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Continuous measurements of CO 2 partial pressure, dissolved oxygen, and the oxygen argon ratio (O 2 /Ar) in surface waters, complemented by discrete observations of inorganic carbon, along a late-summer south-to-north transect in the Australian Sector of the Southern Ocean (115°E, WOCE I9S) are presented. The largest net community production (NCP, based on O 2 /Ar), and air–sea CO 2 disequilibrium (ΔDpCO 2 ) were found in three regions: (1) between the southern boundary of the Antarctic Circumpolar Current (63.6°S) and southern extent of the Polar Front (58.6°S, NCP = 30 mmol C m − 2 d − 1 , ΔpCO 2 = 30 to 50 μatm); (2) between the northern extent of the Sub-Antarctic Front (45.5°S) and the Sub-Tropical Front (39.8°S, NCP = 50 mmol C m − 2 d − 1 , ΔpCO 2 = 25 μatm); and (3) near 35°S (NCP = 50 mmol C m − 2 d − 1 , ΔpCO 2 = 20 μatm). Areas of enhanced NCP were correlated with shallow mixed layer depths, suggesting that production is controlled in part by light limitation. We found good agreement between estimates of NCP based on O 2 /Ar measurements and those derived from seasonal (mixed layer) inorganic carbon deficits. In ice covered areas, and in areas where surface temperature changes act on shorter timescales than the equilibration of oxygen in the mixed layer, we find that physical controls on surface O 2 are of equal magnitude to biological controls, which has important implications for the use of oxygen sensors on autonomous platforms to infer NCP. [ABSTRACT FROM AUTHOR]

The Subantarctic Zone (SAZ), which covers the northern half of the Southern Ocean between the Subtropical and Subantarctic Fronts, is important for air-sea CO2 exchange, ventilation of the lower thermocline, and nutrient supply for global ocean productivity. Here we present the first high-resolution autonomous observations of mixed layer CO2 partial pressure ( pCO2) and hydrographic properties covering a full annual cycle in the SAZ. The amplitude of the seasonal cycle in pCO2 (∼60 μatm), from near-atmospheric equilibrium in late winter to ∼330 μatm in midsummer, results from opposing physical and biological drivers. Decomposing these contributions demonstrates that the biological control on pCO2 (up to 100 μatm), is 4 times larger than the thermal component and driven by annual net community production of 2.45 ± 1.47 mol C m−2 yr−1. After the summer biological pCO2 depletion, the return to near-atmospheric equilibrium proceeds slowly, driven in part by autumn entrainment into a deepening mixed layer and achieving full equilibration in late winter and early spring as respiration and advection complete the annual cycle. The shutdown of winter convection and associated mixed layer shoaling proceeds intermittently, appearing to frustrate the initiation of production. Horizontal processes, identified from salinity anomalies, are associated with biological pCO2 signatures but with differing impacts in winter (when they reflect far-field variations in dissolved inorganic carbon and/or biomass) and summer (when they suggest promotion of local production by the relief of silicic acid or iron limitation). These results provide clarity on SAZ seasonal carbon cycling and demonstrate that the magnitude of the seasonal pCO2 cycle is twice as large as that in the subarctic high-nutrient, low-chlorophyll waters, which can inform the selection of optimal global models in this region. [ABSTRACT FROM AUTHOR]

The Southern Ocean (44° S-75° S) plays a critical role in the global carbon cycle, yet remains one of the most poorly sampled ocean regions. Different approaches have been used to estimate sea-air CO2 fluxes in this region: synthesis of surface ocean observations, ocean biogeochemical models, and atmospheric and ocean inversions. As part of the RECCAP (REgional Carbon Cycle Assessment and Processes) project, we combine these different approaches to quantify and assess the magnitude and variability in Southern Ocean sea-air CO2 fluxes between 1990-2009. Using all models and inversions (26), the integrated median annual sea-air CO2 flux of -0.42±0.07 Pg C yr-1 for the 44° S-75° S region is consistent with the -0.27±0.13 Pg C yr-1 calculated using surface observations. The circumpolar region south of 58° S has a small net annual flux (model and inversion median: -0.04±0.07 Pg C yr-1 and observations: +0.04±0.02 Pg C yr-1), with most of the net annual flux located in the 44° S to 58° S circumpolar band (model and inversion median: -0.36±0.09 Pg C yr-1 and observations: -0.35±0.09 Pg C yr-1 ). Seasonally, in the 44° S-58° S region, the median of 5 ocean biogeochemical models captures the observed sea-air CO2 flux seasonal cycle, while the median of 11 atmospheric inversions shows little seasonal change in the net flux. South of 58° S, neither atmospheric inversions nor ocean biogeochemical models reproduce the phase and amplitude of the observed seasonal sea-air CO2 flux, particularly in the AustralWinter. Importantly, no individual atmospheric inversion or ocean bio-geochemical model is capable of reproducing both the observed annual mean uptake and the observed seasonal cycle. This raises concerns about projecting future changes in Southern Ocean CO2 fluxes. The median interannual variability from atmospheric inversions and ocean biogeochemical models is substantial in the Southern Ocean; up to 25% of the annual mean flux with 25% of this inter-annual variability attributed to the region south of 58° S. Trends in the net CO2 flux from the inversions and models are not statistically different from the expected increase of -0.05 Pg C yr-1 decade-1 due to increasing atmospheric CO2 concentrations. However, resolving long term trends is difficult due to the large interannual variability and short time frame (1990-2009) of this study. [ABSTRACT FROM AUTHOR]

The roles of iron and light in controlling biomass and primary productivity are clearly established in the Southern Ocean. However, their influence on net community production (NCP) and carbon export remains to be quantified. To improve our understanding of NCP and carbon export production in the Subantarctic Zone (SAZ) and the northern reaches of the Polar Frontal Zone (PFZ), we conducted continuous onboard determinations of NCP as part of the Sub-Antarctic Sensitivity to Environmental Change (SAZ-Sense) study, which occurred in January-February 2007. Biological O2 supersaturation was derived from measuring O2/Ar ratios by equilibrator inlet mass spectrometry. Based on these continuous measurements, NCP during the austral summer 2007 in the Australian SAZ was approximately 43 mmolO2 m-2 d-1. Both gross primary productivity (estimated from the oxygen triple isotope anomaly) and NCP showed significant spatial variability, with larger values near the Subtropical front, and a general southward decrease. For shallower mixed layers (<50 m), dissolved Fe concentrations and Fe sufficiency, estimated from variable fluorescence, correlated strongly with NCP. At stations with deeper mixed layers, NCP was consistently low, regardless of iron sufficiency, consistent with light availability also being an important control of NCP. Our new observations provide independent evidence for the critical roles of iron and light in mediating carbon export from the Southern Ocean mixed layer. [ABSTRACT FROM AUTHOR]

During late 2002 and early 2003, southern Australia was in the grip of drought and experienced one of its most active dust storm seasons in the last 40 years with large dust plumes frequently advected over the adjacent Southern Ocean. We use meteorological records of dust activity, satellite ocean color, and aerosol optical depth data and dust transport modeling to investigate the transport and deposition of mineral dust from Australia over adjacent ocean regions and to correlate it with biological response in phytoplankton standing stock as measured by chlorophyll a concentration in 5 degree latitude bands from 40° to 60°S. Seasonal maxima in mean surface chlorophyll a of -0.5 mg m3 were not achieved until late January 2003 or during February in the more southerly bands, which when compared with a 9 year satellite mean climatology suggests the phenology of the bloom in 2002-2003 was atypical. Contemporaneous field data on CO2 fugacity collected on transects between Tasmania and Antarctica show that significant atmospheric CO2 drawdown occurred as far south as 60°S during February 2003. Our results provide strong evidence for a large-scale natural dust fertilization event in the Australian sector of the Southern Ocean and highlight the importance of dust-derived nutrients in the marine carbon cycle of the Southern Ocean. [ABSTRACT FROM AUTHOR]

The article focuses on the quality control of the Southern Ocean data from the Pacific sector which are included in Carbon In the Atlantic (CARINA). It notes the use of crossover analysis between stations and inversion analysis of all crossover data to check the quality control of the Pacific sector. It infers that the outcome of the effort is an internally consistent, high-quality carbon data set for all cruises including the reference cruises.

The article reports on the extension of the North Atlantic project to include the three sectors of the Southern Ocean including the Indian sector. It notes the examination of the parameters such as total alkalinity, oxygen and phosphate for cruise-to-cruise and overall consistency. The outcome is the other properties of the carbon system that can be used to investigate the natural variability or stability of ocean chemistry and the accumulation of anthropogenic carbon.