Sensitivity of coastal polynyas and high-salinity shelf water production in the Ross Sea,Antarctica, to the atmospheric forcing

Coastal polynyas around Antarctica are the place of intense air–sea exchanges which eventually lead to the formation of high-salinity shelf waters (HSSW) over continental shelves. Here, the influence of atmospheric forcing on coastal polynyas in the Ross Sea is studied by contrasting the response of a regional ocean/sea-ice circulation model to two different atmospheric forcing sets. A first forcing (DFS3) is based on ERA40 atmospheric surface variables and satellite products. A second forcing (MAR) is produced on the basis of ERA40 with a dynamical downscaling procedure. As compared to DFS3, MAR forcing is shown to improve substantially the representation of small-scale patterns of coastal winds with stronger katabatic winds along the coast. The response of the ocean/sea-ice model to the two forcing sets shows that the MAR forcing improves substantially the geographical distribution of polynyas in the Ross Sea. With the MAR forcing, the polynya season is also shown to last longer with a greater ice-production rate. As a consequence, a greater flow of dense water out of the polynyas is found with the MAR forcing and the properties of HSSW are notably improved as compared to the DFS3 forcing. The factors contributing to the activity of Terra Nova Bay and Ross Ice Shelf polynyas in the model are studied in detail. The general picture that emerges from our simulations is that the properties of HSSW are mostly set by brine rejection when the polynya season resume. We found that coastal polynyas in the Ross Sea export about 0.4 Sv of HSSW which then flows along three separate channels over the Ross Shelf. A 6-month time lag is observed between the peak of activity of polynyas and the maximum transport across the sills in the channels with a maximum transport of about 1 Sv in February. This lag corresponds to the time it takes to the newly formed HSSW to spread from the polynya to the sills (at a speed of nearly 2 cm s⁻¹).     

Unstructured-mesh modeling of the Congo river-to-sea continuum

With the second largest outflow in the world and one of the widest hydrological basins, the Congo River is of a major importance both locally and globally. However, relatively few studies have been conducted on its hydrology, as compared to other great rivers such as the Amazon, Nile, Yangtze, or Mississippi. The goal of this study is therefore to help fill this gap and provide the first high-resolution simulation of the Congo river-estuary-coastal sea continuum. To this end, we are using a discontinuous-Galerkin finite element marine model that solves the two-dimensional depth-averaged shallow water equations on an unstructured mesh. To ensure a smooth transition from river to coastal sea, we have considered a model that encompasses both hydrological and coastal ocean processes. An important difficulty in setting up this model was to find data to parameterize and validate it, as it is a rather remote and understudied area. Therefore, an important effort in this study has been to establish a methodology to take advantage of all the data sources available including nautical charts that had to be digitalized. The model surface elevation has then been validated with respect to an altimetric database. Model results suggest the existence of gyres in the vicinity of the river mouth that have never been documented before. The effect of those gyres on the Congo River dynamics has been further investigated by simulating the transport of Lagrangian particles and computing the water age.     

撞击坑统计定年法及对月球虹湾地区的定年结果

撞击作用是行星形成和表面重塑的重要地质过程,记录和揭示了行星的演化历史.撞击作用形成的撞击坑可用于研究天体表面地质单元形成的时间.依据内太阳系天体表面的撞击历史,总结了通过对撞击坑的直径和频率分布进行统计,计算天体表面模式年龄的原理和方法.在此基础上,利用美国“月球勘测轨道器(LRO)”广角相机获得的图像,对月球虹湾地区的撞击坑进行了直径-频率分布统计研究,获得其3个主要地质单元的绝对模式年龄分别为3.33 Ga、3.21 Ga和2.60 Ga,有效限定了本区主要地质事件发生的时间.      

北京市高尔夫旅游资源空间分布特征及影响因素

高尔夫旅游不仅是中国旅游资源体系中的重要组成部分,也是旅游产业从观光型向休闲度假型调整的重要支撑点。选取北京市作为研究区域,对18洞及以上共51处标准高尔夫旅游资源空间分布特征及影响因素进行研究,得出以下结论:①在区域经济发展水平的影响下,北京市高尔夫旅游资源发展可分为两个阶段:1985-2000年缓慢发展阶段,2001-2011年蓬勃发展阶段。②北京市高尔夫旅游资源的空间分布形态已经出现多中心特征,由空间点状集聚分布转向扩散化并形成线状网络体系。③从球场面积的空间容量分布来看,北京市高尔夫旅游资源呈现出空间不均衡的集聚特征格局。中心城区球场密度大,但空间容量规模低;外围新兴区域球场密度相对较低,但开发强度高,空间容量规模大。总体上看,区域地形特征、重要水系分布、交通区位条件、配套服务设施、关联产业开发、土地价格、规划及政策引导等各种要素,通过综合作用机制共同影响北京市高尔夫旅游资源空间分布特征。     

Unreported fishing, hungry people and political turmoil: the recipe for a food security crisis in Madagascar?

Madagascar, the world's fourth largest island, is one of the world's poorest developing countries, and its people depend heavily on marine resources for subsistence and income. Exports of these resources and foreign fishing access agreements are also important, at least from a large-scale economic perspective. In recent years, concerns have been voiced amongst local fishers and industry groups regarding the growth of the country's fishing effort. Despite these concerns, existing knowledge of the scale, composition and trends of Malagasy fisheries remains poor, and there is negligible information regarding unreported catches and illegal fishing in Madagascar's waters. Small-scale fisheries, which are often substantial in developing countries such as Madagascar, are often unreported or underestimated. Unfortunately, fisheries legislations, management plans and foreign fishing access agreements are often influenced by these incomplete data, leading to serious over-estimations of resource availability. This also appears to be the situation in Madagascar, where the reconstruction of total catches by all Malagasy fisheries sectors conducted here showed that total catches between 1950 and 2008 were twice the volume reported by national fisheries agencies. Most importantly, much of the subsistence sector is missing from official statistics, and signs of decline have already been observed in several stocks, suggesting that current levels of catches are likely to be exceeding sustainable yields. This has profound implications for the economic and ecological sustainability of fisheries, as well as food security in a country where people rely heavily on the ocean for their daily protein needs and livelihoods.     

Bivalve larvae transport and connectivity within the Ahe atoll lagoon (Tuamotu Archipelago), with application to pearl oyster aquaculture management

Patterns of bivalve larvae dispersal in the deep Ahe atoll lagoon was studied by using a numerical 3D transport model (MARS3D) coupled with a vertical swimming sub-model, forced mainly by tide and wind-induced currents. The simulations were validated against observations of larval dispersal monitored several days throughout the lagoon. Connectivity matrices describing larval exchanges inside the lagoon were inferred. Larvae displayed a significant dispersal capacity at the lagoon scale, especially with dominant eastern winds. With southeastern winds, larvae mostly remained in their origin sector. The total export rate of the larvae, toward the ocean through the pass and shallow lagoon borders, was independent of the wind conditions, with 1% of the total concentration exported per day. However, the tide-driven currents efficiently flushed larvae in sectors close to the pass. Connectivity matrices suggest that the south and west sectors were more suitable for spat collecting and that central sectors would be efficient sanctuaries if genitors were accumulated.     

Multi-scale distribution and dynamics of bivalve larvae in a deep atoll lagoon (Ahe, French Polynesia)

Bivalve larvae and hydrographic parameters were sampled over a range of spatio-temporal scales in a deep atoll lagoon. Bivalve larvae abundances were very high throughout the year: 18,550 m(-3) in average. Larvae were (i) concentrated at mid-depth with nocturnal ascent and diurnal descent, (ii) heterogeneously dispersed at the lagoon scale, (iii) subject to day-to-day variation in abundance and (iv) transferred between different parts of the lagoon providing evidence of intra-lagoonal connectivity. The primacy of physical factors was seen on large spatial scale with the diluting effect of water renewal and transfers by hydrodynamics. On smaller spatial scale, the primacy of biological processes was recognised, with larval swimming activity leading to dial vertical migration correlated with food concentration. Variations in larval abundance were driven by bivalve reproductive activity correlated with meteorological conditions (i.e. windy periods). Finally, relationship between bivalve larvae patterns and pearl oyster (Pinctada margaritifera) settlement structuring is discussed.     

Influence of plankton concentration on gametogenesis and spawning of the black lip pearl oyster Pinctada margaritifera in Ahe atoll lagoon (Tuamotu archipelago, French polynesia)

Pearl culture industry represents one of the dominant business sector of French Polynesia. However, it still entirely relies on unpredictable spat collection success. Our aim was to assess the influence of natural plankton concentration fluctuations on maturation and spawning of the black lip pearl oyster Pinctada margaritifera, during a 4months survey conducted in Ahe atoll lagoon. Plankton concentration was assessed by chlorophyll a extraction and by microscope counts while gonadic index, gonado-visceral dry weights and histology were used to measure pearl oysters reproduction activity. We found that (i) plankton concentration fluctuations were mainly related to wind regime, (ii) gametogenesis rate was mainly related to plankton concentration, (iii) spawning occurred when maximal gonad storage was reached, (iv) plankton concentration was the main spawning synchronizing factor. These results contribute explaining P. margaritifera spat collection variability in French Polynesian atoll lagoon.     

Greenhouse Gases, Aerosols and Reducing Future Climate Uncertainties

The past record of global earth surface temperatures is unable to offer quantitative evidence about the amplitude of climate sensitivity, due to the competing effects of long-lived greenhouse gases and short-lived aerosols. This factor constitutes one of the reasons why uncertainties about climate sensitivity have remained almost unchanged for more than 30 years, and it is also limiting our current capacity to propose reliable climate projections for the coming century. This paper offers a short review of the studies that have dealt with this issue. A number of approaches aim at a process-oriented diagnostic of current models. These studies are in constant progress since the launch of remote-sensing instruments, such as those from the A-train satellite constellation. Past climate fluctuations may also offer some limited possibilities to discriminate the effects of greenhouse gases and aerosols. There is therefore a real hope that climate projections may eventually become more accurate, which would be extremely useful in monitoring global warming during the next decades.