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Quantifying Tropical Cyclone's Effect on the Biogeochemical Processes Using Profiling Float Observations in the Bay of Bengal
Author(s) -
Girishkumar M. S.,
Thangaprakash V. P.,
Udaya Bhaskar T. V. S.,
Suprit K.,
Sureshkumar N.,
Baliarsingh S. K.,
Jofia J.,
Pant Vimlesh,
Vishnu S.,
George G.,
Abhilash K. R.,
Shivaprasad S.
Publication year - 2019
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2017jc013629
Subject(s) - biogeochemical cycle , upwelling , oceanography , mixed layer , argo , biogeochemistry , phytoplankton , bay , environmental science , chlorophyll a , tropical cyclone , geology , nutrient , chemistry , environmental chemistry , biochemistry , organic chemistry
Physical and biogeochemical observations from an autonomous profiling Argo float in the Bay of Bengal show significant changes in upper ocean structure during the passage of tropical cyclone (TC) Hudhud (7–14 October 2014). TC Hudhud mixed water from a depth of about 50 m into the surface layers through a combination of upwelling and turbulent mixing. Mixing was extended into the depth of nutricline, the oxycline, and the subsurface‐chlorophyll‐maximum and thus had a strong impact on the biogeochemistry of the upper ocean. Before the storm, the near‐surface layer was nutrient depleted and was thus oligotrophic with the chlorophyll‐ a concentration of less than 0.15 mg/m 3 . Storm mixing initially increased the chlorophyll by 1.4 mg/m 3 , increased the surface nitrate concentration to about 6.6 μM/kg, and decreased the subsurface dissolved oxygen (30–35 m) to 31% of saturation (140 μM). These conditions were favorable for phytoplankton growth resulting in an estimated increase in primary productivity averaging 1.5 g C·m −2 ·day −1 over 15 days. During this bloom, chlorophyll‐ a increased by 3.6 mg/m 3 , and dissolved oxygen increased from 111% to 123% of saturation. Similar observations during TC Vardah (6–12 December 2016) showed much less mixing. Our analysis suggests that relatively small (high) translation speed and the presence of cold (warm) core eddy leads to strong (weak) oceanic response during TC Hudhud (TC Vardah ). Thus, although cyclones can cause strong biogeochemical responses in the Bay of Bengal, the strength of response depends on the properties of the storm and the prevailing upper ocean structure such as the presence of mesoscale eddies.