Mapping observations using AUV and numerical simulations of leaked CO2 diffusion in sub-seabed CO2 release experiment at Ardmucknish Bay

Abstract

A controlled sub-seabed CO release experiment (QICS: Quantifying and Monitoring Potential Impacts of Geological Carbon Storage) was conducted in Ardmucknish Bay, Scotland, in 2012, to quantify the effect of leaked CO 2 on marine environments. In this experiment, CO 2 was injected beneath the seafloor, and closely monitored as the CO 2 was allowed to leak into the overlying water column. We performed mapping observations using an autonomous underwater vehicle (AUV) equipped with sensors to monitor physical and chemical conditions in the vicinity of the CO 2 leakage. We also numerically simulated the behavior of the low-pH plume caused by the CO 2 leakage, within the calculated tidal current in the bay. The results of AUV mapping observations showed that physical and chemical characteristics of the water mass in Ardmucknish bay are sensitive to tidal variations (low or high tide), and the ascent speed of the leaked CO 2 bubble and the pH decrease in the vicinity of the CO 2 leakage area are predominantly controlled by the tidal phase in the bay. The observations using an acoustic Doppler current profiler (ADCP) installed in the AUV indicated that the current in the bay flows westwards at high tide and eastwards at low tide. The simulated tidal current agreed well with the tidal current observed by ADCP. Numerical simulation suggested that the pH decrease due to the leaked CO 2 is restricted to the vicinity of the CO 2 leakage area, and fluctuates greatly with tidal variations. In flood tide periods, diffusion of the low-pH plume caused by the leaked CO 2 is barely detectable because low-pH seawater intrudes into the bay from the bay mouth.

Marine Monitoring for Offshore Geological Carbon Storage—A Review of Strategies, Technologies and Trends

“…In particular, since pH is closely linked to CO 2 (an increase in the CO 2 content causes a reduction in pH), a pH sensor may be used as a proxy for a CO 2 sensor. This requires selection of a pH sensor with high sensitivity, in the order of 0.01, to detect the expected pH change induced by a CO 2 plume [10,42,43].…”

Field trial on Ocean Estimation for Multi-Vessel Multi-Float-based Active perception

“…Active perception is a critical component towards achieving persistent autonomy in marine scientific missions such as underwater habitat mapping [2,17,23], environmental monitoring [6,8,21,26], geological surveying [4,15,25], and plume source detection [11,13,16]. When the vehicles operate in an oceanic environment, any control or planning done to address active perception must account for timevarying, uncertain oceanic flow field; either by compensating for it [18], or exploiting it [10].…”

Hierarchical MCTS for Scalable Multi-Vessel Multi-Float Systems

“…Autonomous underwater vehicles (AUVs) play a critical role in many marine science applications such as underwater habitat mapping [5,27,32], environmental monitoring [15,16,29,42], geological surveying [7,25,40], and plume source detection [19,21,26]. An exciting opportunity to increase the accessibility and availability of marine autonomous systems arises from the idea of replacing highcost, fully featured AUVs with a team of under-actuated robotic floats [1,22,28] as shown in Fig.…”