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Petric, Svetlana; Faucher, Giulia; Riebesell, Ulf (2026): KOSMOS 2023 Helgoland mesocosm study on ocean alkalinity enhancement: phytoplankton and microzooplankton abundance and biomass data [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.996209 (DOI registration in progress)

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Published: 2026-07-31

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Abstract:
This dataset contains species-resolved phytoplankton and microzooplankton abundance and biomass data from the KOSMOS 2023 Helgoland mesocosm experiment conducted in the coastal waters off Helgoland Island in the North Sea, Germany. The experiment investigated the effects of Ocean Alkalinity Enhancement (OAE) on plankton communities during the development of a natural spring bloom. Six mesocosms (~6 m³) were subjected to an immediate dilution OAE scenario, establishing an alkalinity enhancement gradient ranging from ΔTA 0 to 1250 µmol kg⁻¹ in increments of 250 µmol kg⁻¹ through calcium-based alkalinity addition. The dataset includes taxonomically resolved phytoplankton and microzooplankton abundance (cells mL⁻¹), carbon biomass (µg C L⁻¹), functional group classifications, and World Register of Marine Species (WoRMS) taxonomic identifiers. Associated carbonate chemistry measurements, including total alkalinity (TA), dissolved inorganic carbon (DIC), pH, fugacity of carbon dioxide (fCO₂), salinity, temperature, and calculated ΔTA values are provided for each sampling event.
Keyword(s):
Abundance; Biomass; ciliates; community composition; Community composition and diversity; diatoms; Dinoflagellates; enhancement; Field experiment; Helgoland; Marine Carbon Dioxide Removal (mCDR); mesocosm; mesocosm experiment; mesocosm study; microscopy; microzooplankton; North Sea; ocean alkalinity enhancement; Ocean Alkalinity Enhancement (OAE); Phytoplankton; Phytoplankton biomass; Phytoplankton bloom; spring bloom
Project(s):
DAM CDRmare - RETAKE: CO2 removal by alkalinity enhancement: potential, benefits and risks (RETAKE)
Ocean Alk-Align (OceanAlkAlign)
Research Mission of the German Marine Research Alliance (DAM): Marine carbon sinks in decarbonisation pathways (CDRmare)
Funding:
Federal Ministry of Education and Research (BMBF), grant/award no. 03F0895A: DAM CDRmare - RETAKE, GEOMAR
Coverage:
Latitude: 54.183300 * Longitude: 7.900000
Date/Time Start: 2023-03-16T00:00:00 * Date/Time End: 2023-04-21T00:00:00
Event(s):
KOSMOS_2023_Mesocosm-M1 * Latitude: 54.183300 * Longitude: 7.900000 * Date/Time Start: 2023-03-14T00:00:00 * Date/Time End: 2023-04-21T00:00:00 * Location: Helgoland * Campaign: KOSMOS_2023 (KOSMOS Helgoland) * Method/Device: Mesocosm experiment (MESO)
KOSMOS_2023_Mesocosm-M3 * Latitude: 54.183300 * Longitude: 7.900000 * Date/Time Start: 2023-03-14T00:00:00 * Date/Time End: 2023-04-21T00:00:00 * Location: Helgoland * Campaign: KOSMOS_2023 (KOSMOS Helgoland) * Method/Device: Mesocosm experiment (MESO)
KOSMOS_2023_Mesocosm-M5 * Latitude: 54.183300 * Longitude: 7.900000 * Date/Time Start: 2023-03-14T00:00:00 * Date/Time End: 2023-04-21T00:00:00 * Location: Helgoland * Campaign: KOSMOS_2023 (KOSMOS Helgoland) * Method/Device: Mesocosm experiment (MESO)
Parameter(s):
#NameShort NameUnitPrincipal InvestigatorMethod/DeviceComment
1Type of studyStudy typePetric, Svetlana
2Event labelEventPetric, Svetlana
3Sample code/labelSample labelPetric, Svetlana
4DATE/TIMEDate/TimePetric, SvetlanaGeocode
5Day of experimentDOEdayPetric, Svetlana
6Treatment: dilution typeT:dilutionPetric, SvetlanaDilution type
7TreatmentTreatPetric, SvetlanaTargeted alkalinity level and mesocosm
8Treatment: alkalinity, totalT:ATµmol/kgPetric, SvetlanaTreatment level
9Alkalinity, totalATµmol/kgPetric, SvetlanaTitration device, Metrohm, 862 Compact Titrosampler [with built-in PT1000 temperature sensor]
10Carbon, inorganic, dissolvedDICµmol/kgPetric, SvetlanaAutomated Infra Red Inorganic Carbon Analyzer (AIRICA), MARIANDA; coupled with Differential infrared gas analyzer, LI-COR Biosciences, LI-7000
11pHpHPetric, SvetlanaCalculated using the CO2sys_v3.0 software (Pierrot et al. 2021)
12Fugacity of carbon dioxide in seawaterfCO2ppmvPetric, SvetlanaCalculated using the CO2sys_v3.0 software (Pierrot et al. 2021)
13SalinitySalPetric, SvetlanaCTD 60M multiparameter probe (Sea & Sun Technology GmbH, Germany)
14Temperature, waterTemp°CPetric, SvetlanaCTD 60M multiparameter probe (Sea & Sun Technology GmbH, Germany)
15SpeciesSpeciesPetric, SvetlanaReference in WoRMS (WoRMS)
16Species, unique identificationSpecies UIDPetric, SvetlanaReference in WoRMS (WoRMS)
17Functional groupFunctional grPetric, SvetlanaCalculated
18CellCell#/mlPetric, SvetlanaMicroscopyUtermöhl microscopy
19Biomass as carbon per volumeBiom Cµg/lPetric, SvetlanaMicroscopyUtermöhl microscopy
License:
Creative Commons Attribution 4.0 International (CC-BY-4.0) (License comes into effect after moratorium ends)
Status:
Curation Level: Enhanced curation (CurationLevelC)
Size:
58140 data points

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