This study focuses on the vertical distribution of authigenic carbonates (aragonite and high Mg-calcite) in the form of finely disseminated precipitates as well as massive carbonate concretions ...present in and above gas hydrate bearing sediments of the Northern Congo Fan. Analyses of Ca, Mg, Sr and Ba in pore water, bulk sediments and authigenic carbonates were carried out on gravity cores taken from three pockmark structures (Hydrate Hole, Black Hole and Worm Hole). In addition, a background core was retrieved from an area not influenced by fluid seepage. Pore water Sr/Ca and Mg/Ca ratios are used to reveal the current depths of carbonate formation as well as the mineralogy of the authigenic precipitates. The Sr/Ca and Mg/Ca ratios of bulk sediments and massive carbonate concretions were applied to infer the presence and depth distribution of authigenic aragonite and high Mg-calcite, based on the approach presented by Bayon et al. Bayon et al. (2007). Sr/Ca and Mg/Ca ratios in Niger Delta sediments: Implications for authigenic carbonate genesis in cold seep environments. Marine Geology 241(1–4), 93–109. We show that the approach developed by Bayon et al. (2007) for sediments of cold seeps of the Niger Delta is also suitable to identify the mineralogy of authigenic carbonates in pockmark sediments of the Congo Deep-Sea Fan. We expand this approach by combining interstitial with solid phase Sr/Ca and Mg/Ca ratios, which demonstrate that high Mg-calcite is the predominant authigenic carbonate that currently forms at the sulfate/methane reaction zone (SMRZ). This is the first study which investigates both solid phase and pore water signatures typical for either aragonite or high Mg-calcite precipitation for the same sediment cores and thus is able to identify active and fossil carbonate precipitation events. At all investigated pockmark sites fossil horizons of the SMRZ were deduced from high Mg-calcite located above and below the current depths of the SMRZ. Additionally, aragonite enrichments typical for high seepage rates were detected close to the sediment surface at these sites. However, active precipitation of aragonite as indicated by pore water characteristics only occurs at the Black Hole site. Dissolved and solid phase Ba concentrations were used to estimate the time the SMRZ was fixed at the current depths of the diagenetic barite fronts. The combined pore water and solid phase elemental ratios (Mg/Ca, Sr/Ca) and Ba concentrations allow the reconstruction of past changes in methane seepage at the investigated pockmark sites. At the Hydrate Hole and Worm Hole sites the time of high methane seepage was estimated to have ceased at least 600
yr BP. In contrast, a more recent change from a high flux to a more dormant stage must have occurred at the Black Hole site as evidenced by active aragonite precipitation at the sediment surface and a lack of diagenetic Ba enrichments.
► We infer the presence, depth distribution and mineralogy of authigenic carbonates. ► We identify active and fossil carbonate precipitation events. ► We reconstruct past changes in methane seepage at the pockmark sites.
Manganese nodules of the Clarion–Clipperton Fracture Zone (CCFZ) in the NE Pacific Ocean are highly enriched in Ni, Cu, Co, Mo and rare-earth elements, and thus may be the subject of future mining ...operations. Elucidating the depositional and biogeochemical processes that contribute to nodule formation, as well as the respective redox environment, in both water column and sediment, supports our ability to locate future nodule deposits and to evaluate the potential ecological and environmental effects of future deep-sea mining. For these purposes we studied the local hydrodynamics and pore-water geochemistry with respect to the nodule coverage at four sites in the eastern CCFZ. Furthermore, we carried out selective leaching experiments at these sites in order to assess the potential mobility of Mn in the solid phase, and compared them with the spatial variations in sedimentation rates. We found that the oxygen penetration depth is 180–300cm at all four sites, while reduction of Mn and NO3− is only significant below the oxygen penetration depth at sites with small or no nodules on the sediment surface. At the site without nodules, potential microbial respiration rates, determined by incubation experiments using 14C-labeled acetate, are slightly higher than at sites with nodules. Leaching experiments showed that surface sediments covered with big or medium-sized nodules are enriched in mobilizable Mn. Our deep oxygen measurements and pore-water data suggest that hydrogenetic and oxic-diagenetic processes control the present-day nodule growth at these sites, since free manganese from deeper sediments is unable to reach the sediment surface. We propose that the observed strong lateral contrasts in nodule size and abundance are sensitive to sedimentation rates, which in turn, are controlled by small-scale variations in seafloor topography and bottom-water current intensity.
•We evaluated the pore-water geochemistry with respect to nodule coverage in the CCFZ.•We found that hydrogenetic and oxic-diagenetic processes control the present-day nodule growth.•Surface sediments covered with big or medium-sized nodules are enriched in mobilizable Mn.
Here, we present results from sediments collected in the Argentine Basin, a non‐steady state depositional marine system characterized by abundant oxidized iron within methane‐rich layers due to ...sediment reworking followed by rapid deposition. Our comprehensive inorganic data set shows that iron reduction in these sulfate and sulfide‐depleted sediments is best explained by a microbially mediated process—implicating anaerobic oxidation of methane coupled to iron reduction (Fe‐AOM) as the most likely major mechanism. Although important in many modern marine environments, iron‐driven AOM may not consume similar amounts of methane compared with sulfate‐dependent AOM. Nevertheless, it may have broad impact on the deep biosphere and dominate both iron and methane cycling in sulfate‐lean marine settings. Fe‐AOM might have been particularly relevant in the Archean ocean, >2.5 billion years ago, known for its production and accumulation of iron oxides (in iron formations) in a biosphere likely replete with methane but low in sulfate. Methane at that time was a critical greenhouse gas capable of sustaining a habitable climate under relatively low solar luminosity, and relationships to iron cycling may have impacted if not dominated methane loss from the biosphere.
The present paper is the result of a workshop sponsored by the DFG Research Center/Cluster of Excellence MARUM "The Ocean in the Earth System", the International Graduate College EUROPROX, and the ...Alfred Wegener Institute for Polar and Marine Research. The workshop brought together specialists on organic matter degradation and on proxy-based environmental reconstruction. The paper deals with the main theme of the workshop, understanding the impact of selective degradation/preservation of organic matter (OM) in marine sediments on the interpretation of the fossil record. Special attention is paid to (A) the influence of the molecular composition of OM in relation to the biological and physical depositional environment, including new methods for determining complex organic biomolecules, (B) the impact of selective OM preservation on the interpretation of proxies for marine palaeoceanographic and palaeoclimatic reconstruction, and (C) past marine productivity and selective preservation in sediments. It appears that most of the factors influencing OM preservation have been identified, but many of the mechanisms by which they operate are partly, or even fragmentarily, understood. Some factors have not even been taken carefully into consideration. This incomplete understanding of OM breakdown hampers proper assessment of the present and past carbon cycle as well as the interpretation of OM based proxies and proxies affected by OM breakdown. To arrive at better proxy-based reconstructions "deformation functions" are needed, taking into account the transport and diagenesis-related molecular and atomic modifications following proxy formation. Some emerging proxies for OM degradation may shed light on such deformation functions. The use of palynomorph concentrations and selective changes in assemblage composition as models for production and preservation of OM may correct for bias due to selective degradation. Such quantitative assessment of OM degradation may lead to more accurate reconstruction of past productivity and bottom water oxygenation. Given the cost and effort associated with programs to recover sediment cores for paleoclimatological studies, as well as with generating proxy records, it would seem wise to develop a detailed sedimentological and diagenetic context for interpretation of these records. With respect to the latter, parallel acquisition of data that inform on the fidelity of the proxy signatures and reveal potential diagenetic biases would be of clear value.
A high-resolution geochemical record of a 120
cm black shale interval deposited during the Coniacian–Santonian Oceanic Anoxic Event 3 (ODP Leg 207, Site 1261, Demerara Rise) has been constructed to ...provide detailed insight into rapid changes in deep ocean and sediment paleo-redox conditions. High contents of organic matter, sulfur and redox-sensitive trace metals (Cd, Mo, V, Zn), as well as continuous lamination, point to deposition under consistently oxygen-free and largely sulfidic bottom water conditions. However, rapid and cyclic changes in deep ocean redox are documented by short-term (∼15–20
ka) intervals with decreased total organic carbon (TOC), S and redox-sensitive trace metal contents, and in particular pronounced phosphorus peaks (up to 2.5
wt% P) associated with elevated Fe oxide contents. Sequential iron and phosphate extractions confirm that P is dominantly bound to iron oxides and incorporated into authigenic apatite. Preservation of this Fe–P coupling in an otherwise sulfidic depositional environment (as indicated by Fe speciation and high amounts of sulfurized organic matter) may be unexpected, and provides evidence for temporarily non-sulfidic bottom waters. However, there is no evidence for deposition under oxic conditions. Instead, sulfidic conditions were punctuated by periods of anoxic, non-sulfidic bottom waters. During these periods, phosphate was effectively scavenged during precipitation of iron (oxyhydr)oxides in the upper water column, and was subsequently deposited and largely preserved at the sea floor. After ∼15–25
ka, sulfidic bottom water conditions were re-established, leading to the initial precipitation of CdS, ZnS and pyrite. Subsequently, increasing concentrations of H
2S in the water column led to extensive formation of sulfurized organic matter, which effectively scavenged particle-reactive Mo complexes (thiomolybdates). At Site 1261, sulfidic bottom waters lasted for ∼90–100
ka, followed by another period of anoxic, non-sulfidic conditions lasting for ∼15–20
ka. The observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface- to mid-waters from the South Atlantic resulting in a lowering of the oxic–anoxic chemocline in the water column. Alternatively, sea water sulfate might have been stripped by long-lasting high rates of sulfate reduction, removing the ultimate source for HS
− production.
Unemployment is associated with a variety of adverse health-related outcomes, yet little data on primary care services for this risk group exist. Using data from two surveys, we analyzed the ...frequency of GP contacts and patients' experiences with GPs comparing unemployed with employed individuals. Data of the German Health Interview and Examination Survey for Adults (DEGS1), a nationwide cross-sectional study (n = 8151), were analyzed regarding associations between employment status and the number of GP visits. The General Practice Care-1 study (GPCare-1), a cross-sectional questionnaire survey (n = 813), evaluated patients' communication with their GP. Data were collected from June to August 2020 in 12 teaching practices affiliated with our university. The statistical analysis included individuals of working age (18-64 years old) (DEGS1 n = 5659, GPCare-1 n = 587). In both studies, working age subpopulations were analyzed (DEGS1: n = 5659 of 8151, GPCare-1: n = 587 of 813). In DEGS1, the prevalence of unemployment was 6.5% (n = 372). Unemployed individuals had more GP contacts in the last 12 months (4.50 vs. 2.86, p < 0.001). In the GPCare-1 study, unemployed individuals (6.6%, n = 39) were significantly less satisfied with GP communication: enough space in consultations (42.9% vs. 60.3%, p = 0.043), feeling comfortable to address sensitive topics (44.1% vs. 65.9%, p = 0.010), problems taken very seriously by GP (48.6% vs. 70.6%, p = 0.007). Yet, they were more willing to accept GPs' help for psychosocial burdens (67.6% vs. 47.6%, p = 0.024). GPs should be aware that patients with unemployment wish more support to cope with their burdening situation.
A variety of gravel‐ to cobble‐sized rocks, recovered from the Mar del Plata (MdP) Canyon area (Western South Atlantic at 38°S) and interpreted as ice‐rafted debris, represent the first evidence that ...large icebergs have floated in the Falkland (Malvinas) Current from the southern polar high latitudes far northward. Detailed petrographic analyses identified the Antarctic Peninsula, sub‐Antarctic islands in the Scotia Sea, and Tierra del Fuego as plausible source areas. The drift process could have started as early as at the beginning of the last deglaciation, according to an age obtained from a cold‐water coral fragment associated with one of the dropstones. At the end of the Last Glacial Maximum, large icebergs have been supplied to the Antarctic Circumpolar Current, captured by those ocean current branches that circumvent the Falkland (Malvinas) Islands and entered the Argentine Margin. When the iceberg fleets approached the Brazil‐Falkland (Malvinas) Confluence Zone with its steep latitudinal temperature gradient, the icebergs got oceanographically trapped and melted off rapidly. The sediment load sinking down to the seafloor formed a dropstone blanket particularly where the MdP Canyon had incised into the continental slope. Here, mass‐flow processes, induced by local slope instability, and along‐slope sediment resorting, due to the erosional effects of strong and persistent contouritic bottom currents, favored local enrichment in dropstones in the form of a loose, coarse sediment drape inside morphological depressions. The bottom current velocity would be locally strong enough to rework this sediment, leaving coarse rafted debris as a lag deposit.
Plain Language Summary
Icebergs can transport sand‐ to cobble‐sized sediment while drifting with the ocean currents over large distances away from the high latitudes. When seawater temperature forces the ice to melt, this “ice‐rafted debris” will sink down as “dropstones” to the seabed. Offshore dropstone deposits are common in polar regions but rarely found in lower latitudes because icebergs barely survive if the ocean water is not extremely cold. We found evidence of dropstone deposits along the Argentine Margin at the relatively low latitude of 38°S. They rest inside morphological seafloor depressions at the continental slope in association with the Mar del Plata Canyon. Here, also the oceanic Brazil‐Falkland (Malvinas) Confluence Zone is located, which acts as a barrier for northward drifting icebergs. The presence of icebergs in the Argentine Sea was already known; we, however, describe the first finding of rocks that clearly had originated from the Antarctic Peninsula, sub‐Antarctic islands in the Scotia Sea, and Tierra del Fuego, the southern tip of the South American continent. These dropstones are often found together with fragments of cold‐water corals, suggesting that the imported rocks have locally served as hard substrate for coral colonies to establish.
Key Points
Rocks recovered from the Mar del Plata Canyon area, 38°S in the Western South Atlantic, are interpreted as ice‐rafted debris
Antarctic Peninsula, sub‐Antarctic islands in the Scotia Sea and Tierra del Fuego are identified as plausible source areas
Dropstones lie as a coarse sediment drape inside morphological depressions
The interaction between fluid seepage, bottom water redox, and chemosynthetic communities was studied at cold seeps across one of the world's largest oxygen minimum zones (OMZ) located at the Makran ...convergent continental margin. Push cores were obtained from seeps within and below the core-OMZ with a remotely operated vehicle. Extracted sediment pore water was analyzed for sulfide and sulfate concentrations. Depending on oxygen availability in the bottom water, seeps were either colonized by microbial mats or by mats and macrofauna. The latter, including ampharetid polychaetes and vesicomyid clams, occurred in distinct benthic habitats, which were arranged in a concentric fashion around gas orifices. At most sites colonized by microbial mats, hydrogen sulfide was exported into the bottom water. Where macrofauna was widely abundant, hydrogen sulfide was retained within the sediment. Numerical modeling of pore water profiles was performed in order to assess rates of fluid advection and bioirrigation. While the magnitude of upward fluid flow decreased from 11 cm yr−1 to <1 cm yr−1 and the sulfate/methane transition (SMT) deepened with increasing distance from the central gas orifice, the fluxes of sulfate into the SMT did not significantly differ (6.6–9.3 mol m−2 yr−1). Depth-integrated rates of bioirrigation increased from 120 cm yr−1 in the central habitat, characterized by microbial mats and sparse macrofauna, to 297 cm yr−1 in the habitat of large and few small vesicomyid clams. These results reveal that chemosynthetic macrofauna inhabiting the outer seep habitats below the core-OMZ efficiently bioirrigate and thus transport sulfate down into the upper 10 to 15 cm of the sediment. In this way the animals deal with the lower upward flux of methane in outer habitats by stimulating rates of anaerobic oxidation of methane (AOM) with sulfate high enough to provide hydrogen sulfide for chemosynthesis. Through bioirrigation, macrofauna engineer their geochemical environment and fuel upward sulfide flux via AOM. Furthermore, due to the introduction of oxygenated bottom water into the sediment via bioirrigation, the depth of the sulfide sink gradually deepens towards outer habitats. We therefore suggest that – in addition to the oxygen levels in the water column, which determine whether macrofaunal communities can develop or not – it is the depth of the SMT and thus of sulfide production that determines which chemosynthetic communities are able to exploit the sulfide at depth. We hypothesize that large vesicomyid clams, by efficiently expanding the sulfate zone down into the sediment, could cut off smaller or less mobile organisms, as e.g. small clams and sulfur bacteria, from the sulfide source.
Meat quality development, or the transformation of muscle to meat, involves a myriad of biochemical pathways that are largely well-studied in living muscle tissue. However, these pathways are less ...predictable when homeostatic ranges are violated. In addition, there is far less known about how various management or environmental stimuli impact these pathways, either by substrate load or altered cellular environment. Likewise, it is largely accepted that oxygen plays little to no role in the conversion of muscle to meat, as anaerobic metabolism predominates in the muscle tissue. Even so, the oxygen tension within the tissues does not fall precipitously at exsanguination. Therefore, transition to an anaerobic environment may impact energy metabolism postmortem. Antemortem handling, on the other hand, clearly impacts meat quality development, yet the exact mechanisms remain a mystery. In this paper, we will attempt to review those factors known to affect postmortem energy metabolism in muscle and explore those areas where additional work may be fruitful.
•We review Scopes' work with postmortem metabolism.•We review the notion that aerobic metabolism plays a role in postmortem metabolism.•We briefly review biochemical changes in tissues in response to antemortem handling.
The Zambezi deep-sea fan, the largest of its kind along the east African continental margin, is poorly studied to date, despite its potential to record marine and terrestrial climate signals in the ...southwest Indian Ocean. Therefore, gravity core GeoB 9309-1, retrieved from 1219 m water depth, was investigated for various geophysical (magnetic susceptibility, porosity, colour reflectance) and geochemical (pore water and sediment geochemistry, Fe and P speciation) properties. Onboard and onshore data documented a sulphate/methane transition (SMT) zone at ~
450–530 cm sediment depth, where the simultaneous consumption of pore water sulphate and methane liberates hydrogen sulphide and bi-carbonate into the pore space. This leads to characteristic changes in the sediment and pore water chemistry, as the reduction of primary Fe (oxyhydr)oxides, the precipitation of Fe sulphides, and the mobilization of Fe (oxyhydr)oxide-bound P. These chemical processes also lead to a marked decrease in magnetic susceptibility. Below the SMT, we find a reduction of porosity, possibly due to pore space cementation by authigenic minerals. Formation of the observed geochemical, magnetic and mineralogical patterns requires a fixation of the SMT at this distinct sediment depth for a considerable time—which we calculated to be ~
10
000 years assuming steady-state conditions—following a period of rapid upward migration towards this interval. We postulate that the worldwide sea-level rise at the last glacial/interglacial transition (~
10
000 years B.P.) most probably caused the fixation of the SMT at its present position, through drastically reduced sediment delivery to the deep-sea fan. In addition, we report an internal redistribution of P occurring around the SMT, closely linked to the (de)coupling of sedimentary Fe and P, and leaving a characteristic pattern in the solid P record. By phosphate re-adsorption onto Fe (oxyhydr)oxides above, and formation of authigenic P minerals (e.g. vivianite) below the SMT, deep-sea fan deposits may potentially act as long-term sinks for P.
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