Ocean disposal of CO 2 in the North Pacific Ocean: Assessment of CO 2 chemistry and circulation on storage and return to the atmosphere

Abstract

The purpose of this study is to assess changes in the ocean biogeochemistry and oceanic partial pressure of CO 2 (pCO 2) due to CO 2 disposal and its effects, and to discuss the oceanographic parameters affecting the return of disposed CO 2 back to the atmosphere. The primary focus will be on CO 2 scenarios for North Pacific intermediate water (NPIW) and the deep water off the Japanese coast. CO 2 chemistry shows that pCO 2 values in the intermediate and deep North Pacific waters are already higher than the present atmospheric CO 2 level. The factors maintaining high pCO 2 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 CO 2 into the deep water. A review of CO 2 source and sink areas in the Pacific Ocean indicates potential escape routes of disposed CO 2 back to the atmosphere. Several strategies are available for disposing CO 2 into the ocean: (1) Disposal into the upper ocean can be combined with simultaneous fertilization to create a detritus flux, transporting CO 2 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 pCO 2. 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 ( K v) 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 SF 6 tracer and CO 2 storage experiment is a logical approach to tackle these important areas of research.