考洲洋牡蛎养殖海域海-气界面CO2交换通量的时空变化

根据2018年7月、11月和2019年1月、4月对广东考洲洋牡蛎养殖海域进行4个季节调查获得的p H、溶解无机碳(DIC)、水温、盐度、溶解氧(DO)及叶绿素a(Chla)等数据,估算该区域表层海水溶解无机碳体系各分量的浓度、初级生产力(PP)、表层海水CO₂分压[p(CO₂)]和海-气界面CO₂交换通量(FCO₂),分析牡蛎养殖活动对养殖区碳循环的影响。结果表明:牡蛎养殖区表层海水中Chl a、DIC、HCO₃^–和PP显著低于非养殖区;养殖淡季表层海水中pH、DO、DIC、HCO₃^–、和CO₃^2–显著大于养殖旺季,养殖旺季的p(CO₂)和FCO₂显著大于养殖淡季。牡蛎养殖区表层海水夏季、秋季、冬季和春季的海-气界面CO₂交换通量FCO₂平均值分别是(42.04±9.56)、(276...     

冲绳海槽近3.5万a来陆源物质沉积通量及其对气候变化的响应

以冲绳海槽DGKS9603孔沉积物为研究对象,利用元素地球化学成分数据因子分析方法把混合源沉积物分离成陆源、火山源和生物源.结合沉积物干样密度和沉积速率对冲绳海槽近3.5万a以来沉积物中陆源物质沉积通量进行了估计,进而揭示陆源物质供应对气候变化的响应规律.研究表明,冲绳海槽的陆源物质主要来源于长江输运的我国大陆物质.在冰期—间冰期时间尺度上,海平面涨落导致的长江与海槽之间距离的伸缩是制约陆源物质通量变化的主要因素;在盛冰期和气候变冷事件(Heinrich事件)期间,东亚冬季风的增强使更多的粉砂级物质进入冲绳海槽,导致陆源物质通量增加.冲绳海槽沉积物记录的Heinrich事件与增强的东亚冬季风密切相关.     

太湖现代沉积物中磷的沉积通量及空间差异性

在水文状况、水质状况、生态类型均显著不同的三个太湖典型湖区, 利用^210Pb定年测定了近百年来沉积物及磷的沉积通量.结果发现, 三个湖区磷的沉积通量及其变化规律相差很大.发生蓝藻水华暴发的梅梁湾近百年来沉积物和磷的沉积通量都比较小, 只是在近十几年来才有明显增加的趋势; 太湖上游的夹浦沉积物沉积速率近百年来持续增加, 只有表层有所下降, 但表层12cm沉积物中磷的沉积通量却显著下降; 处于太湖下游草型化的胥口湾湖区, 在20世纪60年代以前沉积物沉积通量呈增加趋势, 之后呈下降趋势, 磷的沉积通量则呈振荡下降趋势.研究表明, 太湖沉积物中磷的累积通量具有明显的空间异质性.     

The Southwest Atlantic intertidal burrowing crab Neohelice granulata modifies nutrient loads of phreatic waters entering coastal area

Along the coastal areas of the Southwest Atlantic estuaries and embayments, phreatic water often circulates through very extended areas (up to several hundred meters perpendicular to the coast), dominated by dense assemblages of deep burrows of the crab Neohelice granulata (formerly Chasmagnathus granulatus). This crab inhabits the intertidal area, from mudflats to marshes vegetated by species of Spartina, Sarcocornia and Juncus, generating extensive burrowing beds where burrow density may reach up to 60 burrows m⁻². Since the lower limit of the crab burrows is usually the water table, we investigated through field experiments the effect of N. granulata and their burrows on the chemical characteristics of this phreatic water. Water analysis from experimental (1) occupied burrows (with crabs), (2) unoccupied burrows (where crabs were excluded), and (3) sediment pore water show remarkable differences. Water oxygenation, and nitrate, ammonium and sulphate concentrations inside occupied burrows were higher than in the water inside unoccupied burrows or pore waters. Moreover, directed sampling of phreatic water entering and leaving the crab bed, shows that dissolved inorganic nitrogen concentration is enhanced as the water crosses the crab bed. These results may be ascribed to the fact that in the salt marsh the crabs spend most of their time within burrows, where presumably they store food (plants) and defecate. These activities generate an area of accumulation of excrements and nutrients in different decomposition states. The present work shows a novel way by which bioturbating organisms can affect nutrients exportation from salt marshes to the open waters.     

Derivation and application of new equations for radiation stress and volume flux

In this paper, new expressions of radiation stress and volume flux for long waves have been analytically derived by inclusion of higher-order surface elevations up to the sixth-order. To quantify these expressions, surface elevations along a beach are first simulated using the fully nonlinear Boussinesq-type model COULWAVE. Then, based on the large amount of numerical data, new equations for radiation stress and volume flux are statistically formulated. The research unveils the essential roles of the Ursell parameter, Irribarren number and wave steepness described by the local wave height, wave length and bottom slope. The study shows the importance of nonlinear wave properties in wave-induced currents and mean water levels (set-up/down). The higher-order formulations produce lower values for radiation stress and volume flux than calculated from the lower-order and linear waves. Case studies suggest that the new formulations produce an accurate estimation for mean water level. However, improvement on the computed current profiles is marginal for some cases. This implies that the accurate prediction of the current profile would require more than just the proposed improvement of the radiation stress and volume flux.     

Spectral modification and geographic redistribution of the semi-diurnal internal tide

A realistic-geometry global baroclinic tidal model forced with a single tidal constituent $(M_2)$ is used to investigate the generation of the internal tide and the associated radiated baroclinic energy flux. The model internal wave spectrum is populated at discrete frequency multiples $(1/2\text{,}1\text{,}3/2\text{,}2\text{,}5/2\text{,}\dots )$ of $M_2$. The $1/2M_2$ subharmonic is particularly energetic at its turning latitude of $\pm 28.8°$. Poleward only integer superharmonics of $M_2$ are significantly excited. The subharmonic turning latitude (SHTL) disturbance has high vertical wavenumber and shear, provided that internal tide energy level exceeds a threshold value. Under these circumstances, Richardson numbers smaller than 1/4 occur in the upper few hundred meters in both the realistic-geometry model and in a complimentary idealized geometry two-dimensional (2D) model. In the 2D model, the disturbance enables Richardson number dependent diapycnal entrainment to effect a modification of the stratification of the upper 400 m of the ocean, and poleward cross-SHTL energy flux falls to 10% of its pre-instability value due to energy transfer to the non-propagating (i.e., inertial) subharmonic. Realistic-geometry simulations suggest a more modest 40% decrease in net flux, although the strongest beams are almost entirely shut down. The predicted energy flux-convergence implies a thermocline dissipation rate in the 28.5–30.0°N latitude band of $5\times {10}^{-9}\text{W}{\text{kg}}^{-1}$, with an associated diapycnal diffusivity of ${10}^{-4}{\text{m}}^2{\text{s}}^{-1}$. North of Hawaii the implied regional dissipation rate reaches $4\times {10}^{-8}\text{W}{\text{kg}}^{-1}$ with an associated thermocline diffusivity of $8\times {10}^{-4}{\text{m}}^2{\text{s}}^{-1}$. Investigations of subgridscale parameterization and resolution sensitivity suggest that the basic character and magnitude of the predictions are robust to details of the numerical solutions. The present results are taken as further evidence that an increase in shear-driven turbulent mixing in the upper ocean is predicted at special latitudes. It is suggested that the search should be directed to regions where intense low-mode internal tide beams cross their subharmonic turning latitude.     

STUDY ON FLUXES OF CH4 EMISSION FROM PADDY FIELDS IN CHANGCHUN AREA

CH4 is a kind of important greenhouse gases in atmosphere. The current atmospheric concentration of CH4 is about 1.7ppmv and is increasing at almost 2％ per year. The sources of CH4 include paddies, wetland and tundra, insects, the digestive tracts of ruminants, coal mining, biomass burning, and the leakage of natural gas. The total input to the atmosphere lies in the range 300－ 550Tg per year. CH4 from paddy fields is about 10％ － 20％ of total source of atmospheric CH4 (DING, 1997). …     

利用尺度自适应大气边界层湍流参数化方案对一次陆地浓雾的数值模拟

为提高大气数值模式的模拟能力,改进大气边界层水汽、热量湍流输送计算和大雾天气的模拟效果,选用WRF三维非静力模式,采用具有局地和非局地垂直湍流尺度自适应计算能力的MYNN_SA参数化方案,对2017年12月28—29日我国华北—江淮地区的大范围浓雾过程进行了数值模拟研究,探讨从中尺度到灰区尺度分辨率范围,模式的尺度自适应大气边界层湍流参数化方案对稳定大气边界层发展、湍流输送和大雾天气模拟的影响。利用中国地面气象站观测资料和ERA5再分析数据,在接近灰区尺度的网格分辨率上,利用尺度自适应大气边界层湍流MYNN_SA参数化方案较之中尺度参数化MYNN方案,可明显改善次网格湍流输送计算,以及陆地浓雾的强度、空间分布和时间演变特征,可更精确地模拟云水混合比、逆温层和雾区的垂直结构。     

中国地级市人为热总量的估算及驱动因素分析

人为热一定程度上影响着城市的局地环境和微气候.以2016年中国地级市为研究对象,首先采用了能源消耗清单法结合Suomi-NPP (National Polar-orbiting Partnership)VIIRS (Visible Infrared Imaging Radiometer Suite)夜间灯光数据的方法估...     

硫酸盐-甲烷界面与甲烷通量及下伏天然气水合物赋存的关系

硫酸盐-甲烷界面在富甲烷和含天然气水合物的海洋沉积区已经成为一个重要的生物地球化学识别边界。在硫酸盐-甲烷界面之上,沉积物中的硫酸盐因参与分解有机质和甲烷厌氧氧化反应而被消耗,而其界面之下沉积物中的甲烷则不断生成,含量逐渐增加。根据该界面附近硫酸盐浓度和甲烷浓度的变化特征,可以判断该区甲烷流体通量的大小,从而指示下伏天然气水合物的可能赋存状况。南海北部陆坡的柱状沉积物孔隙水数据的分析显示,硫酸盐-甲烷界面埋深比较浅,表明该海域的甲烷通量较高。这种高甲烷通量很可能是由下伏的天然气水合物所引起的,并暗示着该区下伏海底可能有天然气水合物沉积层赋存。