RV POSEIDON Fahrtbericht / Cruise Report POS518 Baseline Study for the Environmental Monitoring of Subseafloor CO2 Storage Operations Leg 1: Bremerhaven – Bremerhaven (Germany) 25.09.-11.10.2017 Leg 2: Bremerhaven – Kiel (Germany) 12.10.-28.10.2017 GEOMAR REPORT Berichte aus dem GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel Nr. 40 (N. Ser.) January 2018 RV POSEIDON Fahrtbericht / Cruise Report POS518 Baseline Study for the Environmental Monitoring of Subseafloor CO2 Storage Operations Leg 1: Bremerhaven – Bremerhaven (Germany) 25.09.-11.10.2017 Leg 2: Bremerhaven – Kiel (Germany) 12.10.-28.10.2017 Berichte aus dem GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel Nr. 40 (N. Ser.) January 2018 Das GEOMAR Helmholtz-Zentrum für Ozeanforschung Kiel The GEOMAR Helmholtz Centre for Ocean Research Kiel ist Mitglied der Helmholtz-Gemeinschaft is a member of the Helmholtz Association of Deutscher Forschungszentren e.V. German Research Centres Herausgeber / Editors: Peter Linke and Matthias Haeckel GEOMAR Report ISSN Nr.. 2193-8113, DOI 10.3289/GEOMAR_REP_NS_40_2018 Helmholtz-Zentrum für Ozeanforschung Kiel / Helmholtz Centre for Ocean Research Kiel GEOMAR Dienstgebäude Westufer / West Shore Building Düsternbrooker Weg 20 D-24105 Kiel Germany Helmholtz-Zentrum für Ozeanforschung Kiel / Helmholtz Centre for Ocean Research Kiel GEOMAR Dienstgebäude Ostufer / East Shore Building Wischhofstr. 1-3 D-24148 Kiel Germany Tel.: +49 431 600-0 Fax: +49 431 600-2805 www.geomar.de Cruise Report POSEIDON 518 Table of Contents 1 Summary ........................................................................................................................................ 3 2 Research Programme / Objectives ............................................................................................ 4 3 Participant Lists ............................................................................................................................. 5 3.1 Leg 1 ........................................................................................................................................... 5 3.2 Leg 2 ........................................................................................................................................... 6 4 Cruise Narrative ............................................................................................................................ 7 4.1 Leg 1 ........................................................................................................................................... 7 4.2 Leg 2 ........................................................................................................................................... 8 4.2 Acknowledgements .................................................................................................................. 9 5 Methods ........................................................................................................................................ 10 5.1 Hydroacoustic Systems ......................................................................................................... 10 5.1.1 Wärtsilä ELAC SeaBeam 3050 MK II .............................................................................. 10 5.1.2 Imagenex 837B Delta T 260 kHz Multibeam System ................................................... 12 5.2 ROV PHOCA ........................................................................................................................... 13 5.3 Eddy Covariance Technique for O2, CO2 (pH) ................................................................... 16 5.3.1 Eddy Covariance Technique ............................................................................................. 16 5.3.2 Eddy Covariance Instruments ........................................................................................... 16 5.3.3 Eddy Covariance Deployment .......................................................................................... 18 5.4 Bubble Box............................................................................................................................... 19 5.5 Picarro Atmospheric Gas Measurements ........................................................................... 20 5.6 Water Column Sampling ........................................................................................................ 22 5.6.1 “Multi-purpose” Rosette ..................................................................................................... 22 5.6.2 Water Sampling and Subsampling for Dissolved Gas and TA/DIC Analyses ........... 24 5.6.3 Underway Thermosalinograph.......................................................................................... 25 5.6.4 Underway Total Alkalinity (TA) Measurements .............................................................. 25 5.6.5 Gas Bubble Sampling ........................................................................................................ 26 5.6.6 Dissolved Organic Carbon Sampling ............................................................................... 27 5.6.7 Inorganic Nutrient Sampling .............................................................................................. 27 5.7 Lander Deployments .............................................................................................................. 27 5.7.1 NOC Lander......................................................................................................................... 27 5.7.2 SLM Lander ......................................................................................................................... 29 5.7.3 BIGO Lander ....................................................................................................................... 29 5.8 Sediment Coring ..................................................................................................................... 31 1 Cruise Report POSEIDON 518 6 Preliminary Results ..................................................................................................................... 32 6.1 Gas Bubble Seepage ............................................................................................................. 32 6.1.1 Hydroacoustics .................................................................................................................... 32 6.1.2 Gas Composition and Gas Exchange into Atmosphere ............................................... 36 6.2 Hydrographic Investigations .................................................................................................. 39 6.2.1 Water Column Chemistry .................................................................................................. 39 6.2.2 Oxygen, Carbonate System and pH at Goldeneye ....................................................... 48 6.3 Lander Measurements ........................................................................................................... 52 6.3.1 NOC Lander Measurements ............................................................................................. 53 6.3.2 SLM Lander Measurements .............................................................................................. 53 6.3.3 In situ Benthic Flux Measurements .................................................................................. 56 6.4 Sediment Geochemistry ........................................................................................................ 57 6.4.1 Sediment and Porewater Sampling ................................................................................. 57 6.4.2 Porewater Analyses ........................................................................................................... 58 6.4.3 Preliminary Results ............................................................................................................. 59 7 References................................................................................................................................... 64 8 Appendices .................................................................................................................................. 67 8.1 Station Lists of Leg 1 and 2 ................................................................................................... 67 8.2 ROV PHOCA Dive Protocols ................................................................................................ 76 8.3 Core Photos ............................................................................................................................. 80 8.4 Multibeam Data ....................................................................................................................... 85 2 Cruise Report POSEIDON 518 1 Summary Peter Linke, Matthias Haeckel Poseidon cruise 518 (leg 1 and 2) took place in the framework of the Horizon 2020 project STEMM-CCS of the EU. The project’s main goal is to develop and test strategies and technologies for the monitoring of subseafloor CO2 storage operations. In this context a small research-scale CO2 gas release experiment is planned for 2019 in the vicinity of the Goldeneye platform located in the British EEZ (central North Sea). Cruise POS518 aimed at collecting necessary oceanographic and biogeochemical baseline data for this release experiment. During Leg 1 ROV PHOCA was used to deploy MPI’s tool for high-precision measurements of O2, CO2 and pH in the bottom water at Goldeneye. In addition, ROV push cores and gravity cores were collected in the