The origin of metalliferous argillites in the Shoal Arm Formation of north-central Newfoundland

The Middle Ordovician Shoal Arm Formation, which is located in the central volcanic belt of north-central Newfoundland, is a tripartite assemblage of hematitic argillites, grey cherts, and black shales directly underlying a flysch sequence. The hematitic argillites are enriched in Fe, Mn, Ni, Pb, and Co. Factor analysis and principal component analysis indicate the presence of a hydrothermal component, presumably derived from hydrothermal activity in the coeval Lawrence Head volcanics. Unusual, (?) calcareous Mn-Fe-oxide nodules are present in the top parts of turbidites in the hematitic argillites. Electron microprobe analysis of a color transition from a red to a green argillite indicates fractionation of Mn from Fe by diagenetic mobilization of Mn and subsequent precipitation as Mn-carbonate in adjacent green, calcareous argillites. The detrital component of the Shoal Arm Formation is influenced by several, geochemically different, clastic sources. The top part of the Shoal Arm Formation is characterized by a Zr-, Nb-, and Y-rich clastic component that may reflect either erosion or volcanic activity of lateral equivalents of the Lawrence Head volcanics. The hydrothermal component disappeared with erosion of these volcanics. The overlying grey, mottled and laminated cherts reflect a biogenic bloom, which preceded euxinification of the depositional basin. Synchronous and diachronous depositional models are proposed to explain the tectonic history of the Shoal Arm Formation. The synchronous model emphasizes the high biological productivity and limited circulation in a restricted basin as the cause for the observed euxinification. The diachronous model explains the black shale facies with a prograding, deep-water anoxic layer that developed during rapid basin subsidence as the result of thrust-loading. In this model, the black shales were deposited in front of flysch sediments derived from a southeastward prograding thrust stack. The Middle Ordovician Taconic sequence of New York (i.e., the upper part of the Poultney Formation, the Indian River, and the Mt. Merino Formations) exhibits hematitic argillites in a similar lithostratigraphic position relative to black shale and flysch as the Shoal Arm Formation. Comparison of the Shoal Arm Formation with this part of the Taconic sequence indicates that the two tectonic models are also applicable to this sequence. Both the Indian River Formation and the Mt. Merino Formation are slightly enriched in Fe, Mn, and the trace elements Pb and Ni. This modest metal enrichment is explained either by recycling of Fe and Mn into the seawater in expanded oxygen minimum zones and subsequent precipitation at oxic/anoxic interfaces, or by a distal hydrothermal component. A continental source of Fe is excluded. Minor enrichment of biogenically derived material in the Mt. Merino Formation suggests that biological productivity may not have been the determining factor for euxinification. The comparison with Precambrian sequences that contain Superior-type banded iron-formations and black shales in comparable stratigraphic positions indicates little geochemical similarity with the two Ordovician sequences. Enrichments of Fe, Mn, Pb, Ni, Co, and Cr in both iron-formations and black shales are generally stronger than in the Ordovician cases. Interpretations of biological productivity are hampered by the insufficient knowledge of inorganic element associations with biological matter in Precambrian oceans. As a consequence, it is difficult to test the proposed tectonic models with the available geochemical data. Comparisons to that point have to rely upon field observations alone

The origin of metalliferous argillites in the Shoal Arm Formation of north-central Newfoundland

The Middle Ordovician Shoal Arm Formation, which is located in the central volcanic belt of north-central Newfoundland, is a tripartite assemblage of hematitic argillites, grey cherts, and black shales directly underlying a flysch sequence. The hematitic argillites are enriched in Fe, Mn, Ni, Pb, and Co. Factor analysis and principal component analysis indicate the presence of a hydrothermal component, presumably derived from hydrothermal activity in the coeval Lawrence Head volcanics. Unusual, (?) calcareous Mn-Fe-oxide nodules are present in the top parts of turbidites in the hematitic argillites. Electron microprobe analysis of a color transition from a red to a green argillite indicates fractionation of Mn from Fe by diagenetic mobilization of Mn and subsequent precipitation as Mn-carbonate in adjacent green, calcareous argillites. The detrital component of the Shoal Arm Formation is influenced by several, geochemically different, clastic sources. The top part of the Shoal Arm Formation is characterized by a Zr-, Nb-, and Y-rich clastic component that may reflect either erosion or volcanic activity of lateral equivalents of the Lawrence Head volcanics. The hydrothermal component disappeared with erosion of these volcanics. The overlying grey, mottled and laminated cherts reflect a biogenic bloom, which preceded euxinification of the depositional basin. Synchronous and diachronous depositional models are proposed to explain the tectonic history of the Shoal Arm Formation. The synchronous model emphasizes the high biological productivity and limited circulation in a restricted basin as the cause for the observed euxinification. The diachronous model explains the black shale facies with a prograding, deep-water anoxic layer that developed during rapid basin subsidence as the result of thrust-loading. In this model, the black shales were deposited in front of flysch sediments derived from a southeastward prograding thrust stack. The Middle Ordovician Taconic sequence of New York (i.e., the upper part of the Poultney Formation, the Indian River, and the Mt. Merino Formations) exhibits hematitic argillites in a similar lithostratigraphic position relative to black shale and flysch as the Shoal Arm Formation. Comparison of the Shoal Arm Formation with this part of the Taconic sequence indicates that the two tectonic models are also applicable to this sequence. Both the Indian River Formation and the Mt. Merino Formation are slightly enriched in Fe, Mn, and the trace elements Pb and Ni. This modest metal enrichment is explained either by recycling of Fe and Mn into the seawater in expanded oxygen minimum zones and subsequent precipitation at oxic/anoxic interfaces, or by a distal hydrothermal component. A continental source of Fe is excluded. Minor enrichment of biogenically derived material in the Mt. Merino Formation suggests that biological productivity may not have been the determining factor for euxinification. The comparison with Precambrian sequences that contain Superior-type banded iron-formations and black shales in comparable stratigraphic positions indicates little geochemical similarity with the two Ordovician sequences. Enrichments of Fe, Mn, Pb, Ni, Co, and Cr in both iron-formations and black shales are generally stronger than in the Ordovician cases. Interpretations of biological productivity are hampered by the insufficient knowledge of inorganic element associations with biological matter in Precambrian oceans. As a consequence, it is difficult to test the proposed tectonic models with the available geochemical data. Comparisons to that point have to rely upon field observations alone

Methane fluxes from coastal sediments are enhanced by macrofauna

Methane and nitrous oxide are potent greenhouse gases (GHGs) that contribute to climate change. Coastal sediments are important GHG producers, but the contribution of macrofauna (benthic invertebrates larger than 1 mm) inhabiting them is currently unknown. Through a combination of trace gas, isotope, and molecular analyses, we studied the direct and indirect contribution of two macrofaunal groups, polychaetes and bivalves, to methane and nitrous oxide fluxes from coastal sediments. Our results indicate that macrofauna increases benthic methane efflux by a factor of up to eight, potentially accounting for an estimated 9.5% of total emissions from the Baltic Sea. Polychaetes indirectly enhance methane efflux through bioturbation, while bivalves have a direct effect on methane release. Bivalves host archaeal methanogenic symbionts carrying out preferentially hydrogenotrophic methanogenesis, as suggested by analysis of methane isotopes. Low temperatures (8 °C) also stimulate production of nitrous oxide, which is consumed by benthic denitrifying bacteria before it reaches the water column. We show that macrofauna contributes to GHG production and that the extent is dependent on lineage. Thus, macrofauna may play an important, but overlooked role in regulating GHG production and exchange in coastal sediment ecosystems

Sulfide oxidation in deep Baltic Sea sediments upon oxygenation and colonization by macrofauna

Coastal and shelf sediments affected by transient or long-term bottom water anoxia and sulfidic conditions undergo drastic changes in macrofauna communities and abundances. This study investigates how early colonization by two macrofaunal functional traits (epifauna vs. infauna) affects oxygen, sulfide, and pH dynamics in anoxic sediment upon recent bottom water oxygenation. Large mesocosms (area 900 cm 2) with 150-m-deep Baltic Sea soft sediments were exposed to three treatments: (1) no animals; (2) addition of 170 polychaetes (Marenzelleria arctia); (3) addition of 181 amphipods (Monoporeia affinis). Porewater chemistry was investigated repeatedly by microsensor profiling over a period of 65 days. Colonization by macrofauna did not significantly deepen penetration of oxygen compared to the animal-free sediment. Bioturbation by M. affinis increased the volume of the oxidized, sulfide-free sediment by 66% compared to the animal-free control already after 13 days of incubation. By the end of the experiment M. affinis and M. arctia increased the oxidized sediment volume by 87 and 35%, respectively. Higher efficiency of epifaunal amphipods in removing hydrogen sulfide than deep-burrowing polychaetes is likely due to more substantial re-oxidation of manganese and/or nitrogen compounds associated with amphipod mixing activity. Our results thus indicate that early colonization of different functional groups might have important implications for the later colonization by benthic macrofauna, meiofauna and microbial communities that benefit from oxidized and sulfide-free sediments

Methane emissions offset atmospheric carbon dioxide uptake in coastal macroalgae, mixed vegetation and sediment ecosystems

Publisher Copyright: © 2023, The Author(s).Coastal ecosystems can efficiently remove carbon dioxide (CO2) from the atmosphere and are thus promoted for nature-based climate change mitigation. Natural methane (CH4) emissions from these ecosystems may counterbalance atmospheric CO2 uptake. Still, knowledge of mechanisms sustaining such CH4 emissions and their contribution to net radiative forcing remains scarce for globally prevalent macroalgae, mixed vegetation, and surrounding depositional sediment habitats. Here we show that these habitats emit CH4 in the range of 0.1 – 2.9 mg CH4 m−2 d−1 to the atmosphere, revealing in situ CH4 emissions from macroalgae that were sustained by divergent methanogenic archaea in anoxic microsites. Over an annual cycle, CO2-equivalent CH4 emissions offset 28 and 35% of the carbon sink capacity attributed to atmospheric CO2 uptake in the macroalgae and mixed vegetation habitats, respectively, and augment net CO2 release of unvegetated sediments by 57%. Accounting for CH4 alongside CO2 sea-air fluxes and identifying the mechanisms controlling these emissions is crucial to constrain the potential of coastal ecosystems as net atmospheric carbon sinks and develop informed climate mitigation strategies.Peer reviewe

Nitrous Oxide Dynamics in the Siberian Arctic Ocean and Vulnerability to Climate Change

Nitrous oxide (N2O) is a strong greenhouse gas and stratospheric ozone-depleting substance. Around 20% of global emissions stem from the ocean, but current estimates and future projections are uncertain due to poor spatial coverage over large areas and limited understanding of drivers of N2O dynamics. Here, we focus on the extensive and particularly data-lean Arctic Ocean shelves north of Siberia that experience rapid warming and increasing input of land-derived nitrogen with permafrost thaw. We combine water column N2O measurements from two expeditions with on-board incubation of intact sediment cores to assess N2O dynamics and the impact of land-derived nitrogen. Elevated nitrogen concentrations in water column and sediments were observed near large river mouths. Concentrations of N2O were only weakly correlated with dissolved nitrogen and turbidity, reflecting particulate matter from rivers and coastal erosion, and correlations varied between river plumes. Surface water N2O concentrations were on average close to equilibrium with the atmosphere, but varied widely (N2O saturation 38%–180%), indicating strong local N2O sources and sinks. Water column N2O profiles and low sediment-water N2O fluxes do not support strong sedimentary sources or sinks. We suggest that N2O dynamics in the region are influenced by water column N2O consumption under aerobic conditions or in anoxic microsites of particles, and possibly also by water column N2O production. Changes in biogeochemical and physical conditions will likely alter N2O dynamics in the Siberian Arctic Ocean over the coming decades, in addition to reduced N2O solubility in a warmer ocean.publishedVersio

Sediment med nyckelroll i näringsväven

I sedimenten sker processer som kan vara helt avgörande för näringsbalansen i havsvattnet. Omvandlingen av fosfor till olika former är relativt väl känd, medan detaljerna i kvävets kretslopp är betydligt mindre kända. Mer än hälften av den årliga tillförseln av kväve till Östersjön beräknas omsättas till kvävgas i sedimentet, vilket sedan går förlorat för de flesta marina organismer

Sediment med nyckelroll i näringsväven

I sedimenten sker processer som kan vara helt avgörande för näringsbalansen i havsvattnet. Omvandlingen av fosfor till olika former är relativt väl känd, medan detaljerna i kvävets kretslopp är betydligt mindre kända. Mer än hälften av den årliga tillförseln av kväve till Östersjön beräknas omsättas till kvävgas i sedimentet, vilket sedan går förlorat för de flesta marina organismer

(Figure 1 and 2) Phosphorus pools in the investigated sediments quantified by SEDEX sequential extraction and distribution of recovered 33P spike between sedimentary P pools after incubation

Phosphorus is an essential nutrient for life. In the ocean, phosphorus burial regulates marine primary production**1, 2. Phosphorus is removed from the ocean by sedimentation of organic matter, and the subsequent conversion of organic phosphorus to phosphate minerals such as apatite, and ultimately phosphorite deposits**3, 4. Bacteria are thought to mediate these processes**5, but the mechanism of sequestration has remained unclear. Here, we present results from laboratory incubations in which we labelled organic-rich sediments from the Benguela upwelling system, Namibia, with a 33P-radiotracer, and tracked the fate of the phosphorus. We show that under both anoxic and oxic conditions, large sulphide-oxidizing bacteria accumulate 33P in their cells, and catalyse the nearly instantaneous conversion of phosphate to apatite. Apatite formation was greatest under anoxic conditions. Nutrient analyses of Namibian upwelling waters and sediments suggest that the rate of phosphate-to-apatite conversion beneath anoxic bottom waters exceeds the rate of phosphorus release during organic matter mineralization in the upper sediment layers. We suggest that bacterial apatite formation is a significant phosphorus sink under anoxic bottom-water conditions. Expanding oxygen minimum zones are projected in simulations of future climate change**6, potentially increasing sequestration of marine phosphate, and restricting marine productivity

Sea-Air Exchange of Methane in Shallow Inshore Areas of the Baltic Sea

We report sea-air fluxes of methane in physically and biologically distinct inshore habitats of the Baltic Sea with the goal to establish empirical relationships that allow upscaling of local site-specific flux measurements. Flux measurements were conducted using floating chambers with and without bubble shields, and by using a boundary layer gas transfer model before, during, and after an annually occurring algal bloom from June to October 2019. Water and air temperature, salinity, wind, sediment organic content, and organic content of floating algal biomass were found to successfully discriminate the different habitats in terms of methane flux, both over periods of days and over a season. Multivariate statistical analysis was used to establish the relative environmental forcing of methane emissions over one growth season for each flux method. Floating algal biomass carbon and sediment organic content were identified as the most important controlling factors for methane emissions based on flux chamber measurements over a period of days to weeks, whereas water and air temperature and wind velocity were the most important factors based on the gas transfer model on these time scales. Over the season, water and air temperature were the most important controlling factors with both methods. We present a first attempt how our observations can be extrapolated to determine the coastal methane emission along the coastline