Sulfur speciation in the upper Black Sea sediments


Yucel M., Konovalov S. K. , Moore T. S. , Janzen C. P. , Luther G. W.

CHEMICAL GEOLOGY, vol.269, pp.364-375, 2010 (Peer-Reviewed Journal) identifier identifier

  • Publication Type: Article / Article
  • Volume: 269
  • Publication Date: 2010
  • Doi Number: 10.1016/j.chemgeo.2009.10.010
  • Journal Name: CHEMICAL GEOLOGY
  • Journal Indexes: Science Citation Index Expanded, Scopus
  • Page Numbers: pp.364-375
  • Keywords: Black Sea, Anoxic sediment, Sulfur, Iron, Elemental sulfur, Humic sulfur, Pyrite, 125 DEGREES-C, PYRITE FORMATION, MARINE-SEDIMENTS, EARLY DIAGENESIS, ORGANIC-MATTER, VOLTAMMETRIC MICROELECTRODE, CHROMIUM REDUCTION, SULFATE REDUCTION, SURFACE SEDIMENTS, AQUEOUS-SOLUTIONS

Abstract

We report solid phase sulfur speciation of six cores from sediments underlying oxic, suboxic and anoxic-sulfidic waters of the Black Sea. Our dataset includes the five sulfur species [pyrite-sulfur, acid volatile sulfides (AVS), zerovalent sulfur (S(0)), organic polysulfides (RS(x)), humic sulfur] together with reactive iron and manganese, as quantified by dithionite extraction, and total organic carbon. Pyrite - sulfur was the major phase in all cores [200-400 mu mol (g dry wt)(-1)] except for the suboxic core. However, zerovalent sulfur and humic sulfur also reached very significant levels: up to about 109 and 80 mu mol (g dry wt)(-1), respectively. Humic sulfur enrichment was observed in the surface fluff layers of the eastern central basin sediments where Unit-1 type depositional conditions prevail. Elemental sulfur accumulated as a result of porewater sulfide oxidation by reactive iron oxides in turbidities from the anoxic basin margin and western central basin sediments. The accumulation of elemental sulfur to a level close to that of pyrite-S in any part of central Black Sea sediments has never been reported before and our finding indicates deep basin turbidites prevent the build-up of dissolved sulfide in the sediment. This process also contributes to diagenetic pyrite formation whereas in the non-turbiditic parts of the deep basin water column formed (syngenetic) pyrite dominates the sulfur inventory. In slope sediments under suboxic waters, organic sulfur (humic sulfur + organic polysulfides) account for 33-42% of total solid phase S, indicating that the suboxic conditions favor organosulfur formation. Our study shows that the interactions between depositional patterns (Unit 1 vs. turbidite), redox state of overlying waters (oxic-suboxic-sulfidic) and organic matter content determine sulfur speciation and enable the accumulation of elemental sulfur and organic sulfur species close to a level of pyrite-S. (C) 2009 Elsevier B.V. All rights reserved.