Turbidite deposition and diagenesis in the southwestern Black Sea: Implications for biogeochemical cycling in an anoxic basin

Kraal, Peter
Yücel, Mustafa
Slomp, Caroline P.
The biogeochemical cycles of iron, phosphorus and sulfur are intimately linked and the fate of these elements is highly redox-dependent. Under anoxic conditions, iron is reduced to Fe(II), for an important part driven by reaction with sulfide. Reduction and sulfidation diminish the affinity of iron for phosphorus, thereby affecting sedimentary phosphorus retention. The coupled cycling of iron-phosphorus-sulfur as a function of redox conditions thereby helps control nutrient availability and primary productivity in marine systems. The Black Sea is the world's largest permanently stratified basin with a strong gradient from oxic surface waters to anoxic and strongly sulfidic deep waters, and is therefore well-suited to investigate redox-dependent changes in coupled iron-phosphorus-sulfur cycling. The presence of sulfide in the deep Black Sea alters the chemical speciation of iron (Fe) and phosphorus (P) in particulate matter in the water column and sediment. These alterations and their impact are poorly constrained for turbidites, which are deposits formed by mass transport from the continental slope into the deep basin of the Black Sea through turbidity currents. Here, we compare the geochemistry of sediments on the southwestern (SW) Black Sea slope overlain by oxygenated waters (234 m below sea surface, mbss) with that of a sediment record with turbidite intervals from the sulfidic SW deep basin (2169 mbss). The aims were to investigate the potential of SW slope sediment as source material for turbidites, and to assess the geochemical impact of reaction with sulfide. The bulk chemistry (Al, CaCO3, Fe) of the SW deep Black Sea turbidite intervals was similar to that of SW Black Sea slope sediments (234 m water depth), suggesting that the latter are source material for deep SW Black Sea turbidites. The source sediment is characterized by strong enrichments in highly reactive Fe(III) and Mn phases, high rates of sulfate reduction and the presence of methane. Similar total Fe contents in the slope and deep turbidite sediments suggest that Fe is efficiently retained in the sediment. In contrast, Mn is depleted during down-slope transport and P contents in the turbidite intervals are about 50% lower than in the slope sediment, indicating significant P release during and after turbidite deposition. Calculations using the obtained data and conservative estimates of the areal extent of turbidite deposition in the SW Black Sea indicate that turbidity currents have the potential to impact coupled Fe-P-S biogeochemical cycling by boosting Fe input, dissolved P accumulation, sulfide oxidation and FeS2 burial in the deep Black Sea.


Hydrothermal vents as a kinetically stable source of iron-sulphide-bearing nanoparticles to the ocean
Yücel, Mustafa; Chan, Clara S.; Luther, George W. (2011-06-01)
Hydrothermal vents emit sulphur and metals to the ocean(1). Particular attention has been paid to hydrothermal fluxes of iron(2-4), a limiting micronutrient of marine primary production(5). Vent-derived iron was previously thought to rapidly oxidize and precipitate around vents(6). However, organic matter can bind to and stabilize dissolved and particulate iron in hydrothermal plumes(7-9), facilitating its dispersion into the open ocean(10). Here, we report measurements of the chemical speciation of sulphid...
Earthquake-induced turbidite deposition as a previously unrecognized sink for hydrogen sulfide in the Black Sea sediments
Yücel, Mustafa; Moore, Willard S. (2010-08-20)
The depth profiles of excess Pb-210, Cs-137, elemental sulfur, reactive iron and porewater hydrogen sulfide of a western central basin sediment core in the Black Sea collectively point to the presence of a 20 cm thick reactive iron rich turbidite layer. This layer was most probably deposited there after the 1999 earthquakes in Northwestern Turkey, which caused oxidation of porewater hydrogen sulfide and anomalous accumulation of the product elemental sulfur in the solid phase.
Polyhydroxybutyrate-Coated Magnetic Nanoparticles for Doxorubicin Delivery: Cytotoxic Effect Against Doxorubicin-Resistant Breast Cancer Cell Line
Yalcin, Serap; Unsoy, Gozde; Mutlu, Pelin; Khodadust, Rouhollah; Gündüz, Ufuk (2014-11-01)
In this study, polyhydroxybutyrate (PHB)-coated magnetic nanoparticles (MNPs) were prepared by coprecipitation of iron salts (Fe2+ and Fe3+) by ammonium hydroxide. Characterizations of PHB-coated MNPs were performed by Fourier transform infrared spectroscopy, x-ray diffraction, dynamic light scattering, thermal gravimetric analysis, vibrating sample magnetometry, and transmission electron microscopy analyses. Doxorubicin was loaded onto PHB-MNPs, and the release efficiencies at different pHs were studied un...
Metal Oxides Supported Cobalt nanoparticles: Active Electrocatalysts for Oxygen Evolution Reaction
Önal, Ahmet Muhtar; Akbayrak, Merve (2021-08-01)
Besides precious metal oxides, non-noble metal oxides are found to be promising materials especially, in the alkaline medium for OER. In this work, Co/MO 2 (M = Ti, Zr, and Ce) catalysts were synthesized with- out using any harsh steps such as pyrolization, annealing, calcination, and carbonization. Cobalt nanopar- ticles with ∼2.6 nm particle size were loaded on metal oxides by simple impregnation and reduction method. Considering the low onset and overpotential values, low Tafel slopes, high exchange curr...
Sulfur speciation in the upper Black Sea sediments
Yücel, Mustafa; Moore, Tommy S.; Janzen, Christopher P.; Luther, George W. (2010-01-30)
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 ...
Citation Formats
P. Kraal, M. Yücel, and C. P. Slomp, “Turbidite deposition and diagenesis in the southwestern Black Sea: Implications for biogeochemical cycling in an anoxic basin,” MARINE CHEMISTRY, pp. 48–61, 2019, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/32528.