Impact of variable air-sea O2 and CO2 fluxes on atmospheric potential oxygen (APO) and land-ocean carbon sink partitioning

© 2008 Author(s). This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 5 (2008): 875-899, doi:10.5194/bg-5-875-2008A three dimensional, time-evolving field of atmospheric potential oxygen (APO ~O2/N2+CO2) was estimated using surface O2, N2 and CO2 fluxes from the WHOI ocean ecosystem model to force the MATCH atmospheric transport model. Land and fossil carbon fluxes were also run in MATCH and translated into O2 tracers using assumed O2:CO2 stoichiometries. The modeled seasonal cycles in APO agree well with the observed cycles at 13 global monitoring stations, with agreement helped by including oceanic CO2 in the APO calculation. The modeled latitudinal gradient in APO is strongly influenced by seasonal rectifier effects in atmospheric transport. An analysis of the APO-vs.-CO2 mass-balance method for partitioning land and ocean carbon sinks was performed in the controlled context of the MATCH simulation, in which the true surface carbon and oxygen fluxes were known exactly. This analysis suggests uncertainty of up to ±0.2 PgC in the inferred sinks due to variability associated with sparse atmospheric sampling. It also shows that interannual variability in oceanic O2 fluxes can cause large errors in the sink partitioning when the method is applied over short timescales. However, when decadal or longer averages are used, the variability in the oceanic O2 flux is relatively small, allowing carbon sinks to be partitioned to within a standard deviation of 0.1 Pg C/yr of the true values, provided one has an accurate estimate of long-term mean O2 outgassing.We acknowledge the support of NASA grant NNG05GG30G and NSF grant ATM0628472

Contribution of ocean, fossil fuel, land biosphere, and biomass burning carbon fluxes to seasonal and interannual variability in atmospheric CO2

Author Posting. © American Geophysical Union, 2008. 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 113 (2008): G01010, doi:10.1029/2007JG000408.Seasonal and interannual variability in atmospheric carbon dioxide (CO2) concentrations was simulated using fluxes from fossil fuel, ocean and terrestrial biogeochemical models, and a tracer transport model with time-varying winds. The atmospheric CO2 variability resulting from these surface fluxes was compared to observations from 89 GLOBALVIEW monitoring stations. At northern hemisphere stations, the model simulations captured most of the observed seasonal cycle in atmospheric CO2, with the land tracer accounting for the majority of the signal. The ocean tracer was 3–6 months out of phase with the observed cycle at these stations and had a seasonal amplitude only ∼10% on average of observed. Model and observed interannual CO2 growth anomalies were only moderately well correlated in the northern hemisphere (R ∼ 0.4–0.8), and more poorly correlated in the southern hemisphere (R < 0.6). Land dominated the interannual variability (IAV) in the northern hemisphere, and biomass burning in particular accounted for much of the strong positive CO2 growth anomaly observed during the 1997–1998 El Niño event. The signals in atmospheric CO2 from the terrestrial biosphere extended throughout the southern hemisphere, but oceanic fluxes also exerted a strong influence there, accounting for roughly half of the IAV at many extratropical stations. However, the modeled ocean tracer was generally uncorrelated with observations in either hemisphere from 1979–2004, except during the weak El Niño/post-Pinatubo period of the early 1990s. During that time, model results suggested that the ocean may have accounted for 20–25% of the observed slowdown in the atmospheric CO2 growth rate.We acknowledge the support of NASA grant NNG05GG30G and NSF grant ATM0628472

Perspectives and Integration in SOLAS Science

Why a chapter on Perspectives and Integration in SOLAS Science in this book? SOLAS science by its nature deals with interactions that occur: across a wide spectrum of time and space scales, involve gases and particles, between the ocean and the atmosphere, across many disciplines including chemistry, biology, optics, physics, mathematics, computing, socio-economics and consequently interactions between many different scientists and across scientific generations. This chapter provides a guide through the remarkable diversity of cross-cutting approaches and tools in the gigantic puzzle of the SOLAS realm. Here we overview the existing prime components of atmospheric and oceanic observing systems, with the acquisition of ocean–atmosphere observables either from in situ or from satellites, the rich hierarchy of models to test our knowledge of Earth System functioning, and the tremendous efforts accomplished over the last decade within the COST Action 735 and SOLAS Integration project frameworks to understand, as best we can, the current physical and biogeochemical state of the atmosphere and ocean commons. A few SOLAS integrative studies illustrate the full meaning of interactions, paving the way for even tighter connections between thematic fields. Ultimately, SOLAS research will also develop with an enhanced consideration of societal demand while preserving fundamental research coherency. The exchange of energy, gases and particles across the air-sea interface is controlled by a variety of biological, chemical and physical processes that operate across broad spatial and temporal scales. These processes influence the composition, biogeochemical and chemical properties of both the oceanic and atmospheric boundary layers and ultimately shape the Earth system response to climate and environmental change, as detailed in the previous four chapters. In this cross-cutting chapter we present some of the SOLAS achievements over the last decade in terms of integration, upscaling observational information from process-oriented studies and expeditionary research with key tools such as remote sensing and modelling. Here we do not pretend to encompass the entire legacy of SOLAS efforts but rather offer a selective view of some of the major integrative SOLAS studies that combined available pieces of the immense jigsaw puzzle. These include, for instance, COST efforts to build up global climatologies of SOLAS relevant parameters such as dimethyl sulphide, interconnection between volcanic ash and ecosystem response in the eastern subarctic North Pacific, optimal strategy to derive basin-scale CO2 uptake with good precision, or significant reduction of the uncertainties in sea-salt aerosol source functions. Predicting the future trajectory of Earth’s climate and habitability is the main task ahead. Some possible routes for the SOLAS scientific community to reach this overarching goal conclude the chapter

On the processes controlling the seasonal cycles of the air&#x2013;sea fluxes of O2 and N2O: A modelling study

The seasonal dynamics of the air&#x2013;sea gas flux of oxygen (O2) are controlled by multiple processes occurring simultaneously. Previous studies showed how to separate the thermal component from the total O2 flux to quantify the residual oxygen flux due to biological processes. However, this biological signal includes the effect of both net euphotic zone production (NEZP) and subsurface water ventilation. To help understand and separate these two components, we use a large-scale ocean general circulation model (OGCM), globally configured, and coupled to a biogeochemical model. The combined model implements not only the oceanic cycle of O2 but also the cycles of nitrous oxide (N2O), argon (Ar) and nitrogen (N2). For this study, we apply a technique to distinguish the fluxes of O2 driven separately by thermal forcing, NEZP, and address the role of ocean ventilation by carrying separate O2 components in the model driven by solubility, NEZP and ventilation. Model results show that the ventilation component can be neglected in summer compared to the production and thermal components polewards but not equatorward of 30&#x00B0; in each hemisphere. This also implies that neglecting the role of ventilation in the subtropical areas would lead to overestimation of the component of O2 flux due to NEZP by 20&#x2013;30%. Model results also show that the ventilation components of air&#x2013;sea O2 and N2O fluxes are strongly anti-correlated in a ratio that reflects the subsurface tracer/tracer relationships (~0.1 mmol N2O/mol O2) as derived from observations. The results support the use of simple scaling relationships linking together the thermally driven fluxes of Ar, N2 and O2. Furthermore, our study also shows that for latitudes polewards of 30&#x00B0; of both hemispheres, the Garcia and Keeling (2001) climatology, when compared to our model results, has a phasing error with the fluxes being too early by ~2&#x2013;3 weeks

NPP_VgpmFromQaa_25_2.0_1997-2012

Series of 5-day NPP for period 1997-2012 in HDF4 file

Data from: Effects of sea ice cover on satellite-detected primary production in the Arctic Ocean

The influence of decreasing Arctic sea ice on net primary production (NPP) in the Arctic Ocean has been considered in multiple publications but is not well constrained owing to the potentially large errors in satellite algorithms. In particular, the Arctic Ocean is rich in coloured dissolved organic matter (CDOM) that interferes in the detection of chlorophyll a concentration of the standard algorithm, which is the primary input to NPP models. We used the quasi-analytic algorithm (Lee et al. 2002 Appl. Opti. 41, 5755−5772. (doi:10.1364/AO.41.005755)) that separates absorption by phytoplankton from absorption by CDOM and detrital matter. We merged satellite data from multiple satellite sensors and created a 19 year time series (1997–2015) of NPP. During this period, both the estimated annual total and the summer monthly maximum pan-Arctic NPP increased by about 47%. Positive monthly anomalies in NPP are highly correlated with positive anomalies in open water area during the summer months. Following the earlier ice retreat, the start of the high-productivity season has become earlier, e.g. at a mean rate of −3.0 d yr−1 in the northern Barents Sea, and the length of the high-productivity period has increased from 15 days in 1998 to 62 days in 2015. While in some areas, the termination of the productive season has been extended, owing to delayed ice formation, the termination has also become earlier in other areas, likely owing to limited nutrients

N2O production in the eastern South Atlantic: analysis of N2O stable isotopic and concentration data

The stable isotopic composition of dissolved nitrous oxide (N2O) is a tracer for the production, transport, and consumption of this greenhouse gas in the ocean. Here we present dissolved N2O concentration and isotope data from the South Atlantic Ocean, spanning from the western side of the mid-Atlantic Ridge to the upwelling zone off the southern African coast. In the eastern South Atlantic, shallow N2O production by nitrifier denitrification contributed a flux of isotopically depleted N2O to the atmosphere. Along the African coast, N2O fluxes to the atmosphere of up to 46 µmol/m2/d were calculated using satellite-derived QuikSCAT wind speed data, while fluxes at the offshore stations averaged 0.04 µmol/m2/d. Comparison of the isotopic composition of the deeper N2O in the South Atlantic (800 m to 1000 m) to measurements made in other regions suggests that water advected from one or more of the major oxygen deficient zones contributed N2O to the mesopelagic South Atlantic via the Southern Ocean. This deeper N2O was isotopically and isotopomerically enriched (δ15Nbulk − N2O = 8.7 ± 0.1‰, δ18O − N2O = 46.5 ± 0.2‰, and Site Preference = 18.7 ± 0.6‰) relative to the shallow N2O source, indicating that N2O consumption by denitrification influenced its isotopic composition. The N2O concentration maximum was observed between 200 m and 400 m and reached 49 nM near the Angolan coast. The depths of the N2O concentration maximum coincided with those of sedimentary particle resuspension along the coast. The isotopic composition of this N2O (δ15Nbulk − N2O = 5.8 ± 0.1‰, δ18O − N2O = 39.7 ± 0.1‰, and Site Preference = 9.8 ± 1.0‰) was consistent with production by diffusion-limited nitrate (NO3−) reduction to nitrite (NO2−), followed by NO2− reduction to N2O by denitrification and/or nitrifier denitrification, with additional N2O production by NH2OH decomposition during NH3 oxidation. The sediment surface, benthic boundary layer, or particles resuspended from the sediments are likely to have provided the physical and chemical conditions necessary to produce this N2O

Net primary productivity in Arctic Ocean from Effects of sea ice cover on satellite-detected primary production in the Arctic ocean

Time Monthly NPP, Pg C NPP per open water area, mgC/m2/day Year Annual NPP, PgC Max monthly NPP, Pg C NPP/are