KOSMOS 2021 Gran Canaria mesocosm study on ocean alkalinity enhancement: phytoplankton metabolic rates

• Main Authors: Marín-Samper, Laura, Arístegui, Javier, Hernández-Hernández, Nauzet, Ortiz Cortes, Joaquin, Archer, Stephen, Ludwig, Andrea, Riebesell, Ulf
• Format: Dataset
• Language: English
• Published: PANGAEA 2024
• Subjects: 14C-DOC; 14C-POC; 14C uptake; AQUACOSM; Canarias Sea; Chlorophyll a; total; chlorophyll-a concentration; Chlorophyll a microplankton; Chlorophyll a nanoplankton; Chlorophyll a picoplankton; Day of experiment; Depth; water; experiment; bottom/maximum; top/minimum; Event label; Extracellular release; Field experiment; flow cytometry; Gross community production/respiration rate; oxygen; ratio; Gross community production of oxygen; Identification; KOSMOS_2021; KOSMOS_2021_Mesocosm-M1; KOSMOS_2021_Mesocosm-M2; KOSMOS_2021_Mesocosm-M3; KOSMOS_2021_Mesocosm-M4; KOSMOS_2021_Mesocosm-M5; KOSMOS_2021_Mesocosm-M6; KOSMOS_2021_Mesocosm-M7; KOSMOS_2021_Mesocosm-M8; KOSMOS_2021_Mesocosm-M9; KOSMOS Gran Canaria; MESO; mesocosm experiment; Mesocosm label; Nanoeukaryotes; Net community production of oxygen; Network of Leading European AQUAtic MesoCOSM Facilities Connecting Mountains to Oceans from the Arctic to the Mediterranean; Ocean-based Negative Emission Technologies; OceanNETs; Arctic; Ocean acidification; Phytoplankton
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.964537; https://doi.org/10.1594/PANGAEA.964537

Ocean Alkalinity Enhancement (OAE) could augment long-term carbon storage and mitigate ocean acidification by increasing the bicarbonate ion concentration in ocean water. However, the side effects and/or potential co-benefits of OAE on natural planktonic communities remain poorly understood. To address this knowledge gap, 9 mesocosms were deployed in the oligotrophic waters of Gran Canaria, from September 14th to October 16th, 2021. A CO2-equilibrated Total Alkalinity (TA) gradient was employed in increments of 300 µmol·L-1, ranging from ~2400 to ~4800 µmol·L-1. The carbonate chemistry conditions in terms of TA and Dissolved Inorganic Carbon (DIC), which were then used to calculate pCO2 and pH, and the nitrate+nitrite, phosphate and silicate concentrations were measured every two days over the course of the 33-day experiment alongside the following biotic parameters. Net Community Production (NCP), Gross Production (GP), Community Respiration (CR) rates, as well as the metabolic balance (GP:CR), were monitored every two days through oxygen production and consumption using the winkler method. Fractionated 14C uptake and chlorophyll a were also determined every four days although, initially, the total PO14C and DO14C production were also measured every 4 days, in between, up to day 13. Finally, flow cytometry was also carried out every two days and synecococcus, picoeukaryote and nanophytoplankton abundances were obtained. No damaging effect of CO2-equilibrated OAE in the range applied here, on phytoplankton primary production, community metabolism and composition could be inferred from our results. In fact, a potential co-benefit to OAE was observed in the form of the positive curvilinear response to the DIC gradient up to the ∆TA1800 treatment. Further experimental research at this scale is key to gain a better understanding of the short and long-term effects of OAE on planktonic communities.