scholarly journals Manganese and iron reduction dominate organic carbon oxidation in surface sediments of the deep Ulleung Basin, East Sea

2017 ◽  
Vol 14 (4) ◽  
pp. 941-958 ◽  
Author(s):  
Jung-Ho Hyun ◽  
Sung-Han Kim ◽  
Jin-Sook Mok ◽  
Hyeyoun Cho ◽  
Tongsup Lee ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Iron Reduction ◽  
Surface Sediments ◽  
Ulleung Basin ◽  
Oxide Content ◽  
Nutrient Regeneration ◽  
Relative Significance ◽  
Oxidation Pathway ◽  
Mn Oxide ◽  
Geochemical Analyses

Abstract. Rates and pathways of benthic organic carbon (Corg) oxidation were investigated in surface sediments of the Ulleung Basin (UB) characterized by high Corg contents ( >  2.5 %, dry wt.) and very high contents of Mn oxides ( >  200 µmol cm−3) and Fe oxides (up to 100 µmol cm−3). The combination of geochemical analyses and independently executed metabolic rate measurements revealed that Mn and Fe reduction were the dominant Corg oxidation pathways in the center of the UB, comprising 45 and 20 % of total Corg oxidation, respectively. By contrast, sulfate reduction was the dominant Corg oxidation pathway, accounting for 50 % of total Corg mineralization in sediments of the continental slope. The relative significance of each Corg oxidation pathway matched the depth distribution of the respective electron acceptors. The relative importance of Mn reduction for Corg oxidation displays saturation kinetics with respect to Mn oxide content with a low half-saturation value of 8.6 µmol cm−3, which further implies that Mn reduction can be a dominant Corg oxidation process even in sediments with lower MnO2 content as known from several other locations. This is the first report of a high contribution of manganese reduction to Corg oxidation in offshore sediments on the Asian margin. The high manganese oxide content in the surface sediment in the central UB was maintained by an extreme degree of recycling, with each Mn atom on average being reoxidized ∼ 3800 times before permanent burial. This is the highest degree of recycling so far reported for Mn-rich sediments, and it appears linked to the high benthic mineralization rates resulting from the high Corg content that indicate the UB as a biogeochemical hotspot for turnover of organic matter and nutrient regeneration.

scholarly journals Manganese and iron reduction dominate organic carbon oxidation in deep continental margin sediments of the Ulleung Basin, East Sea

2016 ◽  
Author(s):  
Jung-Ho Hyun ◽  
Sung-Han Kim ◽  
Jin-Sook Mok ◽  
Hyeyoun Cho ◽  
Tongsup Lee ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Iron Reduction ◽  
Sea Water ◽  
Ulleung Basin ◽  
Oxide Content ◽  
Organic Carbon Content ◽  
Nutrient Regeneration ◽  
Relative Significance ◽  
Oxidation Pathway ◽  
High Organic Carbon Content

Abstract. Rates and pathways of benthic organic carbon (Corg) oxidation were investigated in surface sediments of the Ulleung Basin (UB) characterized by high organic carbon contents (> 2.5 %, dry wt.) and very high concentrations of Mn oxides (> 200 μmol cm−3) and Fe oxides (up to 100 μmol cm−3). The combination of geochemical analyses and independently executed metabolic rate measurements revealed that Mn and Fe reduction were the dominant Corg oxidation pathways in the center of the UB, comprising 45 % and 20 % of total Corg oxidation, respectively. By contrast, sulfate reduction was the dominant Corg oxidation pathway accounting for 50 % of total Corg mineralization in the continental slope. The relative significance of each Corg oxidation pathway matched the depth distribution of the respective electron acceptors. The relative importance of Mn reduction for Corg oxidation displays saturation kinetics with respect to Mn oxide content with a low half-saturation value of 8.6 µmol cm−3, which further implies that Mn reduction can be a dominant Corg oxidation process even in sediments with lower MnO2 content as known from several other locations. This is the first report of a high contribution of manganese reduction to Corg oxidation in offshore sediments on the Asian margin. The high manganese oxide content in the surface sediment in the central UB was maintained by an extreme degree of recycling, with each Mn atom on average being reoxidized ~ 3800 times before permanent burial. This is the highest degree of recycling so far reported for Mn-rich sediments, and it appears linked to the high benthic mineralization rates resulting from the high organic carbon content that indicate the UB as a biogoechemical hotspot for turnover of organic matter and nutrient regeneration. Thus, it is important to monitor any changes in the rates and partitioning of Corg oxidation to better understand the biogeochemical cycling of carbon, nutrients and metals associated with long-term climatic changes in the UB, where the fastest increase in sea water temperature has been reported for the past two decades.

Phosphorus dynamics associated with partitioning of organic carbon oxidation pathways in the surface sediments of the deep Ulleung Basin, East Sea

2020 ◽  
Author(s):  
Jin-Sook Mok ◽  
Bomina Kim ◽  
Hyeyoun Cho ◽  
Sung-Uk An ◽  
Hyun-Ji Lee ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Sulfate Reduction ◽  
Surface Sediments ◽  
Global Scale ◽  
East Sea ◽  
Ulleung Basin ◽  
Reductive Dissolution ◽  
Fe Oxide ◽  
Mn Oxide ◽  
Organic Carbon Oxidation

<p>As sediments play an important role as either a sink or a source of phosphorus (P) for water column, it is important to elucidate the major P fractions and behaviors (i.e., mobilization and immobilization) in the sediments to better understand P cycles in local and global scale. We investigated major P speciation associated with the partitioning of organic carbon (C<sub>org</sub>) oxidation in the sediments to elucidate the P dynamics at two contrasting sediments in the continental shelf (EB1) and rise (EC1) in the Ulleung Basin (UB), East Sea. Sulfate reduction (SR) pre-dominated C<sub>org</sub> oxidation at shelf site (EB 1), comprising % of C<sub>org</sub> oxidation, whereas Mn- and Fe-reduction combined accounted for >80% of C<sub>org</sub> oxidation in Mn-oxide and Fe-oxide-rich basin site (EC 1). Under SR-dominated condition (EB 1), H<sub>2</sub>S oxidation coupled to reductive dissolution of FeOOH to form precipitation of FeS induced the accumulation of dissolved iron and phosphate in the pore water. On the other hand, phosphate in the Mn- and Fe-oxide-rich basin sediments (EC 1) was depleted because the P released through organic matter decomposition or reductive dissolution of Fe oxide/Mn oxide was effectively adsorbed to the metal-oxides in the surface sediments. Sequential extraction of P phases revealed that Fe bound P (52-65% of total P) was the major phase in the surface sediments of both sites. Interestingly, the organic P (P<sub>org</sub>) fraction was 2.4-times higher at the basin site (12 μmol g<sup>-1</sup>) than at the shelf site (5 μmol g<sup>-1</sup>). C<sub>org</sub> : P<sub>org</sub> ratios presented as redox proxies in sediments were 644 and 191 for EB1 and EC1, respectively,. The results indicate that P<sub>org</sub> has an effective preservation relative to C<sub>org</sub> under sub-oxic conditions (EC1), whereas P<sub>org</sub> was preferentially regenerated under anoxic conditions (EB1). Overall, the dynamics of P in the UB sediments were largely regulated by the partitioning of C<sub>org</sub> oxidation pathways (i.e., sulfate reduction vs. metal reduction) and resultant interaction between Fe/Mn-S-P.</p>

Littoral zones as sources of biodegradable dissolved organic carbon in lakes

2008 ◽  
Vol 65 (11) ◽  
pp. 2454-2460 ◽  
Author(s):  
E. G. Stets ◽  
J. B. Cotner
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Aquatic Macrophytes ◽  
Trophic Status ◽  
Surface Sediments ◽  
Decay Curve ◽  
Lake Area ◽  
Lake Trophic Status ◽  
Littoral Zones ◽  
Biodegradable Dissolved Organic Carbon

A survey of 12 lakes in Minnesota, USA, was conducted to examine the factors controlling variability in biodegradable dissolved organic carbon (BDOC) concentration. The principal question addressed was whether BDOC concentration was more strongly related to lake trophic status or morphometric parameters. BDOC concentration was determined by incubating filtered lake water for a period of 15 months and fitting an exponential decay curve to measured DOC concentrations. BDOC concentrations varied from 73 to 427 µmol C·L–1 and composed 15%–63% of the total DOC pool. There were no significant correlations between BDOC and measures of lake trophic status. Instead, BDOC was most closely associated with the percentage of lake area covered by littoral zone, suggesting a significant source of BDOC from aquatic macrophytes and lake surface sediments.

scholarly journals Organic Carbon Cycling in Ulleung Basin Sediments, East Sea

2010 ◽  
Vol 32 (2) ◽  
pp. 145-156 ◽  
Author(s):  
Tae-Hee Lee ◽  
Dong-Seon Kim ◽  
Boo-Keun Khim ◽  
Dong-Lim Choi
Keyword(s):  
Organic Carbon ◽  
Carbon Cycling ◽  
East Sea ◽  
Ulleung Basin ◽  
Organic Carbon Cycling

scholarly journals Sources and accumulation of organic carbon in the Pearl River Estuary surface sediment as indicated by elemental, stable carbon isotopic, and carbohydrate compositions

2010 ◽  
Vol 7 (2) ◽  
pp. 2889-2926 ◽  
Author(s):  
B. He ◽  
M. Dai ◽  
W. Huang ◽  
Q. Liu ◽  
H. Chen ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Surface Sediments ◽  
River Estuary ◽  
Pearl River Estuary ◽  
Outer Shelf ◽  
Pearl River ◽  
Terrestrial Organic Matter ◽  
The Pearl River Estuary ◽  
The Pearl River

Abstract. Organic matter in surface sediments from the upper reach of the Pearl River Estuary and Lingdingyang Bay, as well as the adjacent northern South China Sea shelf was characterized by a variety of techniques, including elemental (C and N), stable carbon isotopic (δ 13C) composition, as well as molecular-level analyses. Total organic carbon (TOC) content was 1.61±1.20% in the upper reach down to 1.00±0.22% in Lingdingyang Bay and to 0.80±0.10% on the inner shelf and 0.58±0.06% on the outer shelf. δ13C values ranged from −25.11‰ to −21.28‰ across the studied area, with a trend of enrichment seaward. The spatial trend in C/N ratios mirrored that of δ13C, with a substantial decrease in C/N ratio from 10.9±1.3 in the Lingdingyang Bay surface sediments to 6.5±0.09 in the outer shelf surface sediments. Total carbohydrate yields ranged from 22.1 to 26.7 mg (100 mg OC)−1, and typically followed TOC concentrations in the estuarine and shelf sediments, suggesting that the relative abundance of total carbohydrate was fairly constant in TOC. Total neutral sugars as detected by the nine major monosaccharides (lyxose, rhamnose, ribose, arabinose, fucose, xylose, galactose, mannose, and glucose) yielded between 4.0 and 18.6 mg (100 mg OC)−1 in the same sediments, suggesting that a significant amount of carbohydrates were not neutral aldoses. The bulk organic matter properties, isotopic composition and C/N ratios, combined with molecular-level carbohydrate compositions were used to assess the sources and accumulation of terrestrial organic matter in the Pearl River Estuary and the adjacent northern South China Sea shelf. Results showed a mixture of terrestrial riverine organic carbon with in situ phytoplankton organic carbon in the areas studied. Using a two end-member mixing model based on δ13C values and C/N ratios, we estimated that the terrestrial organic carbon contribution to the surface sediment TOC was ca. 57±13% for Lingdingyang Bay, 19±2% for the inner shelf, which decreased further to 4.3±0.5% on the outer shelf. The molecular composition of the carbohydrate in surface sediments also suggested that the inner estuary was rich in terrestrial-derived carbohydrates but that the contribution of terrestrial-derived carbohydrates decreased offshore. Terrestrial organic carbon accumulation flux was estimated as 1.37±0.92×1011 g yr−1 in Lingdingyang Bay, which accounted for 37±25% of the terrestrial organic carbon transported to the Bay. The burial efficiency of terrestrial organic matter was markedly lower than that of suspended particulate substance (~71%) suggesting that the riverine POC undergoes significant degradation and replacement during transportation through the estuary.

scholarly journals Radiocarbon Dating of Individual Fatty Acids as a Tool for Refining Antarctic Margin Sediment Chronologies

Radiocarbon ◽  
2003 ◽  
Vol 45 (1) ◽  
pp. 17-24 ◽  
Author(s):  
Naohiko Ohkouchi ◽  
Timothy I Eglinton ◽  
John M Hayes
Keyword(s):  
Fatty Acids ◽  
Organic Matter ◽  
Organic Carbon ◽  
Radiocarbon Dating ◽  
Inorganic Carbon ◽  
Surface Sediments ◽  
Ross Sea ◽  
Dissolved Inorganic Carbon ◽  
Accumulation Rate ◽  
Sea Surface

We have measured the radiocarbon contents of individual, solvent-extractable, short-chain (C14, C16, and C18) fatty acids isolated from Ross Sea surface sediments. The corresponding 14C ages are equivalent to that of the post-bomb dissolved inorganic carbon (DIC) reservoir. Moreover, molecular 14C variations in surficial (upper 15 cm) sediments indicate that these compounds may prove useful for reconstructing chronologies of Antarctic margin sediments containing uncertain (and potentially variable) quantities of relict organic carbon. A preliminary molecular 14C chronology suggests that the accumulation rate of relict organic matter has not changed during the last 500 14C yr. The focus of this study is to determine the validity of compound-specific 14C analysis as a technique for reconstructing chronologies of Antarctic margin sediments.

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