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Historical water chemistry monitoring records from multiple stations between 1959 and 2017

Long-term water-chemistry measurements from multiple Elbe River monitoring stations establish a baseline for carbonate-system variability and were used to assess the alkalinity transport potential. The dataset from 1959 to 1977 was digitized from handwritten notes provided by Dr. Mewius (Kempe 1982). The water chemistry data from 1984 to 2017 (e.g., pH, water temperature, and major ions) was obtained from the Fachinformationssystem (FIS) der FGG Elbe (data source: www.fgg-elbe.de, accessed on 2021-02-26).To generate a single river chemistry time series, data from (Zollenspieker (Strom-km 598,7), Geesthacht (Strom-km 585,9), Schnackenburg (Strom-km 474,5), Boizenburg (Strom-km 559,0), Doemitz (Strom-km 505,0), and Hamburg Waterworks (Strom-km ~623,1) were used. Saturation state of calcite and aragonite were calculated using phreeqpython, a Python wrapper of the PhreeqC engine (Vitens 2021) with pH, water temperature, total alkalinity, and major ions as major input, and phreeqc.dat as database for the thermodynamic data (Parkhurst and Appelo 2013).

Schwerpunktprogramm (SPP) 1689: Climate Engineering: Risiken, Herausforderungen, Möglichkeiten?, Modellvergleichende Analyse von CDR Methoden (CDR-MIA)

Die voranschreitenden, anthropogenen CO2-Emissionen verändern das Klima mit bedrohlichen, weit reichenden und irreversiblen Auswirkungen. Daher steigt das Interesse an sogenannten Carbon Dioxide Removal (CDR) Maßnahmen, um so zusätzlich zur Migration und Adaption, die Möglichkeit negativer Emissionen zu eröffnen. Die potenziellen positiven und negativen Auswirkungen durch CDR sind jedoch nicht ausreichend verstanden und quantifiziert. Das Hauptziel des Projektes ist die Analyse der Experimente aus der 1. Phase des Carbon Dioxide Removal Model Intercomparison Projects (CDR-MIP), um das Potenzial und die Risiken großskaliger CDR Methoden besser bewerten zu können. CDR-MIP ist eine neu gegründete Initiative, die eine Reihe von Erdsystemmodellen zusammenbringt, um CDR in einem einheitlichen Rahmen zu untersuchen. Die erste Projektphase, bestehend aus idealisierten Experimenten zu CO2 Entnahme aus der Atmosphäre, Aufforstung und Ozean-Alkalinisierung. Sie dient der Beantwortung folgender Kernfragen a) Reversibilität der Klimaänderung (z.B. zu heutige oder vorindustrielle CO2 Konzentration in der Atmosphäre) und b) potenzielle Wirksamkeit, Feedbacks, zeitlicher Rahmen und Nebenwirkungen unterschiedlicher CDR Maßnahmen. Die bisherige Arbeit diente der Entwicklung der Struktur des CDR-MIPs und weltweit haben sich einige Modellgruppen dazu bereit erklärt die entsprechenden Simulationen durchzuführen. Das Projekt beruht bislang auf freiwilliger Basis. Das macht eine schnelle Verarbeitung der Ergebnisse unwahrscheinlich. Folglich wird eine gezielte Förderung benötigt, um eine zeitnahe Analyse der Ergebnisse und deren öffentlichen Verbreitung zu gewährleisten. Die Analyseergebnisse sollen darüber hinaus die angenommenen Effektivität von CDR Technologien in den 'Integrated Assessment Model (IAM) - generierten Shared Socioeconomic Pathway (SSP) Szenarien informieren, welche die Forschung und Bewertung des Klimawandels unterstützen. Bislang werden bei in den IAM Simulation mit CDR keine Feedbacks des Kohlenstoffkreislaufes berücksichtigt. Eine Wissenslücke die wir schließen wollen. Wir schlagen vor die Ergebnisse aus CDR-MIP zu nutzen, um eine auf den Feedbacks im Kohlenstoffkreislaufes basierende Discount-Rate zu berechnen, die dann für die Kalibrierung der SSP Szenarien und erneuter Modellläufe in einem IAM genutzt werden kann. Zusätzlich werden neue Experimente erstellt und durchgeführt, um die Reaktion des Klimasystems auf die gleichzeitige Anwendung mehrerer CDR Methoden analysieren zu können. Die Kombination der Methoden basiert auf den gegebenen CDR-MIP Experimenten und beinhaltet z.B. eine Kombination von Aufforstung und der Ozean-Alkalinisierung. Anschließende Analysen ermöglichen den Vergleich der Wirksamkeit und Risiken kombinierter und einzelner CDR Methoden. Die Projektergebnisse würden eine umfassende Bewertung von CDR bieten, die allen Projekten innerhalb des SPP verfügbar gemacht und mit den Projektpartnern iterativ diskutiert werden.

Particulate fucoidan concentrations during 24-days of incubations in mesocosm experiments with brown algae

Six mesocosm experiments with specimens of Fucales or Laminariales were conducted across six georegions (3 mesocosms with brown algae, 3 mesocosms without brown algae). Incubations lasted 24 days, followed by a year-long monitoring of incubation water. During the first 12 days, brown algae were maintained in mesocosms adjacent to control mesocosms, with 1 L of water sampled every second day. Half of the mesocosm water was replaced with fresh seawater after each sampling. Environmental conditions and primary productivity of specimens was recorded during the incubation. After 12 days, specimens were removed and incubation continued for another 12 days, maintaing the same sampling routine. At the end of the 24 day- incubation period, long-term monitoring was set-up with 6-10L of incubation water in two different conditions: one exposed to a controlled light cycle at 20°C, the second set in darkness at 4°C with added nutrients (40 µM NO3- and 3µM PO43-). Additional water samples were collected along transects extending from near-shore brown algae poplulations. Water samples were filtered over pre-combusted GFF filters (450°C, 4.5h), and both the filtrate and filters were analysed for dissolved organic carbon (DOC), particulate organic carbon (POC). Fucoidan was quantified in dissolved (>1kDa) fraction and surface active fraction (SAF) (> 1kDa and negative charged fraction purified with anion exchange chromatography) fractions through monosaccharide quantification after acid-hydrolysis (100°C, 24h) using HPAEC-PAD, according to Engel and Händel, 2011. Intact polysaccharides were detected using structure-sensitive monoclonal antibodies (Torode et al., 2015; Vidal-Melgosa et al., 2021). Microbial cells were quantified using DAPI-cell staining and counting. Semi-quantitative measurements of particulate fucoidan were performed via acid hydrolysis of GFF filter pieces, followed by monosaccharide analysis via HPAEC-PAD. Sedimented particles to bottom of mesocosms were scooped out on day 24 for monosaccharide analysis and BAM1 antibody binding specific to fucoidan.

Element concentrations from two benthic chambers and the ambient bottom water during an in-situ incubation experiment in July 2025

The dataset contains major and trace element concentrations measured by inductively coupled plasma optical emission spectrometry (ICP-OES) from water samples collected during a 16-day in-situ incubation experiment in the Baltic Sea (2025-07-12 to 2025-07-29). Samples were collected using an automated glass-syringe sampler deployed within two benthic chambers of a Biogeochemical Observatory (BIGO, Sommer et al., 2009) at 54° 34.432' N, 10° 10.776' E, at 22 m water depth. In one chamber, 29 g of fine calcite powder were added to the bottom water to assess the potential of enhanced benthic calcite weathering as an ocean alkalinity enhancement (OAE) strategy. Seven samples per chamber and from the ambient bottom water were analyzed to trace elemental changes associated with calcite dissolution.

Nutrient concentrations from two benthic chambers and the ambient bottom water during an in-situ incubation experiment in July 2025

The dataset contains dissolved nutrient concentrations from water samples collected during a 16-day in-situ incubation experiment in the Baltic Sea (2025-07-12 to 2025-07-29). Samples were collected using an automated glass-syringe sampler deployed within two benthic chambers of a Biogeochemical Observatory (BIGO, Sommer et al., 2009) at 54° 34.432' N, 10° 10.776' E, at 22 m water depth. In one chamber, 29 g of fine calcite powder were added to the bottom water as part of an enhanced benthic calcite weathering experiment. Seven samples per chamber and from the ambient bottom water were analyzed to assess potential nutrient fluxes associated with the calcite addition and benthic biogeochemical processes.

Alkalinity concentrations from two benthic chambers and the ambient bottom water during an in-situ incubation experiment in July 2025

The dataset contains total alkalinity measurements from water samples collected during a 16-day in-situ incubation experiment in the Baltic Sea (2025-07-12 to 2025-07-29). Samples were collected using an automated glass-syringe sampler deployed within two benthic chambers of a Biogeochemical Observatory (BIGO, Sommer et al., 2009) at 54° 34.432' N, 10° 10.776' E, at 22 m water depth. In one chamber, 29 g of fine calcite powder were added to the bottom water. Seven samples per chamber and from the ambient bottom water were taken to monitor alkalinity changes resulting from calcite dissolution, providing a direct measure of the ocean alkalinity enhancement (OAE)

KOSMOS 2023 Helgoland mesocosm study on ocean alkalinity enhancement: sediment trap particle flux data and water column biogeochemistry

The data presented herein originates from a mesocosm study conducted as part of the BMBF CDRmare, Retake project (grant agreement no. 03F0895A), aimed at investigating the ecological ramifications of ocean alkalinity enhancement (OAE). Twelve mesocosms were deployed in Helgoland South Harbor, Germany, and systematically sampled using integrated water samplers over the period spanning from March 12th to April 20th, 2023. Six alkalinity levels under two dilution scenarios were established to differentiate between localized and uniform OAE additions. Alkalinity was increased stepwise to ΔTAmax = 1250 μmol kg-1 (250 μmol TA kg-1 increments) using sodium hydroxide (NaOH) with calcium chloride (CaCl2) to simulate cation release during calcium-based mineral dissolution, causing strong carbonate chemistry perturbations (e.g., pHT > 9.25). The dataset encompasses a spectrum of sediment trap particle flux data, water column biogeochemistry including pigment variables, inorganic nutrients, carbonate chemistry parameters. The study and data set offer insights into impacts of alkalinity enhancement on marine ecosystems and their associated biogeochemistry.

Processed flow discharge data from the Neu Darchau gauging station between 1969 and 2019

The dataset includes processed flow discharge data from Neu Darchau gauging station (Elbe-km 536.4) that provided hydrological information for calculating alkalinity transport potential. The monthly sums were calculated from daily mean discharge measurements from Neu Darchau (station number: 6340110) available from the Global Runoff Data Centre (https://grdc.bafg.de/).

Bottom water chemistry during in-situ incubation experiments on enhanced benthic calcite weathering in July 2025

The data was produced during a 16 day in-situ incubation experiment in the Baltic Sea. In order to assess the potential for enhanced benthic calcite weathering as a ocean alkalinisation and thus negative emissions strategy, a Biogeochemical Observatory (BIGO, Sommer et al., 2009) was deployed at 54° 34.432 N, 10° 10.776 E, at 22 m water depth between 2025-07-12 and 2025-07-29. The BIGO is equipped with two benthic chambers that were lowerd to the sea floor. In chamber two, 29 g of fine calcite powder were added to the bottom water. 7 Samples were taken via an automatted glassyringe sampler from each chamber and the ambient bottom water.

Carbonate chemistry from laboratory incubation experiments using water samples from the Elbe conducted in 2023

This dataset comprises key carbonate chemistry parameters measured and calculated in incubation experiments under different experimental conditions. pH, water temperature, and salinity were measured with a WTW multimeter (MultiLine® Multi 3630 IDS). Total alkalinity was determined by open-cell titration with an 888 Titrando (Metrohm). Saturation state of calcite and aragonite were calculated using phreeqpython, a Python wrapper of the PhreeqC engine (Vitens 2021) with pH, water temperature, total alkalinity, and major ions as major input, and phreeqc.dat as database for the thermodynamic data (Parkhurst and Appelo 2013). As the original Elbe water was supersaturated with carbon dioxide (CO2) with respect to the atmosphere, its partial pressure of CO2 (pCO2) level decreased during the incubation period with open flasks, which caused an adjustment of calcite saturation state (ΩC) for ambient air conditions. To adapt for the impact of pCO2 variations during the experiment, saturation state of calcite and aragonite was calculated assuming an equilibrium with an atmospheric pCO2 of 415 ppm (normalized ΩC and normalized aragonite sautration state ΩA). Since ion concentrations were measured for only a small number of samples, the ion concentrations of the remaining samples were reconstructed using stoichiometry based on the initial solution composition and total alkalinity. The concentrations of conservative ions (Na+, K+, Cl-, SO42-) were assumed remain constant, while ions related to carbonate precipitation (Ca2+, Mg2+) were calculated based on changes in measured alkalinity (see Figure 5 of the associated paper). Detailed analysis and calculation procedures are described in the Method section of the associated paper.

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