scholarly journals Atmospheric dissolved iron deposition to the global oceans: effects of oxalate-promoted Fe dissolution, photochemical redox cycling, and dust mineralogy

2013 ◽  
Vol 6 (1) ◽  
pp. 1901-1947 ◽  
Author(s):  
M. S. Johnson ◽  
N. Meskhidze
Keyword(s):  
Transport Model ◽  
Mineral Dust ◽  
Atmospheric Transport ◽  
Redox Cycling ◽  
Dust Particles ◽  
Dust Deposition ◽  
Chemical Transport Model ◽  
Cloud Processing ◽  
Form Model ◽  
Global Oceans

Abstract. Mineral dust deposition is suggested to be a significant atmospheric supply pathway of bioavailable iron (Fe) to Fe-depleted surface oceans. In this study, mineral dust and dissolved Fe (Fed) deposition rates are predicted for March 2009 to February 2010 using the 3-D chemical transport model GEOS-Chem implemented with a comprehensive dust-Fe dissolution scheme. The model simulates Fed production during the atmospheric transport of mineral dust taking into account inorganic and organic (oxalate)-promoted Fe dissolution processes, photochemical redox cycling between ferric (Fe(III)) and ferrous (Fe(II)) forms of Fe, dissolution of three different Fe-containing minerals (hematite, goethite, and aluminosilicates), and detailed mineralogy of wind-blown dust from the major desert regions. Our calculations suggest that during the yearlong simulation ~ 0.26 Tg (1 Tg = 1012 g) of Fed was deposited to global oceanic regions. Compared to simulations only taking into account proton-promoted Fe dissolution, the addition of oxalate to the dust-Fe mobilization scheme increased total annual model-predicted Fed deposition to global oceanic regions by ~ 75%. The implementation of Fe(II)/Fe(III) photochemical redox cycling in the model allows for the distinction between different oxidation states of deposited Fed. Our calculations suggest that during the daytime, large fractions of Fed deposited to the global oceans is likely to be in Fe(II) form, while nocturnal fluxes of Fed are largely in Fe(III) form. Model simulations also show that atmospheric fluxes of Fed can be strongly influenced by the mineralogy of Fe-containing compounds. This study indicates that Fed deposition to the oceans is controlled by total dust-Fe mass concentrations, mineralogy, the surface area of dust particles, atmospheric chemical composition, cloud processing, and meteorological parameters and exhibits complex and spatiotemporally variable patterns. Our study suggests that the explicit model representation of individual processes leading to Fed production within mineral dust are needed to improve the understanding of the atmospheric Fe cycle, and quantify the effect of dust-Fe on ocean biological productivity, carbon cycle, and climate.

scholarly journals Atmospheric dissolved iron deposition to the global oceans: effects of oxalate-promoted Fe dissolution, photochemical redox cycling, and dust mineralogy

2013 ◽  
Vol 6 (4) ◽  
pp. 1137-1155 ◽  
Author(s):  
M. S. Johnson ◽  
N. Meskhidze
Keyword(s):  
Transport Model ◽  
Mineral Dust ◽  
Atmospheric Transport ◽  
Redox Cycling ◽  
Dust Particles ◽  
Dust Deposition ◽  
Chemical Transport Model ◽  
Cloud Processing ◽  
Form Model ◽  
Global Oceans

Abstract. Mineral dust deposition is suggested to be a significant atmospheric supply pathway of bioavailable iron (Fe) to Fe-depleted surface oceans. In this study, mineral dust and dissolved Fe (Fed) deposition rates are predicted for March 2009 to February 2010 using the 3-D chemical transport model GEOS-Chem implemented with a comprehensive dust-Fe dissolution scheme. The model simulates Fed production during the atmospheric transport of mineral dust, taking into account inorganic and organic (oxalate)-promoted Fe dissolution processes, photochemical redox cycling between ferric (Fe(III)) and ferrous (Fe(II)) forms of Fe, dissolution of three different Fe-containing minerals (hematite, goethite, and aluminosilicates), and detailed mineralogy of wind-blown dust from the major desert regions. Our calculations suggest that during the year-long simulation ~0.26 Tg (1 Tg = 1012 g) of Fed was deposited to global oceanic regions. Compared to simulations only taking into account proton-promoted Fe dissolution, the addition of oxalate and Fe(II)/Fe(III) redox cycling to the dust-Fe mobilization scheme increased total annual model-predicted Fed deposition to global oceanic regions by ~75%. The implementation of Fe(II)/Fe(III) photochemical redox cycling in the model also allows for the distinction between different oxidation states of deposited Fed. Our calculations suggest that during the daytime, large fractions of Fed deposited to the global oceans is likely to be in Fe(II) form, while nocturnal fluxes of Fed are largely in Fe(III) form. Model sensitivity simulations suggest Fed fluxes to the oceans can range from ~50% reduction to ~150% increase associated with the uncertainty in Fe-containing minerals commonly found in dust particles. This study indicates that Fed deposition to the oceans is controlled by total dust-Fe mass concentrations, mineralogy, the surface area of dust particles, atmospheric chemical composition, cloud processing, and meteorological parameters and exhibits complex and spatiotemporally variable patterns. Our study suggests that the explicit model representation of individual processes leading to Fed production within mineral dust are needed to improve the understanding of the atmospheric Fe cycle, and quantify the effect of dust-Fe on ocean biological productivity, carbon cycle, and climate.

scholarly journals Influence of measurement uncertainties on soluble aerosol iron over the oceans

2015 ◽  
Vol 12 (17) ◽  
pp. 14377-14400 ◽  
Author(s):  
N. Meskhidze ◽  
M. S. Johnson ◽  
D. Hurley ◽  
K. Dawson
Keyword(s):  
Transport Model ◽  
Mineral Dust ◽  
Operational Definition ◽  
Dust Aerosol ◽  
Global Ocean ◽  
Dust Particles ◽  
Chemical Transport Model ◽  
Water Leaching ◽  
Wide Range ◽  
Flow Through

Abstract. The atmospheric supply of dust iron (Fe) plays a crucial role in the Earth's biogeochemical cycle and is of specific importance as a micronutrient in the marine environment. Observations show several orders of magnitude variability in the fractional solubility of Fe in dust aerosols, making it hard to assess the role of mineral dust for global ocean biogeochemical Fe cycle. In this study we compare the operational solubility of dust aerosol Fe associated with one of the flow-through leaching protocols to the results of the global 3-D chemical transport model GEOS-Chem. In the protocol aerosol Fe is defined soluble by first deionized water leaching of mineral dust through a 0.45 μm pore size membrane followed by acidification and storage of the leachate over a long period of time prior to the analysis. To assess the concentrations of soluble Fe inferred by this flow-through leaching protocol we are using in situ measurements of dust size distribution with the prescribed of 50 % fractional solubility of Fe in less than 0.45 μm sized dust particles collected in the leachate. In the model, the fractional solubility of Fe is either explicitly calculated using complex dust Fe dissolution module, or prescribed to be 1 and 4 %. Calculations show that the fractional solubility of Fe derived through the flow-through leaching is typically higher compared to the model results. The largest differences (>30 %) are predicted to occur farther away from the dust source regions, over the areas where sub-0.45 μm sized mineral dust particles contribute a larger fraction of the total dust mass. This study suggests that inconsistences in the operational definition of soluble Fe could contribute to the wide range of the fractional solubility of dust aerosol Fe reported in the literature.

scholarly journals Modelling of mineral dust for interglacial and glacial climate conditions with a focus on Antarctica

2015 ◽  
Vol 11 (5) ◽  
pp. 765-779 ◽  
Author(s):  
N. Sudarchikova ◽  
U. Mikolajewicz ◽  
C. Timmreck ◽  
D. O'Donnell ◽  
G. Schurgers ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Mineral Dust ◽  
Atmospheric Transport ◽  
Ice Cores ◽  
Dust Particles ◽  
Dust Deposition ◽  
Transport Efficiency ◽  
Dust Emissions ◽  
Last Glacial ◽  
The Last Glacial

Abstract. The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide unique information about deposition of aeolian dust particles transported over long distances. These cores are a palaeoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol–climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission, atmospheric transport and precipitation, which will help to interpret palaeodata from Antarctic ice cores. The investigated periods include four interglacial time slices: the pre-industrial control (CTRL), mid-Holocene (6000 yr BP; hereafter referred to as "6 kyr"), last glacial inception (115 000 yr BP; hereafter "115 kyr") and Eemian (126 000 yr BP; hereafter "126 kyr"). One glacial time interval, the Last Glacial Maximum (LGM) (21 000 yr BP; hereafter "21 kyr"), was simulated as well to be a reference test for the model. Results suggest an increase in mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two-thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one-third of the increase in dust deposition. The moderate change in dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher Southern Hemisphere dust emissions, 2 times stronger atmospheric transport towards Antarctica, and 30% weaker precipitation over the Southern Ocean. The model is able to reproduce the order of magnitude of dust deposition globally and in Antarctica for the pre-industrial and LGM climates.

scholarly journals A new dust cycle model with dynamic vegetation: LPJ-dust version 1.0

2011 ◽  
Vol 4 (1) ◽  
pp. 85-105 ◽  
Author(s):  
S. Shannon ◽  
D. J. Lunt
Keyword(s):  
Transport Model ◽  
Surface Concentration ◽  
Reanalysis Data ◽  
Dust Particles ◽  
Dust Deposition ◽  
Chemical Transport Model ◽  
Cycle Model ◽  
Dynamic Global Vegetation Model ◽  
Cloud Scavenging ◽  
Global Vegetation

Abstract. This paper presents a new offline dust cycle model which uses the Lund-Potsdam-Jena dynamic global vegetation model (Sitch et al., 2003) to calculate time varying dust sources. Surface emissions are calculated by simulating the processes of saltation and sandblasting using an existing model (Tegen et al., 2002). Dust particles are transported using the TOMCAT chemical transport model (Chipperfield, 2006). Dust particles are removed from the atmosphere by dry deposition and sub-cloud scavenging. The model is designed so that it can be driven using reanalysis data or GCM derived fields. To improve the performance of the model, threshold values for vegetation cover, soil moisture, snow depth and threshold friction velocity, used to determine surface emissions are tuned. The effectiveness of three sub-cloud scavenging schemes are also tested. An ensemble of tuning experiments are evaluated against dust deposition and surface concentration measurements. Surface emissions which produce the best agreement with observations range from 1600 to 2400 Mtyr−1.

scholarly journals Impacts of long-range-transported mineral dust on summertime convective cloud and precipitation: a case study over the Taiwan region

2021 ◽  
Vol 21 (23) ◽  
pp. 17433-17451
Author(s):  
Yanda Zhang ◽  
Fangqun Yu ◽  
Gan Luo ◽  
Jiwen Fan ◽  
Shuai Liu
Keyword(s):  
Long Range ◽  
Transport Model ◽  
Mineral Dust ◽  
Convective Cloud ◽  
Dust Particles ◽  
Chemical Transport Model ◽  
Dust Aerosols ◽  
Convective Clouds ◽  
Water Contents

Abstract. As one of the most abundant atmospheric aerosols and effective ice nuclei, mineral dust affects clouds and precipitation in the Earth system. Here numerical experiments are carried out to investigate the impacts of dust aerosols on summertime convective clouds and precipitation over the mountainous region of Taiwan by acting as ice-nucleating particles. We run the Weather Research and Forecasting model (WRF) with the Morrison two-moment and spectral-bin microphysics (SBM) schemes at 3 km resolution, using dust number concentrations from a global chemical transport model (GEOS-Chem-APM). The case study indicates that the long-range-transported mineral dust, with relatively low number concentrations, can notably affect the properties of convective clouds (ice and liquid water contents, cloud top height, and cloud coverage) and precipitation (spatial pattern and intensity). The effects of dust are evident during strong convective periods, with significantly increased ice water contents in the mixed-phase regime via the enhanced heterogeneous freezing. With both the Morrison and SBM schemes, we see the invigoration effects of dust aerosols on the convective intensity through enhanced condensation and deposition latent heating. The low-altitude dust particles are uplifted to the freezing level by updrafts, which, in turn, enhance the convective cloud development through immersion freezing and convective invigoration. Compared to the Morrison scheme, the SBM scheme predicts more realistic precipitation and different invigoration effects of dust. The differences are partially attributed to the saturation adjustment approach utilized in the bulk scheme, which leads to a stronger enhancement of condensation at midlatitudes to low altitudes and a weaker deposition increase at the upper level.

scholarly journals Impact of mineral dust on nitrate, sulfate, and ozone in transpacific Asian pollution plumes

2010 ◽  
Vol 10 (8) ◽  
pp. 3999-4012 ◽  
Author(s):  
T. D. Fairlie ◽  
D. J. Jacob ◽  
J. E. Dibb ◽  
B. Alexander ◽  
M. A. Avery ◽  
...  
Keyword(s):  
Transport Model ◽  
Mineral Dust ◽  
Surface Ozone ◽  
Asian Dust ◽  
Dust Deposition ◽  
Chemical Transport Model ◽  
Model Studies ◽  
The Pacific ◽  
Reactive Uptake Coefficient ◽  
Global Chemical Transport Model

Abstract. We use a 3-D global chemical transport model (GEOS-Chem) to interpret aircraft observations of nitrate and sulfate partitioning in transpacific dust plumes during the INTEX-B campaign of April–May 2006. The model includes explicit transport of size-resolved mineral dust and its alkalinity, nitrate, and sulfate content. The observations show that particulate nitrate is primarily associated with dust, sulfate is primarily associated with ammonium, and Asian dust remains alkaline across the Pacific. This can be reproduced in the model by using a reactive uptake coefficient for HNO3 on dust (γ(HNO3) ~10−3) much lower than commonly assumed in models and possibly reflecting limitation of uptake by dust dissolution. The model overestimates gas-phase HNO3 by a factor of 2–3, typical of previous model studies; we show that this cannot be corrected by uptake on dust. We find that the fraction of aerosol nitrate on dust in the model increases from ~30% in fresh Asian outflow to 80–90% over the Northeast Pacific, reflecting in part the volatilization of ammonium nitrate and the resulting transfer of nitrate to the dust. Consumption of dust alkalinity by uptake of acid gases in the model is slow relative to the lifetime of dust against deposition, so that dust does not acidify (at least not in the bulk). This limits the potential for dust iron released by acidification to become bio-available upon dust deposition. Observations in INTEX-B show no detectable ozone depletion in Asian dust plumes, consistent with the model. Uptake of HNO3 by dust, suppressing its recycling to NOx, reduces Asian pollution influence on US surface ozone in the model by 10–15% or up to 1 ppb.

scholarly journals Dust deposition in Antarctica in glacial and interglacial climate conditions: a modelling study

2014 ◽  
Vol 10 (5) ◽  
pp. 3715-3753 ◽  
Author(s):  
N. Sudarchikova ◽  
U. Mikolajewicz ◽  
C. Timmreck ◽  
D. O'Donnell ◽  
G. Schurgers ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Mineral Dust ◽  
Atmospheric Transport ◽  
Ice Cores ◽  
Dust Particles ◽  
Dust Deposition ◽  
Long Distance ◽  
Transport Efficiency ◽  
Dust Emissions ◽  
Last Glacial

Abstract. The mineral dust cycle responds to climate variations and plays an important role in the climate system by affecting the radiative balance of the atmosphere and modifying biogeochemistry. Polar ice cores provide a unique information about deposition of aeolian dust particles transported over long distance. These cores are a paleoclimate proxy archive of climate variability thousands of years ago. The current study is a first attempt to simulate past interglacial dust cycles with a global aerosol-climate model ECHAM5-HAM. The results are used to explain the dust deposition changes in Antarctica in terms of quantitative contribution of different processes, such as emission, atmospheric transport and precipitation, which will help to interpret paleodata from Antarctic ice cores. The investigated periods include four interglacial time-slices such as the pre-industrial control (CTRL), mid-Holocene (6000 yr BP), last glacial inception (115 000 yr BP) and Eemian (126 000 yr BP). One glacial time interval, which is Last Glacial Maximum (LGM) (21 000 yr BP) was simulated as well as to be a reference test for the model. Results suggest an increase of mineral dust deposition globally, and in Antarctica, in the past interglacial periods relative to the pre-industrial CTRL simulation. Approximately two thirds of the increase in the mid-Holocene and Eemian is attributed to enhanced Southern Hemisphere dust emissions. Slightly strengthened transport efficiency causes the remaining one third of the increase in dust deposition. The moderate change of dust deposition in Antarctica in the last glacial inception period is caused by the slightly stronger poleward atmospheric transport efficiency compared to the pre-industrial. Maximum dust deposition in Antarctica was simulated for the glacial period. LGM dust deposition in Antarctica is substantially increased due to 2.6 times higher Southern Hemisphere dust emissions, two times stronger atmospheric transport towards Antarctica, and 30% weaker precipitation over the Southern Ocean. The model is able to reproduce the order of magnitude of dust deposition globally and in Antarctica for the pre-industrial and LGM climates.

scholarly journals Impact of mineral dust on nitrate, sulfate, and ozone in transpacific Asian pollution plumes

2009 ◽  
Vol 9 (6) ◽  
pp. 24477-24510 ◽  
Author(s):  
T. D. Fairlie ◽  
D. J. Jacob ◽  
J. E. Dibb ◽  
B. Alexander ◽  
M. A. Avery ◽  
...  
Keyword(s):  
Transport Model ◽  
Mineral Dust ◽  
Surface Ozone ◽  
Asian Dust ◽  
Dust Deposition ◽  
Chemical Transport Model ◽  
Model Studies ◽  
The Pacific ◽  
Reactive Uptake Coefficient ◽  
Global Chemical Transport Model

Abstract. We use a 3-d global chemical transport model (GEOS-Chem) to interpret aircraft observations of nitrate and sulfate partitioning in transpacific dust plumes during the INTEX-B campaign of April–May 2006. The model includes explicit transport of size-resolved mineral dust and its alkalinity, nitrate, and sulfate content. The observations show that particulate nitrate is primarily associated with dust, sulfate is primarily associated with ammonium, and Asian dust remains alkaline across the Pacific. This can be reproduced in the model by using a reactive uptake coefficient for HNO3 on dust (γ(HNO3)~10−3) much lower than commonly assumed in models and likely reflecting limitation of uptake by dust dissolution. The model overestimates gas-phase HNO3 by a factor of 2–3, typical of previous model studies; we show that this cannot be corrected by uptake on dust. We find that the fraction of aerosol nitrate on dust in the model increases from ~30% in fresh Asian outflow to 80–90% over the Northeast Pacific, reflecting in part the volatilization of ammonium nitrate and the resulting transfer of nitrate to the dust. Consumption of dust alkalinity by uptake of acid gases in the model is slow relative to the lifetime of dust against deposition, so that dust in general does not acidify. This argues against the hypothesis that dust iron released by acidification could become bio-available upon dust deposition. Observations in INTEX-B show no detectable ozone depletion in Asian dust plumes, consistent with the model. Uptake of HNO3 by dust, suppressing its recycling to NOx, reduces Asian pollution influence on US surface ozone in the model by 10–15% or up to 1 ppb.

scholarly journals A new dust cycle model with dynamic vegetation: LPJ-dust version 1.0

2010 ◽  
Vol 3 (2) ◽  
pp. 473-515
Author(s):  
S. Shannon ◽  
D. J. Lunt
Keyword(s):  
Transport Model ◽  
Surface Concentration ◽  
Reanalysis Data ◽  
Dust Particles ◽  
Dust Deposition ◽  
Chemical Transport Model ◽  
Cycle Model ◽  
Dynamic Global Vegetation Model ◽  
Cloud Scavenging ◽  
Global Vegetation

Abstract. This paper presents a new offline dust cycle model which uses the Lund-Potsdam-Jena dynamic global vegetation model (Sitch et al., 2003) to calculate time varying dust sources. Surface emissions are calculated by simulating the processes of saltation and sandblasting using an existing model (Tegen et al., 2002). Dust is transported using the TOMCAT chemical transport model (Chipperfield, 2006). Dust particles are removed from the atmosphere by dry deposition and sub-cloud scavenging. The model is designed so that it can be driven using reanalysis data or GCM derived fields. To improve the performance of the model, threshold values for vegetation cover, soil moisture, snow depth and threshold friction velocity, used to determine surface emissions are tuned. The effectiveness of three sub-cloud scavenging schemes are also tested. An ensemble of tuning experiments are evaluated against dust deposition and surface concentration measurements.

scholarly journals Impacts of long-range transported mineral dust on summertime convective cloud and precipitation: a case study over the Taiwan region

2021 ◽  
Author(s):  
Yanda Zhang ◽  
Fangqun Yu ◽  
Gan Luo ◽  
Jiwen Fan ◽  
Shuai Liu
Keyword(s):  
Long Range ◽  
Transport Model ◽  
Mineral Dust ◽  
Convective Cloud ◽  
Dust Particles ◽  
Chemical Transport Model ◽  
Dust Aerosols ◽  
Low Altitude ◽  
Water Contents

Abstract. As one of the most abundant atmospheric aerosols and effective ice nuclei, mineral dust particles affect clouds and precipitation in the Earth system. Here numerical experiments are carried out to investigate the impacts of dust aerosols on summertime convective clouds and precipitation over the mountainous region in Taiwan. We run the Weather Research and Forecasting model (WRF) coupled with the spectral-bin microphysics (SBM) and Morrison two-moment (Morr2) schemes at 3 km resolution, with the dust number concentrations from a global chemical transport model (GEOS-Chem-APM). The case study indicates that the long-range transported dust, with relatively low number concentrations, can notably affect the properties of convective cloud (ice/liquid water contents, cloud top height, and cloud coverage) and precipitation (spatial pattern and intensity). The dust effects are evident during the strong convective periods, significantly increasing the ice water contents in the mixed-phase regime via the enhanced heterogeneous freezing. With both the Morr2 and SBM schemes, we see invigoration effects of dust aerosols on the convective intensity through enhanced condensation and deposition latent heating. In this process, the low-altitude dust particles are uplifted to the freezing level by updrafts which, in turn, enhance the convective cloud development through immersion freezing and convective invigoration. Comparing to the Morr2 scheme, the SBM scheme predicts more realistic precipitation and different invigoration effects of dust. The differences are partially attributed to the saturation adjustment approach utilized in the bulk scheme, leading to the stronger enhancement of condensation at mid-low altitude and weaker deposition increase at the upper level.

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