Preprints
https://doi.org/10.5194/egusphere-2024-1776
https://doi.org/10.5194/egusphere-2024-1776
20 Jun 2024
 | 20 Jun 2024
Status: this preprint is open for discussion.

Responses of microbial metabolic rates to non-equilibrated silicate vs calcium-based ocean alkalinity enhancement

Laura Marin-Samper, Javier Arístegui, Nauzet Hernández-Hernández, and Ulf Riebesell

Abstract. This study contributes to the inaugural exploration of non-equilibrated Ocean Alkalinity Enhancement (OAE). The manipulation of Total Alkalinity (TA), involving silicate and calcium-based ∆TA gradients ranging from 0 to 600 µmol · L-1, was conducted without prior CO2 sequestration, under natural conditions and at a mesocosm scale (~60 m3). The resulting impact included an increase in pH and a decrease in pCO2, sustained across the experiment, as full natural equilibration via sea-gas exchange did not occur. Implemented in a neritic system under post-bloom conditions, a midway mixing event was simulated. Following an inorganic nutrient addition, discernible delays in bloom formation, as indicated by the Gross Production (GP) and Net Community Production (NCP) rates, as well as by the chlorophyll-a (Chla) concentrations, in relation to the ∆TA gradient, were observed. Notably, the delay was more pronounced for the calcium treatment set compared to the silicate one, where low TA treatments exhibited earlier responses than high TA ones. This delay is likely attributed to the previously documented, species-specific negative relationships between high pH/lowCO2 levels and phytoplankton growth rates. This study underscores the need for further investigation into the implications of this response pattern in terms of trophic transfer and seasonal suitability. Further, it is anticipated that a wider delay in bloom formation would be evident with a larger non equilibrated TA gradient. Thus, highlighting the importance of exploring variations in TA limits for a comprehensive understanding of the OAE’s impacts.

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Laura Marin-Samper, Javier Arístegui, Nauzet Hernández-Hernández, and Ulf Riebesell

Status: open (until 01 Aug 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on egusphere-2024-1776', Steve Rackley, 22 Jun 2024 reply
    • AC1: 'Reply on CC1', Laura Marín-Samper, 28 Jun 2024 reply
  • RC1: 'Comment on egusphere-2024-1776', Anonymous Referee #1, 08 Jul 2024 reply
    • AC2: 'Reply on RC1', Laura Marín-Samper, 11 Jul 2024 reply
  • RC2: 'Comment on egusphere-2024-1776', Anonymous Referee #2, 22 Jul 2024 reply
Laura Marin-Samper, Javier Arístegui, Nauzet Hernández-Hernández, and Ulf Riebesell
Laura Marin-Samper, Javier Arístegui, Nauzet Hernández-Hernández, and Ulf Riebesell

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Short summary
This study exposed a natural community to two non-CO2 equilibrated ocean alkalinity enhancement (OAE) deployments using different minerals. Adding alkalinity in this manner decreases dissolved CO2, essential for photosynthesis. While photosynthesis was not suppressed, bloom formation was delayed, potentially impacting marine food webs. The study emphasizes the need for further research on OAE without prior equilibration and its ecological implications