Detection of CO\u3csub\u3e2\u3c/sub\u3e leakage from a simulated sub-seabed storage site using three different types of pCO\u3csub\u3e2\u3c/sub\u3e sensors

© 2015 Elsevier Ltd. All rights reserved. This work is focused on results from a recent controlled sub-seabed in situ carbon dioxide (CO2) release experiment carried out during May-October 2012 in Ardmucknish Bay on the Scottish west coast. Three types of pCO2 sensors (fluorescence, NDIR and ISFET-based technologies) were used in combination with multiparameter instruments measuring oxygen, temperature, salinity and currents in the water column at the epicentre of release and further away. It was shown that distribution of seafloor CO2 emissions features high spatial and temporal heterogeneity. The highest pCO2 values (~1250 μatm) were detected at low tide around a bubble stream and within centimetres distance from the seafloor. Further up in the water column, 30-100 cm above the seabed, the gradients decreased, but continued to indicate elevated pCO2 at the epicentre of release throughout the injection campaign with the peak values between 400 and 740 μatm. High-frequency parallel measurements from two instruments placed within 1 m from each other, relocation of one of the instruments at the release site and 2D horizontal mapping of the release and control sites confirmed a localized impact from CO2 emissions. Observed effects on the water column were temporary and post-injection recovery took O2, and when it was influenced by purposefully released CO2. Use of a hydrodynamic circulation model, calibrated with in situ data, was crucial to establishing background conditions in this complex and dynamic shallow water system

Detection of CO2 leakage from a simulated sub-seabed storage site using three different types of pCO2 sensors

This work is focused on results from a recent controlled sub-seabed in situ carbon dioxide (CO2) release experiment carried out during May–October 2012 in Ardmucknish Bay on the Scottish west coast. Three types of pCO2 sensors (fluorescence, NDIR and ISFET-based technologies) were used in combination with multiparameter instruments measuring oxygen, temperature, salinity and currents in the water column at the epicentre of release and further away. It was shown that distribution of seafloor CO2 emissions features high spatial and temporal heterogeneity. The highest pCO2 values (∼1250 μatm) were detected at low tide around a bubble stream and within centimetres distance from the seafloor. Further up in the water column, 30–100 cm above the seabed, the gradients decreased, but continued to indicate elevated pCO2 at the epicentre of release throughout the injection campaign with the peak values between 400 and 740 μatm. High-frequency parallel measurements from two instruments placed within 1 m from each other, relocation of one of the instruments at the release site and 2D horizontal mapping of the release and control sites confirmed a localized impact from CO2 emissions. Observed effects on the water column were temporary and post-injection recovery took <7 days. A multivariate statistical approach was used to recognize the periods when the system was dominated by natural forcing with strong correlation between variation in pCO2 and O2, and when it was influenced by purposefully released CO2. Use of a hydrodynamic circulation model, calibrated with in situ data, was crucial to establishing background conditions in this complex and dynamic shallow water system

High-resolution observations in the Western Mediterranean Sea: The REP14-MED experiment

The observational part of the REP14-MED experiment was conducted in June 2014 in the Sardo-Balearic Sea west of Sardinia Island (Western Mediterranean Sea). Two research vessels collected high-resolution oceanographic data by means of hydrographic casts, towed systems, and underway measurements. In addition, a vast amount of data was provided by a fleet of 11 gliders, time series were available from moored instruments, and information on Lagrangian flow patterns were obtained from surface drifters and one profiling float. The spatial resolution of the observations encompasses a spectrum over four orders of magnitude from O(101 m) to O(105 m), and the time series from the moored instruments cover a spectral range of five orders from O(101 s) to O(106 s). The objective of this article is to provide an overview of the huge data set which is utilized by various ongoing studies, focusing on (i) sub-mesoscale and mesoscale pattern analyses, (ii) operational forecasting in terms of the development and assessment of sampling strategies, assimilation methods, and model validation, (iii) modeling the variability of the ocean, and (iv) testing of new payloads for gliders

Net community production in the northwestern Mediterranean Sea from glider and buoy measurements

The Mediterranean Sea comprises just 0.8 % of the global oceanic surface, yet considering its size, it is regarded as a disproportionately large sink for anthropogenic carbon due to its physical and biogeochemical characteristics. An underwater glider mission was carried out in March–April 2016 close to the BOUSSOLE and DyFAMed time series moorings in the northwestern Mediterranean Sea. The glider deployment served as a test of a prototype ion-sensitive field-effect transistor pH sensor. Dissolved oxygen (O2) concentrations and optical backscatter were also observed by the glider and increased between 19 March and 1 April, along with pH. These changes indicated the start of a phytoplankton spring bloom, following a period of intense mixing. Concurrent measurements of CO2 fugacity and O2 concentrations at the BOUSSOLE mooring buoy showed fluctuations, in qualitative agreement with the pattern of glider measurements. Mean net community production rates (N) were estimated from glider and buoy measurements of dissolved O2 and inorganic carbon (DIC) concentrations, based on their mass budgets. Glider and buoy DIC concentrations were derived from a salinity-based total alkalinity parameterisation, glider pH and buoy CO2 fugacity. The spatial coverage of glider data allowed the calculation of advective O2 and DIC fluxes. Mean N estimates for the euphotic zone between 10 March and 3 April were (-17±36) for glider O2, (44±94) for glider DIC, (17±37) for buoy O2 and (49±86)  mmolm-2d-1 for buoy DIC, all indicating net metabolic balance over these 25 d. However, these 25 d were actually split into a period of net DIC increase and O2 decrease between 10 and 19 March and a period of net DIC decrease and O2 increase between 19 March and 3 April. The latter period is interpreted as the onset of the spring bloom. The regression coefficients between O2 and DIC-based N estimates were 0.25 ± 0.08 for the glider data and 0.54 ± 0.06 for the buoy, significantly lower than the canonical metabolic quotient of 1.45±0.15. This study shows the added value of co-locating a profiling glider with moored time series buoys, but also demonstrates the difficulty in estimating N, and the limitations in achievable precision

Detection and impacts of leakage from sub-seafloor deep geological carbon dioxide storage

Fossil fuel power generation and other industrial emissions of carbon dioxide are a threat to global climate1, yet many economies will remain reliant on these technologies for several decades2. Carbon dioxide capture and storage (CCS) in deep geological formations provides an effective option to remove these emissions from the climate system3. In many regions storage reservoirs are located offshore4, 5, over a kilometre or more below societally important shelf seas6. Therefore, concerns about the possibility of leakage7, 8 and potential environmental impacts, along with economics, have contributed to delaying development of operational CCS. Here we investigate the detectability and environmental impact of leakage from a controlled sub-seabed release of CO2. We show that the biological impact and footprint of this small leak analogue (&lt;1 tonne CO2 d?1) is confined to a few tens of metres. Migration of CO2 through the shallow seabed is influenced by near-surface sediment structure, and by dissolution and re-precipitation of calcium carbonate naturally present in sediments. Results reported here advance the understanding of environmental sensitivity to leakage and identify appropriate monitoring strategies for full-scale carbon storage operations

Strategies for Detection and Monitoring of CO2 Leakage in Sub-seabed CCS

AbstractCarbon dioxide (CO2) capture and storage (CCS) in sub-seabed geological formations is currently being studied as a potential option to mitigate the accumulation of anthropogenic CO2 in the atmosphere. For the verification of CO2 storage integrity in the sub-seafloor, developments of the techniques to detect and monitor CO2 leaked from the seafloor is vital. Seafloor-based acoustic tomography is a technique that can be used to detect emissions of liquid CO2 droplets or gas CO2 bubbles from the seafloor. An in-situ pH/pCO2 sensor can provide rapid and high-precision measurements in seawater, and is therefore able to detect pH and pCO2 changes caused by the leaked CO2. An autonomous underwater vehicle (AUV) installed with the pH/pCO2 sensor provides an automated observation technology that can detect and monitor CO2 leakage from the seafloor. By towing a multi-layer monitoring system consisting of a number of pH/pCO2 sensors and transponders, the dispersed area of leaked CO2 overlying a CCS site can also be identified. The seafloor-mounted automatic elevator consists of a buoy equipped with pH/pCO2 and depth sensors, collecting intermittently a CTD-like data as it ascends and descends. Hence, CO2 leakage from the seafloor is detected and monitored as follows. Step 1: detect the CO2 leakage by the seafloor-based acoustic tomography. Step 2: map the distribution of the leakage points using the pH/pCO2 sensor installed on the AUV. Step 3: monitor the impacted area using a remotely operated underwater vehicle or the automatic elevator or by towing the multi-layer monitoring system