ABSTRACT

The influence of mesoscale dynamics on variability of phytoplankton biomass in terms of chlorophyll-a (chl-a) concentration was studied in the coastal waters of the South Eastern Arabian Sea (SEAS) using long-term satellite data. Satellite-derived chl-a, sea level anomaly, sea surface temperature, and sea surface wind data for the period 1998–2016 were compiled from various sources and analysed to investigate the chl-a variability associated with coastal upwelling and mesoscale eddies. The Empirical Orthogonal Function and Morlet wavelet analyses were performed to estimate the quantitative variability and the result showed strong seasonal and interannual modulation in chl-a concentration and associated environmental variables. The Okubo–Weiss criterion was applied for the identification of mesoscale eddies. The results indicated the presence of cyclonic (cold core) eddies during the summer monsoon season (June–September). The wind-induced upwelling and the cyclonic eddies were most intense during the summer monsoon season, causing higher values of chl-a compared with other season. It is revealed that the variability of chl-a, which might be attributed to seasonal and interannual differences in the surface and sub-surface nutrients, is caused either by coastal upwelling or cyclonic eddies. In particular, the wind-induced upwelling strongly controls the spatial and temporal variability of chl-a compared with mesoscale eddies along the SEAS. The regression model we adopted points out the dominant role played by the wind and its forcing bring about variability in chl-a. The occurrence of extreme climatic events such as El Niño, La Niña and Indian Ocean Dipole (IOD) was noticed during the study period and particularly taken into account to understand the interannual fluctuations in chl-a and associated environmental variables. The relative variability in chl-a concentration was prominent during strong El Niño, La Niña, and IOD. We have attempted to determine the relationship between chl-a with coastal upwelling and mesoscale eddies, the overall importance of such physical forcings, and their influence on bio-production in the SEAS.

摘要

使用长期卫星数据，研究了阿拉伯东南海（SEAS）沿海水域中尺度动力学对叶绿素-a（chl -a）浓度浮游植物生物量变异性的影响。从各种来源收集了1998-2016年期间卫星衍生的chl -a，海平面异常，海面温度和海面风的数据，并进行了分析，以研究与沿海上升流和中尺度涡旋有关的chl -a变异性。进行了经验正交函数和Morlet小波分析以估计定量变异性，结果显示在chl -a中强烈的季节和年际调制浓度和相关的环境变量。Okubo-Weiss标准适用于中尺度涡旋的识别。结果表明在夏季季风季节（6月至9月）存在气旋（冷芯）涡流。在夏季风季节，风起流和旋风涡旋最强烈，与其他季节相比，导致较高的chl -a值。结果表明，chl -a的变异性可能是由于海岸上升流或旋风涡旋引起的，而这种变异可能归因于地表和次表层养分的季节性和年际差异。特别是，风诱发的上升流强烈控制了chl -a的时空变化与SEAS沿途的中尺度涡流相比。我们采用的回归模型指出了风所起的主导作用，它的强迫导致了chl- a的变化。极端气候事件，如厄尔尼诺，拉尼娜和印度洋偶极子（IOD）的发生在研究期间被发现，特别是考虑到理解chl-际波动一个和相关的环境变量。在chl-的相对变动一个集中在强厄尔尼诺，拉尼娜和IOD明显突出。我们试图确定chl -a之间的关系 沿海上升流和中尺度涡旋，这种物理强迫的总体重要性及其对SEAS中生物生产的影响。