ALBERT

Description: Author Posting. © American Geophysical Union, 2021. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 126(8), (2021): e2021JC017510, https://doi.org/10.1029/2021JC017510.

Description: The air-sea exchange of oxygen (O2) is driven by changes in solubility, biological activity, and circulation. The total air-sea exchange of O2 has been shown to be closely related to the air-sea exchange of heat on seasonal timescales, with the ratio of the seasonal flux of O2 to heat varying with latitude, being higher in the extratropics and lower in the subtropics. This O2/heat ratio is both a fundamental biogeochemical property of air-sea exchange and a convenient metric for testing earth system models. Current estimates of the O2/heat flux ratio rely on sparse observations of dissolved O2, leaving it fairly unconstrained. From a model ensemble we show that the ratio of the seasonal amplitude of two atmospheric tracers, atmospheric potential oxygen (APO) and the argon-to-nitrogen ratio (Ar/O2), exhibits a close relationship to the O2/heat ratio of the extratropics (40–70°). The amplitude ratio, A APO/A ArN2, is relatively constant within the extratropics of each hemisphere due to the zonal mixing of the atmosphere. A APO/A ArN2 is not sensitive to atmospheric transport, as most of the observed spatial variability in the seasonal amplitude of δAPO is compensated by similar variations in δ(Ar/N2). From the relationship between O2/heat and A APO/A ArN2 in the model ensemble, we determine that the atmospheric observations suggest hemispherically distinct O2/heat flux ratios of 3.3 ± 0.3 and 4.7 ± 0.8 nmol J-1 between 40 and 70° in the Northern and Southern Hemispheres respectively, providing a useful constraint for O2 and heat air-sea fluxes in earth system models and observation-based data products.

Description: The recent atmospheric measurements of the Scripps program have been supported via funding from the NSF and the National Oceanographic and Atmospheric Administration (NOAA) under grants 1304270 and OAR-CIPO-2015-2004269. M. Manizza and R. F. Keeling thank NSF for financial support via the OCE-1130976 grant. M. Manizza thanks additional financial support from NSF via the ARRA OCE-0850350 grant. S. C. Doney acknowledges support from NSF PLR-1440435. Keith Rodgers acknowledges support from IBS-R028-D1. Gael Forget and the ECCO group kindly provided the ECCOv4 heat fluxes.

Description: 2022-01-22

Description: The Southern Ocean plays a critical role in the global climate system by mediating atmosphere–ocean partitioning of heat and carbon dioxide. However, Earth system models are demonstrably deficient in the Southern Ocean, leading to large uncertainties in future air–sea CO2 flux projections under climate warming and incomplete interpretations of natural variability on interannual to geologic time scales. Here, we describe a recent aircraft observational campaign, the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study, which collected measurements over the Southern Ocean during January and February 2016. The primary research objective of the ORCAS campaign was to improve observational constraints on the seasonal exchange of atmospheric carbon dioxide and oxygen with the Southern Ocean. The campaign also included measurements of anthropogenic and marine biogenic reactive gases; high-resolution, hyperspectral ocean color imaging of the ocean surface; and microphysical data relevant for understanding and modeling cloud processes. In each of these components of the ORCAS project, the campaign has significantly expanded the amount of observational data available for this remote region. Ongoing research based on these observations will contribute to advancing our understanding of this climatically important system across a range of topics including carbon cycling, atmospheric chemistry and transport, and cloud physics. This article presents an overview of the scientific and methodological aspects of the ORCAS project and highlights early findings.

Description: Fluxes of halogenated volatile organic compounds (VOCs) over the Southern Ocean remain poorly understood, and few atmospheric measurements exist to constrain modeled emissions of these compounds. We present observations of CHBr3, CH2Br2, CH3I, CHClBr2, CHBrCl2, and CH3Br during the O2∕N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study and the second Atmospheric Tomography mission (ATom-2) in January and February of 2016 and 2017. Good model–measurement correlations were obtained between these observations and simulations from the Community Earth System Model (CESM) atmospheric component with chemistry (CAM-Chem) for CHBr3, CH2Br2, CH3I, and CHClBr2 but all showed significant differences in model : measurement ratios. The model : measurement comparison for CH3Br was satisfactory and for CHBrCl2 the low levels present precluded us from making a complete assessment. Thereafter, we demonstrate two novel approaches to estimate halogenated VOC fluxes; the first approach takes advantage of the robust relationships that were found between airborne observations of O2 and CHBr3, CH2Br2, and CHClBr2. We use these linear regressions with O2 and modeled O2 distributions to infer a biological flux of halogenated VOCs. The second approach uses the Stochastic Time-Inverted Lagrangian Transport (STILT) particle dispersion model to explore the relationships between observed mixing ratios and the product of the upstream surface influence of sea ice, chl a, absorption due to detritus, and downward shortwave radiation at the surface, which in turn relate to various regional hypothesized sources of halogenated VOCs such as marine phytoplankton, phytoplankton in sea-ice brines, and decomposing organic matter in surface seawater. These relationships can help evaluate the likelihood of particular halogenated VOC sources and in the case of statistically significant correlations, such as was found for CH3I, may be used to derive an estimated flux field. Our results are consistent with a biogenic regional source of CHBr3 and both nonbiological and biological sources of CH3I over these regions.

Description: We present observations of CHBr3, CH2Br2, CH3I, CHClBr2, and CHBrCl2 from the Trace Gas Organic Analyzer (TOGA) during the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study and the 2nd Atmospheric Tomography mission (ATom-2), in January and February of 2016 and 2017. We also use CH3Br from the University of Miami Advanced Whole Air Sampler (AWAS) on ORCAS and from the UC Irvine Whole Air Sampler (WAS) on ATom-2. We compare our observations with simulations from the Community Atmosphere Model with Chemistry (CAM-Chem). We report regional enrichment ratios of CHBr3 and CH2Br2 to O2 of 0.19 ± 0.01, and 0.07 ± 0.004 pmol : mol, poleward of 60° S between 180° W and 55° W, and of 0.32 ± 0.02, 0.07 ± 0.004 pmol : mol over the Patagonian Shelf, between 40° S and 55° S and between 70° W and 55° W where we also report enrichment ratios of CH3I to O2 of 0.38 ± 0.03 pmol : mol and of CH2ClBr2 to O2 of 0.19 ± 0.04 pmol: mol. Using the Stochastic Time-Inverted Lagrangian Transport (STILT) particle dispersion model, we use correlations between halogenated hydrocarbon mixing ratios and the upwind influences of chlorophyll a, sea ice, solar radiation, and dissolved organic material to investigate previously hypothesized sources of halogenated volatile organic compounds (HVOCs) in the southern high latitudes. Our results are consistent with a biogenic regional source of CHBr3, and both non-biological and biological sources of CH3I over these regions, but do not corroborate a regional sea-ice source of HVOCs in January and February. Based on these relationships, we estimate the average two-month (Jan.-Feb.) emissions poleward of 60° S between 180° W and 55° W of CHBr3, CH2Br2, CH3I, and CHClBr2 to be 91 ± 8, 31 ± 17, 35 ± 29, and 11 ± 4 pmol m−2 hr−1, and regional emissions of these gases over the Patagonian Shelf to be 329 ± 23, 69 ± 5, 392 ± 32, 24 ± 4 pmol m−2 hr−1 respectively.

Description: Ground-based atmospheric observations of CO2, δ(O2∕N2), N2O, and CH4 were used to make estimates of the air–sea fluxes of these species from the Lüderitz and Walvis Bay upwelling cells in the northern Benguela region, during upwelling events. Average flux densities (±1σ) were 0.65±0.4 µmol m−2 s−1 for CO2, -5.1±2.5 µmol m−2 s−1 for O2 (as APO), 0.61±0.5 nmol m−2 s−1 for N2O, and 4.8±6.3 nmol m−2 s−1 for CH4. A comparison of our top-down (i.e., inferred from atmospheric anomalies) flux estimates with shipboard-based measurements showed that the two approaches agreed within ±55 % on average, though the degree of agreement varied by species and was best for CO2. Since the top-down method overestimated the flux density relative to the shipboard-based approach for all species, we also present flux density estimates that have been tuned to best match the shipboard fluxes. During the study, upwelling events were sources of CO2, N2O, and CH4 to the atmosphere. N2O fluxes were fairly low, in accordance with previous work suggesting that the evasion of this gas from the Benguela is smaller than for other eastern boundary upwelling systems (EBUS). Conversely, CH4 release was quite high for the marine environment, a result that supports studies that indicated a large sedimentary source of CH4 in the Walvis Bay area. These results demonstrate the suitability of atmospheric time series for characterizing the temporal variability of upwelling events and their influence on the overall marine greenhouse gas (GHG) emissions from the northern Benguela region.

Description: Ground-based atmospheric observations of CO2, δ(O2/N2), N2O, and CH4 were used to make top-down estimates of the air–sea fluxes of these species from the Lüderitz and Walvis Bay upwelling cells in the northern Benguela region, during upwelling events. Average flux densities (±1σ) were 0.64 ± 0.4 μmol m−2 sec−1 for CO2, −5.1 ± 1.4 μmol m−2 sec−1 for O2 (as APO), 0.57 ± 0.3 nmol m−2 sec−1 for N2O, and 4.3 ± 5.5 nmol m−2 sec−1 for CH4. A comparison of our top-down flux estimates with shipboard-based measurements showed good agreement between both approaches. During the study, upwelling events were sources of CO2, N2O, and CH4 to the atmosphere. N2O fluxes were fairly low, in accordance with previous work suggesting that the evasion of this gas from the Benguela is smaller than for other Eastern Boundary Upwelling Systems (EBUS). Conversely, CH4 release was quite high for the marine environment, a result that supports studies that indicated a large sedimentary source of CH4 in the Walvis Bay area. These results demonstrate the suitability of atmospheric time series for characterizing the temporal variability of upwelling events and their influence on the overall marine GHG emissions from the northern Benguela region.

Description: Nitrous oxide (N2O) and carbon monoxide (CO) are atmospheric trace gases which significantly influence Earth’s climate through their role as greenhouse gases. In addition, N2O is currently considered to be main ozone-depleting substance of the 21st century. Despite its importance, N2O and CO emission estimates from vast areas of the ocean are associated with large uncertainties mainly due to the lack of adequate temporal and spatial resolution. By making use of a novel technique based upon off-axis integrated cavity output spectroscopy (OA-ICOS) in combination with custom equilibration systems, we developed a method which allows measuring along-track N2O and CO in surface waters and the overlying atmosphere. Performance tests demonstrated the high stability of the analytic system, with low optimal integration times of 2 and 4 min for N2O and CO respectively, as well as detection limits 〈 40 ppt and precision better than 0.3 ppb Hz−1/2. Comparison of our method and well-established discrete methods for dissolved N2O and atmospheric CO evidenced a reliable operation of the setup in the field. The applicability of the system for continuous measurements both in research ships and vessels of opportunity is discussed in light of the results obtained during different deployments carried out in the tropical and North Atlantic.

Description: A new, near-coastal background site was established for observations of greenhouse gases (GHGs) and atmospheric oxygen in the central Namib Desert near Gobabeb, Namibia. The location of the site was chosen to provide observations in a data-poor region in the global sampling network for GHGs. Semi-automated, continuous measurements of carbon dioxide, methane, nitrous oxide, carbon monoxide, atmospheric oxygen, and basic meteorology are made at a height of 21 m a.g.l., 50 km from the coast at the northern border of the Namib Sand Sea. Atmospheric oxygen is measured with a differential fuel cell analyzer. Carbon dioxide and methane are measured with an early-model cavity ring-down spectrometer; nitrous oxide and carbon monoxide are measured with an off-axis integrated cavity output spectrometer. Instrument-specific water corrections are employed for both instruments in lieu of drying. The representativity of the site was assessed within the context of atmospheric transport. During austral summer, strong equatorward winds are present as a result of the Hadley circulation. This brings marine boundary layer air inland to Gobabeb. In austral winter, the descending branch of the southern Hadley cell is at the same latitude as NDAO, which encourages the establishment of anticyclonic conditions over southern Africa. The variability of air mass history during this time of year is quite high, alternating between marine and terrestrial air masses, as well as air that was recently in contact with the surface and air that had descended from heights greater than 2 km. NOAA ask samples taken at Gobabeb from 1996 to the present appeared to respond to these seasonal patterns in atmospheric dynamics, when compared to other marine background sites at the same latitude as NDAO. Two years of data are presented from the observatory. Diurnal variability was noted at times for all species, particularly for atmospheric oxygen. Through stoichiometry and phasing, this was attributed primarily to the local wind system, which features a prominent sea breeze, and daily boundary layer oscillations. Large anomalies in carbon monoxide and methane were observed in the time series on a synoptic time scale, during the ascending portion of the seasonal cycle. These were attributed to an alternation between polluted air masses from the continental interior and marine boundary layer air. The continental air masses were progressively in uenced by biomass burning as the fire season developed. The concentration of re activity close to the station increased throughout the year, peaking in September, a fact re ected in the enhancement ratio of CH4 to CO. During such synoptic events the molar exchange ratio of O2 to CO2 also supported this interpretation. Finally, the NDAO time series was used to make top-down estimates of air-sea fl uxes of the main measurands from the Lüderitz and Walvis Bay upwelling cells in the Benguela Current region, during upwelling events. Flux densities were evaluated using shipboard measurements within the study area, showing good agreement with the top-down estimates. Average flux densities for CO2 were 0.450.4 µmol m-2 sec-1, -3.92.6 µmol m-2 sec-1 for O2, 6.05.0 nmol m-2 sec-1 for CH4, 0.50.4 nmol m-2 sec-1 for N2O, and 2.71.7 nmol m-2 sec-1 for CO. N2O uxes were fairly low, in accord with previous work, suggesting that the evasion of this gas from the Benguela is smaller than in other upwelling systems. Conversely, methane release was very high for the marine environment, which adds to mounting evidence of a large sedimentary source of methane in the Walvis Bay area. Carbon dioxide and oxygen uxes were substantial and probably not accounted for in current budgets.