Nilgün Kubilay

Global distribution of atmospheric phosphorus sources, concentrations and deposition rates, and anthropogenic impacts

A worldwide compilation of atmospheric total phosphorus (TP) and phosphate (PO4) concentration and deposition flux observations are combined with transport model simulations to derive the global distribution of concentrations and deposition fluxes of TP and PO4. Our results suggest that mineral aerosols are the dominant source of TP on a global scale (82%), with primary biogenic particles (12%) and combustion sources (5%) important in nondusty regions. Globally averaged anthropogenic inputs are estimated to be similar to 5 and 15% for TP and PO4, respectively, and may contribute as much as 50% to the deposition over the oligotrophic ocean where productivity may be phosphorus-limited. There is a net loss of TP from many (but not all) land ecosystems and a net gain of TP by the oceans (560 Gg P a(-1)). More measurements of atmospheric TP and PO4 will assist in reducing uncertainties in our understanding of the role that atmospheric phosphorus may play in global biogeochemistry.

An illustration of the transport and deposition of mineral dust onto the eastern Mediterranean

Abstract The analyses of aerosol samples and deposition (wet) measurements during August 1991–December 1992 at Erdemli (36°N, 34°E) located on the Turkish coast of the eastern Mediterranean has shown higher dust concentration and total deposition during transitional seasons (spring and autumn) compared to summer and winter seasons. The data, complemented by three-dimensional (3D) air mass back trajectories and satellite observations suggest that North African and Middle East desert derived dust particles are transported to the region during transitional seasons. Transport events in the last part of March 1992 and early October 1992 are studied through combined analyses of ground based and satellite observations and modelling results. It is shown that dust transport constitutes a large fraction of the annual atmospheric deposition in the eastern Mediterranean, with two deposition events of short duration accounting up to 30% of the total annual flux. Therefore, the dissolved and particulate species associated with dust could be extremely variable in the mixing layer during large deposition events and could easily be missed in a short-term sampling program. The possible impact of large pulses on biological productivity of the sea also warrants consideration.

Trace elements in atmospheric particulates over the Eastern Mediterranean; Concentrations, sources, and temporal variability

Abstract The first long-term, land-based sampling of the atmosphere above the Turkish coast of the Northeastern Mediterranean Sea (36° 33′ 54″ N and 34° 15′ 18″ E) has demonstrated the dominance of Sahara desert particles over the basin. Atmospheric samples, collected on Whatman-41 filter papers, had been analyzed for Al, Fe, Ca, Mg, Mn, Ni, Cr, Co, Cd, Pb, Zn, V and Na by flame and flameless modes of AAS. Analysis of 339 samples collected during the period August 1991 to December 1992 has shown that pulses of desert particles invade the region from March–May and October–November and during such events the concentrations of the crustal elements (Al, Fe) in atmospheric particulate increase by an order of magnitude. The concentrations of such anthropogenic elements as Zn and Cd reach their maximum levels during the dry season. Three days backward, three-dimensional air-mass trajectory analysis has confirmed the invasion of the basin by sporadic but intense concentrations of dust originating from the Sahara. The elemental composition of size fractionated samples collected over the basin in summer and fall also verifies the existence of particles of both anthropogenic and crustal origins. The geographic position of the sampling tower lies downstream of the tracks of all major air masses affecting the area and therefore the data set can be used to define the atmospheric particulate over the Eastern Mediterranean.

Impacts of atmospheric nutrient deposition on marine productivity: Roles of nitrogen, phosphorus, and iron

Nutrients are supplied to the mixed layer of the open ocean by either atmospheric deposition or mixing from deeper waters, and these nutrients drive nitrogen and carbon fixation. To evaluate the importance of atmospheric deposition, we estimate marine nitrogen and carbon fixation from present-day simulations of atmospheric deposition of nitrogen, phosphorus, and iron. These are compared with observed rates of marine nitrogen and carbon fixation. We find that Fe deposition is more important than P deposition in supporting N fixation. Estimated rates of atmospherically supported carbon fixation are considerably lower than rates of marine carbon fixation derived from remote sensing, indicating the subsidiary role atmospheric deposition plays in total C uptake by the oceans. Nonetheless, in high-nutrient, low-chlorophyll areas, the contribution of atmospheric deposition of Fe to the surface ocean could account for about 50% of C fixation. In marine areas typically thought to be N limited, potential C fixation supported by atmospheric deposition of N is only ~1%-2% of observed rates. Although these systems are N-limited, the amount of N supplied from below appears to be much larger than that deposited from above. Atmospheric deposition of Fe has the potential to augment atmospherically supported rates of C fixation in N-limited areas. In these areas, atmospheric Fe relieves the Fe limitation of diazotrophic organisms, thus contributing to the rate of N fixation. The most important uncertainties in understanding the relative importance of different atmospheric nutrients are poorly understood speciation and solubility of Fe as well as the N:Fe ratio of diazotrophic organisms.

Structure of Emiliania huxleyi blooms in the Black Sea surface waters as detected by SeaWIFS imagery

The temporal and spatial characteristics of coccolithoprid Emiliania huxleyi blooms in the surface waters of the Black Sea are studied using the SeaWIFS mean normalized water-leaving radiances data for 1998-2000. It is shown that the Black Sea consistently experiences high reflectance patches of coccolith platelets throughout the basin each year during the May-July period. Although the Black Sea is masked by clouds, the data also suggest enhanced activity for some period during autumn and early winter. Their spatial patterns resemble very closely the circulation system derived from the altimeter data, and exhibit pronounced differences between cyclones and anticyclones. The cyclonic cell, which covers the entire interior part of the basin, appears as a more favourable site for more intense bloom formation. This is related with its relatively shallower mixed layer thickness and stronger mixed layer average water leaving radiance.

Seasonal chemical and mineralogical variability of atmospheric particles in the coastal region of the Northeast Mediterranean

Abstract A time-serial analysis of atmospheric particles collected since 1990 at a coastal site bordering the northeastern Mediterranean Sea shows that the collected samples, display seasonal patterns in both concentration and color. The 1990–91 and 1992 collections yield an annualised average of around 0.5 g/day dust loading reducing to around 0.3 g/day when the sea-salt contribution is excluded. The highest concentrations of atmospheric particles of continental origin for both natural (e.g. Fe, Mn) and anthropogenic (e.g. Cd, Pb) materials are observed between April and October and this variability is inversely related to the frequency and the amount of rainfall. Sea-salt aerosol (Na) contents do not follow this pattern but are related to local wind speeds. Trace elements in the dusts also display seasonal variations in enrichment factors (EF), with respect to average elemental abundances in crustal rocks. The non-enriched (crustal) elements appear to be indicators of long-distance supply while the strongly enriched (anthropogenic) and moderately enriched suites of elements represents inputs from local or “anomalous” sources. The similar morphology of quartz and calcite grains and the uniformity of the clay mineral assemblages in samples collected over a two-year period strongly indicate a common source for the bulk of the atmospheric particles. The dominant clay types (palygorskite and smectite) document a desertic source areas.

A hemispheric dust storm affecting the Atlantic and Mediterranean in April 1994: Analyses, modeling, ground-based measurements and satellite observations

One of the largest recorded dust transport events originating from the great Sahara desert during April 1994 affected the entire region extending from the Caribbean to the Eurasian continent. This hemispherical transport of airborne dust took place during a series of storms that developed during the first three weeks of April in a background of low-index circulation. These repeated events are studied through the combined analyses and interpretation of atmospheric data, ground-based aerosol measurements, visibility observations, AVHRR and Meteosat visible band satellite data, and the results of Eta model simulations, including an aerosol transport component. The observations produce a consistent picture of the temporal and spatial development of the dust events, whose main features are used in parts to verify the model results. The rate of dust suspension from some areas of the western Sahara desert exceeded 1.5 mg m−2 h−1 and the maximum column integrated dust load reached 2 g m−2 during April 3–5 1994, when the first major suspension event produced two simultaneous pulses of dust moving in opposite directions across the subtropical Atlantic Ocean and the eastern Mediterranean Sea. These dust suspensions were created by surface winds resulting from subsidence on the northeastern side of a blocking anticyclone in the Atlantic region and subsequent winds of an intense developing cyclone in the Mediterranean-African region. In the following period, maximum dust loads of 4.5 and 2.5 g m−2 occurred on April 12 and 17, respectively, when new cyclones transported dust across the Mediterranean from Africa to Europe. The generation of the two dust pulses during the first even and the recurrent cyclone transport in the following period is shown to be the result of a large-scale, anomalous atmospheric circulation connected with blocking in the Atlantic Ocean and the interactions of upper air jets downstream of the blocking. The particular state of the hemispheric circulation during the studied period corresponded to the positive phase of the North Atlantic Oscillation (NAO). While previous statistical evidence has consistently linked dust transport in the region with the NAO signatures, we show the same connection on the basis of this case study.

Airborne material collections and their chemical composition over the Black Sea

Abstract The chemical composition of the Black Sea aerosol was studied during the July 1992 CoMSBLACK 92 cruise on board R V Bilim. It has been shown that the chemical composition of the Black Sea aerosols can change very rapidly in accordance with changes in the wind regime. The influence of the Saharan desert particles can alter the elemental concentrations of trace metals. The result has been summarized on Enrichment Factor diagrams to permit comparison with previous and future studies. The atmospheric input of oxidized nitrogen (NO3+NO2−N) can reach 13% of the total inorganic nitrogen input of the Danube. Lead (Pb) input reaches 39% of this riverine input. Such loads can play an important role in the present state of the sea.

Aerosol Nitrate and Non-Sea-Salt Sulfate Over the Eastern Mediterranean

Among the biogenic sources of sulfate aerosols, reduced sulfur gases such as DMS constitute and control a significant fraction of the atmospheric nss-sulfate budget (Charlson et al., 1987, e.g.). Certain species of phytoplankton; particularly the dinoflagellate Phaeocystis pouchetii and the coccolithophore Emiliana huxleyi are known to be important producers of dimethylsulfide (DMS) (Matrai and Keller, 1993, e.g.). Biogenic sulfur, created mainly by seasonal phytoplanktonic activity, could be particularly rich sources in certain regions and dominate the atmospheric sulfur cycle.

Concentration and Chemical Composition of PM2.5 and PM10-2.5 in the Northeastern Mediterranean

Two stage aerosol samples (PM10-2.5 and PM2.5) were collected at a rural site (Erdemli) located on the coast of the Northeastern Mediter- ranean, between April 2001 and April 2002. A total of 581 aerosol samples were analysed for trace elements (Fe, Ti, Mn, Ca, V, Ni, Zn, Cr) and water soluble ions (Na + , NH4 + , K + , Mg 2+ , Ca 2+ , Cl - , Br - , NO3 - , SO4 2- , C2O4 2- and MS - ). The annual mean PM10 and PM2.5 levels were 36.4 ± 27.8 µg m -3 and 9.7 ± 5.9, respectively. The highest levels of PM10 were observed during the transition period (March, April and May) due to mineral dust transported from North Africa and during winter due to sea spray generation. However, PM2.5 levels exhibited higher concentrations during summer resulting from an enhanced production of secondary aerosols. PM10, crustal elements, sea salt aerosols and NO3 - were mainly associated with the coarse mode whereas nssSO4 2- , C2O4 2- , MS - , NH4 + , Cr and Ni were found predominantly in the fine fraction. Ionic balance analysis performed in the coarse and fine aerosol fractions indicated anion and cation deficiency due to CO3 2- and H + , respec- tively. A relationship between nssSO4 2- and NH4 + denoted that sulphate particles were partially neutralized (70%) by ammonium. Excess-K/BC pre- sented two distinct ratios for winter and summer, indicating two different sources: Fossil fuel burning in winter and biomass burning in summer.