Preprints
https://doi.org/10.5194/egusphere-2024-3302
https://doi.org/10.5194/egusphere-2024-3302
07 Nov 2024
 | 07 Nov 2024
Status: this preprint is open for discussion.

Marine snow morphology drives sinking and attenuation in the ocean interior

Yawouvi Dodji Soviadan, Miriam Beck, Joelle Habib, Alberto Baudena, Laetitia Drago, Alexandre Accardo, Remi Laxenaire, Sabrina Speich, Peter Brandt, Rainer Kiko, and Lars Stemmann

Abstract. Simultaneous measurements of marine snow (particles larger than 600 µm) morphologies, estimates of their in situ sinking speeds and midwater attenuation in export plumes were performed for the first time using a BGC-Argo float equipped with optical and imaging sensors. The float was deployed and recovered after one year drifting in the sluggish flow regime of the Angola basin. Six consecutive chlorophyll-a and particulate matter accumulation events were recorded at the surface, each followed by an export plume of sinking aggregates. Objects larger than 600 µm were classified using machine learning recognition and clustered into four morphological categories of marine aggregates. Plankton images were validated by an expert in a few broad categories. Results show that different types of aggregates were produced and exported from the different blooms. The different morphological categories of marine snow had different sinking speeds and attenuation for similar size indicating the effect of morphology on sinking speed. However, the typical size-to-sinking relationship for two of the categories and over the larger observed size range (100 µm-few mm) was also observed, indicating the importance of size for sinking. Surprisingly, calculated in situ sinking speeds were constantly in the lower range of known values usually assessed ex situ, suggesting a methodological effect which is discussed. Moving away from purely size-based velocity relationships and incorporating these additional morphological aggregates properties will help to improve mechanistic understanding of particle sinking and provide more accurate flux estimates. When used from autonomous platforms at high frequency, they will also provide increased spatio-temporal resolution for the observation of intermittent export events naturally occurring or induced by human activities associated with marine Carbon Dioxide Removal.

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Yawouvi Dodji Soviadan, Miriam Beck, Joelle Habib, Alberto Baudena, Laetitia Drago, Alexandre Accardo, Remi Laxenaire, Sabrina Speich, Peter Brandt, Rainer Kiko, and Lars Stemmann

Status: open (until 26 Dec 2024)

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Yawouvi Dodji Soviadan, Miriam Beck, Joelle Habib, Alberto Baudena, Laetitia Drago, Alexandre Accardo, Remi Laxenaire, Sabrina Speich, Peter Brandt, Rainer Kiko, and Lars Stemmann
Yawouvi Dodji Soviadan, Miriam Beck, Joelle Habib, Alberto Baudena, Laetitia Drago, Alexandre Accardo, Remi Laxenaire, Sabrina Speich, Peter Brandt, Rainer Kiko, and Lars Stemmann

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Short summary
Key parameters representing the gravity flux in global models are the sinking speed and the vertical attenuation of the exported material. We calculate for the first time, these parameters in situ for 6 intermittent blooms followed by export events using high-resolution (3 days) time series of 0–1000 m depth profiles from imaging sensor mounted on an Argo float. We show that sinking speed depends not only on size but also on the morphology of the particles, density being an important property.