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- Title
Spatiotemporal Variability in Phytoplankton Size Class Modulated by Summer Monsoon Wind Forcing in the Central Arabian Sea.
- Authors
Chowdhury, Mintu; Biswas, Haimanti; Silori, Saumya; Sharma, Diksha
- Abstract
The Arabian Sea is an area of intense ocean‐atmospheric coupling that impacts its physicochemical, and biological processes. During the summer monsoon (June‐September), in the central Arabian Sea, a low‐level atmospheric jet blows parallel to the Arabian Peninsula causing open ocean upwelling in the north and downwelling in the south of the jet axis. High wind speeds are witnessed in the jet axis which advect nutrients from the Somali coast. Consequently, hydrography and physicochemical parameters show high spatial variability. In this dynamic region, phytoplankton size class distribution, directly controlled by nutrient supply, can be modulated by monsoon wind variability via upwelling, advection, and entrainment, however, has not been investigated recently. We studied phytoplankton size class related to atmospheric forcing, hydrography, and nutrient stoichiometry in August 2017 and 2018 along 64°E (11°N–21°N). Chemical taxonomy‐based analysis (CHEMTAX and manual) revealed that in the north, upwelling‐driven nutrient enrichment supported microphytoplankton, mostly diatoms contributing ∼50% to phytoplankton biomass. A stronger upwelling due to higher wind forcing in 2018 compared to 2017 resulted in an enhanced nutrient supply as well as an increased contribution of diatoms. Prymnesiophytic nanophytoplankton distribution was linked to mixed layer depths with insignificant spatial variability (20%–30%). Conversely, in the nutrient‐poor southern region, zeaxanthin and DV‐Chla containing picocyanobacteria and prochlorophytes contributed >50% to the total phytoplankton biomass and were associated with high temperatures. Likely, increasing warming and related changes in monsoon intensity might directly influence phytoplankton size classes impacting trophic transfer and carbon cycling. Plain Language Summary: The Arabian Sea, a part of the North Indian Ocean, is an area of strong ocean‐atmospheric coupling and high biological productivity. This basin provides livelihood to the surrounding countries; however, the increasing rate of sea surface temperature (SST) raises our concern about the subsequent changes in ecosystem services. During the summer monsoon, high biological productivity occurs at certain locations due to upwelling when nutrients are added to the surface by physical forcing. In this study, we have described the results from two cruises (August 2017 and 2018) along the central Arabian Sea that experiences open ocean upwelling in its northern flank and downwelling in the south during the summer monsoon. Atmospheric forcing was found to directly control the hydrography, nutrient availability, and phytoplankton size class distribution across the central Arabian Sea with a distinct interannual difference. The phytoplankton size classes (micro, nano, and picophytoplankton) constructed using the marker pigment data showed prominent spatial and interannual variability that was consistent with the microscopic study. Any future change in the strength and onset of monsoon or increase in SST may directly impact nutrient distribution that can be cascaded to the phytoplankton community, higher trophic level, and carbon export flux. Key Points: Marker pigment‐based phytoplankton community and size classes were analyzed during the summer monsoon (2017–2018) in the central Arabian SeaPhytoplankton community and size classes were mostly governed by hydrography and nutrient stoichiometry induced by monsoon wind forcingAny future change in monsoon strength could impact phytoplankton size classes and can be cascaded to trophic transfer and carbon export
- Subjects
ARABIAN Peninsula; WIND pressure; OCEAN temperature; UPWELLING (Oceanography); PHYTOPLANKTON; BIOLOGICAL productivity; MONSOONS; HYDROGRAPHY
- Publication
Journal of Geophysical Research. Oceans, 2024, Vol 129, Issue 1, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2023JC019880