春季季风转换期间孟加拉湾的初级生产力

Primary production in the Bay of Bengal during spring intermonsoon period

2010年中国科学院东北印度洋科学考察期间,对孟加拉湾水域初级生产力展开了研究。孟加拉湾表层水体的水温较高,盐度变化范围较大,且上层水体营养盐含量较低,在真光层底部营养盐浓度突然增加。表层叶绿素a浓度较低(<0.1 mg/m3),叶绿素a最大值常出现在75 m水深处,上层水体浮游植物的生长受氮限制明显。表层潜在初级生产力低于0.2 mgCm-3h-1,且初级生产速率在50—75 m出现最大值。水柱中初级生产力变化范围为199—367 mgCm-2d-1,高值出现在88°—89°(E)附近。浮游植物固碳的主要贡献者是微微型浮游生物(<3μm),其次是小型浮游生物(>20μm)和微型浮游生物(3—20μm),但表层与75 m水深处固碳浮游植物的结构有一定差异。将孟加拉湾与阿拉伯海初级生产力进行对比,孟加拉湾水体初级生产力显著低于阿拉伯海,且初级生产力的影响因素有着显著的差异。

Phytoplankton biomass and primary production were studied in the Bay of Bengal （BOB） to better understand the element cycle and energy flow in the northeastern Indian Ocean. The northeastern Indian Ocean cruise was conducted by ＂Shiyan I＂ RV from April 23 to May 2, 2010, initiated by South China Sea Institute of Oceanology, Chinese Academy of Science. The seawater surface temperature in the BOB was higher than that of the South China Sea, and the salinity showed great variation. Stratification phenomena were prevalent in the water column during the study period. Dissolved inorganic nitrogen （NO3- ＋NO2- ） （〈1 μmol/L） were deficient in the upper layer, and increased intensively below the euphotic layer. Surface chlorophyll a concentration was lower than 0. 1 mg,/m3, and the maximum value were mostly appeared at 75 m depth. Integrated chlorophyll a concentration in the water column ranged from 14.7 to 27.0 mg/m2, and the high value was found at 88°--89° （E） adjacent area. Primary production in the surface water was lower than 0.2 mgCm-3h-1, and the maximum value was found between 50 m and 75 m. Assimilation number in the water column was used to calculated Integrated primary production, with the mean value of 1.44 mgC mg-1 Chl a h-1. 199 mgCm-2d-1 to 367 mgCm-2d-1 in the BOB during the study period, with adjacent sea. Pico-phytoplankton （44. 3% ） was the main contributor to Integrated primary production ranged from the high value occurred at 88--89° （E） the carbon fixation, followed by microphytoplankton （29.6%） and nano-phytoplankton （26.1% ）, despite that phytoplankton community structure varied with depth. Low values of DIN ： P and DIN ： Si indicated that nitrogen might limit the phytoplankton growth in the upper water of the BOB. The Arabian Sea and the BOB have different geographical characteristics and various physical dynamics. In the Arabian Sea, both vertieal mixing in winter and upwelling in summer carried the nutrients into the euphoric layer and could stimulate the phytoplankton growth. In the BOB, stratifieation impeded the nutrients moving upward, and the cloudy weather could also deerease the light penetration, so the primary production in the BOB was lower than that of the Arabian Sea.