Simulating CO2 transport into the ocean from a CO2 lake at the seafloor using a z- and a σ-coordinate model

Abstract

The ocean takes up approximately 2 GT carbon per year due to the enhanced CO 2 concentrations in the atmosphere. Several options have been suggested in order to reduce the emissions of CO 2 into the atmosphere, and among these are CO 2 storage in the deep ocean. Topographic effects of dissolution and transport from a CO 2 lake located at 3,000-m depth have been studied using the z-coordinate model Massachusetts Institute of Technology general circulation model (MITgcm) and the σ -coordinate model Bergen ocean model (BOM). Both models have been coupled with the general ocean turbulence model (GOTM) in order to account for vertical subgrid processes. The chosen vertical turbulence mixing scheme includes the damping effect from stable stratification on the turbulence intensity. Three different topographic scenarios are presented: a flat bottom and the CO 2 lake placed within a trench with depths of 10 and 20 m. The flat case scenario gives good correlation with previous numerical studies of dissolution from a CO 2 lake. When topography is introduced, it is shown that the z-coordinate model and the σ -coordinate model give different circulation patterns in the trench. This leads to different dissolution rates, 0.1 μmol cm −2 s −1 for the scenario of a 20-m-deep trench using BOM and 0.005-0.02 μmol cm −2 s −1 for the same scenario using the MITgcm. The study is also relevant for leakages of CO 2 stored in geological formations and to the ocean.