Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea
Abstract Occurrence of phytoplankton bloom in the northern Arabian Sea (NAS) during the winter monsoon is perplexing. The convective mixing leads to a deeper and well-oxygenated (> 95% saturation) mixed layer. We encountered low chlorophyll conditions though the nutrient conditions were favorable...
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2021-06-01
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doaj-d19c7009b0ea47b9ad24386c679b719e2021-07-04T11:28:56ZengNature Publishing GroupScientific Reports2045-23222021-06-0111111010.1038/s41598-021-92897-3Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian SeaR. S. Lakshmi0Satya Prakash1Aneesh A. Lotliker2Sanjiba K. Baliarsingh3Alakes Samanta4Teesha Mathew5Abhisek Chatterjee6Biraja K. Sahu7T. M. Balakrishnan Nair8Indian National Centre for Ocean Information Services, Ministry of Earth Sciences, Government of IndiaIndian National Centre for Ocean Information Services, Ministry of Earth Sciences, Government of IndiaIndian National Centre for Ocean Information Services, Ministry of Earth Sciences, Government of IndiaIndian National Centre for Ocean Information Services, Ministry of Earth Sciences, Government of IndiaIndian National Centre for Ocean Information Services, Ministry of Earth Sciences, Government of IndiaIndian National Centre for Ocean Information Services, Ministry of Earth Sciences, Government of IndiaIndian National Centre for Ocean Information Services, Ministry of Earth Sciences, Government of IndiaAtal Centre for Ocean Science and Technology for Islands, National Institute of Ocean Technology, Ministry of Earth Sciences, Government of IndiaIndian National Centre for Ocean Information Services, Ministry of Earth Sciences, Government of IndiaAbstract Occurrence of phytoplankton bloom in the northern Arabian Sea (NAS) during the winter monsoon is perplexing. The convective mixing leads to a deeper and well-oxygenated (> 95% saturation) mixed layer. We encountered low chlorophyll conditions though the nutrient conditions were favorable for a bloom. The mean ratio of silicate (Si) to DIN (Dissolved Inorganic Nitrogen: nitrate + nitrite + ammonium) in the euphotic zone was 0.52 indicating a “silicate-stressed” condition for the proliferation of diatoms. Also, the euphotic depth was much shallower (~ 49 m) than the mixed layer (~ 110 m) suggesting the Sverdrup critical depth limitation in the NAS. We show that the bloom in this region initiates only when the mixed layer shoals towards the euphotic zone. Our observations further suggest that two primary factors, the stoichiometric ratio of nutrients, especially the Si/DIN ratio, in the mixed layer and re-stratification of the upper water column, govern the phytoplankton blooming in NAS during the later winter monsoon. The important finding of the present study is that the Sverdrup’s critical depth limitation gives rise to the observed low chl-a concentration in the NAS, despite having enough nutrients.https://doi.org/10.1038/s41598-021-92897-3 |
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DOAJ |
language |
English |
format |
Article |
sources |
DOAJ |
author |
R. S. Lakshmi Satya Prakash Aneesh A. Lotliker Sanjiba K. Baliarsingh Alakes Samanta Teesha Mathew Abhisek Chatterjee Biraja K. Sahu T. M. Balakrishnan Nair |
spellingShingle |
R. S. Lakshmi Satya Prakash Aneesh A. Lotliker Sanjiba K. Baliarsingh Alakes Samanta Teesha Mathew Abhisek Chatterjee Biraja K. Sahu T. M. Balakrishnan Nair Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea Scientific Reports |
author_facet |
R. S. Lakshmi Satya Prakash Aneesh A. Lotliker Sanjiba K. Baliarsingh Alakes Samanta Teesha Mathew Abhisek Chatterjee Biraja K. Sahu T. M. Balakrishnan Nair |
author_sort |
R. S. Lakshmi |
title |
Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea |
title_short |
Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea |
title_full |
Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea |
title_fullStr |
Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea |
title_full_unstemmed |
Physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the Arabian Sea |
title_sort |
physicochemical controls on the initiation of phytoplankton bloom during the winter monsoon in the arabian sea |
publisher |
Nature Publishing Group |
series |
Scientific Reports |
issn |
2045-2322 |
publishDate |
2021-06-01 |
description |
Abstract Occurrence of phytoplankton bloom in the northern Arabian Sea (NAS) during the winter monsoon is perplexing. The convective mixing leads to a deeper and well-oxygenated (> 95% saturation) mixed layer. We encountered low chlorophyll conditions though the nutrient conditions were favorable for a bloom. The mean ratio of silicate (Si) to DIN (Dissolved Inorganic Nitrogen: nitrate + nitrite + ammonium) in the euphotic zone was 0.52 indicating a “silicate-stressed” condition for the proliferation of diatoms. Also, the euphotic depth was much shallower (~ 49 m) than the mixed layer (~ 110 m) suggesting the Sverdrup critical depth limitation in the NAS. We show that the bloom in this region initiates only when the mixed layer shoals towards the euphotic zone. Our observations further suggest that two primary factors, the stoichiometric ratio of nutrients, especially the Si/DIN ratio, in the mixed layer and re-stratification of the upper water column, govern the phytoplankton blooming in NAS during the later winter monsoon. The important finding of the present study is that the Sverdrup’s critical depth limitation gives rise to the observed low chl-a concentration in the NAS, despite having enough nutrients. |
url |
https://doi.org/10.1038/s41598-021-92897-3 |
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