Metal complexation, FT-IR characterization, and plankton abundance in the marine surface microlayer of coastal areas in the Eastern Mediterranean

Abstract

Barely any data exist on metal speciation in the marine surface microlayer (SML), a rather complex environment, the study of which contributes to enhancement of knowledge on metal speciation and its effect to the ocean. Metal speciation is significant since life requires a wide variety of trace metals that are essential for the growth of the organisms. Ligand concentrations (L) of copper (Cu), zinc (Zn), and cadmium (Cd) were studied by anodic stripping voltammetry (ASV) in the SML of coastal areas within the Aegean Sea in the Eastern Mediterranean. Complexing capacities in the SML in decreasing order ranged for Cu from 29 to 201 nM (median 101 nM), for Zn 24–149 nM (45 nM), and for Cd 1.0–1.5 nM (1.4 nM). Average enrichment factors (EFs) of SML samples compared to subsurface ones (SSW) were calculated equal to 0.9 ± 0.8, 1.2 ± 0.5, and 1.7 ± 1.6 for LZn, LCu, and LCd, respectively. In five out of the six total paired samples of SML and SSW, lower concentrations of LZn were measured in the SML, which is not the case for LCu and LCd. Due to elevated dissolved Zn concentrations in the SML, its complexation is incomplete, contrary to those of Cu and Cd, which are fully complexed. These trace metals are essential nutrients for biological functions, hence any differences on their concentration and chemical speciation may directly influence the distribution of phytoplankton species in the upper water column and neuston. EFs of SML relatively to subsurface water ranged in average between 1.2 and 2.4 for total organic carbon (TOC), chlorophyll a (Chla), and plankton, being generally >2 for most of the amino acids detected, demonstrating a relative enrichment of the SML in organic matter. A significant correlation was found between Cu ligands and dinoflagellates <20 μm, confirming older findings supporting that marine dinoflagellates of Gymnodinium genera produce Cu ligands. New insights are provided in the study and the importance of investigating bio-essential metal ions (Cu, Zn, Cd) and their organic complexes in the SML is pointed. Data on Zn and Cd complexing capacities in the SML are the first published so far.

How do certain atmospheric aerosols affect Cu-binding organic ligands in the oligotrophic coastal sea surface microlayer?

“…To our knowledge, the electrochemical study of Cu-binding organic ligands in the SML has only been reported for a few marine areas. In Table 4, we compared obtained Middle Adriatic CuCC parameters, EF-s, and L tot /DOC ratios for the SML and corresponding ULW with those published for the Mediterranean Sea, 49,50,57 the Norwegian ords, 48 and the Yellow Sea, 58 taking into account their specic environment and trophic conditions. The range of L tot concentrations found for the SML in the middle Adriatic Sea is comparable to the values reported for the oligotrophic E Mediterranean Sea, but is lower than the L tot concentrations in the SML in the mesotrophic NW Mediterranean Sea, which is considered the second most productive part of the Mediterranean area due to nutrient supply from the Rhone and Ebro rivers.…”

“…The range of L tot concentrations found for the SML in the middle Adriatic Sea is comparable to the values reported for the oligotrophic E Mediterranean Sea, but is lower than the L tot concentrations in the SML in the mesotrophic NW Mediterranean Sea, which is considered the second most productive part of the Mediterranean area due to nutrient supply from the Rhone and Ebro rivers. 59 The biological molecules and products formed during the rapid transformation of fresh organic matter are the predominant Cu-binding ligands in the SML of the E Mediterranean, 50,57 while there may be autochthonous as well as additional sources of ligands such as atmospheric inputs in the SML of the NW Mediterranean. 49 The average values for L tot concentrations in the ULW of the Adriatic Sea were up to ve times lower than those in the E and NW Mediterranean, con-rming the low autochthonous production of ligands.…”

Spatial distribution of trace elements and potential contamination sources for surface sediments of the North-Western Black Sea, Romania

“…TEs enter the sea mostly through the river discharges, either adsorbed onto inorganic and organic suspended particles or in dissolved form (Remeikaite-Nikienėet al, 2018;Sun et al, 2020). Dissolved TEs rapidly come into the particulate phase, e.g., via adsorption onto suspended particles, precipitation, flocculation (Karbassi et al, 2014;Karavoltsos et al, 2022). TEs associated with inorganic and organic suspended matter settle and accumulate in sediments, but they can be remobilized and released into the water under specific conditions, being more available to the biota, which could have significant detrimental effects on the ecosystem and human health (Omar et al, 2015;Oros, 2019).…”