Geomorphic activity of rabbits on a coastal sand dune,De Blink dunes,the Netherlands

A study of the erosion rate and the stability of sandy slopes was conducted on an eastern arm of a parabolic coastal sand dune, De Blink, central Netherlands. The contribution of rabbits to these processes was found to depend on two types of activity; the building of caves and sand mounds of up to 1·5 m² in area; and the digging of shallow burrows, whereby amounts of sand up to 1 kg per burrow were excavated. The burrowing activity was found over the whole dune, while cave holes were dug mainly on the northern slope. The total amount of sand actually transported on the dune due to this activity is not clear yet, but their influence on the development of stepped slopes is well established.     

Biogenic Graphite as a Potential Geomarker—Application to Continental Reconstructions of Pan-African Gondwana Terrains

Graphite is present in nature in several forms. Genetically they may be broadly classified as biogenic and abiogenic. The biogenic forms are those that are clearly derived from an organic precursor while the abiogenic or inorganic forms are more complex from the point of view of their origin, nature and geological relations.As a geomarker, biogenic graphite has certain advantages. It is easily recognized and shows different degrees of crystallinity depending on the relative grades of metamorphism it had undergone. Once it attains a certain degree of crystalline order, it does not revert to a lower state even under changing metamorphic conditions, thereby making it a good mineral geothermometer. It is also found in specific, restricted geological environments and is therefore useful as a boundary marker of ancient sedimentary terrains.These special characteristics of the biogenic type of graphite can be effectively used to trace sites of sedimentary basins and subsequent ocean closures that may have resulted in geosutures. Studies of the Pan-African terrains of the Gondwana crustal fragments as exemplified by the sutures of the Mozambique Belt running through East Africa, Madagascar, Sri Lanka and Antarctica illustrate this point. A further example comes from the Mashan Group of East China, one of the most productive graphite - bearing regions of the world.     

On the reconstruction of upwelling history: Namibia upwelling in context

Eastern boundary upwelling is an important aspect of the modern ocean, despite the relatively small area involved. Consequences of increased upwelling during the Neogene, as a result of intensifying trade winds, include increased heat transport by the ocean, increased mixing, increased fractionation of phosphate from silicate, and opportunities for evolution of new species. Coastal upwelling has been studied since the first decade of the 20th century. The processes involved are complex, and differ depending on geographic setting. Off Namibia, upwelling history has been studied by a number of drilling expeditions; the last of these was ODP Leg 175, which occupied seven sites on the continental slope between Walvis Ridge and Cape Town, during September and October of 1997. Productivity proxies all along southwestern Africa suggest the presence of increased upwelling and organic matter supply to the sea floor during glacial periods. At the same time, there is a decrease in the supply of diatoms and other siliceous plankton remains. This is the Walvis Opal Paradox, established through the contrasting results of studies by Diester-Haass (1985) and Oberhänsli (1991). We propose that the Walvis Opal Paradox is fundamental to the understanding of glacial–interglacial productivity fluctuations on a global scale. Furthermore, a central feature of the history of late Neogene upwelling off Namibia is the Matuyama Opal Maximum, centered between Gauss and Olduvai magnetic chrons [Wefer et al., Proc. ODP 175 (1998)]. It is due to the fact that diatom supply first increases (during the Gauss) when the planet cools and then decreases again during additional cooling, on entering the Quaternary. On a 400 000-year scale, peak productions are coincident with (or slightly lag) maximum seasonal contrast potential in the high-latitude insolation curve. We suggest that this is further evidence that the nutrient content of thermocline waters was diminished during glacial periods. The reasons why this should be so remain to be discovered.     

Silicon transfers in a rice field in Camargue (France)

We conducted a study of the biogeochemical cycle of silicon in a rice field in Camargue (France) in order to evaluate the role of biogenic silicon particles (BSi) in the cycle. Opal-A biogenic particles (phytoliths, diatoms…), which dissolve more rapidly than other forms of silicate usually present in soils, are postulated to represent the easiest bioavailable Si for rice. We found 0.03–0.06 wt.% of BSi in soils (mainly phytoliths). This value is lower than other values from the literature. Each year, the exportation of BSi from rice cultivation is 270 ± 80 kg Si ha^− 1. We show that BSi input by irrigation is mostly composed of diatoms and we estimate it at 100 kg Si ha^− 1 year^− 1. This value is more than a third of the annual Si need for rice. The budget of the dissolved silicon (DSi) fluxes gives the following results: the atmospheric and irrigation inputs represents 1% and roughly 10%, respectively, of the annual need for rice; the drainage and infiltration outputs represent 17 ± 14 and 12 ± 9 kg Si ha^− 1 year^− 1, respectively; the balance of our budget shows that at least 170 kg Si ha^− 1 year^− 1 are exported from the soil. If we consider the soil BSi as the only source of dissolved silicon, this stock could be exhausted in 5 years.     

Bioavailability of different chemical forms of dissolved silica can affect marine diatom growth

In this study, we demonstrate that dissolved silica obtained from mineral (crystalline quartz), biogenic amorphous (diatomaceous earth) and artificial amorphous sources (Aerosil) influence the growth rate of two marine diatoms, Chaetoceros sp. and Skeletonema marinoi. Diatoms were reared in four different experimental conditions in artificial seawater containing either dissolved silica previously obtained through dissolution of the mineral crystalline quartz or two amorphous substrates, biogenic diatomaceous earth or artificial Aerosil silica. Sodium metasilicate was used as control. When the silica in the different media reached concentrations higher than 107 μm , particles were eliminated by filtration and the diatom cells were inoculated. Maximum cell density, growth and silica assimilation rates of both species in the presence of dissolved silica derived from crystalline quartz and metasilicate were higher than those obtained with the other silica sources. These results are discussed against the background of previous geochemical studies that have shown that silica–water interactions are strictly dependent on the silica polymorphs involved and on the ionic composition of the solution. Our results demonstrate that the soluble silicon compounds generated in seawater by crystalline sources are highly bioavailable compared with those generated by biogenic and amorphous materials. These findings are potentially of considerable ecological importance and may contribute to clarifying anomalous spatial and temporal distributions of siliceous organisms with respect to the presence of lithogenic or biogenic silica sources in marine environments.     

Preliminary investigation of biogenic gas production in Indonesian low rank coals and implications for a renewable energy source

Indonesia has abundant coal resources at depths suitable to contain substantial volumes of naturally occurring methane, which are currently being explored. Most Indonesian coals are thermally immature, but are composed of hydrogen-rich organic components that are presumed to make them excellent substrates for biogenic methane production. Gas isotope results from pilot wells in South Sumatra, reported in this study, are interpreted to indicate biogenic origins for the methane. Corresponding formation water samples were collected and incubated, and show the presence of indigenous microbial communities capable of producing methane from Indonesian and Australian coal. Although these results are only preliminary, they are promising and support the possibility of Indonesia developing bio renewable energy from coal seams.     

19th century eutrophication of a remote boreal lake: a consequence of climate warming?

To investigate the response of a remote boreal lake to recent climate warming, a 200-year varved sediment record from Rainbow Lake A (RLA), located in the northern boreal forest of Wood Buffalo National Park, straddling northern Alberta and the Northwest Territories (Canada), was investigated using diatom assemblages and biogenic silica concentrations. Diatom community composition, trends in diatom-inferred total phosphorus (TP) and biogenic silica levels all showed significant changes beginning between circa 1830 and 1840, coincident with the onset of increasingly warm June/July temperatures in northern Canada. We evaluated several hypotheses which may have caused these nutrient changes, including local anthropogenic disturbances, forest fires, increased atmospheric deposition of nutrients or pollen, and internal sources of nutrient regeneration. We concluded that TP is likely increasing as a result of enhanced internal cycling of phosphorus due to either increased thermal stratification in response to warmer summer temperatures and/or decreased meromictic stability. The results presented here, in combination with other recent paleolimnological research in northern latitude regions, suggest widespread aquatic response to increasing temperatures beginning in the 19th century.     

The biogenic gas potential of the submarine canyon systems of Plio-Peistocene foreland Basin,southwestern Taiwan

Biogenic gas was accidentally discovered and produced from the Plio/Pleistocene formation of the Hsinying gas field in southwestern Taiwan in 1989. A stratigraphic trapping mechanism related to the evolution of submarine canyon systems in the Plio-Peistocene foreland basin has been proposed in a previous study which explained underestimated recoverable gas reserve before drilling. To verify this shallow gas exploration hypothesis and to systematically evaluate the biogenic gas generation and entrapment potential of the submarine canyon systems, seismic interpretation, high-resolution sequence stratigraphic interpretation, seismic attribute analysis and geochemical analysis were performed and integrated in this study. Twenty-nine submarine canyons mapped mainly trend in a NE direction, except the NW trending Eurchungchi submarine canyons located near the Chiali paleo-high. Bright seismic amplitudes were often observed at the incised valley heads of the canyon systems. The shales located near the incised valley heads and deposited during flooding stage possess the highest biogenic gas generation potential, as canyon fill reveals the second highest. Due to the high sediment accumulation rate in the foreland basin, organic matter in such a depositional environment tends to become diluted. A Class III AVO anomaly, inverted impedance lower than 4.7 e + 6 kg/M³*M/S and A/B (the ratio between the target horizon amplitude and the RMS amplitude from the background strata) greater than 1.78 were identified as valid direct gas indicators as sand is buried shallower than 1000 m. Class IV AVO anomaly and A/B greater than 1.4 were concluded to be the indicators of gas sand in the case that sand is buried deeper than 1600 m. Based on the results of sequence stratigraphic interpretation and the consistency between spatial geometries of seismic attributes and those of the submarine canyons, a stratigraphic trap associated with the incised valley heads was concluded to be the original gas entrapment style of the Hsinying and the Kuantian gas fields. Biogenic gas migrated after being trapped startigraphically, hence contributing to the present-day gas field structure. Due to the prevalent erosional features of the submarine canyons on the time structural maps, different types of stratigraphic traps formed in combination with faults and submarine canyons can be recognized easily.     

北冰洋西部沉积物有机碳、氮同位素特征及其环境指示意义

通过对楚科奇海及邻近的北冰洋深水区表层沉积物中有机碳同位素含量(δ13C)、氮同位素含量(δ15N)及生物成因SiO₂(BSiO₂)含量分析,结果表明海源和陆源有机质的分布受海区环流结构和营养盐结构所制约.楚科奇海中西部和楚科奇海台受太平洋富营养盐海水的影响,海洋生产力高,沉积物中海源有机质和BSiO₂含量高;靠阿拉斯加一侧海域海水的营养盐含量和生产力都偏低,沉积物中陆源有机质比重增加;在研究区北部和东北部的楚科奇高地和加拿大海盆,冰封时间较长,营养盐供应少,海洋生产力低,但来自马更些河和阿拉斯加北部的陆源有机质增多,沉积物中BSiO₂含量小于5%,海源有机质百分含量小于40%.由于亚北极太平洋水通过楚科奇海向北冰洋海盆输送,研究区营养盐池表现为开放系统,营养盐的利用率与它的供应成反比,与海洋生产力成反比.     

Biological productivity, terrigenous influence and noncrustal elements supply to the Central Indian Ocean Basin: Paleoceanography during the past ∼ 1 Ma

A 2m-long sediment core from the siliceous ooze domain in the Central Indian Ocean Basin (CIOB; 13‡03′S: 74‡44′E; water depth 5099m) is studied for calcium carbonate, total organic carbon, total nitrogen, biogenic opal, major and few trace elements (Al, Ti, Fe, K, Mg, Zr, Sc,V, Mn, Cu, Ni, Zn, Co, and Ba) to understand the productivity and intensity of terrigenous supply. The age model of the sediment core is based on U-Th dating, occurrence of Youngest Toba Tuff of ∼ 74 ka and Australasian microtektites of ∼ 770 ka. Low carbonate content (< 1%) of sediment core indicates deposition below the carbonate compensation depth. Organic carbon content is also very low, almost uniform (mean 0.2 wt%) and is of marine origin. This suggests a well-oxygenated bottom water environment during the past ∼ 1100ka. Our data suggest that during ∼ 1100 ka and ∼ 400 ka siliceous productivity was lower, complimented by higher supply of terrigenous material mostly derived from the metasedimentary rocks of High Himalayan crystalline. However, during the last ∼ 400 ka, siliceous productivity increased with substantial reduction in the terrigenous sediment supply. The results suggest that intensity of Himalayan weathering, erosion associated with monsoons was comparatively higher prior to 400 ka. Manganese, Ba, Cu, Ni, Zn, and Co have around 90% of their supply from noncrustal (excess) source and their burial to seafloor remained unaffected throughout the past ∼ 1100 ka.