Satellite-based observation of ocean productivity in southeast Arabian Sea using chlorophyll, sea surface temperature and wind datasets,Journal of Earth System Science

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Satellite-based observation of ocean productivity in southeast Arabian Sea using chlorophyll, sea surface temperature and wind datasets
Journal of Earth System Science ( IF 1.9 ) Pub Date : 2021-02-02 , DOI: 10.1007/s12040-020-01512-y
S N Nagendra Jaiganesh , Ranjit Kumar Sarangi , Shital Shukla

Abstract

The phytoplankton variability and ocean productivity have been studied with the retrieval of chlorophyll concentration (CC) from various satellite ocean colour missions. The phytoplankton distribution is related to ocean processes and physical parameters such as temperature, wind speed, currents, etc., at regional and global scales. In the current study, the phytoplankton productivity has been observed in the southeast Arabian Sea during southwest (SW, June–September) and northeast (NE, October–December) monsoon seasons using merged chlorophyll product datasets during the years 2017 and 2018. There has been an observation of high chlorophyll concentration (~5.0 mg m⁻³) in the southeast Arabian Sea (southern tip of India) during SW monsoon and less in NE monsoons (~1.0 mg m⁻³). The spread in CC has been observed maximum during July–September. High anomaly of CC was observed along north-eastern Arabian Sea during northeast monsoon months of 2017 due to the very severe cyclonic storm Ockhi. Similarly, during August 2018, high chlorophyll concentration was observed (18.8 mg m⁻³) in south-eastern tip as a result of heavy rainfall and discharge of nutrient rich riverine water. The sea surface temperature (Modis-Aqua SST) has been observed to be cooler (26–27°C) in the SE Arabian Sea coastal waters during July–August as compared to warmer (28–30°C) surrounding waters. During the SW monsoon (June–August), the wind speed has been observed to be of high magnitude (~10 m/s), which was not evident during September. The alongshore (north-westerly) wind has been observed during July–September in the near coastal water that causes coastal to offshore moving Ekman mass transport (EMT). Similarly, the alongshore (north-easterly) wind has been observed during December in the southern tip of India and off Sri Lankan west coast. The strong zonal EMT (–1500 to –500 kg/m/s) has been observed in the southeast Arabian Sea during July–September 2017 and 2018 which is weak to moderate (> –500 kg/m/s) in NE monsoon months. Statistical analysis has been made between SST, wind speed and CC which shows significant correlation coefficient (r > 0.6, p < 0.001). Hence, the present study confers that the alongshore wind and high wind speed regions are favourable to upwelling events and have been responsible for cooling of SST resulting in high productivity zones in the southeast Arabian Sea, which is important from the point of view of marine fishery and ecosystem assessment.

Research Highlights

During August 2018, high anomaly of chlorophyll concentration (CC) was observed (18.8 mg m^–3) in south-eastern tip as a result of heavy rainfall, flood and discharge of nutrient rich riverine water from Kerala.
Very severe cyclonic storm Ockhi results in high CC (2 mg m^–3) in north-eastern Arabian Sea during December 2017.
High magnitude of north-westerly wind (~ 7 m/s) in the southwest monsoon months (July–September) favours the upwelling event in south-eastern Arabian Sea.
Single and multiple correlation analysis confirms the manifestation of low SST due to high magnitude of north-westerly winds for the enhancement in CC with significant correlation coefficient (r > 0.6, p < 0.001).

中文翻译：

利用叶绿素，海面温度和风数据集进行的基于卫星的阿拉伯东南海海洋生产力观测

摘要

通过从各种卫星海洋颜色任务中检索叶绿素浓度（CC），研究了浮游植物的变异性和海洋生产力。在区域和全球范围内，浮游植物的分布与海洋过程和物理参数（例如温度，风速，洋流等）有关。在当前研究中，使用合并的叶绿素产品数据集在2017年和2018年的阿拉伯季风东南部西南风（6月至9月）和东北部东北风（10月至12月）观察到了浮游植物的生产力。是观察到西南风季风期间阿拉伯海东南部（印度南端）叶绿素浓度较高（〜5.0 mg m ^-3），东北风季风中的叶绿素浓度较低（〜1.0 mg m ^-3））。在7月至9月期间，CC的扩散已达到最大。由于非常严重的飓风奥基（Ockhi），在2017年东北季风月份期间，在阿拉伯东北东北部观察到CC高度异常。同样，在2018年8月，叶绿素浓度很高（18.8 mg m ^-3），因为暴雨和营养丰富的河水的排放。据观察，7月至8月期间，东南阿拉伯沿海水域的海表温度（Modis-Aqua SST）较凉（26–27°C），而周围水较暖（28–30°C）。在西南风季风期间（6月至8月），观测到的风速很高（〜10 m / s），在9月期间没有发现。在7月至9月期间，在近岸水域观察到了沿海（西北风）风，这导致沿海到近海的Ekman大众运输（EMT）移动。同样，在12月的印度南端和斯里兰卡西海岸外也观察到了沿海（东北风）风。在2017年7月至9月和2018年9月至9月的阿拉伯海东南部，观测到强的纬向EMT（–1500至–500 kg / m / s），而在东北季风月份则弱至中度（> –500 kg / m / s）。在SST，风速和CC之间进行了统计分析，显示出显着的相关系数（r > 0.6，p <0.001）。因此，本研究赋予近海风和高风速区有利于上升流事件，并且是造成海表温度下降的原因，导致阿拉伯海东南部的高产区，这从海洋渔业的角度来看很重要。和生态系统评估。