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- Title
Microplankton size structure induced by a warm-core eddy in the western Bay of Bengal: Role of Trichodesmium abundance.
- Authors
Chinnadurai, Karnan; Retnamma, Jyothibabu; Nagarathinam, Arunpandi; Subramanian, Pandiyarajan Rethinam; Singaram, Parthasarathi; Shoba, Santhikrishnan
- Abstract
• The authors presented the effect of the warm-core eddy on the size of the microplankton in the BoB. • Warm-core eddy decreased the overall abundance and biomass of microautotrophs. • Chlorophyll- a in warm-core eddy was extremely low in the surface with a DCM. • Warm-core eddy also facilitated a high abundance of Trichodesmium filaments. • This caused an increase in the overall size of the micro-autotrophs. Mesoscale warm-core eddies are common in the Bay of Bengal (BoB), and this study in the western BoB during Pre-Southwest Monsoon (April 2015) presents how a prolonged warm-core core eddy could modify the microplankton biomass and size structure. To investigate this, field sampling and laboratory analyses were augmented with satellite data sets of sea surface temperature (SST), winds, mean sea level anomaly (MSLA), geostrophic currents and chlorophyll- a. High SST with positive MSLA (≥ 20 cm) and a clockwise circulation, represented the occurrence of a large warm-core eddy in the western BoB. Time series data evidenced that it was originated in the mid of March and persistent there till early June, which in turn caused a decrease in the surface nutrients and chlorophyll- a. The abundance and biomass of microplankton were negligible in the warm-core eddy region. FlowCAM data showed a significant decrease in the autotrophic microplankton parameters in the warm-core eddy (av. 13 ± 9 ind. L−1 and 0.1 ± 0.04 µgC L−1, respectively) as compared to the surrounding locations (av. 227 ± 143 ind. L−1 and 0.8 ± 0.5 µgC L−1, respectively). Low nutrients level in the warm core eddy region favoured high abundance of needle-shaped phytoplankton cells dominated by Trichodesmium cells. As a result, the size of micro-autotrophs in the warm-core eddy was larger (av. 91,760 ± 12,902 µm3 ind.−1) than its outside (av. 50,115 ± 21,578 µm3 ind.−1). This is a deviation from our belief that the oligotrophy decreases the phytoplankton size. We showed here that the above understanding might not be infallible in warm-core eddies in the northern Indian Ocean due to its inducing effect on the Trichodesmium abundance.
- Subjects
TRICHODESMIUM; SEA level; GEOSTROPHIC currents; OCEAN temperature; MESOSCALE eddies; EDDIES
- Publication
Oceanologia, 2021, Vol 63, Issue 3, p283
- ISSN
0078-3234
- Publication type
Article
- DOI
10.1016/j.oceano.2021.02.003