Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, PR China.
Third Institute of Oceanography, State Oceanic Administration, Xiamen 361005, PR China.
Mar Pollut Bull. 2018 Aug;133:606-615. doi: 10.1016/j.marpolbul.2018.06.018. Epub 2018 Jun 19.
We analyzed the data obtained from field observations on a gas hydrate drilling area in Dongsha of northern South China Sea (SCS) in middle May (before drilling) and early October (after drilling) in 2013. The variation in the phytoplankton communities and biomass as well as the impacts of environmental factors including dissolved methane was studied. Results indicated that the gas hydrate drilling area in Dongsha, SCS exhibited a typical low-nutrients low-chlorophyll a (LNLC) environment accompanied with low phytoplankton abundance. A total of 103 taxa belonging to 52 genera of 5 classes were identified, with diatoms and dinoflagellates dominating the community. Both phytoplankton abundance and chlorophyll a (Chl a) were highest at the subsurface maximum layer. The subsurface chlorophyll maximum (SCM) before and after drilling were stabilized at 75 m (0.30 ± 0.06 mg/m and 0.51 ± 0.29 mg/m, respectively), while the subsurface maximum of abundance after drilling went deeper to 75 m (604.17 ± 313.22 cells/L) from the surface (707.14 ± 243.98 cells/L) before drilling. After drilling, phosphate and Chl a increased significantly, but no significant differences were observed on abundance. Dominant species of diatoms were basically constant with dinoflagellates becoming more apparent in higher occurrence and abundance, while Cyanophyta was diverse after drilling. Redundancy analysis (RDA) and Spearman's correlation analysis both indicated that temperature, pH and phosphates were major factors causing fluctuation in phytoplankton community structure, while dissolved methane had non-significant impact directly. We clearly found both abundance and Chl a increased in particular water layers (between 50 and 75 m) and at stations (DS06, DS08 and DS15) where dissolved methane concentrations were also abnormally high. This study appeared to partly coincide with the findings of natural oil seeps in the Gulf of Mexico, which assumed that the turbulence from the natural oil and gas leaking zone could raise the bottom water through the rising bubbles and bring cold nutrient rich waters to the thermocline from the deep seeps. This plume-generated upwelling could then fuel a bottom-up effect on the photosynthetic species in the upper pelagic waters within the euphotic zone.
我们分析了 2013 年 5 月中旬（钻探前）和 10 月初（钻探后）在南海北部东沙海域天然气水合物钻探区获得的实地观测数据。研究了浮游植物群落和生物量的变化以及包括溶解甲烷在内的环境因素的影响。结果表明，南海东沙天然气水合物钻探区呈现典型的低营养低叶绿素 a（LNLC）环境，浮游植物丰度较低。共鉴定出 5 个类群 52 属 103 个分类单元，以硅藻和甲藻为主。浮游植物丰度和叶绿素 a（Chl a）均在次表层最大层最高。钻探前后的次表层叶绿素最大值（SCM）稳定在 75m（分别为 0.30±0.06mg/m 和 0.51±0.29mg/m），而钻探后丰度的次表层最大值从表面（707.14±243.98 细胞/L）更深至 75m（604.17±313.22 细胞/L）。钻探后，磷酸盐和 Chl a 显著增加，但丰度没有显著差异。硅藻的优势种基本保持不变，甲藻的出现和丰度更为明显，而蓝藻在钻探后种类繁多。冗余分析（RDA）和 Spearman 相关分析均表明，温度、pH 和磷酸盐是浮游植物群落结构波动的主要因素，而溶解甲烷的直接影响不显著。我们清楚地发现，特别是在甲烷浓度异常高的 DS06、DS08 和 DS15 站位和特定水层（50-75m 之间），丰度和 Chl a 都有所增加。这项研究似乎与墨西哥湾自然石油泄漏的发现部分吻合，后者假设自然石油和天然气泄漏区的湍流可以通过上升的气泡将底层水提升，并将富含营养的冷水从深海渗漏带到温跃层。这种羽状上升流可以为透光带内上层浮游水层中的光合作用物种提供自下而上的影响。
