Atmospheric CO2 seasonality and the air-sea flux of CO2.

The amplitude, phase, and form of the seasonal cycle of atmospheric CO₂ concentrations varies on many time and space-scales (Peters et al., 2007). Intra-annual CO₂ variation is primarily driven by seasonal uptake and release of CO₂ by the terrestrial biosphere (Machta et al., 1977; Buchwitz et al., 2007), with a small (Cadule et al., 2010), but potentially changing (Gorgues et al., 2010) contribution from the ocean. Variability in the magnitude, spatial distribution, and seasonal drivers of terrestrial Net Primary Productivity (NPP) will be induced by, amongst other factors, anthropogenic CO₂ release (Keeling et al., 1996), land-use change (Zimov et al., 1999) and planetary orbital variability, and will lead to changes in CODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. seasonality. Here I describe two separate mechanisms by which co-variability of the seasonal cycles in atmospheric CO₂ concentration, ocean temperature, and sea-ice extent could potentially lead to rapid changes in the air-sea flux of CO₂ at high latitudes. One mechanism responds to an increase in CODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. seasonality by pumping CO₂ into the ocean, and the other by releasing CO₂ from the ocean (in a relative sense). The relative importance of the two mechanisms is determined by the seasonal extent of sea-ice, the net sign of their operation may therefore have interesting implications for glacial-interglacial and future climate change. To capture the described feedbacks within earth system models, CODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. concentrations must be allowed to evolve freely, forced only by anthropogenic emissions, rather than prescribed CODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. concentrations. The decision to prescribe CODue to image rights restrictions, multiple line equation(s) cannot be graphically displayed. concentrations within model simulations for the fifth IPCC climate assessment (Taylor et al., 2009) may therefore result in an underestimation of changes in marine CO₂ sources and sinks. [ABSTRACT FROM AUTHOR]