Annual budget of benthic production in Mont Saint-Michel Bay considering cloudiness,microphytobenthos migration,and variability of respiration rates with tidal conditions

In order to provide an accurate annual rate of net benthic community production, community photosynthetic response to incident irradiance and respiration were measured at different times of the year, at mid-tide level on the muddiest part of the Mont Saint-Michel Bay. As the water turbidity prevented any photosynthesis by the microphytobenthos during immersion periods, primary production was measured only during emersion periods. In contrast respiration was expected to vary according to the tidal cycle and was measured during both emersion and immersion periods. Primary production and respiration rates under emersion were assessed using in situ infra-red gas analysis of CO₂ exchange measured in a benthic chamber. Respiration rates under immersion were assessed through total CO₂ concentration variations in incubated cores.     

平台中心角对岩石抗拉强度测定影响的数值分析

岩石抗拉强度是岩石的一个重要力学参数,在测试岩石抗拉强度的平台巴西盘劈裂试验中,平台中心角对测试结果会产生重要影响,但测试中对此角度尚无严格规定,从而造成抗拉强度测试结果有很大的离散性。从细观的角度着手,应用数字图像技术对岩石材料内部不同细观介质的空间分布进行精确测量和数值表达,建立与有限元网格之间的相互映射关系,并引入到原有的岩石破坏过程分析系统RFPA中,建立了能反映岩石非均匀性的平台巴西盘数值模型。通过对花岗岩断面图像进行处理,运用数值模型研究了平台中心角对平台巴西盘轴线应力分布、劈裂破坏模式和抗拉强度测定的影响,确定平台中心角的合理值应在20～30?的范围内,这与试验结果相一致,从机制上进一步分析验证了平台中心角的取值范围,为测试中平台中心角的选取提供了理论依据。     

江苏条子泥岸滩剖面形态的时空异质性

在江苏条子泥岸滩选择3个典型剖面，对其进行了3a定期的观测，将所得剖面数据绘制成剖面形态曲线。通过对岸滩剖面形态的分析，发现3a来岸滩冲淤变化明显，岸滩剖面形态内部及其相互间都有变化，呈现不同的类型。探讨了其变化的机制，包括自然因素和人为因素。主要的研究结果将丰富人们对江苏条子泥近期岸滩及辐射沙洲演变的认识，为条子泥促淤并陆和海岸防护等工程提供科学依据。     

苏北近岸海域表层沉积物粒度及其对环境动力的响应

对2007年9—11月在南黄海辐射沙脊区和江苏北部潮滩采集的表层底质样品进行粒度分析,获得了平均粒径、分选系数、偏态、峰态等粒度参数,并对其进行了聚类分析。结果表明,9 m以浅和20 m以深的样品可归为两种类型的沉积物,而水深9～20 m之间的沉积物两种类型都有,多样性较大。由Gao-Collins粒径趋势分析模型获得的沉积物净输运趋势显示,除外毛竹砂处沉积物有向外海输运的趋势之外,其他外围的断面均显示泥砂向辐射沙洲中心输运,这与历史资料中记录的结果相一致,表明粒径趋势分析适用于大型辐射沙洲海域。根据Stern-berg图分析,粒度参数的空间分布是由差异性输运造成,沉积物从射阳河口岸外向大丰潮间带上部输运的过程中,众数粒径几乎全部以悬移质的形式输运,而小庙洪向东灶潮滩上部输运的众数粒径以悬移方式输运的概率只有60%,从而使射阳河口岸外与大丰潮间带上部的沉积物粒度参数相同,而小庙洪与东灶潮间带上部的沉积物粒度参数有显著差异。     

A quantitative approach to sedimentary surface structures contoured by the interplay of microbial colonization and physical dynamics

In the tidal flats of Mellum Island (southern North Sea), biofilms and microbial mats, generated largely by cyanobacteria, colonize the sedimentary surfaces. Biostabilization effects and biomass enrichment influence erosional and depositional dynamics resulting from tidal flushing and storm surges. The overlapping of both biological and physical forces causes the development of characteristic sedimentary structures. To obtain a quantitative expression of the degree of effectiveness of microbial colonization in the formation of structures in an extended tidal area, a modification index (MOD-I) was developed based on the following values: (i) the proportion of mat-covered area related to a defined investigation area (I_A); (ii) the degree of steepness of slope angles of raised erosional remnants (I_S); and (iii) the degree of microbial levelling of a rippled sedimentary surface (I_N). The MOD-I was calculated for several defined regions within the study area, and both winter and summer situations were considered. The MOD-I values show, first, that the lower intertidal zone is characterized by index values approaching zero. This implies that microbially induced effects in this zone are negligible, even in summer. Second, the upper intertidal zone is characterized by lower index values in winter and relatively high values in summer. This implies a predominantly seasonal control on the biofilm development in this zone. Third, in the lower supratidal zone, the index values are almost identical during both winter and summer. This implies non-seasonal biological effects in this zone. Concomitant empirical studies on the composition of microbial mats and films suggest that the dominant microbial type influences the MOD-I value.     

Invading cord grass vegetation changes analyzed from Landsat-TM imageries: a case study from the Wanggang area, Jiangsu coast, eastern China

Cord grass colonization on the Jiangsu coast, eastern China, modifies the native salt marshes in terms of ecosystem structure. The Landsat TM images from 1992 to 2003 were analyzed to identify salt-marsh vegetation distribution patterns and their changes over this coastal region, in order to evaluate the effects of the spreading of the artificially introduced halophyte Spartina. Supervised classification was performed using Bands 3, 4 and 5 in conjunction with in situ training samples, to derive the distribution pattern of the vegetation in the study area. Further, in order to identify the intertidal areas with different tidal elevations, a data treatment procedure was designed to combine regional water level data using harmonic analysis with the waterlines on the TM images extracted by density slice. The results show that: (1) the Spartina alterniflora area has been expanding towards the sea rapidly since it was introduced, especially at initial stages; (2) in the upper part of the inter-tidal zone, the local marsh plant Suaeda salsa and the exotic species Spartina anglica were present only near the sea dyke, occupying only a small part of the entire salt marsh, and the area of these two species has been reduced by land reclamation; (3) there has been a trend for Spartina alterniflora to become the dominant species in the salt marshes in the study area; and (4) the elevation of Spartina alterniflora’s seaward fringe was close to mean high water on neaps, and its landward boundary was slightly higher than mean high water. The salt marsh environment of the study area has been modified rapidly by the Spartina vegetation for the last 12 years.     

A DEM Inversion Method for Inter-Tidal Zone Based on MODIS Dataset: A Case Study in the Dongsha Sandbank of Jiangsu Radial Tidal Sand-Ridges, China

Surface elevation is the basic data for geo-science. It is difficult to retrieve tidal-flats’ elevation from single Remote Sensing (RS) image because of the complicated sediment dynamical environment and huge spatial difference in tidal-flats’ moisture content. A Digital Elevation Model (DEM) construction method for inconstant inter-tidal zone based on high tempo-resolution MODIS data set in a short period is proposed in a case study on the Dongsha Sandbank of the Jiangsu Radial Tidal Sand-ridges. In the present study, a batch-preprocessing method based on image partition to handle massive MODIS 1B images is developed and applied to 8163 scenes of MODIS images. The dataset of short-period and multi-temporal MODIS images for inter-tidal flats’ DEM inversion is selected and the usability of MODIS dataset is analyzed. Shorelines of the Dongsha Sandbank are extracted by use of batch supervised classification. In accord with tidal-level forecasted by the Chenjiawu Tidal Gauge Station at the overpass moment of each RS image, DEMs of inter-tidal flats in January and summer(Jul, Aug and Sept), 2003 were built under ArcGIS9.2. Studies show that: (1) The dataset of short-duration and multi-phase MODIS images can be used to retrieve the historical DEM of tidal-flats at changeful tidal flats. (2) Analysis on usability of MODIS images from Aqua and Terra indicates that there are more usable and high-quality MODIS images in spring, autumn and winter, but less in summer. Therefore, the period for building inter-tidal flats’ DEM is suggested to be one month in spring, autumn and winter and three months in summer.     

Do shorebirds graze down zoobenthic biomass at the Banc d'Arguin tidal flats in Mauritania?

The 500 km² of tidal flats at the Banc d'Arguin, Mauritania, are a wintering site for over 2 million shorebirds, making this one of the areas with the highest density of shorebirds in the world. In earlier studies, it was found that these huge numbers of birds are dependent on a rather low biomass of benthic animals. To explain this paradoxical situation, we hypothesized that the earlier assessments of biomass in late winter and early spring do not reflect a year-round situation. Benthic biomass may be high when the birds arrive in autumn to be subsequently grazed down in the course of winter. To test this hypothesis, we have determined benthic biomass in September 1988. The result has been compared with a biomass value obtained in February–April 1986 with the same methods and at the same stations. These two biomass values do not differ significantly; so our hypothesis has to be rejected. It has to be admitted, however, that our experimental design cannot discern between differences due to the year of sampling and those due to the season.     

Microbially induced sedimentary structures in Archean sandstones: A new window into early life

Until now, the most valuable information on the early life on the Archean Earth derived from bacterial fossils and stromatolites preserved in precipitated lithologies such as chert or carbonates. Also, shales contain complex biomarker molecules, and specific isotopes constitute an important evidence for biogeneicity.In contrast, because of their low potential of fossil preservation, sandstones have been less investigated. But recent studies revealed a variety of ‘microbially induced sedimentary structures — MISS’ that differ greatly from any other fossils or sedimentary structures. ‘Wrinkle structures’, ‘multidirected ripple marks’, ‘biolaminites’, and other macrostructures indicate the former presence of photoautotrophic microbial mats in shallow-marine to tidal paleoenvironments. The MISS form by the mechanical interaction of microbial mats with physical sediment dynamics that is the erosion and deposition by water agitation. The structures occur not only in Archean tidal flats, but in equivalent settings throughout Earth history until today.MISS are not identified alone by their macroscopic morphologies. In thin-sections, the structures display the carpet-like fabrics of intertwined filaments of the ancient mat-constructing microorganisms. Geochemical analyses of the filaments proof their composition of iron minerals associated with organic carbon.In conclusion, microbial mats colonize sandy tidal settings at least for 3.2 Ga years. Therefore, Archean sandstones constitute an important archive for the exploration of early life.     

Sequence stratigraphic framework for mixed aeolian,peritidal and marine environments: Insights from the Pennsylvanian subtropical record of Western Pangaea

Due to difficulties in correlating aeolian deposits with coeval marine facies, sequence stratigraphic interpretations for arid coastal successions are debated and lack a unifying model. The Pennsylvanian record of northern Wyoming, USA, consisting of mixed siliciclastic–carbonate sequences deposited in arid, subtropical conditions, provides an ideal opportunity to study linkages between such environments. Detailed facies models and sequence stratigraphic frameworks were developed for the Ranchester Limestone Member (Amsden Formation) and Tensleep Formation by integrating data from 16 measured sections across the eastern side of the Bighorn Basin with new conodont biostratigraphic data. The basal Ranchester Limestone Member consists of dolomite interbedded with thin shale layers, interpreted to represent alternating deposition in shallow marine (fossiliferous dolomite) and supratidal (cherty dolomite) settings, interspersed with periods of exposure (pedogenically modified dolomites and shales). The upper Ranchester Limestone Member consists of purple shales, siltstones, dolomicrites and bimodally cross‐bedded sandstones in the northern part of the basin, interpreted as deposits of mixed siliciclastic–carbonate tidal flats. The Tensleep Formation is characterized by thick (3 to 15 m) aeolian sandstones interbedded with peritidal heteroliths and marine dolomites, indicating cycles of erg accumulation, preservation and flooding. Marine carbonates are unconformably overlain by peritidal deposits and/or aeolian sandstones interpreted as lowstand systems tract deposits. Marine transgression was often accompanied by the generation of sharp supersurfaces. Lags and peritidal heteroliths were deposited during early stages of transgression. Late transgressive systems tract fossiliferous carbonates overlie supersurfaces. Highstand systems tract deposits are lacking, either due to non‐deposition or post‐depositional erosion. The magnitude of inferred relative sea‐level fluctuations (>19 m), estimated by comparison with analogous modern settings, is similar to estimates from coeval palaeotropical records. This study demonstrates that sequence stratigraphic terminology can be extended to coastal ergs interacting with marine environments, and offers insights into the dynamics of subtropical environments.