Bacterial growth rate and the relative abundance of bacteria to heterotrophic nanoflagellates in the euphotic and disphotic layers in temperate coastal waters of Sagami Bay,Japan

This study aimed to clarify the vertical differences in bacterial growth and grazing pressure on bacteria by heterotrophic nanoflagellates (HNF) and to identify the controlling factors of bacterial growth in temperate coastal waters of Sagami Bay, Japan. In addition to environmental factors, the annual monthly variations in bacterial growth rate (BGR) and the relative abundance of bacteria to HNF (BA/HNFA) were investigated in the euphotic and disphotic layers between May 2012 and May 2013. Significant vertical differences in BGR and BA/HNFA were evident between the two layers during the thermal stratification times of May to October 2012 and April to May 2013. BGR indicated significantly stronger limitation of bacterial growth in the euphotic layer compared to the disphotic layer. In contrast, significantly lower BA/HNFA was observed in the euphotic layer, suggesting significantly higher grazing pressure on bacteria by HNF. However, significant differences in BGR and BA/HNFA were not observed between the two layers from November 2012 to Match 2013, when the water column was well-mixed vertically due to the cooling and wind-induced mixing of surface water. This study indicates that bacteria in the euphotic layer grow less actively and are more vulnerable to predatory grazing by HNF relative to the disphotic layer during the stratification period. Further, multiple regression analyses indicate that bacterial growth was most controlled by the concentrations of chlorophyll a and dissolved organic carbon in the euphotic and disphotic layers, respectively.     

临夏盆地新生代沉积物高分辨率岩石磁学记录与亚洲内陆干旱化过程及原因

亚洲内陆干旱化是全球新生代大陆环境变化中最引人瞩目的重大事件,与新生代全球变冷和青藏高原隆升密切相关.文章通过对甘肃临夏盆地几乎连续的新生代沉积物系统岩石磁学性质研究,获取了高分辨率磁化率和非磁滞剩磁记录,揭示在29.0～8.6 Ma的漫长的以湖相粉砂岩和泥岩为主的渐新世晚期和中新世早、中期没有明显的长期变化,从8.6Ma开始持续增加,尤其从6.4Ma和5.3Ma开始表现出两次快速持续增加.同时,以8.6Ma为界磁性矿物相对含量发生明显变化,此前以赤铁矿为主,磁铁矿和磁赤铁矿次之,此后以磁铁矿和磁赤铁矿为主,赤铁矿次之,磁性矿物类型和性质类似于风成红粘土和黄土.因此,我们将这种沉积物中磁性矿物组合、性质和含量的长期变化解释为流域外风成物质的加入,指示我国西北内陆现代干旱气候可能从8.6Ma开始,7.4～6.4 Ma后急剧加速变干,5.3Ma后再次加速变干,并最终形成今天的干旱区的过程.9～8 Ma开始的青藏高原阶段性快速隆升和随后的全球变冷可能是驱动亚洲内陆干旱化进程的动力.     

Partitioning Eddy-Covariance Methane Fluxes from a Shallow Lake into Diffusive and Ebullitive Fluxes

Methane (\(\mathrm {CH}_{4}\)) is known to be emitted from lakes to the atmosphere via processes such as diffusion and ebullition (i.e., bubble emission). We developed a practical method for partitioning eddy-covariance \(\mathrm {CH}_{4}\) fluxes from a shallow lake into diffusive and ebullitive fluxes using a wavelet analysis based on local scalar similarity between the \(\mathrm {CH}_{4}\) concentration and other reference scalars, such as the air temperature or water vapour concentration, in the wavelet time-scale domain, with the hypothesis that similar and dissimilar fluctuation components are related to diffusive and ebullitive \(\mathrm {CH}_{4}\) fluxes, respectively. Our method is applied to approximately two weeks of data obtained at a shallow mid-latitude lake. The partitioned diffusive flux has a physically sound relationship with wind speed, supporting the validity of the method. The ratio of the diffusive flux to the total flux is typically 0.11 with flow from an area of steady bubble emission, but otherwise 0.36. Further validation is required using a larger dataset and data from other lakes. The proposed method can be easily applied to historical data because it requires only 10-Hz data of \(\mathrm {CH}_{4}\) concentration and other reference scalars, along with an empirical parameter.