The Influence of Qatari Dust on the Element Composition of Marine Plankton

Abstract

The Exclusive Economic Zone (EEZ) of Qatar is affected by extreme dust and extensive industrialization, making it an ideal location to examine influences of coastal processes on biological activity, which greatly affects marine biogeochemical cycling. In this study, the influence of dust on the trace element composition of plankton and how distance from shore effects elemental concentrations in marine plankton was investigated. Samples were collected using net tows with mesh sizes of 50 (bulkplankton) and 200 (zooplankton) mm size-fractions in 2012 and 2014 to examine temporal and spatial variabilities. The samples were strong acid digested and analyzed using ICP-OES. Trace metal clean techniques were used. The biogenic concentrations of trace metals were determined by correcting the bulk analyses for the lithogenic contribution using aluminum content of Qatari dust as a lithogenic tracer. The relative trace metal composition of plankton from EEZ of Qatar is Fe > Zn ≈ Cu > V ≈ Ni ≈ Cr ≈ As ≈ Mo > Cd ≈ Co. Small and large size planktonic compositions were similar, except for Ba, Mn, Pb, Mo which were higher in zooplankton than bulkplankton. It was not clear if the variability was due to differences in biology, proximity to the coast or interannual effects. The geochemical and statistical analysis suggested that the concentrations of Al, Fe, Cr, Co, Mn, Ni, Pb, Li in net-tow plankton samples were mostly of lithogenic (dust) and Cd, Cu, Mo, Zn, Ca are most likely of biogenic/anthropogenic origin. The excess concentrations relative to average dust from Qatar for most elements (except Cd) decreased with distance from shore. This may be due to contamination or uncertainties with the lithogenic correction or due to our sampling locations in a marginal sea, dominated by dust input. This is an aspect of this study that warrants more research.