lagoonal marsh and correlative with inlet sections identified in Shackleford Banks drill holes. The correlation of flood tidal delta deposits with inlet sequences in this microtidal environment indicates a close relationship between barrier and backbarrier inlet controlled sedimentation.     

Chert spheroids of the Monterey Formation,California (USA): early‐diagenetic structures of bedded siliceous deposits

Chert spheroids are distinctive, early‐diagenetic features that occur in bedded siliceous deposits spanning the Phanerozoic. These features are distinct in structure and genesis from similar, concentrically banded ‘wood‐grain’ or ‘onion‐skin’ chert nodules from carbonate successions. In the Miocene Monterey Formation of California (USA), chert spheroids are irregular, concentrically banded nodules, which formed by a unique version of brittle differential compaction that results from the contrasting physical properties of chert and diatomite. During shortening, there is brittle fracture of diatomite around, and horizontally away from, the convex surface of strain‐resistant chert nodules. Unlike most older siliceous deposits, the Monterey Formation still preserves all stages of silica diagenesis, thus retaining textural, mineralogical and geochemical features key to unravelling the origin of chert spheroids and other enigmatic chert structures. Chert spheroids found in opal‐A diatomite form individual nodules composed of alternating bands of impure opal‐CT chert and pure opal‐CT or chalcedony. With increased burial diagenesis, surrounding diatomite transforms to bedded porcelanite or chert, and spheroids no longer form discrete nodules, yet still display characteristic concentric bands of pure and impure microcrystalline quartz and chalcedony. Petrographic observations show that the purer silica bands are composed of void‐filling cement that precipitated in curved dilational fractures, and do not reflect geochemical growth‐banding in the manner of Liesegang phenomena invoked to explain concentrically banded chert nodules in limestone. Chertification of bedded siliceous sediment can occur more shallowly (< 100 m) and rapidly (< 1 Myr) than the bulk silica phase transitions forming porcelanite or siliceous shale in the Monterey Formation and other hemipelagic/pelagic siliceous deposits. Early diagenesis is indicated by physical properties, deformational style and oxygen‐isotopic composition of chert spheroids. Early‐formed cherts formed by pore‐filling impregnation of the purest primary diatomaceous beds, along permeable fractures and in calcareous–siliceous strata.