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Does atmospheric CO2 seasonality play an important role in governing the air-sea flux of CO2?
- Source :
- Biogeosciences; 2012, Vol. 9 Issue 6, p2311-2323, 13p
- Publication Year :
- 2012
-
Abstract
- The amplitude, phase, and form of the seasonal cycle of atmospheric CO<subscript>2</subscript> concentrations varies on many time and space scales (Peters et al., 2007). Intra-annual CO<subscript>2</subscript> variation is primarily driven by seasonal uptake and release of CO<subscript>2</subscript> by the terrestrial biosphere (Machta et al., 1977; Buchwitz et al., 2007), with a small (Cadule et al., 2010; Heimann et al., 1998), but potentially changing (Gorgues et al., 2010) contribution from the ocean. Variability in the magnitude, spatial distribution, and seasonal drivers of terrestrial net pri- mary productivity (NPP) will be induced by, amongst other factors, anthropogenic CO<subscript>2</subscript> release (Keeling et al., 1996), land-use change (Zimov et al., 1999) and planetary orbital atm variability, and will lead to changes in CO<superscript>atm</superscript><subscript>2</subscript> seasonality. Despite CO<superscript>atm</superscript><subscript>2</subscript> seasonality being a dynamic and prominent feature of the Earth System, its potential to drive changes in the air-sea flux of CO<subscript>2</subscript> has not previously (to the best of my knowledge) been explored. It is important that we investigate the impact of CO<superscript>atm</superscript><subscript>2</subscript> seasonality change, and the potential for carbon-cycle feedbacks to operate through the modification of the CO<superscript>atm</superscript><subscript>2</subscript> seasonal cycle, because the decision had been made to prescribe CO<superscript>atm</superscript><subscript>2</subscript> concentrations (rather than emissions) within model simulations for the fifth IPCC climate assessment (Taylor et al., 2009). In this study I undertake ocean-model simulations within which different magnitude CO<superscript>atm</superscript><subscript>2</subscript> seasonal cycles are prescribed. These simulations allow me to examine the effect of a change in CO<superscript>atm</superscript><subscript>2</subscript> seasonal cycle magnitude on the air-sea CO<subscript>2</subscript> flux. I then use an offline model to isolate the drivers of the identified air-sea CO<subscript>2</subscript> flux change, and propose mechanisms by which this change may come about. Three mechanisms are identified by which co-variability of the seasonal cycles in atmospheric CO<subscript>2</subscript> concentration, and seasonality in sea-ice extent, wind-speed and ocean temperature, could potentially lead to changes in the air-sea flux of CO<subscript>2</subscript> at mid-to-high latitudes. The sea-ice driven mechanism responds to an increase in CO<superscript>atm</superscript><subscript>2</subscript> seasonality by pumping CO<subscript>2</subscript> into the ocean, the wind-speed and solubility-driven mechanisms, by releasing CO<subscript>2</subscript> from the ocean (in a relative sense). The relative importance of the mechanisms will be determined by, amongst other variables, the seasonal extent of sea-ice. To capture the described feedbacks within earth system models, CO<superscript>atm</superscript><subscript>2</subscript> concentrations must be allowed to evolve freely, forced only by anthropogenic emissions rather than prescribed CO<superscript>atm</superscript><subscript>2</subscript> concentrations; however, time-integrated ocean simulations imply that the cumulative net air-sea flux could be at most equivalent to a few ppm CO<superscript>atm</superscript><subscript>2</subscript>. The findings presented here suggest that, at least under pre-industrial conditions, the prescription of CO<superscript>atm</superscript><subscript>2</subscript>concentrations rather than emissions within simulations will have little impact on the marine anthropogenic CO<subscript>2</subscript> sink. [ABSTRACT FROM AUTHOR]
- Subjects :
- CARBON dioxide
OCEAN-atmosphere interaction
BIOSPHERE
CLIMATOLOGY
ATMOSPHERE
Subjects
Details
- Language :
- English
- ISSN :
- 17264170
- Volume :
- 9
- Issue :
- 6
- Database :
- Complementary Index
- Journal :
- Biogeosciences
- Publication Type :
- Academic Journal
- Accession number :
- 84417913
- Full Text :
- https://doi.org/10.5194/bg-9-2311-2012