The impact of diurnal variability in sea surface temperature on the central Atlantic air-sea CO2 flux H. Kettle1, C. J. Merchant1, C. D. Jeffery2, M. J. Filipiak1, and C. L. Gentemann3 1School of GeoSciences, The University of Edinburgh, UK 2National Oceanography Centre, Southampton, UK 3Remote Sensing Systems, Santa Rosa, CA, USA
Abstract. The effect of diurnal variations in sea surface temperature (SST) on the
air-sea flux of CO2 over the central Atlantic ocean and Mediterranean Sea
(60 S–60 N, 60 W–45 E) is evaluated for 2005–2006. We use high spatial resolution hourly satellite ocean skin temperature data
to determine the diurnal warming (ΔSST). The CO2 flux is then
computed using three different temperature fields – a foundation temperature
(Tf, measured at a depth where there is no diurnal variation), Tf, plus
the hourly ΔSST and Tf, plus the monthly average of the ΔSSTs. This is
done in conjunction with a physically-based parameterisation for the gas
transfer velocity (NOAA-COARE). The differences between the fluxes evaluated
for these three different temperature fields quantify the effects of both
diurnal warming and diurnal covariations. We find that including diurnal
warming increases the CO2 flux out of this region of the Atlantic for 2005–2006 from
9.6 Tg C a−1 to 30.4 Tg C a−1 (hourly ΔSST) and
31.2 Tg C a−1 (monthly average of ΔSST measurements). Diurnal warming in this region, therefore, has a
large impact on the annual net CO2 flux but diurnal covariations are negligible.
However, in this region of the Atlantic the uptake and outgassing of CO2 is
approximately balanced over the annual cycle, so although we find diurnal
warming has a very large effect here, the Atlantic as a whole is a very
strong carbon sink (e.g. −920 Tg C a−1 Takahashi et al., 2002)
making this is a small contribution to the Atlantic carbon budget.
Citation: Kettle, H., Merchant, C. J., Jeffery, C. D., Filipiak, M. J., and Gentemann, C. L.: The impact of diurnal variability in sea surface temperature on the central Atlantic air-sea CO2 flux, Atmos. Chem. Phys., 9, 529-541, doi:10.5194/acp-9-529-2009, 2009.