Impact of depositional regimes on biogeochemical cycling of iron and stable Fe signatures in sediments from the Argentina Continental Margin

2020 ◽  
Author(s):  
Anne-Christin Melcher ◽  
Susann Henkel ◽  
Thomas Pape ◽  
Anette Meixner ◽  
Simone A. Kasemann ◽  
...  
Keyword(s):  
Continental Margin ◽  
Water Depth ◽  
Surface Sediments ◽  
Depositional Environments ◽  
Anaerobic Oxidation Of Methane ◽  
Sedimentation Rates ◽  
Biogeochemical Processes ◽  
High Sedimentation ◽  
Terrace Site ◽  
Fe Reduction

<p>The Argentina Continental Margin represents a unique geologic setting where fundamental interactions between bottom currents and sediment deposition as well as their impact on biogeochemical processes and element cycling, in particular iron, can be studied. The aims of this study were to investigate 1) the consequences of different depositional conditions on biogeochemical processes and 2) diagenetic cycling of Fe mineral phases in surface sediments. Furthermore, it was 3) studied how sedimentary stable Fe isotope signatures (δ<sup>56</sup>Fe) are affected during early diagenesis and finally 4) evaluated, under which conditions δ<sup>56</sup>Fe might be used as proxy for microbial Fe reduction in methanic sediments. During RV SONNE expedition SO260, carried out in the framework of the DFG-funded Cluster of Excellence “The Ocean in the Earth System”, surface sediments from two depositional environments were sampled each using gravity corer and multi corer. One study site is located on the lower continental slope at 3605 m water depth (Biogeochemistry Site), while the other site is situated in a contourite system on the Northern Ewing Terrace at 1078 m water depth (Contourite Terrace Site). Sequential Fe extractions were performed on the collected sediments to determine four operationally defined reactive Fe phases targeting Fe carbonates, (easily) reducible Fe (oxyhydr)oxides and hardly reducible Fe oxides [1]. Purification of extracts for δ<sup>56</sup>Fe analysis of the Fe carbonates and easily reducible Fe (oxyhydr)oxide fractions followed [2]. The dataset was combined with pore-water data obtained during the cruise and complemented by concentrations and stable carbon isotope signatures of dissolved methane determined post-cruise. The extent of the redox zonation and depth of the sulfate-methane-transition (SMT) differ between the two sites. It is suggested that sedimentation rates at the Biogeochemistry Site are low and that steady state conditions prevail, leading to a strong diagenetic overprint of sedimentary Fe phases. In contrast the Contourite Terrace Site is characterized by high sedimentation rates and a lack of pronounced diagenetic overprint [3]. Reactive Fe phases are subject to reductive dissolution at the SMT. Nevertheless, significant amounts of reactive Fe phases are preserved below the SMT as evidenced by the presence of dissolved Fe in the methanic sediments, and are available for deep Fe reduction possibly through Fe-mediated anaerobic oxidation of methane [4]. In this study, δ<sup>56</sup>Fe signatures of reactive Fe phases in methanic sediments were determined for the first time. These data suggest significant microbial fractionation of Fe isotopes during deep Fe reduction at the Biogeochemistry Site, whereas at the Contourite Terrace Site the δ<sup>56</sup>Fe signatures do not indicate remarkable microbial Fe isotope fractionation. It is concluded that the applicability of δ<sup>56</sup>Fe signatures as tracer for microbial Fe reduction might be sensitive to the depositional regime, and thus may be limited in high sedimentation areas.</p><p>References:<br>Poulton, SW. and Canfield, DE., 2005. <em>Chemical Geology</em> 214: 209-221.<br>Henkel, S. et al., 2016. <em>Chemical Geology</em> 421: 93-102.<br>Riedinger, N. et al., 2005. <em>Geochimica et Cosmochimica Acta</em> 69: 4117-4126.<br>Riedinger, N. et al., 2014. <em>Geobiology</em> 12: 172-181.</p>

Sedimentary signals of the upwelling along the Zhejiang coast, China

2020 ◽  
Author(s):  
Xin Zhang ◽  
Jian Liu ◽  
Yoshiki Saito
Keyword(s):  
Surface Sediments ◽  
Middle Part ◽  
Published Data ◽  
Sedimentation Rates ◽  
High Concentration ◽  
Sedimentary Processes ◽  
Deposition Patterns ◽  
Source To Sink ◽  
High Sedimentation ◽  
Muddy Area

<p>The muddy deposits of the Zhe-Min coastal area are of great importance to understand "source to sink" processes. However, the sedimentary processes that dominate along the Zhejiang coast remain controversial. Determining sedimentation rates is an important element of our understanding of sedimentary processes and deposition patterns. Therefore, 23 vibrocores were collected from the muddy area along the Zhejiang coast to analyse their sedimentation rates using <sup>210</sup>Pb geochronology. The spatial distribution of the sedimentation rates derived from the 23 vibrocores, as well as previously published data, demonstrated that the middle part of the study area around 29°N experienced relatively high sedimentation rates, which has never been reported in previous studies. This location of high sedimentation rates is approximately consistent with that of the Holocene maximum thickness deposition, finest surface sediments and high concentration of chlorophyll, resulting from the existence of upwelling along the Zhejiang coast besides the fluvial inputs. </p>

scholarly journals Bottom-trawling along submarine canyons impacts deep sedimentary regimes

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Sarah Paradis ◽  
Pere Puig ◽  
Pere Masqué ◽  
Xènia Juan-Díaz ◽  
Jacobo Martín ◽  
...  
Keyword(s):  
Continental Margin ◽  
Trophic Status ◽  
Surface Sediments ◽  
Benthic Communities ◽  
Ecological Impacts ◽  
Sedimentation Rates ◽  
Submarine Canyons ◽  
Bottom Trawling ◽  
Sedimentary Environments

Abstract Many studies highlight that fish trawling activities cause seafloor erosion, but the assessment of the remobilization of surface sediments and its relocation is still not well documented. These impacts were examined along the flanks and axes of three headless submarine canyons incised on the Barcelona continental margin, where trawling fleets have been operating for decades. Trawled grounds along canyon flanks presented eroded and highly reworked surface sediments resulting from the passage of heavy trawling gear. Sedimentation rates on the upper canyon axes tripled and quadrupled its natural (i.e. pre-industrialization) values after a substantial increase in total horsepower of the operating trawling fleets between 1960 s and 1970 s. These impacts affected the upper canyon reaches next to fishing grounds, where sediment resuspended by trawling can be transported towards the canyon axes. This study highlights that bottom trawling has the capacity to alter natural sedimentary environments by promoting sediment-starved canyon flanks, and by enhancing sedimentation rates along the contiguous axes, independently of canyons’ morphology. Considering the global mechanisation and offshore expansion of bottom trawling fisheries since the mid-20th century, these sedimentary alterations may occur in many trawled canyons worldwide, with further ecological impacts on the trophic status of these non-resilient benthic communities.

scholarly journals Distribution and sources of organic matter in surface sediments of the eastern continental margin of India

2013 ◽  
Vol 118 (4) ◽  
pp. 1484-1494 ◽  
Author(s):  
M. S. Krishna ◽  
S. A. Naidu ◽  
Ch. V. Subbaiah ◽  
V. V. S. S. Sarma ◽  
N. P. C. Reddy
Keyword(s):  
Organic Matter ◽  
Continental Margin ◽  
Surface Sediments

scholarly journals Facies and depositional environments for the coquinas of the Morro do Chaves Formation, Sergipe-Alagoas Basin, defined by taphonomic and compositional criteria

2015 ◽  
Vol 45 (3) ◽  
pp. 415-429 ◽  
Author(s):  
Ana Carolina Tavares ◽  
Leonardo Borghi ◽  
Patrick Corbett ◽  
Jane Nobre-Lopes ◽  
Raphael Câmara
Keyword(s):  
Continental Margin ◽  
Carbonate Rocks ◽  
Sedimentary Facies ◽  
High Energy ◽  
Depositional Environments ◽  
Campos Basin ◽  
Lacustrine Carbonate ◽  
Paleoenvironmental Interpretation ◽  
Reservoir Description ◽  
Facies Succession

Lacustrine carbonate rocks form important hydrocarbon accumulations along the Brazilian continental margin, some of which are contained in oil fields in which coquinas are one of the main reservoirs (viz. Campos Basin). The complexity and heterogeneity of these deposits make them a challenge in terms of reservoir description. For the necessary classification and paleoenvironmental interpretation of the coquinas, it is essential to evaluate many aspects including biological (such as carbonate productivity), sedimentological (energy regime in the depositional environment, transport of bioclasts, terrigenous supply), taphonomic (fragmentation of shells, abrasion) and diagenetic processes. The facies analysis applied in this study is considered a more appropriate classification approach to understand these coquinas, since it is more flexible and comprehensive than the existing classifications for carbonate rocks. The material investigated here consists of rock samples of the coquinas from the Atol Quarry of the Morro do Chaves Formation (Barremian/Aptian), Sergipe-Alagoas Basin. These rocks that crop out in the Atol quarry complex can be considered as a case study for similar coquinas reservoirs found in the Brazilian continental margin basins. Six sedimentary facies were described, using the main taphonomic (fragmentation of shells) and compositional (presence of micrite and siliciclastic matrix) features as a diagnostic criteria. Two carbonate facies, two mixed carbonate-siliciclastic facies and two siliciclastic facies (mudstones) were identified. From the facies succession, combined with a review of the literature on the subject, the following depositional paleoenvironments were defined: high-energy lake platform, lacustrine delta in a high-energy lake platform and lake-centre. In this paper, a new facies model for the studied coquinas succession is proposed.

scholarly journals Fracture-controlled fluid transport supports microbial methaneoxidizing communities at the Vestnesa Ridge

2018 ◽  
Author(s):  
Haoyi Yao ◽  
Wei-Li Hong ◽  
Giuliana Panieri ◽  
Simone Sauer ◽  
Marta E. Torres ◽  
...  
Keyword(s):  
Fluid Transport ◽  
Surface Sediments ◽  
Dissolved Inorganic Carbon ◽  
Total Alkalinity ◽  
Anaerobic Oxidation Of Methane ◽  
Gas Migration ◽  
Near Surface ◽  
Recent Onset ◽  
Oxidation Of Methane ◽  
Lipid Biomarker

Abstract. We report on a rare observation of a mini-fracture in near-surface sediments (30 cm below the seafloor) visualized using rotational scanning X-ray of a core recovered from the Lomvi pockmark, Vestnesa Ridge west of Svalbard (1200 m water depth). Porewater geochemistry and lipid biomarker signatures revealed clear differences in the geochemical and biogeochemical regimes of this core compared with two additional ones recovered from pockmarks sites at Vestnesa Ridge, which we attribute to differential methane transport mechanisms. In the sediments core featuring the shallow mini-fracture at pockmark Lomvi, we observed high concentrations of both methane and sulfate throughout the core in tandem with moderately elevated values for total alkalinity, 13C-depleted dissolved inorganic carbon (DIC), and 13C-depleted lipid biomarkers (diagnostic for the slow-growing microbial communities mediating the anaerobic oxidation of methane with sulfate – AOM). In another core recovered from the same pockmark about 80 m away from the fractured core, we observed complete sulfate depletion in the top centimeters of the sediment and much more pronounced signatures of AOM than in the fractured core. Our data indicate a gas advection-dominated transport mode in both cores facilitating methane migration into sulfate-rich surface sediments. However, the more moderate expression of AOM signals suggest a rather recent onset of gas migration at the site of the fractured core, while the geochemical evidence for a well-established AOM community at the second coring site at the Lomvi pockmark suggest that gas migration has been going on for a longer period of time. A third core recovered from Lunde pockmark was dominated by diffusive transport with only weak geochemical and biogeochemical evidence for AOM. Our study highlights that advective fluid and gas transport supported by mini-fractures can be important in modulating methane dynamics in surface sediments.

scholarly journals Biogeochemical processes in sediments of the Manfredonia Gulf (Southern Adriatic Sea): early diagenesis of carbon and nutrient and benthic exchange

2004 ◽  
Vol 1 (1) ◽  
pp. 803-823 ◽  
Author(s):  
F. Spagnoli ◽  
G. Bartholini ◽  
M. Marini ◽  
P. Giordano
Keyword(s):  
Adriatic Sea ◽  
Water Interface ◽  
Biogeochemical Processes ◽  
Pore Waters ◽  
Dissolved Nutrients ◽  
Dissolved Iron ◽  
High Sedimentation ◽  
Western Adriatic Current ◽  
A Site

Abstract. In order to understand the mechanisms responsible of the recycle of carbon and nutrients at the sediment-water interface and to understand the role of sediments in nutrients mass balance in coastal water, cores were collected (pore waters and solid phases) and benthic fluxes (oxygen, dissolved nutrients, dissolved iron and managanese, alkalinity and TCO2) were measured in two stations in the Gulf of Manfredonia (Southern Adriatic Sea). Stations were chosen to include a site, in the offshore part of the gulf, under the influence of western Adriatic current and another site, in the inner part of the gulf, under influence of gyres occurring inside the gulf. Both stations were placed in areas characterized by high sedimentation rate. Fluxes at sediment water interface show higher values in S2 site during the summer. Bio-irrigation seems to be the main transport mechanism characterizing both sites, with more evident effects during summer in S1 site.

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