CO2 clouds, CAPE and convection on Mars: Observations and general circulation modeling

The thermal emission spectrometer (TES) and the radio science (RS) experiment flying on board the Mars Global Surveyor (MGS) spacecraft have made observations of atmospheric temperatures below the saturation temperature of carbon dioxide (CO₂). This supersaturated air provides a source of convective available potential energy (CAPE), which, when realized may result in vigorous convective mixing. To this point, most Mars atmospheric models have assumed vertical mixing only when the dry adiabatic lapse rate is exceeded. Mixing associated with the formation of CO₂ clouds could have a profound effect on the vertical structure of the polar night, altering the distribution of temperature, aerosols, and gasses.Presented in this work are estimates of the total planetary inventory of CAPE and the potential convective energy flux (PCEF) derived from RS and TES temperature profiles. A new Mars Global Circulation Model (MGCM) CO₂ cloud model is developed to better understand the distribution of observed CAPE and its potential effect on Martian polar dynamics and heat exchange, as well as effects on the climate as a whole. The new CO₂ cloud model takes into account the necessary cloud microphysics that allow for supersaturation to occur and includes a parameterization for CO₂ cloud convection. It is found that when CO₂ cloud convective mixing is included, model results are in much better agreement with the observations of the total integrated CAPE as well as total column non-condensable gas concentrations presented by Sprague et al. [2005a, GRS measurements of Ar in Mars’ atmosphere, American Astronomical Society, DPS meeting #37, #24.08, and 2005b, Distribution and Abundance of Mars’ Atmospheric Argon, 36th Annual Lunar and Planetary Science Conference, #2085] When the radiative effects of water ice clouds are included the agreement is further improved.     

Expression of the Toarcian Oceanic Anoxic Event: New insights from a Swiss transect

A sedimentological, biostratigraphical and geochemical (stable isotopes and Rock‐Eval parameters) analysis was performed on four Swiss successions, in order to examine the expression of the Toarcian Oceanic Anoxic Event along a north–south transect, from the Jura through the Alpine Tethys (Sub‐Briançonnais and Lombardian basins). The locations were selected to represent a range of palaeoceanographic positions from an epicontinental sea to a more open marine setting. The Toarcian Oceanic Anoxic Event was recognized by the presence of the characteristic negative carbon‐isotope excursion in carbonate (ca 2 to 4‰) and organic matter (ca 4 to 5‰) at the base of the falciferum ammonite Zone (NJT6 nannofossil Zone). The sedimentary expression of the Toarcian Oceanic Anoxic Event varies along the transect from laminated mudstone rich in total organic carbon (≤11 wt.%) in the Jura, to thin‐bedded marl (≤5 wt.% total organic carbon) in the Sub‐Briançonnais Basin and to hemipelagic reddish marly limestone (total organic carbon <0·05 wt.%) in equivalent levels from the Lombardian Basin. The carbon‐isotope excursion is thus independent of facies and palaeoceanographic position. The low nannofossil abundance and the peak in Calyculaceae in the Jura and the Sub‐Briançonnais Basin indicate low salinity surface waters and stratified water masses in general. Sedimentological observations (for example, obliquely‐bedded laminae and homogeneous mud layers containing rip‐up clasts) indicate the presence of dynamic conditions, suggesting that water mass stratification was episodically disrupted during the Toarcian Oceanic Anoxic Event. The proposed correlation highlights a stratigraphic gap and/or condensed interval between the Pliensbachian–Toarcian boundary and the Toarcian Oceanic Anoxic Event interval (most of the tenuicostatum ammonite Zone is missing), which is also observed in coeval European sections and points to the influence of sea‐level change and current dynamics. This transect shows that the sedimentary expression of the Toarcian Oceanic Anoxic Event is not uniform across the Alpine Tethys, supporting the importance of local conditions in determining how this event is recorded across different palaeoceanographic settings.     

Origin of facies zonation in microbial carbonate platform slopes: Clues from trace element and stable isotope geochemistry (Middle Triassic,Dolomites, Italy)

Limestones containing radiaxial fibrous cements were sampled along the southern slope of the late Anisian (Middle Triassic) Latemar carbonate platform in the Dolomites, northern Italy. The Latemar upper slopes comprise massive microbial boundstone, whereas lower slopes are made of clinostratified grainstone, rudstone and breccia. Samples are representative of a seawater column from near sea‐level to an aphotic zone at about 500 m water depth. Radiaxial fibrous cements were analyzed for carbon (δ¹³C) and oxygen (δ¹⁸O) stable isotopic composition, as well as major and trace element content, to shed light on the origin of the slope facies zonation. The δ¹³C vary between 1·7‰ and 2·3‰ (Vienna Pee‐Dee Belemnite), with lowest values at palaeo‐water depths between 70 m and 300 m. Radiaxial fibrous cements yielded seawater‐like rare earth element patterns with light rare earth element depletion (Nd_SN/Yb_SN ≈ 0·4), superchondritic yttrium/holmium ratios (≈55) and negative cerium anomalies. Cadmium reaches maximum values of ca 0·5 to 0·7 μg/g at palaeo‐water depths between 70 m and 300 m; barium contents (0·8 to 1·8 μg/g) increase linearly with depth. The downslope patterns of δ¹³C and cadmium suggest increased nutrient and organic matter contents at depths between ca 70 m and 300 m and point to an active biological pump. The peak in cadmium and the minimum of δ¹³C mark a zone of maximum organic matter respiration and high nutrient and organic matter availability. The base of this zone at ca 300 m depth corresponds with the transition from massive microbial boundstone to clinostratified grainstone, rudstone and breccia. The microbial boundstone facies apparently formed only in seawater enriched in organic matter, possibly because this organic matter sustained benthic microbial communities at Latemar. The base of slope microbialites on high‐relief microbial carbonate platforms may be a proxy for the depth to maximum respiration zones of Palaeozoic and Mesozoic periplatform basins.     

The Application of Alkenone-Based pCO2 Reconstructions

The changing of atmospheric carbon dioxide concentration is closely related with the changing of global ice sheet,temperature and sea level. Knowledge of the past atmospheric carbon dioxide concentration and its relationship with climate is an important method of predicting the future climate change. Coccolith derived long-chain alkenone carbon isotope is one of the important proxies to reconstruct past carbon dioxide, which is wildly applied in the reconstruction of the Cenozoic atmospheric carbon dioxide. In this paper, we focused on the method of alkenone-based atmospheric carbon dioxide concentration, including the geochemical properties of long-chain alkenone, carbon diffusive model and the carbon isotope fraction. Then, we introduced the development of alkenone-based carbon dioxide proxy and its uncertainty. Coccolith cell geometry and growth rate have great influence on carbon dioxide fraction. Besides, there are some uncertainties about carbon concentration mechanisms in coccolithes, which may have some influence on alkenone-based carbon dioxide method to reconstruct ancient carbon dioxide more accurately. At the end, we summarized the Cenozoic carbon dioxide record with various proxies including alkenone carbon dioxide, boron isotope, palaeosol carbonate nodules and stomatal indices of fossil leaves.     

Reassessment of historical sections from the Paleogene marine margin of the Congo Basin reveals an almost complete absence of Danian deposits

The early Paleogene is critical for understanding global biodiversity patterns in modern ecosystems. During this interval, Southern Hemisphere continents were largely characterized by isolation and faunal endemism following the breakup of Gondwana. Africa has been proposed as an important source area for the origin of several marine vertebrate groups but its Paleogene record is poorly sampled, especially from sub-Saharan Africa. To document the early Paleogene marine ecosystems of Central Africa, we revised the stratigraphic context of sedimentary deposits from three fossil-rich vertebrate localities: the Landana section in the Cabinda exclave(Angola), and the Manzadi and Bololo localities in western Democratic Republic of Congo.We provide more refined age constraints for these three localities based on invertebrate and vertebrate faunas, foraminiferal and dinoflagellate cyst assemblages, and carbon isotope records. We find an almost complete absence of Danian-aged rocks in the Landana section, contrary to prevailing interpretations over the last half a century(only the layer 1, at the base of the section, seems to be Danian). Refining the age of these Paleocene layers is crucial for analyzing fish evolution in a global framework, with implications for the early appearance of Scombridae(tunas and mackerels) and Tetraodontiformes(puffer fishes). The combination of vertebrate fossil records from Manzadi and Landana sections suggests important environmental changes around the K/Pg transition characterized by an important modification of the ichthyofauna. A small faunal shift may have occurred during the Selandian. More dramatic is the distinct decrease in overall richness that lasts from the Selandian to the Ypresian. The Lutetian of West Central Africa is characterized by the first appearance of numerous cartilaginous and bony fishes. Our analysis of the ichthyofauna moreover indicates two periods of faunal exchanges: one during the Paleocene, where Central Africa appears to have been a source for the European marine fauna, and another during the Eocene when Europe was the source of the Central Africa fauna. These data indicate that Central Africa has had connections with the Tethyian realm.     

Benthic-pelagic coupling and export of organic carbon from a tropical Atlantic continental shelf—Sierra Leone

An approximate carbon budget for the Sierra Leone River Estuary and adjacent inner continental shelf indicates that phytoplankton production is balanced by grazers only in the wet season estuary; on the continental shelf, and in the dry season estuary, phytoplankton production exceeds demand of consumer populations by 70–90%. Regional production is dominated by the dry season estuary where diatom blooms support large population of the phytophagous clupeid fish Ethmalosa fimbriata. It is suggested that as well as what is used in bacterial respiration, not quantified in the study, important amounts of inshore organic carbon production are available for export, or burial, or both, either in inshore mudbanks or at the shelf edge by slumping. This carbon budget for a tropical continental shelf having neither coral-reefs nor coastal upwelling appears to correspond with what is emerging as a generic distinction between shelves and open ocean ecosystems: surplus production on shelves, balance between producers and consumers in the open ocean.     

地质历史时期碳循环的研究

可以近似地把地质历史时期的碳循环看做为在沉积碳酸盐和沉积有机碳化学库之间的平衡。碳循环研究直接关系重建地球古大气、古海洋、古气候和古环境演变的历史，关系正确认识沉积矿产的成因。现在，人们已经对显生宙时期、对晚元古代碳循环进行了较多的研究，并取得了进展，但是对整个元古代和太古代碳循环的研究工作十分薄弱。预料元古代和太古代碳循环研究将成为未来地球科学重要的前沿研究领域。我国存在适于元古代碳循环研究的地质条件，建议开展相应的研究工作.     

黔中沉积磷灰石的硫碳同位素及其地质意义

本文研究了黔中磷块岩中磷灰石的结构硫同位素组成。磷灰石的δ３４Ｓ值为３４．２‰～４２．４‰，它高于同期海水的δ３４Ｓ（约３４．２‰），也高于共生的成岩黄铁矿的δ３４Ｓ（１５．４‰～１９．８‰），表明磷灰石形成于富有机质沉积物早期成岩作用硫酸盐还原带的最上部，其间同时伴有大量硫酸盐细菌的还原过程。磷灰石的碳同位素组成（δ１３Ｃ＝－３．６３‰～１．０‰），表明它含有微生物有机质分解演化而来的ＣＯ２－３，而磷灰石比胶结白云石更富集轻同位素则反映出沉积阶段生物作用的影响比成岩阶段更为明显     

广东长坑金银矿床石英和方解石的地球化学特征

石英和方解石是长坑金银矿床的主要脉石矿物，石英的自然热发光曲线为单峰型，方解石包括单峰型、双峰型和多峰型；石英、方解石的热发光强度和峰型与深度和矿化类型有关，可作为找矿标志。二者的稀土总量均很低，其中方解石的ＲＥＥ显著低于与岩浆热液有关方解石，而具有围岩侧分泌或加热大气水成因特点。碳、氧同位素特征也支持二者来源于沉积地层的观点。     

同位素古温度与海平面变化的关系初探

用稳定同位素地球化学古温度的测定方法对北京周口店石笋进行氧、碳同位素测定，获得的古温度与年龄值与同期的海平面变化进行比较，表明古温度的变化与海平面变化密切相关。