Exploring the sensitivity of interannual basin-scale air-sea CO2 fluxes to variability in atmospheric dust deposition using ocean carbon cycle models and atmospheric CO2 inversions

Author Posting. © American Geophysical Union, 2007. 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 112 (2007): G02012, doi:10.1029/2006JG000236.Estimates of sources/sinks of carbon dioxide (CO2) at the Earth's surface are commonly made using atmospheric CO2 inverse modeling, terrestrial and oceanic biogeochemical modeling, and inventory-based studies. In this study, we compare sea-air CO2 fluxes from the Time-Dependent Inverse (TDI) atmosphere model and the marine Biogeochemical Elemental Cycling (BEC) model to study the processes involved in ocean carbon cycling at subbasin scales. A dust generation and transport model, based on analyzed meteorology and terrestrial vegetation cover, is also used to estimate the interannual variability in dust and iron deposition to different ocean basins. Overall, a fairly good agreement is established between the TDI and BEC model results for the net annual patterns and seasonal cycle of sea-air CO2 exchange. Sensitivity studies with the ocean biogeochemical model using increased or reduced atmospheric iron inputs indicate the relative sensitivity of air-sea CO2 exchange. The simulated responses to changes in iron inputs are not instantaneous (peak response after ∼2−3 years). The TDI model derived seasonal cycles for the Southern Ocean (South Atlantic) are better matched by the BEC model by increasing (decreasing) iron inputs through atmospheric aerosols. Our results suggest that some of the interannual variability in TDI model air-sea CO2 fluxes during the past decade may be explainable by dust variability that relaxes/increases iron limitation in high-nitrate, low-chlorophyll (HNLC) ocean regions.S. C. Doney and N. Mahowald acknowledge support from NASA grant NNG05GG30G. J. K. Moore was funded by NSF grant OCE-0452972

Atmospheric Organic Material and the Nutrients Nitrogen and Phosphorus It Carries to the Ocean

[1] The global tropospheric budget of gaseous and particulate non‐methane organic matter (OM) is re‐examined to provide a holistic view of the role that OM plays in transporting the essential nutrients nitrogen and phosphorus to the ocean. A global 3‐dimensional chemistry‐transport model was used to construct the first global picture of atmospheric transport and deposition of the organic nitrogen (ON) and organic phosphorus (OP) that are associated with OM, focusing on the soluble fractions of these nutrients. Model simulations agree with observations within an order of magnitude. Depending on location, the observed water soluble ON fraction ranges from ∼3% to 90% (median of ∼35%) of total soluble N in rainwater; soluble OP ranges from ∼20–83% (median of ∼35%) of total soluble phosphorus. The simulations suggest that the global ON cycle has a strong anthropogenic component with ∼45% of the overall atmospheric source (primary and secondary) associated with anthropogenic activities. In contrast, only 10% of atmospheric OP is emitted from human activities. The model‐derived present‐day soluble ON and OP deposition to the global ocean is estimated to be ∼16 Tg‐N/yr and ∼0.35 Tg‐P/yr respectively with an order of magnitude uncertainty. Of these amounts ∼40% and ∼6%, respectively, are associated with anthropogenic activities, and 33% and 90% are recycled oceanic materials. Therefore, anthropogenic emissions are having a greater impact on the ON cycle than the OP cycle; consequently increasing emissions may increase P‐limitation in the oligotrophic regions of the world\u27s ocean that rely on atmospheric deposition as an important nutrient source

Observation- and model-based estimates of particulate dry nitrogen deposition to the oceans

Anthropogenic nitrogen (N) emissions to the atmosphere have increased significantly the deposition of nitrate (NO3-) and ammonium (NH4+) to the surface waters of the open ocean, with potential impacts on marine productivity and the global carbon cycle. Global-scale understanding of the impacts of N deposition to the oceans is reliant on our ability to produce and validate models of nitrogen emission, atmospheric chemistry, transport and deposition. In this work, ~2900 observations of aerosol NO3- and NH4+ concentrations, acquired from sampling aboard ships in the period 1995 - 2012, are used to assess the performance of modelled N concentration and deposition fields over the remote ocean. Three ocean regions (the eastern tropical North Atlantic, the northern Indian Ocean and northwest Pacific) were selected, in which the density and distribution of observational data were considered sufficient to provide effective comparison to model products. All of these study regions are affected by transport and deposition of mineral dust, which alters the deposition of N, due to uptake of nitrogen oxides (NOx) on mineral surfaces. Assessment of the impacts of atmospheric N deposition on the ocean requires atmospheric chemical transport models to report deposition fluxes, however these fluxes cannot be measured over the ocean. Modelling studies such as the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP), which only report deposition flux are therefore very difficult to validate for dry deposition. Here the available observational data were averaged over a 5° x 5° grid and compared to ACCMIP dry deposition fluxes (ModDep) of oxidised N (NOy) and reduced N (NHx) and to the following parameters from the TM4-ECPL (TM4) model: ModDep for NOy, NHx and particulate NO3- and NH4+, and surface-level particulate NO3- and NH4+ concentrations. As a model ensemble, ACCMIP can be expected to be more robust than TM4, while TM4 gives access to speciated parameters (NO3- and NH4+) that are more relevant to the observed parameters and which are not available in ACCMIP. Dry deposition fluxes (CalDep) were calculated from the observed concentrations using estimates of dry deposition velocities. Model – observation ratios, weighted by grid-cell area and numbers of observations, (RA,n) were used to assess the performance of the models. Comparison in the three study regions suggests that TM4 over-estimates NO3- concentrations (RA,n = 1.4 – 2.9) and under-estimates NH4+ concentrations (RA,n = 0.5 – 0.7), with spatial distributions in the tropical Atlantic and northern Indian Ocean not being reproduced by the model. In the case of NH4+ in the Indian Ocean, this discrepancy was probably due to seasonal biases in the sampling. Similar patterns were observed in the various comparisons of CalDep to ModDep (RA,n = 0.6 – 2.6 for NO3-, 0.6 – 3.1 for NH4+). Values of RA,n for NHx CalDep - ModDep comparisons were approximately double the corresponding values for NH4+ CalDep - ModDep comparisons due to the significant fraction of gas-phase NH3 deposition incorporated in the TM4 and ACCMIP NHx model products. All of the comparisons suffered due to the scarcity of observational data and the large uncertainty in dry deposition velocities used to derive deposition fluxes from concentrations. These uncertainties have been a major limitation on estimates of the flux of material to the oceans for several decades. Recommendations are made for improvements in N deposition estimation through changes in observations, modelling and model – observation comparison procedures. Validation of modelled dry deposition requires effective comparisons to observable aerosol-phase species concentrations and this cannot be achieved if model products only report dry deposition flux over the ocean

Atmospheric transport of anthropogenic substances to the surrounding marine environment : A view from biogeochemical cycles

Abstracts of 2nd UNU-ORI joint international workshop for marine environment第2回海洋環境国際ワークショップ講演要

Size-resolved sulfate and ammonium measurements in marine boundary layer over the North and South Pacific

Marine background levels of non-sea-salt- (nss-) SO42− (5.0–9.7 neq m−3), NH4+ (2.1–4.4 neq m−3) and elemental carbon (EC) (40–80 ngC m−3) in aerosol samples were measured over the equatorial and South Pacific during a cruise by the R/V Hakuho-maru from November 2001 to March 2002. High concentrations of nss-SO42− (47–94 neq m−3), NH4+ (35–94 neq m−3) and EC (130–460 ngC m−3) were found in the western North Pacific near the coast of the Asian continent under the influence of the Asian winter monsoon. Particle size distributions of ionic components showed that the equivalent concentrations of nss-SO42− were balanced with those of NH4+ in the size range of 0.060.22 μm were decreased with increase in particle size. We estimated the source contributions of those aerosol components in the marine background air over the equatorial and South Pacific. Biomass burning accounted for the large fraction (80–98% in weight) of EC and the minor fraction (2–4% in weight) of nss-SO42−. Marine biogenic source accounted for several tens percents of NH4+ and nss-SO42−. In the accumulation mode, 70% of particle number existed in the size range of 0.1<D<0.2 μm. In the size rage of 0.06<D<0.22 μm, the dominant aerosol component of (NH4)2SO4 would be mainly derived from the marine biogenic sources

Experimental study for adjustment of prediction model of solid-liquid solubility in salicylic acid-ethanol-water system.

Para representar o equilíbrio existem modelos termodinâmicos empíricos e semi-empíricos, porém nenhum deles tem aplicação generalizada. Muitos dos modelos utilizados para o equilíbrio sólido-líquido advêm dos modelos desenvolvidos para o equilíbrio líquido-vapor (ELV) e, em alguns casos, podem não representar adequadamente os sistemas reais, tornando-se mais críticos os desvios quando o sólido, ou o líquido, ou ambos, são polares. Para o estudo dos modelos e realizar as devidas comparações foram inicialmente realizados experimentos em laboratório com sistemas binários e ternários utilizando como solventes o etanol, a água e as suas misturas e como soluto o ácido salicílico, todas substâncias polares. Os dados experimentais foram obtidos utilizando uma variante do método isotérmico, tendo como sistemas binários: etanol-ácido salicílico e água-ácido salicílico e, como sistemas ternários as misturas dos solventes. Os experimentos envolveram a variação da concentração mássica de etanol em intervalos de 20%. A variação da temperatura foi feita em intervalos de 5°C de 20 a 55°C. A análise do total de 48 dados experimentais indicou que a solubilidade do ácido salicílico aumenta à medida em que a temperatura e/ou a concentração mássica de etanol no solvente aumenta. Esses dados foram utilizados no ajuste de diferentes modelos para ESL. Os modelos estudados foram: UNIFAC e GSP (de predição baseado no ELV), UNIQUAC, Wilson, NRTL (semi-empíricos de ajuste de parâmetros baseados no ELV), Nývlt e \'lâmbda\'h (semi-empíricos de ajuste de parâmetros baseados no ESL) e Margules (empírico de ajuste de parâmetros). Os resultados mostraram que os modelos de predição têm aplicação restrita quando aplicado ao sistema estudado. Entre os modelos de ajuste, o UNIQUAC resultou em menores desvios em relação aos dados experimentais, considerando-se toda a faixa de condições experimentais adotadas. Os resultados experimentais também foram utilizados no ajuste de um modelo baseado em rede neural, o qual foi utilizado para mapeamento do sistema e comparação com as previsões pelos modelos considerados. Simulações com rede neural resultaram em boa concordância com os resultados experimentais, indicando que tal modelo pode ser usado para prever solubilidade na faixa de condições do presente estudo.The knowledge of solid-liquid equilibrium (SLE) is an important factor in crystallization and dissolution studies. In most of these systems equilibrium is represented by empirical and semi-empirical thermodynamical models, with no general application. Many models used in SLE result from models developed for vapor-liquid equilibrium (VLE) and in some cases these models do not represent real systems adequately, becoming critical when polar solids or liquids are present in the system. In the present work a study of thermodynamical models for SLE was carried out by comparing the performance of different models with experimental data of binary and ternary systems consisting of ethanol, water and their mixtures as solvents, and salicylic acid as solute. The experimental data were obtained using a variant of the isothermal method for the following binary systems: ethanol-salicylic acid and water-salicylic acid. In the study with ternary systems ethanol-water mixtures at different ratios were adopted as solvents, and salicylic acid was the solute. A total of 48 experiments were carried out by changing the ethanol mass fraction in the solvent from 0 to 100%, and the temperature from 20 to 55°C. The solubility of salicylic acid increases with the increase in the temperature and/or ethanol concentration in the solvent. The models considered in the study were: UNIFAC and GSP (prediction models based on vapor-liquid-equilibrium), UNIQUAC, Wilson and NRTL (semi-empirical models of fitted parameters based on vapor-liquid equilibrium), Nývlt and \'lâmbda\'h (semi-empirical models with fitted parameters based on SLE) and Margules (empirical model with fitted parameters). The results showed that the UNIQUAC model with fitted parameters can describe the SLE with reasonable accuracy, while all other methods resulted in poor agreement with the system\'s behavior, with systematic deviations from the experimental results. The system was also mapped with the use of a neural network model with parameters fitted to the experimental data. Simulation results with the neural network provided an accurate map of the system that can be used within the range of conditions considered in this study