Preprints
https://doi.org/10.21203/rs.3.rs-4021986/v2
https://doi.org/10.21203/rs.3.rs-4021986/v2
27 Aug 2025
 | 27 Aug 2025
Status: this preprint is open for discussion and under review for Ocean Science (OS).

Submesoscale horizontal stirring enhances seasonal enrichment of low-chlorophyll surface waters in the Eastern Mediterranean

Yotam Fadida, Vicky Verma, Roy Barkan, Eli Biton, Aviv Solodoch, and Yoav Lehahn

Abstract. The large seasonal increase in marine photosynthetic organisms – i.e., phytoplankton bloom – is a ubiquitous oceanic phenomenon that contributes to the removal of carbon dioxide from the atmosphere and that supports the growth and development of larger organisms throughout the marine ecosystem. The underlying mechanisms controlling the intensity and timing of these blooms have been proposed to be dominated by vertical transport and mixing processes that are enhanced at front and filament circulation patterns, commonly known as submesoscale currents. Here we show that the winter blooms characterizing the ultra oligotrophic waters of the Eastern Mediterranean Sea, which are manifested by a seasonal increase in satellite-derived levels of surface chlorophyll, are intensified by enhanced horizontal stirring induced by the submesoscale currents. Using ocean color remote sensing data and high-resolution numerical simulations, we demonstrate that the intensification of submesoscale currents in winter efficiently connect the coastal waters and the ultra-oligotrophic waters in the sea interior, thereby enriching the latter with chlorophyll-rich water. A comparison of climatological chlorophyll time series indicates that this submesoscale horizontal stirring mechanism is responsible for ∼ 24 % of the seasonal surface chlorophyll increase in the region. These results shed new light on the processes governing phytoplankton bloom intensity and emphasize the important role of submesoscale horizontal stirring in regulating the marine ecosystem.

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Yotam Fadida, Vicky Verma, Roy Barkan, Eli Biton, Aviv Solodoch, and Yoav Lehahn

Status: open (until 06 Nov 2025)

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  • RC1: 'Comment on egusphere-2025-3240', Alexandra Jones-Kellett, 23 Sep 2025 reply
Yotam Fadida, Vicky Verma, Roy Barkan, Eli Biton, Aviv Solodoch, and Yoav Lehahn
Yotam Fadida, Vicky Verma, Roy Barkan, Eli Biton, Aviv Solodoch, and Yoav Lehahn

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Short summary
In the ultra-oligotrophic Eastern Mediterranean, winter phytoplankton blooms are enhanced by submesoscale horizontal stirring. Satellite data and simulations show these currents transport chlorophyll-rich coastal waters offshore, contributing ~24 % to the seasonal surface chlorophyll increase. This highlights the key role of horizontal processes in bloom dynamics and ecosystem regulation.
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