Continental Dust Research Articles

A coherence between the QBO and the amplitude of the Mauna Loa atmospheric transmission annual cycle

The transmission of direct solar radiation through the atmosphere above Mauna Loa, Hawaii, is shown to have a quasi-biennial cyclic component that is coherent with the well-known tropical stratospheric quasi-biennial oscillation (QBO). The QBO-related signal in the 32-year transmission record is manifested as an oscillation in the amplitude of the annual cycle. The transmission annual cycle is known to be caused by seasonal transport of Asian continental dust to and over the island of Hawaii. Variations in water vapour and ozone are eliminated as possible influences in the transmission-QBO relationship, leaving aerosols as the source of the oscillation. The ultimate cause for the quasi-biennial signal in the transmission record is unknown. Small but cyclic modifications to the tropospheric energy budget occur as a result of the transmission variations. The magnitude of the energy budget variations are less than those typically expected to have a significant climatic impact.

Sources of continental dust over Antarctica during the last glacial cycle

The soluble and insoluble parts of 4 major components (Al, Ca, K and Mg) of the continental dust input over East Antarctica, as well as size, distribution parameters of the insoluble part of this dust, have been studied along an ice core which spanns the last climatic cycle (160 kyr). These results provide a better understanding of the respective impact of the different potential dust sources. While Al and K were probably entrapped in illite originating from arid areas and in a lesser extent from shallow marine sediments, Ca and Mg inputs were dominated by marine carbonate of exposed continental shelves emissions.

Saharan dust deposition over Mont Blanc (French Alps) during the last 30 years

Based on continuous and very detailed Al and Ca records along a 70 m long ice core drilled in the Mont Blanc summit area (French Alps, 4270 m asl), continental dust flux at high altitude in the Alps was studied for the past 30 years. From 1955 until 1985, total inputs of 885 and 735 µ g/cm -2 were calculated for Al and Ca respectively. Using mineralogical observations and chemical criteria, the relative importance of the local component was estimated close to 10% for Al and to 30% for Ca continental inputs. It was also possible to point out the predominating influence of soil dust sources located in North Africa, which seems to have significantly increased since the early 1970s with very high inputs occurring after 1980. In 1985, which corresponds to the last complete year of our ice record, the North African influence led to A1 and Ca annual deposition rates of 64 and 23 µ g cm -2 yr -1 . DOI: 10.1034/j.1600-0889.1991.00005.x

Marine aerosols: A review

The background aerosol in the boundary layer over the remote oceans is not aged continental aerosol but, rather, is largely of marine origin. Total particle concentrations are quite uniform throughout the tropical trade wind regions and normally are in the range of 100–300 cm−3. Precipitation reduces particle concentrations, but there is apparently an in situ source of small particles which allows particle concentrations to recover to their normal background level. The fine particle mode (r < 0.3 μm), which comprises 90–95% of the particles but only about 5% of the total mass, cosists primarily of non-sea-salt sulfate (nss-sulfate). There is considerable evidence that nss-sulfate, which is present in concentrations ranging from about 0.2 to 1.5 μg m−3, is formed by gas-to-particle conversion of the oxidation products of organosulfur gases (principally DMS) emitted by the ocean. The principal gas-to-particle conversion mechanisms are particle formation by homogeneous nucleation of low-volatility gas-phase reaction products, condensation of these products on existing particles, and SO2-to-sulfate conversion in cloud droplets. The submicron portion of the particle size distribution is bimodal with peaks at 0.03 μm and 0.1 μm radius. The peak at 0.1 μm is believed to be due to the growth of CCN-sized particles as a result of incloud SO2-to-sulfate conversion. It has been speculated that the sea-to-air flux of DMS affects the number of CCN and thereby affects cloud droplet size, cloud albedo and, consequently, climate. Coarse particles (r > 0.5 μm) are composed primarily of sea salt. The concentration of sea salt shows a strong dependence of wind speed and ranges from about 2 μg m−3 to as much as 50 μg m−3 or more at wind speeds in excess of 15 m s−1. The background coarse mode also contains smaller amounts of nitrate and mineral dust. The concentration of each of these components is normally less than 5% of the mass of sea salt, although dust concentrations can occasionally equal the sea salt loading during fresh intrusions of continental dust. Nitrate is formed by gas-to-particle conversion but the relative importance of the ocean, the stratosphere and lightning as a source of the nitrogen-containing precursor gases remains uncertain. Since nitrate is not found on the fine mode particles, it probably does not result from condensation of gas-phase reaction products or from aqueous-phase oxidation of NOx in cloud droplets.

Beryllium isotope distribution in the western North Atlantic: a comparison to the Pacific

The surface depletion/deep enrichment of the 10Be and 9Be distributions observed in the Pacific is not as conspicuous in the western North Atlantic Ocean between 33° and 42°N. In the case of 9Be, a surface excess sometimes even exists. While 10Be concentrations in the surface waters of the two oceans are comparable, 9Be concentrations in the surface North Atlantic are about five times those in the surface Pacific. Deep waters show an increase of concentrations from the Atlantic (via Antarctic) to the Pacific, but the degree of increase for the two isotopes is different: about 10% for 9Be and 2.5-fold for 10Be. Thus there is a systematic increasing trend in the ration 10Be/ 9Be ( atom/ atom × 10 −7) along the advective flow lines: surface North Atlantic (0.4)→ deep North Atlantic (0.6) → Circumpolar (1.0) → deep Pacific (1.2) → surface Pacific (1–3). These distributional patterns and contrasting North Atlantic-Pacific features can be explained in terms of: (a) a strong fluvial and continental dust input of 9Be to the North Atlantic and an ocean-wide, more-or-less uniform pluvial input of cosmogenically produced 10Be; (b) active participation of Be in the particle recycling involving surface uptake and deep water regeneration; and (c) mean removal time of Be from the ocean, which, based on the 10Be/ 230Th ratios in surface sediments of two deep-sea cores, are estimated as ∼1200 y in the open Pacific and ∼500 a in the open Atlantic, values that are close to water mixing times of the individual ocean basins.

Aluminium in the South Atlantic: Steady state distribution of a short residence time element

The aluminium concentrations of water samples from 18 hydrographic profiles and 35 surface samples in the South Atlantic were determined on board ship during leg III of the South Atlantic Ventilation Experiment (SAVE). The observed surface water distributions (range 0.5 to 57 nM) are thought to arise from the partial dissolution of eoliantransported continental dusts coupled with limited lateral transport by prevailing surface currents. In the deep water the greatest enrichments are observed coincident with the depth of the lower North Atlantic Deep Water. The similarity between the Al∶Si ratios in this water mass in both the south and north Atlantic is taken as evidence that no significant Al additions are being made to this water during its transit. The lower Al concentrations observed in the water masses of Antarctic origin (∼3 nM) are consistent with their formation in areas of limited dust input. The somewhat higher values observed in the Antarctic Bottom Water suggest that the shelf component of this water mass may have elevated Al concentrations.

Redox state of iron in the offshore waters of Peru1

The total concentration and redox state of iron were examined along a transect across the continental shelf off the Peruvian coast during January 1984. Total and dissolved iron (0.4‐µm filter) were measured by the Co‐APDC coprecipitation method. Fe(II) was measured by a preconcentration step with 8‐hydroxyquinoline bonded to silica as the stationary phase, followed by elution and the ferrozine method.Up to 40 nmol kg−1 of Fe(II) was detected in the bottom water at 5–10 km offshore and decreased markedly upward in the water column and with distance offshore. A good correlation between the distribution of Fe(II) and nitrite in the bottom water indicated a common source from the shelf sediments. Elevated Fe(II) concentrations near the sea surface and a diel change were probably due to photochemical reactions involving iron.Total iron levels were &gt;300–500 nmol kg−1 in the surface and the bottom water at 5–6 km offshore. About 80–90% of the iron was in the particulate form, indicating a substantial input of iron from continental dust and from the sediments on the shelf. The total iron level decreased considerably within 35 km of the coastline and the iron seemed to be trapped on the shelf.

Excess 228Th in the airborne dust: an indicator of continental dust from the East Asian deserts

Thorium isotopes in the airborne dust collected at Tsukuba Science City in Japan from January 1981 to December 1982 show clear seasonal variations. Especially 228Th in the airborne particles have a typical maximum cincentration between February and April, which is about an order of magnitude higher than during the remainder of the year. According to the result of size distribution of thorium isotope-bearing particles in the air, about 53% of 228Th is associated with the particles less than 1.6 μm aerodynamic diameter. These results reveal that 228Th in the airborne particles is present in fine soily matters originating from the East Asian deserts.

Late-Glacial Maximum-Holocene Atmospheric and Ice-Thickness Changes from Antarctic Ice-Core Studies

A review of Byrd, Vostok and Dome C Antarctic ice-core records indicates significant changes in atmospheric characteristics between the late glacial maximum (LGM) and the Holocene. This data is relevant to general circulation model (GCM) boundary conditions and validation of output results. Reciprocally, GCM data could help to interpret ice-core results and to extend observed high-latitude changes to a larger scale.During the LGM, low troposphere temperatures were colder by about 5 to 7°C and surface temperatures by 8 to 10°C over the Antarctic ice sheet. There are indications that snow accumulation was slightly lower and isotopic data suggests higher relative humidity over the ocean. A large increase in continental dust (up to a factor of 20) and marine aerosols (up to a factor of 5) is observed on the high Antarctic plateau, both explained by the increased (possibly up to 1.4 to 2 times) intensity of the large-scale atmospheric circulation modulated by desert and sea-ice area extension. Ice-core results show large changes in atmospheric CO2concentrations with LGM values around 200 ppmv and “pre-industrial” values of about 260 ppmv. Finally, determinations of total gas content suggest that central West and East Antarctica were not thicker during the LGM, in contrast with higher surface elevations inferred from coastal-ice studies.

Late-Glacial Maximum-Holocene Atmospheric and Ice-Thickness Changes from Antarctic Ice-Core Studies

A review of Byrd, Vostok and Dome C Antarctic ice-core records indicates significant changes in atmospheric characteristics between the late glacial maximum (LGM) and the Holocene. This data is relevant to general circulation model (GCM) boundary conditions and validation of output results. Reciprocally, GCM data could help to interpret ice-core results and to extend observed high-latitude changes to a larger scale.During the LGM, low troposphere temperatures were colder by about 5 to 7°C and surface temperatures by 8 to 10°C over the Antarctic ice sheet. There are indications that snow accumulation was slightly lower and isotopic data suggests higher relative humidity over the ocean. A large increase in continental dust (up to a factor of 20) and marine aerosols (up to a factor of 5) is observed on the high Antarctic plateau, both explained by the increased (possibly up to 1.4 to 2 times) intensity of the large-scale atmospheric circulation modulated by desert and sea-ice area extension. Ice-core results show large changes in atmospheric CO2 concentrations with LGM values around 200 ppmv and “pre-industrial” values of about 260 ppmv. Finally, determinations of total gas content suggest that central West and East Antarctica were not thicker during the LGM, in contrast with higher surface elevations inferred from coastal-ice studies.

春季北太平洋西部海域における海上大気中のエーロゾル粒子の化学成分の変動について

Concentrations of metallic elements, including Fe, Mn, Cu and Zn in the air over the western North Pacific were determined in the periods from April to May, 1980 and March, 1981. Sampling of airborne particles was done on board by use of a high volume air sampler. During the southward traverse, at the west side of a cold front, the high concentration of iron reaching as high as 2550ng m-3 was observed in the air over the ocean and then it decreased rapidly to the background level. The GMS imageries and meteorological conditions suggest that the high concentrations of iron and manganese in the air over the ocean during the spring season are caused by the transport of the continental dust (load up to 64&mu;g m-3) originating from the east Asian deserts.

Resolution of basaltic and continental aerosol components during spring and summer within the boundary layer of Hawaii

An important continental aerosol component, up to 70% of the total dust load during the spring, has been resolved from the local basaltic component using short time‐step (3.7 hr) sampling at the Hawaiian Volcano Ovservatory (HVO), a site below the inversion layer at 1.2 km altitude. The median continental contribution for approximately 2‐week periods from mid‐March to mid‐June 1979 ranged from 1 to 2μg m−3, whereas from mid‐June to early September 1979 this component was not found, being less than the detection limit of ⅓ its spring magnitude. Over the 6‐month period, the median concentrations for the basaltic aerosol ranged from about 0.2 to 18 μg m−3, a variation associated with local rainfall. This basaltic component exhibits a strong diurnal variation, resulting from the local wind regime, with a ratio of a mid‐afternoon maximum to an early morning minimum of up to 20 or more. Of the six lithophilic elements examined (Al, Si, K, Ca, Ti, and Fe), Si shows the greatest earth/air fractionation, with the continental and local basaltic aerosols being depleted by more than 35% relative to an average crustal and Hawaiian basaltic rock composition, respectively. Time series analysis of the concentrations and a detailed examination of the element ratios indicate that local and continental soils are the only important determinants of the overall aerosol composition at this site for these elements. Compositional differences between the continental dust at HVO and that sampled concurrently at the Mauna Loa Observatory (3.4 km altitude) may be due to the presence of two distinct dust plumes over Hawaii originating from different desert regions in Asia.

Late Glacial Input of Eolian Continental Dust in the Dome C Ice Core: Additional Evidence from Individual Microparticle Analysis

399 individual microparticles in nine samples from the Dome C ice core were studied under scanning electron microscope and analysed by an energy dispersive X-ray system. The studied particles were either continental quartz or various silico-aluminates of continental or volcanic origin. Observations lead to the conclusion that the increase in micro particle concentration by a factor of 10 to 20 during the last glacial stage is explained by a large input of continental dust, as already indicated by trace element analysis (Petit and others 1981) and previously suggested by chemical analysis of other polar ice cores (Cragin and others 1977).This increase is considered to be a consequence of the ice-age climate and earth surface conditions which were characterized by the increase of arid regions and more vigorous atmospheric circulation. Both these conclusions are further supported by the existence of a higher quartz content in the Antarctic ice core as was already found in tropical deep-sea core studies.

Late Glacial Input of Eolian Continental Dust in the Dome C Ice Core: Additional Evidence from Individual Microparticle Analysis

399 individual microparticles in nine samples from the Dome C ice core were studied under scanning electron microscope and analysed by an energy dispersive X-ray system. The studied particles were either continental quartz or various silico-aluminates of continental or volcanic origin. Observations lead to the conclusion that the increase in micro particle concentration by a factor of 10 to 20 during the last glacial stage is explained by a large input of continental dust, as already indicated by trace element analysis (Petit and others 1981) and previously suggested by chemical analysis of other polar ice cores (Cragin and others 1977).This increase is considered to be a consequence of the ice-age climate and earth surface conditions which were characterized by the increase of arid regions and more vigorous atmospheric circulation. Both these conclusions are further supported by the existence of a higher quartz content in the Antarctic ice core as was already found in tropical deep-sea core studies.

Atmospheric contributions to stream water chemistry in the North Cascade Range, Washington

Bulk precipitation contributes significant quantities of cations and trace metals to a subalpine catchment located in the North Cascade Range of Washington. Precipitation loadings account for 30% of the major and more than 50% of the minor element export from the catchment. Preliminary data from larger basins in the North Cascades suggest similar values. Calcium and potassium measured in bulk precipitation are largely derived from continental dusts, while sodium and magnesium originate as marine aerosols. Lead, copper, and arsenic, products of anthropogenic activity in the Puget Lowland, are deposited downwind in the Cascade Mountains; mean precipitation pH at the study site was 4.85 during 1974 and 1975. Elements contributed by precipitation become part of complex upland biogeochemical cycles. With the exception of highly mobile ions like sodium, elemental levels in streamflow reflect biologic and pedogenic cycling processes rather than direct precipitation influence.

Dating of Ross Ice Shelf Cores by Chemical Analysis

AbstractSeasonal variations in sodium concentrations have been measured on surface-pit snow samples and on firn and ice core samples from the Ross Ice Shelf, Antarctica. Site locations include J-9 (82° 22’ S., 168° 40’ W.), Roosevelt Island dome (79° 22’ S, 161° 40’ W), C-7-1 (78° 30’ S., 177° 00’ W.), and C-7-3 (78° 20’S., 179° 51’ E.). The predominant source for the Na is sea salt, indicated by greater concentration levels at seaward sites. Al concentrations of the order of only 10–9g/g show that the input of continental dust is comparable to that at inland Antarctic locations, and that dust contributes only a negligibly small fraction of the Na on the shelf. Maximum Na concentrations occur in the winter or early spring, as is the case for Greenland ice. The annual accumulation-rate at J-9, determined by counting Na concentration peaks with depth, is 90 kg m–2year–1, in agreement with rates determined radiometrically. Annual cycles in Na concentration are also detectable at depth in the J-9 ice core. It is suggested that Na concentration is a useful diagnostic criterion for distinguishing between East Antarctic ice (10–8g Na/g), West Antarctic ice (30 × 10–9g Na/g), and ice that fell as snow on the shelf itself (&amp;gt; 30 × 10–9g Na/g). The transition between snow that is chemically characteristic of the ice-shelf regime to snow of an inland regime is expected to occur near the 500 m elevation contour. This position is up to 200 km inland of the grounding line. A model is presented for the large-scale decrease in Na concentration with distance inland within the ice-shelf regime. Since deeper ice in Ross Ice Shelf cores originated generally further from the ocean, the up-stream origin of shelf ice may be estimated from the chemical profile. The Little America V ice-core chemistry profile shows no discontinuity as would be expected if a recent surge of West Antarctic ice had occurred.

Dating of Ross Ice Shelf Cores by Chemical Analysis

AbstractSeasonal variations in sodium concentrations have been measured on surface-pit snow samples and on firn and ice core samples from the Ross Ice Shelf, Antarctica. Site locations include J-9 (82° 22’ S., 168° 40’ W.), Roosevelt Island dome (79° 22’ S, 161° 40’ W), C-7-1 (78° 30’ S., 177° 00’ W.), and C-7-3 (78° 20’S., 179° 51’ E.). The predominant source for the Na is sea salt, indicated by greater concentration levels at seaward sites. Al concentrations of the order of only 10–9g/g show that the input of continental dust is comparable to that at inland Antarctic locations, and that dust contributes only a negligibly small fraction of the Na on the shelf. Maximum Na concentrations occur in the winter or early spring, as is the case for Greenland ice. The annual accumulation-rate at J-9, determined by counting Na concentration peaks with depth, is 90 kg m–2year–1, in agreement with rates determined radiometrically. Annual cycles in Na concentration are also detectable at depth in the J-9 ice core. It is suggested that Na concentration is a useful diagnostic criterion for distinguishing between East Antarctic ice (10–8g Na/g), West Antarctic ice (30 × 10–9g Na/g), and ice that fell as snow on the shelf itself (&gt; 30 × 10–9g Na/g). The transition between snow that is chemically characteristic of the ice-shelf regime to snow of an inland regime is expected to occur near the 500 m elevation contour. This position is up to 200 km inland of the grounding line. A model is presented for the large-scale decrease in Na concentration with distance inland within the ice-shelf regime. Since deeper ice in Ross Ice Shelf cores originated generally further from the ocean, the up-stream origin of shelf ice may be estimated from the chemical profile. The Little America V ice-core chemistry profile shows no discontinuity as would be expected if a recent surge of West Antarctic ice had occurred.

Dating of Greenland Ice Cores by Flow Models, Isotopes, Volcanic Debris, and Continental Dust

AbstractThe available methods for dating of ice cores are based on radioactive decay, ice-flow calculations, or stratigraphic observations. The two former categories are broadly outlined, and special emphasis is given to stratigraphic methods. Reference horizons are established back to A.D. 1783, in the form of elevated electrical conductivities due to fallout of soluble volcanic debris. Seasonal variations in the concentrations of insoluble microparticles and/or stable isotopes are measured over the entire 400 m lengths of three ice cores, recovered by Greenland Ice Sheet Program (GISP). The resulting absolute time scales are probably accurate within a few years per thousand. Techniques are outlined for re-establishing the approximate, original shape of heavy-isotope profiles that have been more or less smoothed by diffusion in firn and ice. Annual-layer thickness measurements on 24 increments down to 1130 m depth in the Camp Century ice core determine a flow pattern, consistent with that suggested by Dansgaard and Johnsen (1969), and a Camp Century time scale with an estimated uncertainty better than 3% back to 10000 years B.P.

Dating of Greenland Ice Cores by Flow Models, Isotopes, Volcanic Debris, and Continental Dust

AbstractThe available methods for dating of ice cores are based on radioactive decay, ice-flow calculations, or stratigraphic observations. The two former categories are broadly outlined, and special emphasis is given to stratigraphic methods. Reference horizons are established back to A.D. 1783, in the form of elevated electrical conductivities due to fallout of soluble volcanic debris. Seasonal variations in the concentrations of insoluble microparticles and/or stable isotopes are measured over the entire 400 m lengths of three ice cores, recovered by Greenland Ice Sheet Program (GISP). The resulting absolute time scales are probably accurate within a few years per thousand. Techniques are outlined for re-establishing the approximate, original shape of heavy-isotope profiles that have been more or less smoothed by diffusion in firn and ice. Annual-layer thickness measurements on 24 increments down to 1130 m depth in the Camp Century ice core determine a flow pattern, consistent with that suggested by Dansgaard and Johnsen (1969), and a Camp Century time scale with an estimated uncertainty better than 3% back to 10000 years B.P.

The continental component of a Pacific Marine aerosol: Identification by combined neutron activation analysis and scanning electron microscopy with X-ray analysis

The relative merits and sampling requirements of instrumental neutron activation analysis (INAA) and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) analysis as applied to the continental component of marine aerosols are discussed. When correlated with air mass information, the quantitative INAA data on the concentrations of 15 major and minor elements in the continental dust fraction provides information on the geochemical type and location of the land source. Although the SEM/EDS technique provides only qualitative concentrations for 6 additional elements in the aerosol, the important feature of single particle analysis enables more nearly synoptic interpretation of aerosol composition and concentration. A combined INAA and SEM/EDS study of the aerosol samples is therefore preferred.