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To meet temperature goals that limit warming to well below 2 °C requires the removal of hundreds of billions of tonnes of CO2 from the atmosphere over the course of this century. Effective Carbon Dioxide Removal (CDR) methodologies will be required to reduce net emissions in the near term, counterbalance residual CO2 emissions to achieve net-zero in the medium term, and contribute to net-negative emissions in the longer term – all of this in a sustainable and safe manner. This paper summarizes the research objectives and selected initial results of a collaborative project to assess CO2 storage in the upper ocean crust south of Iceland. The AIMS3 project (www.aims3.cdrmare.de) will deliver new insights, monitoring tools and feasibility assessments for CO2 storage in young, reactive basalts with little sedimentary cover. Along the flank of the Mid-Atlantic Ridge, we have done geophysical surveys and drilled a transect of boreholes in order to identify fluid migration in the upper ocean crust. Both in situ heat flow and geochemical signatures provide irrefutable evidence for such transport, which will help distributing injected CO2 in future experiments. In parallel, our project also has mineralization experiments to assess optimal conditions for injection dissolved, liquid, or supercritical CO2), numerical modelling for upscaling our results from seagoing work, and development of cost-effective sensors and smart robotic landers for long-term monitoring of the vicinity of the boreholes. We outline the rationale of AIMS3, provide an overview of the activities, and highlight some of the expedition results, with the goal to stimulate communication and collaboration.

Autonomous on-site monitoring of orthophosphate (PO43−), an important nutrient for primary production in natural waters, is urgently needed. Here, we report on the development and validation of an on-site autonomous electrochemical analyzer for PO43− in seawater. The approach is based on the use of flow injection analysis in conjunction with a dual electrochemical cell (i.e., a bi-potentiostat detector (FIA-DECD) that uses two working electrodes sharing the same reference and counter electrode. The two working electrodes are used (molybdate/carbon paste electrode (CPE) and CPE) to correct for matrix effects. Optimization of squarewave voltammetry parameters (including step potential, amplitude, and frequency) was undertaken to enhance analytical sensitivity. Possible interferences from non-ionic surfactants and humic acid were investigated. The limit of quantification in artificial seawater (30 g/L NaCl, pH 0.8) was 0.014 µM for a linear concentration range of 0.02–3 µM. The system used a Python script for operation and data processing. The analyzer was tested for ship-board PO43- determination during a four-day research cruise in the North Sea. The analyzer successfully measured 34 samples and achieved a good correlation (Pearson’ R = 0.91) with discretely collected water samples analyzed using a laboratory-based colorimetric reference analyzer.

Coastal waters are contaminated globally with millions of metric tons of munitions from the two world wars which constitute a potential threat to ecosystems and humans. Laboratory-based chemical methods for the detection of munition compounds (MCs) in seawater typically take weeks to months between sample collection and analysis. The current work details a novel, field-deployable system for rapid (under 10 min) analysis of four common MCs (1,3-dinitrobenzene (DNB), amino-4,6-dinitrotoluene (ADNT), 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)). The system uses a fluidic preconcentration unit with high-performance liquid chromatography (HPLC) and detection by electrospray-ionization mass spectrometry and UV–vis spectroscopy. The fluidic unit comprises two solid-phase extraction (SPE) columns for preconcentration of target MCs from the seawater matrix and allows loading and analysis of two samples simultaneously. Seven SPE resins were tested for extraction efficiency and robustness, with Porapak RDX showing best performance. Chromatographic separation of target MCs was performed using a C8 reversed-phase HPLC column. Limits of detection (LODs) were 3.7, 1.8, 3.6, and 10.7 ng L–1 for DNB, ADNT, TNT, and RDX, respectively. The system’s analytical performance and automated data processing procedure were demonstrated in the Baltic Sea.

High quality pH measurements are required in estuarine and coastal waters to assess the impacts of anthropogenic atmospheric CO 2 emissions on the marine carbonate system, including the resulting decrease in pH. In addition, pH measurements are needed to determine impacts on carbonate chemistry of phytoplankton blooms and their breakdown, following enhanced anthropogenic nutrient inputs. The spectrophotometric pH technique provides high quality pH data in seawater, and is advantageous for long-term deployments as it is not prone to drift and does not require in situ calibration. In this study, a field application of a fully automated submersible spectrophotometric analyzer for high-resolution in situ pH measurements in dynamic estuarine and coastal waters is presented. A Lab-on-Chip (LOC) pH sensor was deployed from a pontoon in the inner Kiel Fjord, southwestern Baltic Sea, for a total period of 6 weeks. We present a time-series of in situ pH T (total pH scale) and ancillary data, with sensor validation using discretely collected samples for pH T and laboratory analysis. The difference between the sensor and laboratory analyses of discrete samples was within ±0.015 pH T unit, with a mean difference of 0.001 (n=65), demonstrating that the LOC sensor can provide stable and accurate pH T measurements over several weeks.

Highlights • An artificial CO2 release demonstrated MMV techniques for offshore CCS. • Detection of leakage was demonstrated using acoustic, chemical and physical approaches. • Attribution of leakage was proved possible using artificial and natural tracer compounds. • Leakage quantification was possible using approaches not previously applied to CCS studies. • Non-catastrophic leaks were detected at levels below those that would cause environmental harm. Carbon capture and storage is a key mitigation strategy proposed for keeping the global temperature rise below 1.5 °C. Offshore storage can provide up to 13% of the global CO2 reduction required to achieve the Intergovernmental Panel on Climate Change goals. The public must be assured that potential leakages from storage reservoirs can be detected and that therefore the CO2 is safely contained. We conducted a controlled release of 675 kg CO2 within sediments at 120 m water depth, to simulate a leak and test novel detection, quantification and attribution approaches. We show that even at a very low release rate (6 kg day−1), CO2 can be detected within sediments and in the water column. Alongside detection we show the fluxes of both dissolved and gaseous CO2 can be quantified. The CO2 source was verified using natural and added tracers. The experiment demonstrates that existing technologies and techniques can detect, attribute and quantify any escape of CO2 from sub-seabed reservoirs as required for public assurance, regulatory oversight and emissions trading schemes.