Abstract
In this study, the short-term offshore extension of Brahmaputra-Ganges (BG) and Irrawaddy freshwater plumes to the central northern Bay of Bengal (BoB) was investigated based on in situ and satellite observations. In the summer and winter of 2015, two significant freshening events with periods of weeks were observed from a moored buoy at 15°N, 90°E in the BoB. Soil Moisture Active Passive (SMAP) satellite sea surface salinity compares well with the in situ data and shows that these freshening events are directly related to the short-term offshore extension of the BG and Irrawaddy freshwater, respectively. These data combined with the altimeter sea level anomaly data show that the offshore extending plumes result from freshwater modulated by eddies. During summer, the BG freshwater is modulated by a combination of three closely located eddies: a large anticyclonic eddy (ACE) off the northwestern BoB coast and two cyclonic eddies in the northern BoB. Consequently, the freshwater extends offshore from the river mouth and forms a long and narrow tongue-shaped plume extending southwestward to the central BoB. During winter, the Irrawaddy freshwater is modulated by two continuous ACEs evolved from Rossby wave propagating westward from the Irrawaddy Delta off Myanmar, forming a tongue-shaped plume extending to the central BoB. Strong salinity fronts are formed along the boundaries of these tongue-shaped plumes. These findings confirm good capability of the SMAP data to investigate the short-term offshore extension of the BG and Irrawaddy freshwater. This study provides direct evidences of the pathways of the offshore extension of the BG and Irrawaddy freshwater and highlights the role of eddies in the northern BoB freshwater plume variability.
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The National Natural Science Foundation of China under contract Nos 41920104006 and 41776107; the Key Program of the National Natural Science Foundation of China under contract No. 91647209; the Key Special Program on the Science and Technology of Zhejiang Province under contract No. 2015C03015; the Scientific Research Fund of SIO under contract Nos JZ2001 and JT1801; the Scientific Research Fund of the State Key Laboratory of Satellite Ocean Environment Dynamics, SIO under contract No. SOEDZZ2106; the Open Fund of State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, MNR under contract No. QNHX2114.
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Li, Z., Huang, S., Zhu, X. et al. Short-term offshore extension of Brahmaputra-Ganges and Irrawaddy freshwater plumes to the central northern Bay of Bengal based on in situ and satellite observations. Acta Oceanol. Sin. 40, 80–93 (2021). https://doi.org/10.1007/s13131-021-1729-y
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DOI: https://doi.org/10.1007/s13131-021-1729-y