Spatial gradients in trace metal concentrations in the surface microlayer of the Mediterranean Sea

Antonio Tovar-Sã¡Nchez,Sergio A Saã±Udo-Wilhelmy,Carlos M Duarte,Jesãºs M Arrieta

doi:10.3389/fmars.2014.00079

Abstract

The relationship between dust deposition and surface water metal concentrations is poorly understood. Dissolution, solubility, and partitioning reactions of trace metals from dust particles are governed by complex chemical, biological, and physical processes occurring in the surface ocean. Despite that, the role of the sea surface microlayer (SML), a thin, but fundamental component modulating the air-sea exchange of materials has not been properly evaluated. Our study revealed that the SML of the Mediterranean Sea is enriched with bioactive trace metals (i.e., Cd, Co, Cu and Fe), ranging from 8 (for Cd) to 1000 (for Fe) times higher than the dissolved metal pool in the underlying water column. The highest enrichments were spatially correlated with the atmospheric deposition of mineral particles. Our mass balance results suggest that the SML in the Mediterranean Sea contains about 2 tonnes of Fe. However, we did not detect any trends between the concentrations of metals in SML with the subsurface water concentrations and biomass distributions. These findings suggest that future studies are needed to quantify the rate of metal exchange between the SML and the bioavailable pool and that the SML should be considered to better understand the effect of atmospheric inputs on the biogeochemistry of trace metals in the ocean.

Highlights

The sea-surface microlayer (SML) has been defined as the top 1–1000 μm of the surface ocean and it serves as the boundary layer between the atmosphere and the ocean
High concentrations of Cd, Co, Cu, and Fe in the Dissolved water samples (DSSW) pool were measured in the Marmara and Black Seas
Levels of Mo and V in the three pools (SML, the subsurface water (TSSW), and DSSW) in the Marmara and Black Seas were about 50% lower than those measured in other regions of the Mediterranean Sea (120.6 ± 8.1 nM and 25.7 ± 2.6 nM, respectively)

Summary

Introduction

The sea-surface microlayer (SML) has been defined as the top 1–1000 μm of the surface ocean and it serves as the boundary layer between the atmosphere and the ocean. The SML is known to concentrate natural and anthropogenic materials from the atmosphere as well as to be a micro-habitat for a diverse range of organisms (i.e., bacteria, phytoplankton, zooplankton, and icthyo-neuston) (Cincinelli et al, 2001). This environmental compartment plays an important role in the exchange rate of gases and energy on a global scale (Agogué et al, 2004; Wurl and Obbard, 2004; Wurl et al, 2006, 2011; Wurl and Holmes, 2008). The study of the interface between the ocean and atmosphere is important to better understand trace metal distributions, as well as the processes influencing vertical fluxes of materials, phytoplankton uptake, and particulate scavenging occurring in surface waters of the Mediterranean Sea

Methods

Results

Conclusion