| Abstract |
The Mediterranean Sea, due to its unique characteristics, is a region sensitive to the
impacts of observed climate change (increase in atmospheric and sea temperatures, rising sea
levels, changes in rainfall patterns among others). This has attracted the attention of the global
scientific community, leading to numerous studies related to atmospheric chemistry and its effects
on the broader Mediterranean region. The objective of this study is to explore the role of nutrients
(N, P, Fe) in the marine productivity of the Eastern Mediterranean.
Previous studies have indicated that atmospheric deposition is a significant external
pathway enriching the Mediterranean sea with nutrients. Analyzing a long data series of 25 years
of wet deposition (1997 to 2022) revealed a significant temporal increase in rainfall pH values. As
the solubility of wet deposited Fe is influenced by pH, the observed pH increase leads to a
substantial reduction (up to 4-5 times) of the levels of dissolved and thus bioavailable Fe deposited
into the oceans, potentially impacting marine productivity in the near future.
By using a long time series data on atmospheric deposition over a 21-year period (1997-
2017) at Finokalia, Crete and sediment traps at two different depths in the Cretan sea (500m and
1715m), dry deposition was found to be the main mechanism contributing 67% of total insoluble
matter flux, 68% of total dissolved inorganic N flux and 75% of total dissolved inorganic P flux.
Regarding the sea-atmosphere interaction, mass transfer in the water column was found to be
quite rapid, which is attributed to the formation of aggregates between the deposited
atmospheric dust and the organic material produced by marine biological activity.
Knowing that the organic fraction of nitrogen constitutes approximately 20% of total
nitrogen, we attempted, for the first time, to study the sources and factors influencing the
variability of WSON (Water-Soluble Organic Nitrogen) at two locations in Cyprus with contrasting
characteristics (traffic and background locations) over a period covering an entire year. Annual
mean WSON concentrations of 0.20 and 0.16 μgN m-3 were determined at the traffic and regional
background sites, respectively. A traffic WSON enhancement was found to be quite modest, on
an annual basis (9%). However, concentrations of WSON in Nicosia were more than double than
the background during winter. The "Lenschow approach" indicated that during the winter, both
"traffic + heating" and regional aerosol contribute nearly equally to WSON levels, while
contributions from regional sources seem to become more significant (over 80-90%) during the
summer. Regarding sources, the estimated contribution of regional transport of processed
aerosols was found to be more pronounced at the regional background site (59% vs. 38%), while
a sizeable input (35%) was linked to vehicular emissions at the traffic site. An additional
anthropogenic impact, probably related to biomass burning, was estimated at both sites (16%),
while contributions of natural sources like mineral dust (4–8%) and marine aerosol (2–3%) were
smaller.
While numerous studies have focused on the chemical composition of aerosols in various
regions across the entire Mediterranean, this study uniquely attempts to simultaneously
investigate the composition and sources of aerosols across the entire Mediterranean. Analyzing
the available data, it seems that the eastern Mediterranean basin generally experiences higher
inputs of suspended particulate matter (both natural and anthropogenic origin) compared to the
western basin. The Mediterranean seems to be influenced by a variety of aerosol sources, with a
dominant role played by dust (9-44%) and secondary sulfates (17-30%). This is followed by aged
(13-23%) and fresh sea salt (6-16%). Contributions are also observed from heavy oil combustion
(4-12%), industrial emissions (2-12%), biomass burning (5-6%), and vehicle emissions (20%, in
Algeria). Finally, through the comparison of the Finokalia station with a corresponding background
station in the Greek area (NEO), the Finokalia station was identified as a characteristic background
station not only for Greece but also for the broader area of the southeastern Mediterranean.
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