Abstract. Interannual anomalies in the sea–air carbon dioxide (CO2) exchange have been estimated from surface-ocean CO2 partial pressure measurements. Available data are sufficient to constrain these anomalies in large parts of the tropical and North Pacific and in the North Atlantic, in some areas covering the period from the mid 1980s to 2011. Global interannual variability is estimated as about 0.31 Pg C yr−1 (temporal standard deviation 1993–2008). The tropical Pacific accounts for a large fraction of this global variability, closely tied to El Niño–Southern Oscillation (ENSO). Anomalies occur more than 6 months later in the east than in the west. The estimated amplitude and ENSO response are roughly consistent with independent information from atmospheric oxygen data. This both supports the variability estimated from surface-ocean carbon data and demonstrates the potential of the atmospheric oxygen signal to constrain ocean biogeochemical processes. The ocean variability estimated from surface-ocean carbon data can be used to improve land CO2 flux estimates from atmospheric inversions.

Biogeochemical rate processes in the Southern Ocean have an important impact on the global environment. Here, we summarize an extensive set of published and new data that establishes the pattern of gross primary production and net community production over large areas of the Southern Ocean. We compare these rates with model estimates of dissolved iron that is added to surface waters by aerosols. This comparison shows that net community production, which is comparable to export production, is proportional to modeled input of soluble iron in aerosols. Our results strengthen the evidence that the addition of aerosol iron fertilizes export production in the Southern Ocean. The data also show that aerosol iron input particularly enhances gross primary production over the large area of the Southern Ocean downwind of dry continental areas.

[1] We use continuous and discrete measurements of the dissolved O 2 /Ar ratio in the mixed layer to investigate the dynamics of biological productivity during the Southern Ocean Gas Exchange Experiment in March and April 2008. Injections of SF 6 defined two water masses (patches) that were followed for up to 2 weeks. In the first patch, dissolved O 2 /Ar was supersaturated, indicating net biological production of organic carbon. In the second patch, rapidly decreasing O 2 /Ar could only be reasonably explained if the mixed layer was experiencing a period of net heterotrophy. The observations rule out dominant contributions from vertical mixing, lateral dilution, or respiration in the ship's underway seawater supply lines. We also compare nine different estimates of net community, new, primary, or gross production made during the experiment. Net community and new production estimates agreed well in the first patch but disagreed in the second patch, both during an initial net heterotrophic period but also during the apparently autotrophic period at the end of the observations. Rapidly changing productivity during the second patch complicated the comparison of methods that integrate over daily and several week timescales. Primary productivity values from on-deck 24 h 14 C incubations and gross carbon production values from photosynthesis-irradiance experiments were nearly identical even during highly dynamic periods of net heterotrophy, while gross oxygen production measurements were 3.5-4.2 times higher but with uncertainties in that ratio near AE2. These comparisons show that the photosynthesis-irradiance experiments based on 1-2 h 14 C incubations underestimated gross carbon production.Citation: Hamme, R. C., et al. (2012), Dissolved O 2 /Ar and other methods reveal rapid changes in productivity during a

The oxygen (O(2)) concentration in the surface ocean is influenced by biological and physical processes. With concurrent measurements of argon (Ar), which has similar solubility properties as oxygen, we can remove the physical contribution to O(2) supersaturation and determine the biological oxygen supersaturation. Biological O(2) supersaturation in the surface ocean reflects the net metabolic balance between photosynthesis and respiration, i.e., the net community productivity (NCP). We present a new method for continuous shipboard measurements of O(2)/Ar by equilibrator inlet mass spectrometry (EIMS). From these measurements and an appropriate gas exchange parametrization, NCP can be estimated at high spatial and temporal resolution. In the EIMS configuration, seawater from the ship's continuous intake flows through a cartridge enclosing a gas-permeable microporous membrane contactor. Gases in the headspace of the cartridge equilibrate with dissolved gases in the flowing seawater. A fused-silica capillary continuously samples headspace gases, and the O(2)/Ar ratio is measured by mass spectrometry. The ion current measurements on the mass spectrometer reflect the partial pressures of dissolved gases in the water flowing through the equilibrator. Calibration of the O(2)/Ar ion current ratio (32/40) is performed automatically every 2 h by sampling ambient air through a second capillary. A conceptual model demonstrates that the ratio of gases reaching the mass spectrometer is dependent on several parameters, such as the differences in molecular diffusivities and solubilities of the gases. Laboratory experiments and field observations performed by EIMS are discussed. We also present preliminary evidence that other gas measurements, such as N(2)/Ar and pCO(2) measurements, may potentially be performed with EIMS. Finally, we compare the characteristics of the EIMS with the previously described membrane inlet mass spectrometry (MIMS) approach.

Models describing the evolution of the partial pressure of atmospheric oxygen over Phanerozoic time are constrained by the mass balances required between the inputs and outputs of carbon and sulfur to the oceans. This constraint has limited the applicability of proposed negative feedback mechanisms for maintaining levels of atmospheric O(2) at biologically permissable levels. Here we describe a modeling approach that incorporates O(2)-dependent carbon and sulfur isotope fractionation using data obtained from laboratory experiments on carbon-13 discrimination by vascular land plants and marine plankton. The model allows us to calculate a Phanerozoic O(2) history that agrees with independent models and with biological and physical constraints and supports the hypothesis of a high atmospheric O(2) content during the Carboniferous (300 million years ago), a time when insect gigantism was widespread.

[1] Net community production (NCP) and gross primary production (GPP) are two key metrics for quantifying the biological carbon cycle. In this study, we present a detailed characterization of NCP and GPP in the western equatorial Pacific during August and September 2006. We use continuous measurements of dissolved gases (O 2 and Ar) in the surface water in order to quantify NCP at subkilometer scale resolution. We constrain GPP in discrete samples using the triple isotopic composition of O 2 . We find the average NCP in the western equatorial Pacific is 5.9 ± 0.9 mmol O 2 m −2 d −1(equivalent to 1.5 ± 0.2 mol C m −2 yr −1 with error estimates reflecting 1s confidence levels) and the average GPP is 121 ± 34 mmol O 2 m −2 d −1 (equivalent to 32 ± 9 mol C m −2 yr −1 ). The measurements reveal significant spatial variability on length scales as small as 50 km.

The isotopic composition of organic carbon buried in marine sediments is an appealing proxy for palaeo CO2 concentrations due to the well-documented effect of CO2 concentrations on carbon fractionation by phytoplankton. However, a number of factors, in addition to CO2 concentrations, influence this fractionation. Included among these factors are cell geometry, in particular surface/volume ratios, growth rate, and the presence of CO2 concentrating mechanisms. Other potentially confounding factors are calcification, diagenesis, and the nature of the growth-rate-limiting factor, e.g. light vs nutrients. Because of these confounding factors, palaeoreconstructions based on the isotopic composition of organic carbon (δ13C) will almost certainly have to be based on the isotopic signatures of organic compounds that can be associated with a single species, or group of physiologically similar species. Long-chain alkenones produced by certain species of coccolithophores may provide a suitable diagnostic marker. By combining the δ13C of the alkenone carbon with the δ13C of coccolith carbon and the Sr/Ca ratio of the coccoliths, it is possible to calculate the extent of carbon fractionation (εp) and estimate growth rates. However, active transport of inorganic carbon tends to make εp insensitive to CO2 concentrations when the ratio of growth rate to CO2 concentration exceeds 0.285/rkg mol–1d–1, where r is the effective spherical radius of the cell in microns. Palaeo CO2 concentrations calculated from alkenone and coccolith δ13C data capture the gross features of CO2 concentrations in the Vostok ice core, but explain only 30–35% of the variance in the latter. The absence of a higher correlation may in part reflect the impact of active transport, particularly during glacial times. The impact of active transport may have been less severe prior to the Pleistocene, since CO2 concentrations are believed to have been higher than present-day values during most of Phanerozoic time.

[1] Improvements made to an established mass spectrometric method for measuring changes in atmospheric O 2 /N 2 are described. With the improvements in sample handling and analysis, sample throughput and analytical precision have both increased. Aliquots from duplicate flasks are repeatedly measured over a period of 2 weeks, with an overall standard error in each flask of 3-4 per meg, corresponding to 0.6-0.8 ppm O 2 in air. Records of changes in O 2 /N 2 from six global sampling stations (Barrow, American Samoa, Cape Grim, Amsterdam Island, Macquarie Island, and Syowa Station) are presented. Combined with measurements of CO 2 from the same sample flasks, land and ocean carbon uptake were calculated from the three sampling stations with the longest records (Barrow, Samoa, and Cape Grim). From 1994-2002, We find the average CO 2 uptake by the ocean and the land biosphere was 1.7 ± 0.5 and 1.0 ± 0.6 GtC yr À1 respectively; these numbers include a correction of 0.3 Gt C yr À1 due to secular outgassing of ocean O 2 . Interannual variability calculated from these data shows a strong land carbon source associated with the 1997-1998 El Niño event, supporting many previous studies indicating that high atmospheric growth rates observed during most El Niño events reflect diminished land uptake. Calculations of interannual variability in land and ocean uptake are probably confounded by non-zero annual air sea fluxes of O 2 . The origin of these fluxes is not yet understood.