Early winter pico-nanophytoplankton bloom in the Bonifacio cyclonic gyre after an extreme flooding
Abstract
Phytoplankton functional groups distribution and dynamics builds nutrients and carbon energy pathways in the ocean. They respond fast to changes in their environment, and the understanding of their dynamics relies on regular sampling to resolve daily to weekly scales. The Bonifacio Cyclonic Gyre (BCG) is an area prone to intermittent phytoplankton blooms triggered by westerly winds, and close to coastal areas capable of fuelling open waters with nutrients from flooding. To study phytoplankton evolution in this dynamical area, the distribution of phytoplankton functional groups in the surface waters of the western Mediterranean Sea was investigated semi-continuously (30 min) using an automated CytoSense flow cytometer coupled to a FerryBox, onboard the ferry Le Carthage, between October 20, 2016 and January 12, 2017 and along the route from Tunis (Tunisia) to Genova (Italy). The BCG signature was identified by its surface temperature anomaly and evidenced significant higher abundances of the RedPicoProk, the RedPico, the HsNano and the OraNano over the full sampling period, except for the RedNano1, the RedNano2 and the OraPicoProk. Their estimated chlorophyll a concentration per group were higher within the gyre than outside, but did not affect the carbon/chlorophyll a ratio. A high carbon/chlorophyll a ratio can indicate recently uplifted cells that are not yet adapted to high light conditions. In this case, the observed ratios suggest that the cells were not recently upwelled, but instead had time to adjust their photophysiology to surface conditions. During 19-20 December, extreme overflow occurred over Corsica and Sardinia, considered as one of the highest rainfall events of the past 20 years. The runoff was evidenced by the low salinity intrusion that lasted several days after the storm. After the runoff and within the Bonifacio gyre region, biomasses of all groups increased and remained high until the end of the sampling, except for the RedPico. The runoff triggered an early bloom end of December that persisted for several weeks, being trapped and repleted by the uplift of the isopycnals from the BCG. Regular observation of the sea surface temperature and salinity together with phytoplankton community structure provides essential insights into the fast response of phytoplankton communities to an extreme event at unprecedented resolution.
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BibTeX
@article{thyssen2026early,
title = {{Early winter pico-nanophytoplankton bloom in the Bonifacio cyclonic gyre after an extreme flooding}},
author = {Melilotus Thyssen and Pierre Marrec and Isabelle Taupier-Letage and Sana Ben Ismail and Mohamed Anis Ben Ismail and Michel Denis and Soumaya Lahbib and Nagib Bhairy and Malika Bel Hassen and Ismail Boudriga and Cherif Sammari},
journal = {Progress in Oceanography},
year = {2026},
month = sep,
doi = {10.1016/j.pocean.2026.103790},
url = {https://hal.sorbonne-universite.fr/hal-05763039v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Early winter pico-nanophytoplankton bloom in the Bonifacio cyclonic gyre after an extreme flooding
AU - Melilotus Thyssen
AU - Pierre Marrec
AU - Isabelle Taupier-Letage
AU - Sana Ben Ismail
AU - Mohamed Anis Ben Ismail
AU - Michel Denis
AU - Soumaya Lahbib
AU - Nagib Bhairy
AU - Malika Bel Hassen
AU - Ismail Boudriga
AU - Cherif Sammari
PY - 2026
DA - 2026/09/24
JO - Progress in Oceanography
DO - 10.1016/j.pocean.2026.103790
UR - https://hal.sorbonne-universite.fr/hal-05763039v1
AB - Phytoplankton functional groups distribution and dynamics builds nutrients and carbon energy pathways in the ocean. They respond fast to changes in their environment, and the understanding of their dynamics relies on regular sampling to resolve daily to weekly scales. The Bonifacio Cyclonic Gyre (BCG) is an area prone to intermittent phytoplankton blooms triggered by westerly winds, and close to coastal areas capable of fuelling open waters with nutrients from flooding. To study phytoplankton evolution in this dynamical area, the distribution of phytoplankton functional groups in the surface waters of the western Mediterranean Sea was investigated semi-continuously (30 min) using an automated CytoSense flow cytometer coupled to a FerryBox, onboard the ferry Le Carthage, between October 20, 2016 and January 12, 2017 and along the route from Tunis (Tunisia) to Genova (Italy). The BCG signature was identified by its surface temperature anomaly and evidenced significant higher abundances of the RedPicoProk, the RedPico, the HsNano and the OraNano over the full sampling period, except for the RedNano1, the RedNano2 and the OraPicoProk. Their estimated chlorophyll a concentration per group were higher within the gyre than outside, but did not affect the carbon/chlorophyll a ratio. A high carbon/chlorophyll a ratio can indicate recently uplifted cells that are not yet adapted to high light conditions. In this case, the observed ratios suggest that the cells were not recently upwelled, but instead had time to adjust their photophysiology to surface conditions. During 19-20 December, extreme overflow occurred over Corsica and Sardinia, considered as one of the highest rainfall events of the past 20 years. The runoff was evidenced by the low salinity intrusion that lasted several days after the storm. After the runoff and within the Bonifacio gyre region, biomasses of all groups increased and remained high until the end of the sampling, except for the RedPico. The runoff triggered an early bloom end of December that persisted for several weeks, being trapped and repleted by the uplift of the isopycnals from the BCG. Regular observation of the sea surface temperature and salinity together with phytoplankton community structure provides essential insights into the fast response of phytoplankton communities to an extreme event at unprecedented resolution.
SN - 0079-6611
ER -