An Assessment of Direct Dissolved Inorganic Carbon Injection to the Coastal Region: A Model Result

Wei-Jen Huang,Li-Lian Liu,Kai-Jung Kao,Yin-Lung Han,Chi-Wen Liao

doi:10.3390/su10041174

Abstract

The amount of carbon dioxide (CO2) in the atmosphere has increased in the past 60 years and the technology of carbon capture and storage (CCS) has recently been extensively studied. One of the strategies of CCS is to directly inject a high dissolved inorganic carbon (DIC) concentration (or high partial pressure of carbon dioxide, pCO2) solution into the ocean. However, the carbonate dynamics and air-sea gas exchange are usually neglected in a CCS strategy. This study assesses the effect of a DIC-solution injection by using a simple two end-member model to simulate the variation of pH, DIC, total alkalinity (TA) and pCO2 between the river and sea mixing process for the Danshuei River estuary and Hoping River in Taiwan. We observed that the DIC-solution injection can contribute to ocean acidification and can also lead the pCO2 value to change from being undersaturated to oversaturated (with respect to the atmospheric CO2 level). Our model result also showed that the maximum Revelle factors (Δ[CO2]/[CO2])/(Δ[DIC]/[DIC]) among varied pH values (6–9) and DIC concentrations (0.5–3.5 mmol kg−1) were between pH 8.3 and 8.5 in fresh water and were between 7.3 and 7.5 in waters with a salinity of 35, reflecting the changing efficiency of dissolving CO2 gas into the DIC solution and the varying stability of this desired DIC solution. Finally, we suggest this uncoupled Revelle factor between fresh and salty water should be considered in the (anthropogenic) carbonate chemical weathering on a decade to century scale.

Highlights

Increasing atmospheric carbon dioxide (CO2) amounts in the past 60 years are reducing oceanic pH and calcium carbonate saturation, both of which are key factors influencing marine organisms [1,2]
We suggest that if high-dissolved inorganic carbon (DIC) and high-pressure of CO2 (pCO2) water is injected in the bottom water of the continental shelf, it may mix with surface water in the winter
In addition to using this anthropogenic DIC-solution injection as accelerated chemical weathering to compensate for the increasing export of CO2 gas to the atmosphere, we encourage improving energy efficiency and using green energy which can substantially reduce the export of CO2

Summary

Introduction

Increasing atmospheric carbon dioxide (CO2) amounts in the past 60 years are reducing oceanic pH and calcium carbonate saturation, both of which are key factors influencing marine organisms [1,2]. One of the CO2 sequestration methods is a direct dissolved inorganic carbon (DIC) solution (or CO2 gas) injection into the ocean [4]. The effect of direct DIC injection into the ocean has been suggested [5], as well as the effect of increasing atmospheric CO2 level on the ocean [6]; that is, ocean acidification. The effect of a direct DIC injection on the internal carbonate variation, among the above four parameters, is still unclear. We focus on the effect of a DIC-solution injection to the estuary and the ocean. We systematically compare the variations among pH, DIC and pCO2 and suggest the role of buffering capacity of air-sea gas exchange during this CO2 dissolving and the DIC injection processes

Study Sites and Methods

River-to-Sea Simulation Conditions

Injection Scenarios under Controlled pH and pCO2

DIC Buffering Capacity along the Salinity Gradient

A Comparison between Injections on the Shelf and the Open Ocean

Summary and Implications