scholarly journals The GESAMP atmospheric iron deposition model intercomparison study

2018 ◽  
Author(s):  
Stelios Myriokefalitakis ◽  
Akinori Ito ◽  
Maria Kanakidou ◽  
Athanasios Nenes ◽  
Maarten C. Krol ◽  
...  
Keyword(s):  
Mineral Dust ◽  
Global Ocean ◽  
Current Status ◽  
Aerosol Size Distribution ◽  
Model Intercomparison ◽  
Dust Source ◽  
Deposition Fluxes ◽  
Source Regions ◽  
Atmospheric Processing ◽  
The Mean

Abstract. This work reports on the current status of global modelling of iron (Fe) deposition fluxes and atmospheric concentrations and analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry-transport (CTMs) and general circulation (GCMs) models have participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, The Atmospheric Input of Chemicals to the Ocean. The global total Fe (TFe) emissions strength in the models is equal to ~ 72 Tg-Fe yr−1 (38–134 Tg-Fe yr−1) from mineral dust sources and around 2.1 Tg-Fe yr−1 (1.8–2.7 Tg-Fe yr−1) from combustion processes (sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3) Tg-Fe yr−1, accounting for mineral dust and combustion aerosols together. The multi model ensemble global TFe and LFe deposition fluxes into the global ocean are calculated to be ~ 15 Tg-Fe yr−1 and ~ 0.3 Tg-Fe yr−1, respectively. The model intercomparison analysis indicates that the representation of the atmospheric Fe cycle varies among models, in terms of both the magnitude of natural and combustion Fe emissions as well as the complexity of atmospheric processing parametrizations of Fe-containing aerosols. The model comparison with aerosol Fe observations over oceanic regions indicate that most models overestimate surface level TFe mass concentrations near the dust source regions and tend to underestimate the low concentrations observed in remote ocean regions. All models are able to simulate the tendency of higher Fe loading near and downwind from the dust source regions, with the mean normalized bias for the Northern Hemisphere (~ 14), larger than the Southern Hemisphere (~ 2.4) for the ensemble model mean. This model intercomparison and model–observation comparison study reveals two critical issues in LFe simulations that require further exploration: 1) the Fe-containing aerosol size distribution and 2) the relative contribution of dust and combustion sources of Fe to labile Fe in atmospheric aerosols over the remote oceanic regions.

scholarly journals Reviews and syntheses: the GESAMP atmospheric iron deposition model intercomparison study

2018 ◽  
Vol 15 (21) ◽  
pp. 6659-6684 ◽  
Author(s):  
Stelios Myriokefalitakis ◽  
Akinori Ito ◽  
Maria Kanakidou ◽  
Athanasios Nenes ◽  
Maarten C. Krol ◽  
...  
Keyword(s):  
Mineral Dust ◽  
Global Ocean ◽  
Aerosol Size Distribution ◽  
Ensemble Model ◽  
Model Intercomparison ◽  
Dust Source ◽  
Deposition Fluxes ◽  
Source Regions ◽  
Atmospheric Processing ◽  
The Mean

Abstract. This work reports on the current status of the global modeling of iron (Fe) deposition fluxes and atmospheric concentrations and the analyses of the differences between models, as well as between models and observations. A total of four global 3-D chemistry transport (CTMs) and general circulation (GCMs) models participated in this intercomparison, in the framework of the United Nations Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) Working Group 38, “The Atmospheric Input of Chemicals to the Ocean”. The global total Fe (TFe) emission strength in the models is equal to ∼72 Tg Fe yr−1 (38–134 Tg Fe yr−1) from mineral dust sources and around 2.1 Tg Fe yr−1 (1.8–2.7 Tg Fe yr−1) from combustion processes (the sum of anthropogenic combustion/biomass burning and wildfires). The mean global labile Fe (LFe) source strength in the models, considering both the primary emissions and the atmospheric processing, is calculated to be 0.7 (±0.3) Tg Fe yr−1, accounting for both mineral dust and combustion aerosols. The mean global deposition fluxes into the global ocean are estimated to be in the range of 10–30 and 0.2–0.4 Tg Fe yr−1 for TFe and LFe, respectively, which roughly corresponds to a respective 15 and 0.3 Tg Fe yr−1 for the multi-model ensemble model mean. The model intercomparison analysis indicates that the representation of the atmospheric Fe cycle varies among models, in terms of both the magnitude of natural and combustion Fe emissions as well as the complexity of atmospheric processing parameterizations of Fe-containing aerosols. The model comparison with aerosol Fe observations over oceanic regions indicates that most models overestimate surface level TFe mass concentrations near dust source regions and tend to underestimate the low concentrations observed in remote ocean regions. All models are able to simulate the tendency of higher Fe concentrations near and downwind from the dust source regions, with the mean normalized bias for the Northern Hemisphere (∼14), larger than that of the Southern Hemisphere (∼2.4) for the ensemble model mean. This model intercomparison and model–observation comparison study reveals two critical issues in LFe simulations that require further exploration: (1) the Fe-containing aerosol size distribution and (2) the relative contribution of dust and combustion sources of Fe to labile Fe in atmospheric aerosols over the remote oceanic regions.

scholarly journals Development of a global model of mineral dust aerosol microphysics

2008 ◽  
Vol 8 (6) ◽  
pp. 18765-18802
Author(s):  
Y. H. Lee ◽  
K. Chen ◽  
P. J. Adams
Keyword(s):  
Mineral Dust ◽  
Dust Particles ◽  
Base Case ◽  
Dust Source ◽  
Deposition Fluxes ◽  
Surface Mass ◽  
Remote Areas ◽  
Source Regions ◽  
Mass Concentrations

Abstract. A mineral dust module is developed and implemented into the global aerosol microphysics model, GISS-TOMAS. The model is evaluated against long-term measurements of dust surface mass concentrations and deposition fluxes. Predicted mass concentrations and deposition fluxes are in error on average by a factor of 3 and 5, respectively. The comparison shows that the model performs better near the dust source regions but underestimates surface concentrations and deposition fluxes in more remote regions. For example, including only sites with measured dust concentrations of at least 0.5 μg m−3, the model prediction agrees with observations to within a factor of 2. It was hypothesized that the lifetime of dust, 2.6 days in our base case, is too short and causes the underestimation in remote areas. However, a sensitivity simulation with smaller dust particles and increased lifetime, 3.7 days, does not significantly improve the comparison. We conclude that the underestimation of mineral dust in remote areas results from local factors and sources not well described by the dust source function and/or the GCM meteorology. The effect of dust aerosols on CCN(0.2%) concentrations is negligible in most regions of the globe; however, CCN(0.2%) concentrations decrease by 10–20% in dusty regions as a result of coagulational scavenging of CCN particles by dust and a decrease in H2SO4 condensation to CCN particles due to the additional surface area of dust.

scholarly journals Development of a global model of mineral dust aerosol microphysics

2009 ◽  
Vol 9 (7) ◽  
pp. 2441-2458 ◽  
Author(s):  
Y. H. Lee ◽  
K. Chen ◽  
P. J. Adams
Keyword(s):  
Mineral Dust ◽  
Dust Particles ◽  
Base Case ◽  
Dust Source ◽  
Deposition Fluxes ◽  
Surface Mass ◽  
Remote Areas ◽  
Source Regions ◽  
The Impact ◽  
Mass Concentrations

Abstract. A mineral dust module is developed and implemented into the global aerosol microphysics model, GISS-TOMAS. The model is evaluated against long-term measurements of dust surface mass concentrations and deposition fluxes. Predicted mass concentrations and deposition fluxes are in error on average by a factor of 3 and 5, respectively. The comparison shows that the model performs better near the dust source regions but underestimates surface concentrations and deposition fluxes in more remote regions. Including only sites with measured dust concentrations of at least 0.5 μg m−3, the model prediction agrees with observations to within a factor of 2. It was hypothesized that the lifetime of dust, 2.6 days in our base case, is too short and causes the underestimation in remote areas. However, a sensitivity simulation with smaller dust particles and increased lifetime, 3.7 days, does not significantly improve the comparison. These results suggest that the underestimation of mineral dust in remote areas may result from local factors/sources not well described by the global dust source function used here or the GCM meteorology. The effect of dust aerosols on CCN(0.2%) concentrations is negligible in most regions of the globe; however, CCN(0.2%) concentrations change decrease by 10–20% in dusty regions the impact of dust on CCN(0.2%) concentrations in dusty regions is very sensitive to the assumed size distribution of emissions. If emissions are predominantly in the coarse mode, CCN(0.2%) decreases in dusty regions up to 10–20% because dust competes for condensable H2SO4, reducing the condensational growth of ultrafine mode particles to CCN sizes. With significant fine mode emissions, however, CCN(0.2%) doubles in Saharan source regions because the direct emission of dust particles outweighs any microphysical feedbacks. The impact of dust on CCN concentrations active at various water supersaturations is also investigated. Below 0.1%, CCN concentrations increase significantly in dusty regions due to the presence of coarse dust particles. Above 0.2%, CCN concentrations show a similar behavior as CCN(0.2%).

scholarly journals Optical and microphysical properties of natural mineral dust and anthropogenic soil dust near dust source regions over northwestern China

2018 ◽  
Vol 18 (3) ◽  
pp. 2119-2138 ◽  
Author(s):  
Xin Wang ◽  
Hui Wen ◽  
Jinsen Shi ◽  
Jianrong Bi ◽  
Zhongwei Huang ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Mineral Dust ◽  
Particle Diameter ◽  
Northwestern China ◽  
Soil Dust ◽  
Dust Source ◽  
Dust Aerosols ◽  
Microphysical Properties ◽  
Source Regions ◽  
Anthropogenic Soil

Abstract. Mineral dust aerosols (MDs) not only influence the climate by scattering and absorbing solar radiation but also modify cloud properties and change the ecosystem. From 3 April to 16 May 2014, a ground-based mobile laboratory was deployed to measure the optical and microphysical properties of MDs near dust source regions in Wuwei, Zhangye, and Dunhuang (in chronological order) along the Hexi Corridor over northwestern China. Throughout this dust campaign, the hourly averaged (±standard deviation) aerosol scattering coefficients (σsp, 550 nm) of the particulates with aerodynamic diameters less than 2.5 µm (PM2.5) at these three sites were sequentially 101.5 ± 36.8, 182.2 ± 433.1, and 54.0 ± 32.0 Mm−1. Correspondingly, the absorption coefficients (σap, 637 nm) were 9.7 ± 6.1, 6.0 ± 4.6, and 2.3 ± 0.9 Mm−1; single-scattering albedos (ω, 637 nm) were 0.902 ± 0.025, 0.931 ± 0.037, and 0.949 ± 0.020; and scattering Ångström exponents (Åsp, 450–700 nm) of PM2.5 were 1.28 ± 0.27, 0.77 ± 0.51, and 0.52 ± 0.31. During a severe dust storm in Zhangye (i.e., from 23 to 25 April), the highest values of σsp2.5 (∼ 5074 Mm−1), backscattering coefficient (σbsp2.5, ∼ 522 Mm−1), and ω637 (∼ 0.993) and the lowest values of backscattering fraction (b2.5, ∼ 0.101) at 550 nm and Åsp2.5 (∼ −0.046) at 450–700 nm, with peak values of aerosol number size distribution (appearing at the particle diameter range of 1–3 µm), exhibited that the atmospheric aerosols were dominated by coarse-mode dust aerosols. It is hypothesized that the relatively higher values of mass scattering efficiency during floating dust episodes in Wuwei and Zhangye are attributed to the anthropogenic soil dust produced by agricultural cultivations.

scholarly journals Uncertainty in modeling dust mass balance and radiative forcing from size parameterization

2013 ◽  
Vol 13 (7) ◽  
pp. 19649-19700 ◽  
Author(s):  
C. Zhao ◽  
S. Chen ◽  
L. R. Leung ◽  
Y. Qian ◽  
J. Kok ◽  
...  
Keyword(s):  
Mass Balance ◽  
Radiative Forcing ◽  
Dust Emission ◽  
Dust Particles ◽  
Mass Loading ◽  
Dust Source ◽  
Deposition Fluxes ◽  
Source Regions ◽  
Dust Mass ◽  
The Difference

Abstract. This study examines the uncertainties in simulating mass balance and radiative forcing of mineral dust due to biases in the dust size parameterization. Simulations are conducted quasi-globally (180° W–180° E and 60° S–70° N) using the WRF-Chem model with three different approaches to represent dust size distribution (8-bin, 4-bin, and 3-mode). The biases in the 3-mode or 4-bin approaches against a relatively more accurate 8-bin approach in simulating dust mass balance and radiative forcing are identified. Compared to the 8-bin approach, the 4-bin approach simulates similar but coarser size distributions of dust particles in the atmosphere, while the 3-mode approach retains more fine dust particles but fewer coarse dust particles due to its prescribed σg of each mode. Although the 3-mode approach yields up to 10 days longer dust mass lifetime over the remote oceanic regions than the 8-bin approach, the three size approaches produce similar dust mass lifetime (3.2 days to 3.5 days) on quasi-global average, reflecting that the global dust mass lifetime is mainly determined by the dust mass lifetime near the dust source regions. With the same global dust emission (∼6000 Tg yr-1), the 8-bin approach produces a dust mass loading of 39 Tg, while the 4-bin and 3-mode approaches produce 3% (40.2 Tg) and 25% (49.1 Tg) higher dust mass loading, respectively. The difference in dust mass loading between the 8-bin approach and the 4-bin or 3-mode approaches has large spatial variations, with generally smaller relative difference (<10%) near the surface over the dust source regions. The three size approaches also result in significantly different dry and wet deposition fluxes and number concentrations of dust. The difference in dust aerosol optical depth (AOD) (a factor of 3) among the three size approaches is much larger than their difference (25%) in dust mass loading. Compared to the 8-bin approach, the 4-bin approach yields stronger dust absorptivity, while the 3-mode approach yields weaker dust absorptivity. Overall, on quasi-global average, the three size parameterizations result in a significant difference of a factor of 2∼3 in dust surface cooling (-1.02∼-2.87 W m-2) and atmospheric warming (0.39∼0.96 W m-2) and in a tremendous difference of a factor of ∼10 in dust TOA cooling (-0.24∼-2.20 W m-2). An uncertainty of a factor of 2 is quantified in dust emission estimation due to the different size parameterizations. This study also highlights the uncertainties in modeling dust mass and number loading, deposition fluxes, and radiative forcing resulting from different size parameterizations, and motivates further investigation of the impact of size parameterizations on modeling dust impacts on air quality, climate, and ecosystem.

scholarly journals An explicit estimate of the atmospheric nutrient impact on global oceanic productivity

2020 ◽  
Author(s):  
Stelios Myriokefalitakis ◽  
Matthias Gröger ◽  
Jenny Hieronymus ◽  
Ralf Döscher
Keyword(s):  
Primary Production ◽  
Global Scale ◽  
Global Ocean ◽  
Deposition Fluxes ◽  
Nutrient Deposition ◽  
Atmospheric Processing ◽  
Atmospheric Forcings ◽  
Marine Productivity ◽  
Atmospheric Inputs ◽  
The Impact

Abstract. State-of-the-art global nutrient deposition fields are here coupled to the biogeochemistry model PISCES to investigate the effect on ocean biogeochemistry in the context of atmospheric forcings for preindustrial, present, and future periods. Present-day atmospheric deposition fluxes of inorganic N, Fe, and P over the global ocean are accounted equal to ~40 Tg-N yr−1, ~0.28 Tg-Fe yr−1 and ~0.10 Tg-P yr−1. The resulting globally integrated primary production of roughly 47 Pg-C yr−1 is well within the range of satellite-based estimates and other modeling predictions. Preindustrial atmospheric nutrient deposition fluxes are lower compared to present-day (~51 %, ~36 %, and ~40 % for N, Fe, and P, respectively), resulting here in a lower marine primary production by ~3 % globally. Future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean compared to present-day (~13 %, ~14 % and ~20 % for N, Fe and P, respectively), without significantly affecting the projected primary production in the model. The global mean nitrogen-fixation rates changed only marginally from preindustrial to future conditions (111 ± 0.6 Tg-N yr−1). With regard to the atmospheric inputs to the ocean, sensitivity model simulations indicate that the contribution of nutrients' organic fraction results in an increase in primary production by about 2.4 %. This estimate is almost equal to the effect of emissions and atmospheric processing on the oceanic biogeochemistry since preindustrial times in the model when only the inorganic fraction of the nutrients is considered. Although the impact of the atmospheric organic nutrients may imply a relatively weak response of marine productivity on a global scale, stronger regional effects up to ~20 % are calculated in the oligotrophic subtropical gyres. Overall, this work provides a first explicit assessment of the contribution of the organic forms of atmospheric nutrients, highlighting the importance of their representation in biogeochemistry models and thus the oceanic productivity estimates.

scholarly journals 14 kyr of atmospheric mineral dust deposition in north-eastern China: A record of palaeoclimatic and palaeoenvironmental changes in the Chinese dust source regions

The Holocene ◽  
2019 ◽  
Vol 30 (4) ◽  
pp. 492-506 ◽  
Author(s):  
Steve Pratte ◽  
Kunshan Bao ◽  
Atindra Sapkota ◽  
Wenfang Zhang ◽  
Ji Shen ◽  
...  
Keyword(s):  
Late Holocene ◽  
Mineral Dust ◽  
East Asian ◽  
Eastern China ◽  
Dust Deposition ◽  
Dust Source ◽  
Principal Mechanism ◽  
Middle Holocene ◽  
Source Regions ◽  
North Eastern

A multi-proxy record of Holocene and late-Pleistocene aeolian mineral dust is reconstructed using a combination of geochemical (trace elements), mineralogical and grain-size analyses on cores from the Hani peatland in north-eastern (NE) China. The dust record displays a sharp increase in dust deposition during the late Holocene in comparison to the rest of the Holocene. This trend is in line with climatic records from the Chinese dust source regions and their downwind areas, which generally show an increase in aridity and aeolian activity during the late Holocene. The larger part of the Chinese dust source regions experienced a gradual increase in effective moisture and vegetation cover reaching maxima during the middle Holocene (6.0–8.0 kyr cal. BP) co-occurring with the minima in dust deposition in Hani. These changes in the dust source regions are likely to have been modulated by the variations in the East Asian summer monsoon (EASM), which is the principal mechanism controlling climate in the region. The intensified EASM during the middle Holocene is also likely to have resulted in a sediment recharge at the margin of the Chinese drylands providing additional material and enhancing the atmospheric dust load after the late-Holocene aridification of the region. Combined together, these changes promoted a remobilization of dust sources increasing the amount of material available for transport by the East Asian winter monsoon (EAWM) and the Westerlies. Human activities might also have played a role in the increased dust emissions during the late Holocene, but further research is needed to assess the extent of those impacts at a regional level.

A state-of-the-art parameterization of atmospheric nutrient deposition fluxes in the global ocean

2020 ◽  
Author(s):  
Stelios Myriokefalitakis ◽  
Matthias Gröger ◽  
Jenny Hieronymus ◽  
Ralf Döscher
Keyword(s):  
Atmospheric Deposition ◽  
State Of The Art ◽  
Marine Ecosystem ◽  
Open Ocean ◽  
Marine Phytoplankton ◽  
Global Ocean ◽  
Model Calculations ◽  
Deposition Fluxes ◽  
Atmospheric Processing ◽  
The Impact

&lt;p&gt;Atmospheric deposition of trace constituents of natural and anthropogenic origin act as a nutrient source into the open ocean, affecting the marine ecosystem functioning and subsequently the exchange of CO&lt;sub&gt;2&lt;/sub&gt; between the atmosphere and the global ocean. Among other species that are deposited into the open ocean, nitrogen (N), iron (Fe), and phosphorus (P) are considered as highly significant nutrients that can limit marine phytoplankton growth and thus directly impact on ocean carbon fluxes in the ocean, particularly where the nutrient availability is the limiting factor for productivity. For this work, we take into account the up-to-date understanding of the effects of air quality on the atmospheric aerosol cycles to investigate the potential ocean biogeochemistry perturbations via the atmospheric input with the European Community Earth System Model EC-Earth (http://www.ec-earth.org/), which is jointly developed by several European institutes. In more detail, state-of-the-art N, Fe, and P atmospheric deposition fields are coupled to the embedded marine biogeochemistry model and the response of oceanic biogeochemistry to natural and anthropogenic atmospheric aerosols deposition changes is demonstrated and quantified. Model calculations show that compared to the present day, the preindustrial atmospheric deposition fluxes are calculated lower (~1.7, ~1.5, and ~1.4 times for N, Fe, and P, respectively) corresponding to a respective lower marine primary production. On the other hand, future changes in air pollutants under the RCP8.5 scenario result in a modest decrease of the bioaccessible nutrients input into the global ocean (~ -15%, ~ -16% and ~ -22% for N, Fe and P, respectively) and overall to a slightly lower projected export production compared to present day. Although the impact of atmospheric processing on atmospheric inputs to the ocean results in a relatively weak response in total global-scale simulated marine productivity estimates, strong regional changes up to 40-60% are calculated in the subtropical gyres. Overall, this study indicates that both the atmospheric processing and the speciation of the atmospheric nutrients deposited in the ocean should be considered in detail in carbon-cycling studies, since they may significantly affect the marine ecosystems and thus the current estimates of the carbon cycle feedbacks to climate.&lt;/p&gt;&lt;p&gt;This work has been financed by the National Observatory of Athens internal grant (number 5065), the &amp;#8220;Atmospheric deposition impacts on the ocean system&amp;#8221;, and the European Commission's Horizon 2020 Framework Programme, under Grant Agreement number 641816, the &quot;Coordinated Research in Earth Systems and Climate: Experiments, kNowledge, Dissemination, and Outreach (CRESCENDO)&quot;.&lt;/p&gt;

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