Author(s): Pubudu Kumarage; Poojitha D. Yapa; Kisaburo Nakata
Linked Author(s):
Keywords: CO2 droplets; TCO2; Dissolved CO2; PH
Abstract: CO2 coming out from hydrothermal vent sites has a significant influence on the ocean carbon intake and the acidity in the ocean environment. Such releases have been reported in many locations around the world. Since ambient sea water is under-saturated in CO2, droplets of CO2 dissolve while buoyantly rising through the water column. Modelling this fate of CO2 droplets is useful to find the possible ocean acidification in both natural (e.g. hydrothermal vent sites) and accidental anthropogenic (CCS: Carbon Capture and Storage) circumstances. Rate of dissolution and buoyant rising velocity are two key parameters which are required to model the CO2 droplet behavior in the ocean. In this study, the rate of dissolution is modeled as the combined effect of dissolution through the surrounding hydrate layer around the gas bubbles and convective dissolution. Dissolution rate is primarily a function of thermodynamic conditions while buoyant rising velocity depends on the droplet shape and reduced gravity. The model developed can handle both liquid and gaseous state CO2 based on the ambient thermodynamic conditions. Change of droplet diameter and buoyant rising velocities calculated using the model were validated using field data. Dissolved CO2 contribute to increase the Total carbon dioxide (TCO2) in the water column. Increased TCO2 combined with alkalinity and salinity eventually causes ambient seawater to be acidic. In this study, pH value of sea water is evaluated using the elevated TCO 2 profile of the water column. The model developed in this study is used to simulate the release of CO2 droplets from a seabed hydrothermal system in Hatoma knoll in southwest Okinawa trough. Size of the total domain is ~ 1 km by1 km. Dissolved CO2 concentration variation with time progression is calculated inside the model to evaluate the change of TCO2. Ambient conditions were assumed to be time invariant due to lack of detailed available data.
Year: 2016