Modern Carbon Fluxes

Since the pre-industrial period, atmospheric CO2 concentrations have increased from 280 ppm to nearly 380 ppm. This increase in CO2 drives the sea water to absorb CO2 from the atmosphere so that surface sea water is pushed to achieve thermodynamic equilibrium with the atmospheric partial pressure. Figure 3.2 shows a summary of the additional fluxes in the modern ocean resulting from human activity and rising atmospheric CO2. The role of the ocean in the global carbon cycle has changed from being a net source of CO2 to the atmosphere to a net sink for CO2 of ~2 Pg C/year (Sabine et al., 2004a).

Today, the average pCO2 of the atmosphere is ~7 ppm higher than the global ocean pCO2. This small air-sea difference, when spread across the entire surface of the ocean, is sufficient to account for the oceanic uptake of anthropogenic CO2. The pCO2 values in mixed-layer waters, which exchange CO2 directly with the atmosphere, are affected primarily by changes in temperature, dissolved inorganic carbon (DIC) and total alkalinity (TAlk). While the water temperature is regulated by physical processes, including solar energy input, sea-air heat exchanges and mixed-layer thickness, DIC is primarily controlled by the physical processes of sea-air exchange and upwelling of subsurface waters as well as the biological processes of photosynthesis and respiration. Biological production removes carbon from surface waters to form organic material. As organisms die and sink to the ocean interior, they decompose, releasing the carbon once again to the water. This process contributes to higher pCO2 and DIC concentrations in deep ocean waters relative to the surface waters. As pCO2 increases when the water is warmed and decreases as a result of biological uptake, the oceanic uptake and release of CO2 is governed by a balance between the changes in sea water temperature, net biological utilization of CO2 and circulation processes in the upper ocean (Zeebe and Wolf-Gladrow, 2001).

Taro Takahashi of Lamont-Doherty Earth Observatory and his collaborators have amassed a database of more than 1.7 million surface ocean pCO2 measurements, spanning more than 30 years, and derived a pCO2 climatology for the global ocean (Takahashi et al., 2002). These data have been used to determine global and regional sea-air CO2 fluxes with an average annual global open-oceanic uptake of 1.5 ± 0.4 Pg C/year for a nominal year of 1995 (Takahashi et al., 2002; revised by T. Takahashi, New York, 2005, personal communication). This flux estimate represents the total net flux in 1995. The total anthropogenic flux would be the difference between the 1995 net sea-air flux and the pre-industrial net sea-air flux (i.e. -1.5 - 0.6 = -2.1 Pg C/year) - a flux consistent with earlier estimates based on models.

Fig. 3.2. Schematic representation of the ocean carbon cycle with pre-industrial fluxes and reservoir sizes (upright) and average values for the 1980s and 1990s (italic). Fluxes (arrows) are in Pg C/year and reservoir sizes (numbers in square brackets) are in Pg C. (Modified from Sabine et al., 2004a.)

Fig. 3.2. Schematic representation of the ocean carbon cycle with pre-industrial fluxes and reservoir sizes (upright) and average values for the 1980s and 1990s (italic). Fluxes (arrows) are in Pg C/year and reservoir sizes (numbers in square brackets) are in Pg C. (Modified from Sabine et al., 2004a.)

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Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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