https://doi.pangaea.de/10.1594/PANGAEA.996213Marín-Samper, LauraLauraMarín-Samper0000-0002-6825-0992Arístegui, JavierJavierArístegui0000-0002-7526-7741Faucher, GiuliaGiuliaFaucher0000-0001-8930-477XGEOMAR - Helmholtz Centre for Ocean Research KielKittu, LeilaLeilaKittu0000-0002-3986-8179GEOMAR - Helmholtz Centre for Ocean Research KielBoersma, MaartenMaartenBoersma0000-0003-1010-026XAlfred Wegener Institute for Polar and Marine Research, Bremerhaven (1986-2013)Riebesell, UlfUlfRiebesell0000-0002-9442-452XGEOMAR - Helmholtz Centre for Ocean Research KielPANGAEA2026metabolic ratesocean alkalinity enhancementOcean Alkalinity Enhancement (OAE)PhytoplanktonPrimary productionType of studyEvent labelDay of experimentDATE/TIMEIdentification numberTreatment: dilution typeTreatment: alkalinity, totalTreatmentSample code/labelRespiration rate, oxygen, communityNet community production of oxygenGross community production of oxygenBalanceDepth, descriptionMesocosm experimentKOSMOS_2023DAM CDRmare - RETAKE: CO2 removal by alkalinity enhancement: potential, benefits and risks (RETAKE)Ocean Alk-Align (OceanAlkAlign)Ocean-based Negative Emission Technologies (OceanNETs)Research Mission of the German Marine Research Alliance (DAM): Marine carbon sinks in decarbonisation pathways (CDRmare)2023-03-14T00:00:00/2023-04-17T00:00:00Dataset2798 data pointstext/tab-separated-valuesCreative Commons Attribution 4.0 InternationalData access is restricted (moratorium, sensitive data, license constraints)Ocean alkalinity enhancement (OAE) is a marine carbon dioxide removal (mCDR) approach that can also mitigate ocean acidification. However, its biological impacts are expected to depend on the magnitude, timing, and dilution of alkalinity additions. To investigate these factors, a mesocosm experiment simulated hydrated lime additions using two six-level alkalinity gradients (up to ΔTA 1250 µmol kg⁻¹): one with immediate full-column mixing and another with mixing delayed by two days. These treatments simulated rapid (e.g. from a moving vessel in open ocean) and slow (e .g. point source or land-based applications in poorly mixed environments)dilution scenarios, representing different hydrodynamic conditions that may occur following real-world alkalinity additions. Gross production (GP), net community production (NCP) and community respiration (CR), determined from in vitro oxygen production and consumption, together with chlorophyll a, were monitored over a 35-day period. Spring bloom initiation was delayed non-linearly at low fCO₂, with reduced absolute and biomass-normalized production occurring in treatments exposed to fCO₂ below ~70 and 30 µatm respectively. These findings indicate that phytoplankton communities may be generally resilient to realistic OAE scenarios while helping to define ecologically relevant fCO₂ thresholds for safe OAE deployment.7.90000000000000154.183300000000024HelgolandFederal Ministry of Education and Researchhttps://doi.org/10.13039/50110000234703F0895ADAM CDRmare - RETAKE, GEOMARHorizon 2020 of the European Commissionhttps://doi.org/10.13039/501100007601731065Network of Leading European AQUAtic MesoCOSM Facilities Connecting Mountains to Oceans from the Arctic to the MediterraneanHorizon 2020 of the European Commissionhttps://doi.org/10.13039/501100007601869357OceanNETs: Ocean-based Negative Emission Technologies