Organic matter characterization and copper complexing capacity in the sea surface microlayer of coastal areas of the Eastern Mediterranean

Abstract

In a time-series study, surface microlayer (SML) and underlying (ULW) water samples were collected in 3 sampling seasons from 5 coastal microenvironments of the EasternMediterranean. Examination of the isotopic composition (δ18O, δ2H and δ13C) of the water samples demonstrated that most of them lie around the mixing zone between the Greek/local precipitation water line (PWL) and seawater. Samples from the areas of Loutropyrgos, Pahi and Vourkari, within the Saronikos Gulf, correspondmainly to seawater, the Asopos samples are influenced by the local meteoricwaters,whereas Chalkida samples seemto be affected by local freshwater inputs attributed to the discharge site of a sewage treatment plant. In almost half of the samples examined no enrichment of the SML in Cu complexing capacity (LT)was recorded. A wider range of LT was determined at SML (51.5 to 679.6 nMwith an average value of 229.6 nM) than in the ULW (55.2 to 346.4 nM with an average value of 208.5 nM). While the enrichment factor (EF) of a compound is defined as the ratio of the concentration in the SML to that in the corresponding underlying water, themean EF values of dissolved surface active substances (SASd: 5.8±5.8) and transparent exopolymer particles (TEPcolor: 2.2 ± 1.8, TEPmicro: 3.8 ± 5.6) were significantly greater than unity (p = 0.0121, 0.0220 and 0.0404 respectively) indicating a general enrichment of these organic materials in SML. SASs, normalized to DOC concentrations, have shown that the organic matter pool studied was mostly hydrophilic. During winter (February 2013) an enrichment of LT in SML was detected at all of the sampling sites examined, paralleled by TEP aggregation suggesting a role for TEP in copper complexation.