Abstract

This study reports the only recent characterisation of two contrasted wet deposition events collected during the PEACETIME cruise in the Mediterranean open seawater, and their impact on trace metals (TMS) marine stocks. Rain samples were analysed for Al, 12 trace metals (TMs hereafter, including Co, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Ti, V and Zn) and nutrients (N, P, DOC) concentrations. The first rain sample collected in the Ionian Sea (rain ION) was a wet typical regional background deposition event whereas the second rain collected in the Algerian Basin (rain FAST) was a Saharan dust wet deposition. The concentrations of TMs in the two rain samples were significantly lower compared to concentrations in rains collected at coastal sites reported in the literature, suggesting either less anthropogenic influence in the remote Mediterranean environment, or decreased emissions during the last decades in the Mediterranean Sea. The TMs inventories in the surface microlayer and mixed layer (0–20 m) at ION and FAST stations before and after the events, compared to atmospheric fluxes, showed that the atmospheric inputs were a significant source of particulate TMs for both layers. At the scale of the western and central Mediterranean, the atmospheric inputs were of the same order of magnitude as marine stocks within the ML for dissolved Fe, Co and Zn, underlining the role of the atmosphere in their biogeochemical cycle in the stratified Mediterranean Sea. In case of intense wet dust deposition event, the contribution of atmospheric inputs could be critical for dissolved stocks of the majority of TMs.

Highlights

  • Atmospheric deposition of continental aerosol has long been recognized to influence trace element concentrations in remote oceanic surface waters (Buat-Ménard and Chesselet, 1979; Hardy, 1982; Buat-Ménard, 1983)

  • The general meteorological conditions during the cruise indicated that the ION and FAST stations were highly affected by cloudy weather conditions

  • 2 significant rains occurred on the research vessel (R/V) position and have been collected: The first rain was collected during the 4-day ION station in the Ionian Sea in the early morning of 29/05 at 03:08

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Summary

Introduction

Atmospheric deposition of continental aerosol has long been recognized to influence trace element concentrations in remote oceanic surface waters (Buat-Ménard and Chesselet, 1979; Hardy, 1982; Buat-Ménard, 1983). The Mediterranean Sea (Med Sea) is an oligotrophic environment where marine biosphere growth is nutrient-limited during the long Mediterranean summer season characterized by a strong thermal stratification of surface waters (The Mermex Group, 2011). The. Mediterranean atmosphere is characterized by the permanent presence of anthropogenic aerosols from industrial and domestic activities around the basin (e.g., Sciare et al, 2003; Kanakidou et al., 2011). Mediterranean atmosphere is characterized by the permanent presence of anthropogenic aerosols from industrial and domestic activities around the basin (e.g., Sciare et al, 2003; Kanakidou et al., 2011) In addition to this anthropogenic background, the Mediterranean basin is subject to seasonal contributions of particles from biomass fires in summer (Guieu et al, 2005) and to intense sporadic Saharan dust inputs (e.g., Loÿe-Pilot and Martin, 1996; Vincent et al, 2016). Atmospheric dust inputs were identified to have a fertilizing effect on the plankton stocks and fluxes, even in the presence of relatively high nutrients and Fe marine concentrations (Ridame et al, 2011; reviewed in Guieu and Ridame, 2021)

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