The world ocean is a major sink for the vast amount of anthropogenic carbon emitted since the industrial revolution. Future climate change resulting from higher atmospheric CO2 concentration induces different feedback mechanisms that further complicate the prediction of strength and distribution of carbon sinks. A historically important process is the ocean physics, which had been shown to be important in controlling the deep ocean carbon storage, and therefore the regional and temporal air-sea CO2 fluxes.
In a recent study published in Ocean Science, Jerry Tjiputra and co-workers used a complex Earth system model to study the role of ocean circulation in transporting the dissolved anthropogenic carbon. Using one of the IPCC (Intergovernmental Panel for Climate Change)’s ‘business as usual’ future scenarios, the model is able to identify the dominant characteristic of regional oceanic anthropogenic carbon transport and storage attributed to future climate change.
The model shows that the uptake rate in today’s critical regions such as the North Atlantic is predicted to stabilize due to the reduction of CO2-solubility in this region. Weaker Atlantic Meridional Overturning Circulation strength is also expected, which further decreases the penetration rate of anthropogenic carbon into the deeper ocean.
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| Figure 1. lAccumulated anthropogenic carbon fluxes from the atmosphere (blue-line) as compared to lateral fluxes (red-line) into different ocean regions for the1850–2099 period (click on the image for larger version). Positive values represent fluxes into the region and negative otherwise. Arrow and number pairs represent accumulated transport fluxes of anthropogenic carbon between regions for the period 1850-2099. Numbers inside parenthesis represent the storage term of anthropogenic carbon in each region at the end of experiment period. All units are in (Pg C). |
In contrast, the characteristic of the circulation pattern in the Southern Ocean makes it the most efficient pathways for taking up CO2 from the atmosphere. Figure 1 shows that more than half of the anthropogenic carbon taken up in high latitude Southern Ocean is efficiently and continuously exported out of the region. Most importantly, it is transported into the deep ocean, predominantly by the intermediate waters. The model suggests that future uptake rate of anthropogenic carbon in this region will continue to increase toward the end of the 21st century, with annual uptake rate that is more than twice the global mean. The study further underlines the key role of the Southern Ocean in controlling long-term carbon uptake.