Ocean disposal of CO2 in the North Pacific Ocean: Assessment of CO2 chemistry and circulation on storage and return to the atmosphere

The purpose of this study is to assess changes in the ocean biogeochemistry and oceanic partial pressure of CO2 (pCO2) due to CO2 disposal and its effects, and to discuss the oceanographic parameters affecting the return of disposed CO2 back to the atmosphere. The primary focus will be on CO2 scenarios for North Pacific intermediate water (NPIW) and the deep water off the Japanese coast. CO2 chemistry shows that pCO2 values in the intermediate and deep North Pacific waters are already higher than the present atmospheric CO2 level. The factors maintaining high pCO2 in the waters of the North Pacific Ocean are (1) ocean diffusivity, (2) penetration and mixing into deeper water, (3) transport of NPIW, (4) deep Pacific circulation, and (5) the efficiency of the biological pump. Review of recent work on ventilation of deep Pacific waters suggests a mid-depth return flow to Antarctic circumpolar water, increasing the residence time of disposed CO2 into the deep water. A review of CO2 source and sink areas in the Pacific Ocean indicates potential escape routes of disposed CO2 back to the atmosphere. Several strategies are available for disposing CO2 into the ocean: (1) Disposal into the upper ocean can be combined with simultaneous fertilization to create a detritus flux, transporting CO2 into deep waters. (2) Disposal into NPIW will buy 20 to 50 years of time depending on the maintaining of the ventilation rate of NPIW. (3) Disposal into the deep Pacific waters relies on the tightness of the thermocline lid and the continuous action of the biological pump to keep the upper ocean low in pCO2. Thus, certain crucial areas of research need to be looked at to remove uncertainties in knowledge such as: (a) the experimental assessment of vertical diffusivity (Kv) in the upper, the intermediate and deep waters, (b) an assessment of the time-scale of Pacific ventilation, and (c) fertilization to enhance the biological pump. A Pacific SF6 tracer and CO2 storage experiment is a logical approach to tackle these important areas of research.