Estimate of Interhemispheric Ocean Carbon Transport Based on ΣCO₂ and Nutrient Distribution

Abstract

The partial pressure of CO₂ in the atmosphere (pCO₂) has been rising ever since the industrial revolution in the early 1800s. The release of CO₂ from fossil fuel combustion is the main source of the extra amount of CO₂ in the atmosphere. Other sources, such as deforestation and soil disturbances from agricultural practice, may have also contributed to the rise. Although the fossil fuel CO₂ release is relatively well documented [Marland and Boden (1991) give an average of 5.4 gigatons (Gt) of carbon released per year for the 1980s], the release from land use is uncertain (Post et al. 1990). Direct observation of the increase in atmospheric CO₂ partial pressure in the past few decades indicates that approximately 55% to 57% of the amount of carbon released from fossil fuel has remained in the atmosphere (Keeling et al. 1989a). To balance the carbon budget, the remaining anthropogenic CO₂ molecules must have entered the ocean or terrestrial biosphere. The amount of carbon taken up by the ocean is estimated to be in the range between 26% and 35% of fossil fuel CO₂ (Peng 1986). These estimates are made by various ocean models calibrated with the distribution of geochemical tracers in the ocean. An average for oceanic uptake in the 1980s is estimated to be about 2.1 gigatons of carbon per year (Gt C/year). Depending on the magnitude of the amount of carbon released from the land biosphere, we need to search for other carbon sinks (so-called missing sinks) and to quantify their sizes in order to balance the carbon budget.