The Elemental Composition of Size Fractionated Particulate Matter Samples from the Central Arabian Gulf: Biotic and Abiotic sources

Oguz Yigiterhan1, Ibrahim S Al-Ansari1, Alex Nelson2, Mohamed Abdel-Moati3, Jesse Turner4, Hamood A Alsaadi1, Barbara Paul2, Ibrahim Abdullatif Al-Maslamani5, Mehsin Al-Ansi6 and James W Murray2, (1)Qatar University, Environmental Science Center, Doha, Qatar, (2)University of Washington, School of Oceanography, Seattle, WA, United States, (3)Qatar Ministry of Municipality and Environment, Environmental Assessment Department, Doha, Qatar, (4)University of Washington Seattle Campus, Civil and Environmental Engineering, Seattle, WA, United States, (5)Qatar University, Office of Vice President for Research and Graduate Studies, Doha, Qatar, (6)Qatar University, Department of Environmental and Biological Sciences, Doha, Qatar
Abstract:
Samples from the Exclusive Economic Zone (EEZ) of Qatar and the central Arabian Gulf were collected using net tows with mesh sizes of 50 mm (phytoplankton) and 200 mm (zooplankton) to examine the composition of size fractionated plankton populations. Samples were collected in two different years (2012 and 2014) to examine temporal variability. The biogenic concentrations of trace metals were determined by correcting the bulk analyses for the lithogenic contribution using aluminum (Al) as a lithogenic tracer. The elemental composition of atmospheric dust from Qatar was used for this correction. Dust in Qatar is depleted in aluminum (Al) and enriched in calcium (Ca) relative to global average Upper Continental Crust (UCC) due to the geology of the outcropping sedimentary rocks and topsoils in the source areas of the dust. The relative trace metal composition of plankton from this region is Fe > Zn ≈ Cu > V ≈ Ni ≈ Cr ≈ As ≈ Mo > Cd ≈ Co. Phytoplankton and zooplankton compositions were similar, except for Ba, Mn, and Pb (and possibly Mo) which were higher in zooplankton than phytoplankton. This sequence was in good agreement with previous studies of the composition of plankton in open ocean studies. It was not clear if the variability was due to differences in biology, proximity to the coast or interannual effects. The excess concentrations relative to average dust from Qatar for most elements (except Cd) decreased with distance from shore. The Me/P ratios allow comparison with previous open ocean studies. The ratios for Cd and Zn were in agreement with previous values while the ratios for Fe, Mn, Co, and Cu were much higher. 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.
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