Present-day Saharan dust deposition in the Atlantic Ocean and its marine-environmental consequences (original) (raw)
2019, EGUGA
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Abstract
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Mineral dust influences the carbon cycle in the ocean by providing nutrients and metals that can enhance phytoplankton growth and facilitate the sinking of organic matter. This study presents a two-year assessment of dust deposition in the Atlantic, using a network of dust-collecting instruments. The research reveals that summer rains significantly enhance dust nutrient release compared to dry conditions, which may improve surface-ocean productivity and affect broader ecological systems.
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Atmospheric Chemistry and Physics Discussions, 2016
Mineral dust has a large impact on regional and global climate, depending on its particle size. Especially in the Atlantic Ocean downwind of the Sahara, the largest dust source on earth, the effects can be substantial but are poorly understood. This study focuses on seasonal and spatial variations in particle size of Saharan dust deposition across the Atlantic Ocean, using an array of submarine sediment traps moored along a transect at 12˚ N. We show that the particle size decreases downwind with increased distance from the Saharan source, due to higher gravitational settling velocities of coarse particles in the atmosphere. Modal grain sizes vary between 4 and 33 μm throughout the different seasons and at five locations along the transect. This is much coarser than previously suggested and incorporated into climate models. In addition, seasonal changes are prominent, with coarser dust in summer, and finer dust in winter and spring. Such seasonal changes are caused by transport at h...
Compositional changes of present-day transatlantic Saharan dust deposition
Atmospheric Chemistry and Physics Discussions, 2016
Massive amounts of Saharan dust are blown from the African coast across the Atlantic Ocean towards the Americas each year. This dust has, depending on its chemistry, direct and indirect effects on global climate including reflection and absorption of solar radiation as well as transport and deposition of nutrients and metals fertilizing both ocean and land. To determine the temporal and spatial variability of Saharan dust transport and deposition and their marine environmental effects across the equatorial North Atlantic Ocean, we have set up a monitoring experiment using deep-ocean sediment traps as well as land-based dust collectors. The sediment traps were deployed at five ocean sites along a transatlantic transect between northwest Africa and the Caribbean along 12⁰ N, in a down-wind extension of the land-based dust collectors placed at 19⁰ N on the Mauritanian coast in Iwik. In this paper, we lay out the setup of the monitoring experiment and present the particle ...
Atmospheric Transport and Deposition of Mineral Dust to the Ocean: Implications for Research Needs
Environmental Science & Technology, 2012
This paper reviews our knowledge of the measurement and modeling of mineral dust emissions to the atmosphere, its transport and deposition to the ocean, the release of iron from the dust into seawater, and the possible impact of that nutrient on marine biogeochemistry and climate. Of particular concern is our poor understanding of the mechanisms and quantities of dust deposition as well as the extent of iron solubilization from the dust once it enters the ocean. Model estimates of dust deposition in remote oceanic regions vary by more than a factor of 10. The fraction of the iron in dust that is available for use by marine phytoplankton is still highly uncertain. There is an urgent need for a long-term marine atmospheric surface measurement network, spread across all oceans. Because the southern ocean is characterized by large areas with high nitrate but low chlorophyll surface concentrations, that region is particularly sensitive to the input of dust and iron. Data from this region would be valuable, particularly at sites downwind from known dust source areas in South America, Australia, and South Africa. Coordinated field experiments involving both atmospheric and marine measurements are recommended to address the complex and interlinked processes and role of dust/Fe fertilization on marine biogeochemistry and climate.
Atmospheric Chemistry and Physics, 2014
Mass deposition fluxes of mineral dust to the tropical northeast Atlantic Ocean were determined within this study. In the framework of SOPRAN (Surface Ocean Processes in the Anthropocene), the interaction between the atmosphere and the ocean in terms of material exchange were investigated at the Cape Verde atmospheric observatory (CVAO) on the island Sao Vicente for January 2009. Five different methods were applied to estimate the deposition flux, using different meteorological and physical measurements, remote sensing, and regional dust transport simulations. The set of observations comprises micrometeorological measurements with an ultra-sonic anemometer and profile measurements using 2-D anemometers at two different heights, and microphysical measurements of the sizeresolved mass concentrations of mineral dust. In addition, the total mass concentration of mineral dust was derived from absorption photometer observations and passive sampling. The regional dust model COSMO-MUSCAT was used for simulations of dust emission and transport, including dry and wet deposition processes. This model was used as it describes the AOD's and mass concentrations realistic compared to the measurements and because it was run for the time period of the measurements. The four observation-based methods yield a monthly average deposition flux of mineral dust of 12-29 ng m -2 s -1 . The simulation results come close to the upper range of the measurements with an average value of 47 ng m -2 s -1 . It is shown that the mass deposition flux of mineral dust obtained by the combination of micrometeorological (ultra-sonic anemometer) and microphysical measurements (particle mass size distribution of mineral dust) is difficult to compare to modeled mass deposition fluxes when the mineral dust is inhomogeneously distributed over the investigated area.
Marine Geology, 1999
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Vertical and areal distribution of Saharan dust over the western equatorial north Atlantic Ocean
Journal of Geophysical Research, 1972
Aerosol measurements were made as a part of the Barbados Oceanographic and Meteorological Experiment (Bomex) during May, June, and July 1969. Maximum dust concentrations occurred between the altitudes of 1.5 km and 3.7 km, a region which we call the Saharan air layer. The average concentration of mineral aerosol within this layer was 61 t•g m-a; in contrast, the average concentration in the low-level air was 22 t•g m -a. These dust concentrations are comparable to those found in continental surface air. Because of the presence of a strong inversion at the base of the Saharan layer, sea. salt was confined to te lower altitudes where the average concentration was 10 tzg m -8. Thus, sea salt appears to be a relatively minor constituent of the trade wind aerosol during much of the year. On the basis of these measurements and of a model describing the movement of Sararan air outbreaks, we estimate that 25 to 37 million tons of dust are transported through the longitude of Barbados each year. This quantity of dust is sufficient to supply all the material required to maintain the present rate of pelagic sedimentation across the entire northern equatorial Atlantic Ocean. The mineral aerosol concentration in sealevel, trade wind air at Barbados, West Indies (13øN, 59øW), has been measured from the fall of 1965 to the present [Delany et al., 1967; Prospero, 1968; Prospero et al., 1970; Carlson and Prospero, 1972]. During the first four years of this program, the air sampling was essentially continuous. These measurements have shown that large quantities of dust are transported across the northern equatorial Atlantic from the deserts of North Africa during the late spring, summer, and early fall. The average surface air concentration of mineral aerosol at Barbados during the dusty season varies from year to year but generally is of the order of 10/•g m -8 of air; the concentration during the rest of the year is more than an order of magnitude less [Prospero, 1968; Carlson and Prospero, 1972]. equatorial North Atlantic and of the relationship of the aerosol distribution to meteorological parameters. The meteorological aspects of this work, a study of the large-scale movement of Sararan air outbreaks over the northern equatorial Atlantic, are presented by us elsewhere [Carlson and Prospero., 1972]
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Tropical Rains Controlling Deposition of Saharan Dust Across the North Atlantic Ocean
Geophysical Research Letters, 2020
Mineral dust plays an important role in the atmospheric radiation budget as well as in the ocean carbon cycle through fertilization and by ballasting of settling organic matter. However, observational records of open‐ocean dust deposition are sparse. Here, we present the spatial and temporal evolution of Saharan dust deposition over 2 years from marine sediment traps across the North Atlantic, directly below the core of the Saharan dust plume, with highest dust fluxes observed in summer. We combined the observed deposition fluxes with model simulations and satellite observations and argue that dust deposition in the Atlantic is predominantly controlled by summer rains. The dominant depositional pathway changes from wet deposition in summer to dry deposition in winter. Wet deposition has previously been suggested to increase the release of dust‐derived nutrients and their bioavailability, which may be a key contributor to surface‐ocean productivity in remote and oligotrophic parts of...
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Biogeosciences Discussions
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Annales Geophysicae, 2002
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Revisiting atmospheric dust export to the Southern Hemisphere ocean: Biogeochemical implications
Global Biogeochemical Cycles, 2008
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Journal Of Geophysical Research: Atmospheres, 2019
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