Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric carbon dioxide (CO2) levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments. These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an anoxic to hypoxic environment. The sediment cores were incubated with Baltic Sea bottom water. Eight sediment cores were positioned vertically in a rack. Since the sediment surface was slightly oxidized by the bottom water (∼125 μmol l−1 upon recovery), the cores were left plugged on the top for 13 days to settle after recovery until the sediment surface was anoxic. To achieve chemical conditions that are expected in the natural system, 500l of retrieved sea water were degassed via bubbling with pure dinitrogen gas in batches of 100 l. Afterwards, between 50 and 60 l were transferred into an evacuated gas tight bag. After the transfer, pH and total alkalinity (TA) were measured to determine the dissolved inorganic carbon (DIC) of the water. Afterwards the DIC was increased via adding pure CO2 until a CO2 partial pressure (pCO2 ) of ∼2,300–∼3,300 μatm was established mimicking conditions prevailing in Boknis Eck during summer. Stirring heads were installed on the cores. To prevent the development of oxic conditions, it was ensured that as little gas phase as possible was left in the cores. Elimination of pelagic autotrophs, heterotrophs, and suspended particles was achieved by flushing the cores with modified bottom water for 2 days with a flow rate of 1.5 mml min−1. Afterwards, a continuous throughflow of 700 μl min−1 from the reservoir of modified bottom water was applied, leading to a residence time of ∼2.1 days inside the cores. For the experimental incubations, six cores received additions of alkaline materials, three with calcite (Cal1 - Cal3) and three cores with dunite (Dun1 - Dun3), leading to three replicates per treatment. Two control cores remained untreated (C1, C2). The amount of added substrate was based on the rain rate of particulate organic carbon observed in Boknis Eck (0.5 mmol cm−2 a−). The incubation lasted for 25 days. The volume of water in each core was determined at the end of the experiment via measuring the height of the water column after removing the stirring heads. Bottom water samples were taken from the outflow of each core over a time period of several hours. Thus, samples represent the average outflow over the respective time period. Sampling intervals increased from daily during the first two weeks to every three to four days and weekly towards the end of the experiment. All samples were filtered through a 0.2 µm cellulose membrane filter and refrigerated in 25 ml ZinsserTM scintillation vials. Samples for TA were analyzed directly after sampling by titration of 1 ml of bottom water with 0.02N HCl. Titration was ended when a stable purple color appeared. During titration, the sample was degassed by continuous bubbling with nitrogen to remove any generated CO2 and H2S. The acid was standardized using an IAPSO seawater standard. Acidified sub-samples (30 μl suprapure HNO3- + 3 ml sample) were prepared for analyses of major and trace elements (Si, Na, K, Li, B, Mg, Ca, Sr, Mn, Ni and Fe) by inductively coupled plasma optical emission spectroscopy (ICP-OES, Varian 720-ES).

Enhanced benthic weathering has been proposed to serve as a efficient negative emission strategy. The precise weatherig behaviour of calcite and dunite was investigated in leng-term experiments in benthocosms. These experiments were conducted between Sept. 2022 and Sept. 2023 ashore at the Kiel Fjord. The latter are large plastic containers (~0.8 m²) that are partly filled with sediments, with constant flow-through of Baltic Sea bottom water. The sediments, obtained from Boknis Eck in the Eckernförde Bay in March 2022, were amended with calcite and dunite in triplicate (22 mol/m² equivalent) . Three additional benthocosms were left unamended to serve as controls. The used materials were obtained from Sibelco (dunite) and from the german Lime Stone Association (calcite). Samples were obtained using benthic chambers (chamber volume of 400 ml) that were placed on the sediment for three hours. Samples were taken at the beginning (_in) and at the end of the deployment (_out). All samples were filtered through a 0.2 µm cellulose membrane filter and refrigerated in 25 ml ZinsserTM scintillation vials. Samples for total alkalinity (TA) were analyzed directly after sampling by titration of 1 ml of bottom water with 0.02N HCl. Titration was ended when a stable purple color appeared. During titration, the sample was degassed by continuous bubbling with nitrogen to remove any generated CO₂. The acid was standardized using an IAPSO seawater standard.

Enhanced benthic weathering has been proposed to serve as a efficient negative emission strategy. The precise weatherig behaviour of calcite and dunite was investigated in leng-term experiments in benthocosms. These experiments were conducted between Sept. 2022 and Sept. 2023 ashore at the Kiel Fjord. The latter are large plastic containers (~0.8 m²) that are partly filled with sediments, with constant flow-through of Baltic Sea bottom water. The sediments, obtained from Boknis Eck in the Eckernförde Bay in March 2022, were amended with calcite and dunite in triplicate (22 mol/m² equivalent) . Three additional benthocosms were left unamended to serve as controls. The used materials were obtained from Sibelco (dunite) and from the german Lime Stone Association (calcite). Samples were obtained using benthic chambers (chamber volume of 400 ml) that were placed on the sediment for three hours. Samples were taken at the beginning (_in) and at the end of the deployment (_out). All samples were filtered through a 0.2 µm cellulose membrane filter and refrigerated in 25 ml ZinsserTM scintillation vials. Acidified sub-samples (30 μl suprapure HNO3- + 3 ml sample) were prepared for analyses of major and trace elements (Si, Na, K, Li, B, Mg, Ca, Sr, Mn, Ni and Fe) by inductively coupled plasma optical emission spectroscopy (ICP-OES, Varian 720-ES).

Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric carbon dioxide (CO2) levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments (January - May 2022). These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an oxic environment. The sediment cores were incubated with Baltic Sea bottom water. Eight sediment cores were placed in a rack in an upright position. The bottom water was carefully removed via suction and replaced with a known volume (1.5 l – 2.0 l) of filtered (0.2 µm) Baltic Sea bottom water in order to remove pelagic auto- and heterotrophs and suspended particles. The volume of water added depended on the height of sediment in each core which varied slightly due to the recovery method. After this procedure, a gaseous headspace of ca. 10 cm was left in each core. Furthermore, the cores were equipped with adjustable stirring heads that contained ports for inserting optodes to continuously record pH and oxygen (O2) concentrations in the overlying water. In order to prevent anoxic conditions developing, ambient air was bubbled into the water column. The water column in each core was slowly and continuously flushed with a constant throughflow of 40 µl min-1 from a single reservoir of bottom water. The residence time of the water inside the cores was thus about 4 to 5 weeks. At the end of the experiments, the bottom water was removed via suction and the cores were sliced for pore water analysis. The pore waters were recovered by centrifuging each respective sediment layer in 50 ml falcon tubes at 3000 rpm for 10 minutes. Afterwards, the supernatant water was transferred to polyethylene (PE) vials in an Ar-filled glove bag to minimize contact with oxygen. Samples for TA were analyzed directly after sampling by titration of 1 ml of bottom/pore water with 0.02N HCl. Titration was ended when a stable purple color appeared. During titration, the sample was degassed by continuous bubbling with nitrogen to remove any generated CO2 and H2S. The acid was standardized using an IAPSO seawater standard. Anion element concentrations (SO42-, Cl-, Br-) were determined using ion chromatography (IC, METROHM 761 Compact, conductivity mode). Acidified sub-samples (30 μl suprapure HNO3- + 3 ml sample) were prepared for analyses of major and trace elements (Si, Na, K, Li, B, Mg, Ca, Sr, Mn, Ni and Fe) by inductively coupled plasma optical emission spectroscopy (ICP-OES, Varian 720-ES). In addition to the parameters listed above, pore waters were analyzed for sulfite (H2S) and Fe2+. For the analysis of dissolved Fe2+ concentrations, sub-samples of 1 ml were taken within the glove bag, immediately stabilized with ascorbic acid and analyzed within 30 minutes after complexation with 20 μl of Ferrozin. For H2S, an aliquot of pore water was diluted with appropriate amounts of oxygen-free artificial seawater and the H2S was fixed by immediate addition of zinc acetate gelatin solution.

Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric carbon dioxide (CO2) levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments (January - May 2022). These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an oxic environment. The sediment cores were incubated with Baltic Sea bottom water. Eight sediment cores were placed in a rack in an upright position. The bottom water was carefully removed via suction and replaced with a known volume (1.5 l – 2.0 l) of filtered (0.2 µm) Baltic Sea bottom water in order to remove pelagic auto- and heterotrophs and suspended particles. The volume of water added depended on the height of sediment in each core which varied slightly due to the recovery method. After this procedure, a gaseous headspace of ca. 10 cm was left in each core. Furthermore, the cores were equipped with adjustable stirring heads that contained ports for inserting optodes to continuously record pH and oxygen (O2) concentrations in the overlying water. In order to prevent anoxic conditions developing, ambient air was bubbled into the water column. The water column in each core was slowly and continuously flushed with a constant throughflow of 40 µl min-1 from a single reservoir of bottom water. The residence time of the water inside the cores was thus about 4 to 5 weeks. Bottom water samples were taken from the outflow of each core over a time period of several hours. Thus, samples represent the average outflow over the respective time period. Sampling intervals increased from daily during the first two weeks to every three to four days and weekly towards the end of the experiment. All samples were filtered through a 0.2 µm cellulose membrane filter and refrigerated in 25 ml ZinsserTM scintillation vials. Anion element concentrations (SO42-, Cl-, Br-) were determined using ion chromatography (IC, METROHM 761 Compact, conductivity mode). Acidified sub-samples (30 μl suprapure HNO3- + 3 ml sample) were prepared for analyses of major and trace elements (Si, Na, K, Li, B, Mg, Ca, Sr, Mn, Ni and Fe) by inductively coupled plasma optical emission spectroscopy (ICP-OES, Varian 720-ES).

Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric carbon dioxide (CO2) levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments (January - May 2022). These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an oxic environment. The sediment cores were incubated with Baltic Sea bottom water. Eight sediment cores were placed in a rack in an upright position. The bottom water was carefully removed via suction and replaced with a known volume (1.5 l – 2.0 l) of filtered (0.2 µm) Baltic Sea bottom water in order to remove pelagic auto- and heterotrophs and suspended particles. The volume of water added depended on the height of sediment in each core which varied slightly due to the recovery method. After this procedure, a gaseous headspace of ca. 10 cm was left in each core. Furthermore, the cores were equipped with adjustable stirring heads that contained ports for inserting optodes to continuously record pH and oxygen (O2) concentrations in the overlying water. In order to prevent anoxic conditions developing, ambient air was bubbled into the water column. The water column in each core was slowly and continuously flushed with a constant throughflow of 40 µl min-1 from a single reservoir of bottom water. The residence time of the water inside the cores was thus about 4 to 5 weeks. Bottom water samples were taken from the outflow of each core over a time period of several hours. Thus, samples represent the average outflow over the respective time period. Sampling intervals increased from daily during the first two weeks to every three to four days and weekly towards the end of the experiment. All samples were filtered through a 0.2 µm cellulose membrane filter and refrigerated in 25 ml ZinsserTM scintillation vials. Samples for total alkalinity (TA) were analyzed directly after sampling by titration of 1 ml of bottom/pore water with 0.02N HCl. Titration was ended when a stable purple color appeared. During titration, the sample was degassed by continuous bubbling with nitrogen to remove any generated CO2 and H2S. The acid was standardized using an IAPSO seawater standard.

Enhanced mineral dissolution in the benthic environment is currently discussed as a potential technique for ocean alkalinity enhancement (OAE) to reduce atmospheric carbon dioxide (CO2) levels. This study explores how biogeochemical processes affect the dissolution of alkaline minerals in surface sediments during laboratory incubation experiments. These involved introducing dunite and calcite to organic-rich sediments from the Baltic Sea under controlled conditions in an anoxic to hypoxic environment. The sediment cores were incubated with Baltic Sea bottom water. Eight sediment cores were positioned vertically in a rack. Since the sediment surface was slightly oxidized by the bottom water (∼125 μmol l−1 upon recovery), the cores were left plugged on the top for 13 days to settle after recovery until the sediment surface was anoxic. To achieve chemical conditions that are expected in the natural system, 500l of retrieved sea water were degassed via bubbling with pure dinitrogen gas in batches of 100 l. Afterwards, between 50 and 60 l were transferred into an evacuated gas tight bag. After the transfer, pH and total alkalinity (TA) were measured to determine the dissolved inorganic carbon (DIC) of the water. Afterwards the DIC was increased via adding pure CO2 until a CO2 partial pressure (pCO2 ) of ∼2,300–∼3,300 μatm was established mimicking conditions prevailing in Boknis Eck during summer. Stirring heads were installed on the cores. To prevent the development of oxic conditions, it was ensured that as little gas phase as possible was left in the cores. Elimination of pelagic autotrophs, heterotrophs, and suspended particles was achieved by flushing the cores with modified bottom water for 2 days with a flow rate of 1.5 mml min−1. Afterwards, a continuous throughflow of 700 μl min−1 from the reservoir of modified bottom water was applied, leading to a residence time of ∼2.1 days inside the cores. For the experimental incubations, six cores received additions of alkaline materials, three with calcite (Cal1 - Cal3) and three cores with dunite (Dun1 - Dun3), leading to three replicates per treatment. Two control cores remained untreated (C1, C2). The amount of added substrate was based on the rain rate of particulate organic carbon observed in Boknis Eck (0.5 mmol cm−2 a−). The incubation lasted for 25 days. The volume of water in each core was determined at the end of the experiment via measuring the height of the water column after removing the stirring heads. At the end of the experiments, the bottom water was removed via suction and the cores were sliced for pore water analysis. The pore waters were recovered by centrifuging each respective sediment layer in 50 ml falcon tubes at 3000 rpm for 10 minutes. Afterwards, the supernatant water was transferred to polyethylene (PE) vials in an Ar-filled glove bag to minimize contact with oxygen. All samples were filtered through a 0.2 µm cellulose membrane filter and refrigerated in 25 ml ZinsserTM scintillation vials. TA samples (1 ml) were titrated with 0.02N HCl. For H2S, an aliquot of pore water was diluted. A 5 ml aliquot was frozen directly after the sampling procedure for later nutrient analysis. Nutrient measurements were performed either via manual photometric measurement (NH4) or using a Seal – AnalyticalTM QuAAtro autoanalyzer (PO43-). Samples for TA were analyzed directly after sampling by titration of 1 ml of bottom/pore water with 0.02N HCl. Titration was ended when a stable purple color appeared. During titration, the sample was degassed by continuous bubbling with nitrogen to remove any generated CO2 and H2S. The acid was standardized using an IAPSO seawater standard. Acidified sub-samples (30 μl suprapure HNO3- + 3 ml sample) were prepared for analyses of major and trace elements (Si, Na, K, Li, B, Mg, Ca, Sr, Mn, Ni and Fe) by inductively coupled plasma optical emission spectroscopy (ICP-OES, Varian 720-ES). For H2S, an aliquot of pore water was diluted with appropriate amounts of oxygen-free artificial seawater and the H2S was fixed by immediate addition of zinc acetate gelatin solution

This is the second version that was uploaded to make the code available for the paper submission NN-TOC v1: global prediction of total organic carbon in marine sediments using deep neural networks to the Geoscientific Model Development journal. Here we create a deep neural network based approach for the geospatial predicition of total organic carbon percentages in marine sediments.The data folder contains "raw" features and labels, "interim" data for preprocessed features and labels and "output"s produced from the model. While the preprocessed folder contain all the other files that can be produced by running the code. The features are in .nc or .grd file format. The other files are in .xyz or .csv file format.

This is the second version that was uploaded to make the code available for the paper submission NN-TOC v1: global prediction of total organic carbon in marine sediments using deep neural networks to the Geoscientific Model Development journal. Here we create a deep neural network based approach for the geospatial predicition of total organic carbon percentages in marine sediments.The data folder contains "raw" features and labels, "interim" data for preprocessed features and labels and "output"s produced from the model. While the preprocessed folder contain all the other files that can be produced by running the code. The features are in .nc or .grd file format. The other files are in .xyz or .csv file format.

In order to determine the dissolution kinetics of olivine in sea water, commercially available ultra-mafic sand (UMS, supplied by AdL Sand- und Wasserstrahltechnik) was permitted to react with artificial seawater (ASW, Millero et al., 2008) in 250 ml polyethylene (PE) batch reactors. Three different batches with variable amounts of UMS were prepared, each containing three replicates (n = 3) to verify the reproducibility of the experiments. The amount of ASW was 200 ml for all replicates and batches. 50 ml of ambient air were included to allow for equilibration with the atmosphere. The amount of UMS was varied from 20 g for Batch1 to 10 g for Batch2 and 5 g for Batch3 in order to investigate the effect of the solid/liquid ratio. The air was partly exchanged with the laboratory atmosphere every time samples were taken. All batch reactors with artificial seawater, UMS and gas phase were subjected to constant movement in HeidolphTM Reax2© over-head shakers at ~40 rpm. The experiment was conducted under controlled laboratory conditions (p = 1 bar, 21.5 °C < T < 23.9 °C). For each sample (23 in total), two aliquots (2 ml and 5 ml) were taken for further measurements and the same volume of artificial seawater was added to ensure a constant solid/liquid ratio. For the same reason it was made sure that no UMS grains were removed via sample taking. Sampling intervals increased from minutes to hours during day one to every two weeks between day 50 and day 134. The 5 ml aliquot was filtered through a 0.2 µm cellulose membrane filter and refrigerated in 5.2 ml ZinsserTM scintillation bottles. The 2 ml aliquot was used for direct pH measurements (see below) and not filtered to ensure a pristine chemical milieu. At the end of the experiments, the ASW in the batch reactors was carefully decanted over a 0.2 µm regenerated cellulose filter to recover the greyish suspended matter that had formed in the batch reactors during the experiment. Fine particles possibly stuck to the UMS grains were eluted by refilling the batch reactor with fresh ASW, shaking and decanting it. This procedure was repeated until the supernatant was clear. Withal, it was made sure that all precipitates, which left the bottles, were recovered on the filters. Subsequently, the wet cake was rinsed with pH neutral MilliQ water (MQe, 18Ω Ohm/cm) to elute dissolved species (e.g. salinity). Furthermore, the UMS used in Batch1 was recovered, very carefully rinsed with pH neutral MQe (to only elute salinity), and dried for scanning electron microscope energy-dispersive X-ray spectroscopy (SEM−EDX).The water samples were analyzed for pH following Dickson (1993). Total alkalinity was analyzed by titration with diluted hydrochloric acid (HCl) to an end point of pH = 4.5 (Stumm & Morgan, 1996; Gieskes et al., 1991) and element concentrations were determined using inductively coupled plasma optical emission spectrometry (ICP-OES).