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1. Introduction

To help reduce the rate of increase of atmospheric CO2, one could in principle divert CO2 emissions from coastal power plants to the deep ocean and thereby short-circuit the naturally slow air-sea exchange of CO2 (Marchetti, 1977). However two key scientific questions remain to be answered before such a practice could ever be implemented. Accurate answers to these questions are needed in order to fully address other crucial concerns---socioeconomic, political, legal, and technological---all of which must play a role in future decisions that governments must make concerning possible mitigation strategies. The first of these scientific questions is, "how extensively would deep-ocean injection affect the marine biota in the vicinity of the injection site?" The second question is, "if fossil CO2 is to be injected into the ocean, how long might it stay isolated from the atmosphere?"

Our focus is on the second question, using the only means available, simulations in global-scale ocean models. Previous studies have addressed this same question, first with relatively simplistic box models and subsequently with one ocean general circulation model (OGCM) from MPI. A good summary of previous work is provided by Dewey et al. (1996). OGCM's describe ocean circulation in three dimensions. Thus they can be used to make assessments concerning the dependence of injection site location and depth upon the effectiveness of the ocean to retain sequestered CO2. Unfortunately, model estimates can be biased due to model simplifications, omissions, and uncertainties. Substantial effort is usually required in regards to model validation and comparison before one can be sure of predicted results.

Here we provide the necessary protocols, boundary conditions, and code so that different groups using different OGCM's can make ocean CO2 injection simulations in a consistent manner. Our objective is to begin to estimate the effect of uncertainties in model-predicted ocean circulation patterns on model-based estimates of the long term retention of CO2 injected in the ocean. This work is carried out under the framework of GOSAC (Global Ocean Storage of Anthropogenic Carbon), an international effort during 1998 to 2000, which is jointly funded by the EC Environment and Climate Programme and the IEA Greenhouse Gas R& D Programme. GOSAC also provides support for European modeling groups to participate in the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP), a project of the Global, Anlysis, Interpretation, and Modeling Task Force (GAIM) of the International Geosphere-Biosphere Programme (IGBP). Simulations described here are required for the seven GOSAC modeling groups. Non-european modeling groups (those not funded by GOSAC) are also strongly encouraged to make the simulations described in this document and to submit results for common analysis.

The protocols stipulated in this document are nearly the same as those tested in one of the GOSAC models, i.e., that from IPSL. Orr and Aumont (1999) discuss those preliminary tests and compare results to previous work.

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