Air‐sea CO₂ flux variability in frontal regions of the Southern Ocean from CARbon Interface OCean Atmosphere drifters

Abstract

Nine CARbon Interface OCean Atmosphere (CARIOCA) drifters were deployed in the Southern Ocean (south of the subtropical front, STF) between 2001 and 2006. They recorded 65 months of measurements in all seasons between 57uS and 40uS. Hydrological fronts detected by altimetry indicate that one buoy explored the polar zone (PZ) of the Atlantic Ocean and the western Indian Ocean; the remaining buoys explored the northern and southern parts of the subantarctic zone (SAZ) from the mid-Indian Ocean (73uE) to the eastern Pacific Ocean (112uW). The air-sea CO 2 fluxes along the buoy trajectories are primarily driven by the spatial variability of the fugacity of CO 2 in seawater, fCO 2 : in the SAZ, they vary between 21.1 and 24.2 mol m 22 yr 21 , and the largest sinks occur close to the STF; in the PZ they vary between 21.6 and 0.6 mol m 22 yr 21 . When spatially extrapolated over each region, the yearly fluxes amount to 20.8 Pg C yr 21 in the SAZ and to 20.1 Pg C yr 21 in the PZ, with very small seasonal variation. In winter-spring, the sea-surface salinity and sea-surface temperature indicate mixing with deep water close to the subantarctic front and an episodic signature of north Atlantic deep water close to the polar front (PF). These events are associated with fCO 2 close to equilibrium. On a small scale (of a few km), close to the STF, fCO 2 variations of 1-2 Pa (10-20 matm) are associated with the presence of compensated mixed layers.

Sensors and Systems for In Situ Observations of Marine Carbon Dioxide System Variables

“…In developing the program, data validation will be crucial and the limitations of current instrumentation, such as longterm stability and biofouling resistance, must be accepted and dealt with in a realistic manner to ensure optimal quality data. Yearlong deployments are often promoted as a requirement, and in some cases this has been achieved [18,19], but deployment time frames should be dictated by the importance of the information being obtained and the performance of the sensors being utilized. [22], will have sufficient power that deployment durations can be extended to ~1-year periods for a variety of advanced instrumentation.…”

Carbon, oxygen and biological productivity in the Southern Ocean in and out the Kerguelen plume: CARIOCA drifter results

“…Dissolved inorganic carbon, DIC (µmol kg −1 ), is derived from pCO 2 , Alk, SST and SSS us-L. Merlivat et al: Carbon, oxygen and biological productivity in the Southern Ocean 3515 ing the CO 2 dissociation constants of Mehrbach et al (1973) as refitted by Dickson and Millero (1987) and solubility from Weiss (1974). An accuracy of 10.5 µmol kg −1 was estimated as a result of the combined uncertainties linked to the dissociation constants, the accuracy of pCO 2 measurements and the uncertainty of the alkalinity derived from the relationship proposed by Lee et al (2006) (Boutin et al, 2008). The relative precision of successive DIC values is expected to be 0.5 µmol kg −1 Merlivat et al, 2015).…”

“…The hourly air-sea CO 2 flux, F CO 2 (mmol m −2 d −1 ), is derived from wind speed, the air-sea gradient in pCO 2 and the gas transfer velocity (Boutin et al, 2008;Merlivat et al, 2015), following:…”

Observed small spatial scale and seasonal variability of the CO<sub>2</sub> system in the Southern Ocean

“…1a). CARIOCA drifters hourly measure CO 2 fugacity (f CO 2 ), sea surface temperature (SST), sea surface salinity (SSS) and fluorescence at a depth of 2 m (Copin-Montégut et al, 2004;Boutin et al, 2008). Extensive validation of CARIOCA measurements in the Southern Ocean indicate an absolute (relative) precision close to 3 (1) microatm (see Appendix of Boutin et al, 2008).…”

“…For example, Barbero et al (2011) recomputed the CO 2 ocean uptake in the Southern Ocean's Pacific sector using pCO 2 maps extrapolated from observations by McNeil et al (2007); Boutin et al (2008); Takahashi et al (2009); Barbero et al (2011). From these four methods, the oceanic CO 2 uptake varies between 0.05 and 0.50 PgC yr −1 , with highest discrepancies (up to 0.8 PgC yr −1 ) during winter.…”