Alexandra Gogou

Organic aerosols in Eastern Mediterranean: components source reconciliation by using molecular markers and atmospheric back trajectories

Molecular markers, such as n-alkanes, hopanes, PAHs, n-alkanols, n-alkanals, n-alkan-2-ones and n-alkanoic acids, and atmospheric back trajectories have been conjointly used to reconcile Eastern Mediterranean marine organic aerosols with their emission sources. In the urban site, local inputs of polar and non polar lipids control the aerosol composition. In addition the presence of iso- and anteisoalkanes in the aliphatic fraction of all urban samples analysed, demonstrated the contribution of cigarette smoke to urban aerosols. The composition of the aliphatic and aromatic fractions demonstrated a clear petrogenic input. In the rural site the composition and concentrations of the PAH fraction were dependant on the origin of air masses, and showed a rather pyrolytic origin. They were higher for air masses from the north than for air masses originating from the south. Some molecular markers, such as 6,10,14-trimethylpentadecan-2-one and α,ω-dicarboxylic acids with Cn > C20, characterized rural aerosols corresponding to air masses with a pronounced marine origin.

Marine organic geochemistry of the Eastern Mediterranean: 1. Aliphatic and polyaromatic hydrocarbons in Cretan Sea surficial sediments

Abstract As part of a lipid biogeochemical study, aliphatic and polyaromatic hydrocarbons were determined in surficial sediments from the Cretan Sea (South Aegean Sea) in the Eastern Mediterranean. Total concentrations of both aliphatic (AHC) and polyaromatic (PAH) hydrocarbons were low (562–5697 and 14.6–158.5 ng/g, respectively) with respect to other coastal sediments worldwide and compare with concentrations found in open sea areas. The composition of AHC was dominated by unresolved complex mixture (UCM) indicating the presence of petroleum-related hydrocarbon inputs as confirmed by the detection of specific α,β-hopanes. PAH consisted mainly of pyrolytic four- to five-ring compounds. UCM and PAH amounts revealed that Cretan Sea receives low supply of anthropogenic material compared to NW Mediterranean. The spatial distributions of AHC and PAH indicated that urban run-off and transport from the continental self are the major input pathway of anthropogenic and biogenic hydrocarbons from terrestrial sources in the near shore area, whereas atmospheric transport might be the significant source of hydrocarbons in the deep area.

Determination of organic molecular markers in marine aerosols and sediments: one-step flash chromatography compound class fractionation and capillary gas chromatographic analysis

n-Alkanes, polycyclic aromatic hydrocarbons (PAHs), n-alkanals, n-alkan-2-ones, long-chain alkenones, oxy-PAHs, n-alkanols, sterols and free alkanoic acids have been reliably determined in various environmental matrices by using one-step flash chromatography compound class fractionation and subsequent gas chromatography (GC)–MS and/or GC–flame ionization detection analysis. The obtained recoveries, for the whole analytical procedure were 62–98% for n-alkanes, 60–100% for PAHs, 75% for n-alkanals, 96–100% for nitroarenes, 65–73% for oxy-PAHs, 88–98% for n-alkanols, 80–89% for steroidal alcohols and 98% for alkanoic acids. This analytical protocol has been applied, and proved suitable, for the determination of more than 170 organic compounds in samples, such as aerosols and marine sediments, collected during a 1 year period in a coastal environment of Eastern Mediterranean.

Differences in lipid and organic salt constituents of aerosols from eastern and western mediterranean coastal cities

Abstract Aliphatic and polycyclic aromatic hydrocarbons and carboxylic acid salts have been determined in aerosols collected in two urban locations from the eastern and western Mediterranean, Heraclion and Barcelona, respectively. The samples analysed in both cities exhibit a similar composition, with predominant anthropogenic inputs related with vehicular traffic and coal combustion in the hydrocarbon fractions and marine biogenic inputs in the fatty acid salts. In terms of anthropogenic hydrocarbons, the major differences between the aerosols collected in the two cities concern the significant higher concentrations in Barcelona and the higher relative content of uncombusted fossil fuel compounds in Heraclion. In terms of fatty acid salts, the Heraclion samples contain a large proportion of ω-oxo- and a , ω -dicarboxylic acids and a lack of unsaturated fatty acids, whereas these latter are important constituents in Barcelona samples, which in turn contain ω-oxo- and a , ω -dicarboxylic acids in low concentrations. These differences support the photochemically mediated precursor/end product association that has been proposed for these two types of carboxylic acids.

Holocene Climatic Optimum centennial-scale paleoceanography in the NE Aegean (Mediterranean Sea)

Combined micropaleontological and geochemical analyses of the high-sedimentation gravity core M-4G provided new centennial-scale paleoceanographic data for sapropel S1 deposition in the NE Aegean Sea during the Holocene Climatic Optimum. Sapropel layer S1a (10.2–8.0 ka) was deposited in dysoxic to oxic bottom waters characterized by a high abundance of benthic foraminiferal species tolerating surface sediment and/or pore water oxygen depletion (e.g., Chilostomella mediterranensis, Globobulimina affinis), and the presence of Uvigerina mediterranea, which thrives in oxic mesotrophic-eutrophic environments. Preservation of organic matter (OM) is inferred based on high organic carbon as well as loliolide and isololiolide contents, while the biomarker record and the abundances of eutrophic planktonic foraminifera document enhanced productivity. High inputs of terrigenous OM are attributed to north Aegean borderland riverine inputs. Both alkenone-based sea surface temperatures (SSTs) and δO18G. bulloides records indicate cooling at 8.2 ka (S1a) and ~7.8 ka (S1 interruption). Sapropelic layer S1b (7.7–6.4 ka) is characterized by rather oxic conditions; abundances of foraminiferal species tolerant to oxygen depletion are very low compared with the U. mediterranea rise. Strongly fluctuating SSTs demonstrate repeated cooling and associated dense water formation, with a major event at 7.4 ka followed by cold spells at 7.0, 6.8, and 6.5 ka. The prominent rise of the carbon preference index within the S1b layer indicates the delivery of less degraded terrestrial OM. The increase of algal biomarkers, labile OM-feeding foraminifera and eutrophic planktonic species pinpoints an enhanced in situ marine productivity, promoted by more efficient vertical convection due to repeated cold events. The associated contributions of labile marine OM along with fresher terrestrial OM inputs after ~7.7 ka imply sources alternative/additional to the north Aegean riverine borderland sources for the influx of organic matter in the south Limnos Basin, plausibly related to the inflow of highly productive Marmara/Black Sea waters.

Mediterranean circulation perturbations over the last five centuries: Relevance to past Eastern Mediterranean Transient-type events

The Eastern Mediterranean Transient (EMT) occurred in the Aegean Sea from 1988 to 1995 and is the most significant intermediate-to-deep Mediterranean overturning perturbation reported by instrumental records. The EMT was likely caused by accumulation of high salinity waters in the Levantine and enhanced heat loss in the Aegean Sea, coupled with surface water freshening in the Sicily Channel. It is still unknown whether similar transients occurred in the past and, if so, what their forcing processes were. In this study, sediments from the Sicily Channel document surface water freshening (SCFR) at 1910 ± 12, 1812 ± 18, 1725 ± 25 and 1580 ± 30 CE. A regional ocean hindcast links SCFR to enhanced deep-water production and in turn to strengthened Mediterranean thermohaline circulation. Independent evidence collected in the Aegean Sea supports this reconstruction, showing that enhanced bottom water ventilation in the Eastern Mediterranean was associated with each SCFR event. Comparison between the records and multi-decadal atmospheric circulation patterns and climatic external forcings indicates that Mediterranean circulation destabilisation occurs during positive North Atlantic Oscillation (NAO) and negative Atlantic Multidecadal Oscillation (AMO) phases, reduced solar activity and strong tropical volcanic eruptions. They may have recurrently produced favourable deep-water formation conditions, both increasing salinity and reducing temperature on multi-decadal time scales.

Planktonic Lipidome Responses to Aeolian Dust Input in Low-Biomass Oligotrophic Marine Mesocosms

The effect and fate of dry atmospheric deposition on nutrient-starved plankton in the Eastern Mediterranean Sea (EMS; Crete, 2012) by spiking oligotrophic surface seawater mesocosms (3 m3) with Saharan dust (SD; 1.6 g L-1; 23 nmol NOx mg-1; 2.4 nmol PO4 mg-1) or mixed aerosols (A; 1.0 g L-1; 54 nmol NOx mg-1; 3.0 nmol PO4 mg-1) collected from natural and anthropogenic sources. Using high resolution liquid chromatography-mass spectrometry, the concentrations of over 350 individual lipids were measured in suspended particles to track variations in the lipidome associated with dust fertilization. Bacterial and eukaryotic intact polar lipid (IPL) biomarkers were categorized into 15 lipid classes based on headgroup identity, including four novel IPL headgroups. Bulk IPL concentrations and archaeal tetraether lipids were uncoupled with the doubling of chlorophyll concentrations that defined the stimulation response of oligotrophic plankton to SD or A amendment. However, molecular level analysis revealed the dynamics of the IPL pool, with significant additions or losses of specific IPLs following dust spikes that were consistent among treatment mesocosms. Multivariate redundancy analysis further demonstrated that distribution of IPL headgroups and molecular modifications within their alkyl chains were strongly correlated with the temporal evolution of the plankton community and cycling of phosphate. IPLs with phosphatidylcholine, betaine, and an alkylamine-like headgroup increased in the post-stimulated period, when phosphate turnover time had decreased by an order of magnitude and phosphorus uptake was dominated by plankton > 2 µm. For most IPL classes, spiking with SD or A yielded significant increases in the length and unsaturation of alkyl chains. A lack of corresponding shifts in the plankton community suggests that the biosynthesis of nitrogenous and phosphatidyl lipids may respond to physiological controls during episodic additions of dust to the EMS. Furthermore, alkyl chain distributions of IPLs containing N, P, and S invoked a bacterial source, suggesting that bacterioplankton are able to modulate these lipids in response to nutrient stress.