Bottom Water Oxygen Research Articles

Waste water discharge from a large Ni-Zn open cast mine degrades benthic integrity of Lake Nuasjärvi (Finland)

The Talvivaara/Terrafame multi-metal mining company is Europe’s largest nickel open cast mine, it is also known for the largest wastewater leakage in the Finnish mining history and a series of other accidents. In this paleolimnological study, influences of a recently constructed treated waste water discharge pipeline into Lake Nuasjärvi were investigated by analyzing past (pre-disturbance) and present community compositions of key aquatic organism groups, including diatoms, Cladocera and Chironomidae, along spatial (distance, water depth) gradients. In addition to defining ecological changes and impacts of saline mine waters in the lake, chironomids were used to quantitatively reconstruct bottom water oxygen conditions before and after the pipe installation (in 2015). The diatom and cladoceran communities, which reflect more the open-water habitat, showed only relatively minor changes throughout the lake, but a general decrease in diversity was observed within both groups. Chironomids, which live on substrates, showed more significant changes, including complete faunal turnovers and deteriorated benthic quality, especially at the sites close to the pipe outlet, where also chironomid diversity was almost completely lost. Furthermore, the reconstructed hypolimnetic oxygen values indicated a major oxygen decline and even anoxia at the sites near the pipe outlet. The limnoecological influence of the pipe decreased at sites located counter-flow or behind underwater barriers suggesting that the waste waters currently have location-specific impacts. Our study clearly demonstrates that whereas the upper water layers appear to have generally maintained their previous state, the deep-water layers close to the pipe outlet have lost their ecological integrity. Furthermore, the current hypolimnetic anoxia close to the pipe indicates enhanced lake stratification caused by the salinated mine waters. This study clearly exhibits the need to investigate different water bodies at several trophic levels in a spatiotemporal context to be able to reliably assess limnoecological impacts of mining.

Upper Ordovician marine red limestones, Tarim Basin, NW China: A product of an oxygenated deep ocean and changing climate?

Abstract Marine red beds (MRB) have been commonly interpreted as products of bottom water oxygenation (or ventilation) and coeval perturbations of the global carbon cycle during greenhouse climates. The Sandbian (Upper Ordovician) successions at Dawangou and Nanyigou in NW Tarim, China are characterized by deep-shelf nodular red limestones. Using ultraviolet-visible-near infrared (UV-VIS-NIR) diffuse reflectance spectroscopy (DRS), field emission scanning electron microscope (FESEM) equipped with energy dispersive X-ray spectrometer (EDS), and paired inorganic and organic carbon isotope systematics, this study attempts to reveal the origin of these MRBs and coeval carbon cycling during deposition. Both the DRS and FESEM results consistently show that these red limestones are exclusively impregnated with amorphous to poorly crystalline, submicron ferric oxides (mostly hematite), constituting the dominant components of the red pigment. Hematite aggregates (or lumps) occur either in the calcite crystal interstices and pores or within the lattice structure of calcite crystals, implicating early diagenetic or syndepositional origins. Paired organic and inorganic carbon isotope data through the MRB successions demonstrate a time-specific Sandbian positive carbon isotope plateau (~1 to 2‰ VPDB) in both fractions as reported elsewhere around the world. This may have intitially resulted from enhanced burial of organic matter, then a drawdown of atmospheric pCO2 levels, and subsequent climate cooling. This scenario agrees with the decreasing isotope difference (Δ13C = δ13Ccarb−δ13Corg; ~26‰VPDB on average) in the Sandbian MRBs relative to the underlying strata (~29‰ VPDB) from both sections. A cooling climate could have accelerated oceanic ventilation rates and led to increased oxygenation of deep-shelf water masses, eventually facilitating the widespread deposition of MRBs near continental margins. The persistence of a cool climate and the expansion of oxygenated deep-shelf water masses onto the shelf that initiated during the Darriwilian may have stimulated the rapid biodiversification of marine organisms during the Sandbian.

Geochemical characteristics of the lower Silurian Longmaxi Formation on the Yangtze Platform, South China: Implications for depositional environment and accumulation of organic matters

The organic-rich lower Silurian Longmaxi Formation is now regarded as the favorable target for shale gas exploration and production. However, the mechanism of organic matter accumulation in these deposits remains highly controversial. In this study, we investigate the total organic carbon (TOC) content and the major and trace element abundances of a newly recovered core from the Yangtze Platform to reconstruct the paleo-environment and to elucidate the factors that control organic matter accumulation. Our results suggest that the greenhouse conditions during the early Silurian were punctuated by several cooling events. Bottom water redox conditions improve gradually upsection with a transition from anoxic water conditions in the lower Longmaxi Formation to suboxic-oxic water conditions in the upper Longmaxi Formation. The primary productivity on the Yangtze Platform appears to have been high during deposition of the Longmaxi Formation, especially in its lower part, due to an enhanced phosphorus recycling. The strong correlations between TOC and copper and nickel imply that the productivity was especially critical to the organic matter accumulation in the lower Longmaxi Formation. Furthermore, the rapid consumption of dissolved oxygen in bottom water favored the establishment of anoxic water conditions, which facilitated organic matter preservation. The poor correlations between TOC and barium and phosphorus in the lower Longmaxi Formation likely reflect intense recycling of nutrients. The evolution of water redox conditions and accumulation of organic matters in the Longmaxi Formation can be related to global fluctuations in sea level and regional tectonic uplift of the Yangtze Platform.

Sedimentology, geochemistry and reservoir potential of the organic-rich Qusaiba Shale, Tabuk Basin, NW Saudi Arabia

Abstract The Qusaiba Shale Formation of the Qalibah Group is the most prolific source rock for the Paleozoic petroleum system in Saudi Arabia and is recently considered as a potential unconventional shale gas reservoir. Detailed sedimentological, petrographical, and geochemical analyses were undertaken on an ~31 m thick outcrop of this organic-rich shale exposed in the northwest of Tayma City, NW of Saudi Arabia to provide a better understanding of the vertical and lateral lithofacies variations and the effects of such variations on reservoir properties. X-ray diffraction analysis reveals that clay minerals (average: 50%) and quartz (average: 28%) dominate the bulk mineralogical composition while K-feldspar, plagioclase, and pyrite occur as common to minor components in the analyzed samples. An integration of the sedimentological description, petrography and mineralogical composition allows the subdivision of the investigated outcrop section into six lithofacies. These are: Laminated organic-rich shale, Graptolitic concretion, Massive organic-rich shale, Organic-lean shale, Siltstone-shale interbedded, and Cross-stratified siltstone/sandstone lithofacies. TOC content in the laminated and massive organic-rich shale lithofacies ranges between 0.5 and 6.1 wt% (average 2.52 wt%) then it decreases upward (0.04–0.35 wt%, average 0.18 wt%) in the overlying organic-lean shale and siltstone lithofacies. Trace elements (Cu, Mo, As, Ni, Co, U and V) show positive excursions in the lowermost 20 m of the organic-rich, dark-grey shale interval and display abrupt depletions at the contact with overlying organic-lean shale. The enrichment factors of these trace elements are characterized by similar distribution patterns as their measured concentrations. Like the elements, these factors also exhibit a significant depletion at the contact between the organic-rich shale and the overlying organic-lean shale. Out of all the redox indices, V/(V + Cr), V/(V + Ni), Th/U and [Mo]s/TOC were found to best distinguish between the organic-rich and the overlying organic-lean intervals. The laminated organic-rich shale lithofacies indicate deposition of hemipelagic sediments by a relatively low energy quiet anoxic bottom water, most likely in a sulfidic conditions that were associated with a strongly restricted bottom water mass circulation at the time of its deposition. This restricted hydrographic condition was likely enhanced in the study area due to the paleotopography that was created by the deglaciation of the Early Silurian time. The TOC richness, common occurrence of pyrite and high enrichment of redox elements Mo, U and V in the organic-rich shale intervals support the existence of anoxic bottom water at the time of deposition. The abrupt decrease of the TOC and the redox sensitive elements and their associated indices from the underlying organic-rich lithofacies to the overlying organic-lean shale lithofacies is likely due to a gradual increase in oxygen level. This improved bottom water oxygenation condition might have led to a reduction in organic productivity and limited organic matter preservation in the organic-lean shale lithofacies. The graptolitic concretion lithofacies found in the sequence, refers to an in-situ, syngenetic to early diagenetic origin formed close to the sediment-water layer when there was little or no deposition or at periods characterized by low sedimentation rates. The siltstone - fine sandstone lithofacies in the topmost part of the studied section, is interpreted to indicate the dominance of high energy and highly oxygenated shallow bottom water conditions during deposition, probably in a middle to inner shelf depositional settings. The kerogen in QS is a mixture of type III (gas prone) and type IV (inert kerogen), Tmax values with an average of 430 °C, and VRo values (average 0.58) calculated from the Tmax, assigned the studied section as immature. Qualitative evaluation of porosity allows the identification of three different types of porosity including inorganic porosity, organic porosity and natural fracture porosity. Although the ductile clay minerals are the most abundant minerals in the lower part of the studied QS (average 56%), the brittle minerals (Quartz, Feldspar, and Pyrite) form an average of 42% and exhibit a uniform distribution of brittleness in the organic-rich interval.

Palaeoproductivity and associated changes in the north-eastern Indian Ocean since the last glacial: Evidence from benthic foraminifera and stable isotopes

Here we present the first detailed planktonic and benthic δ13C records and benthic foraminiferal assemblage records from the north-eastern Indian Ocean to decipher the palaeoceanographic changes during the last 56 kyr. We identified three different palaeoceanographic stages, clearly differentiated by significant variations in the benthic foraminiferal assemblages and δ13C records. The results of this study indicate that productivity was generally higher during the glacial periods than during the Holocene. Comparison of the benthic foraminiferal assemblage distributions and planktonic and benthic δ13C records show a significant correlation between productivity and the bottom water oxygenation on glacial-interglacial timescales. Productivity gradually increased during the period between 56 and 27.5 kyr. During this period, the dominance of Melonis spp. and Oridosalis umbonatus were correlated with conditions of intermediate to high surface productivity and moderate bottom water oxygenation. Increased higher equatorial productivity and low bottom water oxygenation during the period between 27.5 and 15 kyr are supported by planktonic δ13C and faunal records. During this period, the dominance of benthic foraminifera assemblages characterised by Uvigerina peregrina indicates sustained continuous phytodetritus flux to the seafloor from enhanced surface water productivity and relatively low bottom water oxygenation. The absence or minimal occurrences of high productivity indicating U. peregrina, the dominance of intermediate to low productivity indicating fauna, and relatively low planktonic δ13C records suggest low productivity and active deep-water oxygenation after 15 kyr. Concurrent river discharge and rising sea levels during this period are indicated by negative δ18O of G. ruber at the site.

Scaling laws explain foraminiferal pore patterns

Due to climate warming and increased anthropogenic impact, a decrease of ocean water oxygenation is expected in the near future, with major consequences for marine life. In this context, it is essential to develop reliable tools to assess past oxygen concentrations in the ocean, to better forecast these future changes. Recently, foraminiferal pore patterns have been proposed as a bottom water oxygenation proxy, but the parameters controlling foraminiferal pore patterns are still largely unknown. Here we use scaling laws to describe how both gas exchanges (metabolic needs) and mechanical constraints (shell robustness) control foraminiferal pore patterns. The derived mathematical model shows that only specific combinations of pore density and size are physically feasible. Maximum porosity, of about 30%, can only be obtained by simultaneously increasing pore size and decreasing pore density. A large empirical data set of pore data obtained for three pseudocryptic phylotypes of Ammonia, a common intertidal genus from the eastern Atlantic, strongly supports this conclusion. These new findings provide basic mechanistic understanding of the complex controls of foraminiferal pore patterns and give a solid starting point for the development of proxies of past oxygen concentrations based on these morphological features. Pore size and pore density are largely interdependent, and both have to be considered when describing pore patterns.

Environmental and Geomorphological Changes on the Eastern North American Continental Shelf Across the Paleocene‐Eocene Boundary

AbstractForaminiferal evidence from two sites in southern Maryland, eastern United States, reveals a series of rapid environmental changes on the continental shelf during the onset of the Paleocene‐Eocene Thermal Maximum (PETM). Benthic and planktic foraminifer assemblages from the South Dover Bridge and Mattawoman Creek‐Billingsley Road coreholes in the central Salisbury Embayment record changing latest Paleocene and earliest Eocene environmental conditions that began prior to the carbon isotope excursion that marks the beginning of the PETM. The foraminiferal response reflects increases in productivity in the bottom water, a minor dissolution event, and sea surface warming in the latest Paleocene. Relative sea level changes, a sudden change in sedimentary regime, and a decrease in bottom water oxygenation occurred in this region across the PETM onset. While South Dover Bridge assemblages support a rise in sea level across the PETM onset, Mattawoman Creek‐Billingsley Road assemblages record a reduction in water depth interpreted as delta progradation and possible tectonic activity. Transitional carbon isotope values are recorded in these delta sediments. We present an initial bathymetric reconstruction of the Salisbury Embayment showing the physical effects of the carbon isotope excursion onset on shelf morphology and highlight the importance of understanding coastal zone processes when examining shelf sediments.

Geochemical evidence for expansion of marine euxinia during an early Silurian (Llandovery–Wenlock boundary) mass extinction

Repeated biotic crises have become the hallmark for the Silurian with the three most significant marine turnover events being related to dramatic global environmental perturbations. Causal mechanisms linking these marine extinction events with positive carbon isotope (δ13C) excursions, paleoceanographic change, and climate remain poorly constrained. Here, we examine the positive δ13C excursion across the Llandovery/Wenlock boundary, and the associated Ireviken extinction event. This positive δ13C excursion has been interpreted to reflect a major change in global oceanographic-climate state and enhanced organic carbon burial. New geochemical data from two paleocean basins have been analyzed to determine local and global redox conditions using carbon- and sulfur-isotopes (δ34S), and iodine (I/Ca+Mg) proxies. The high-resolution δ13C and δ34S data from both sections show positive excursions indicative of global perturbations to each of these elemental cycles, with minimal temporal offsets between the two systems. Numerical box modeling of δ13C and δ34S data indicates that these isotopic shifts can be generated by significant increases in the burial of organic carbon and pyrite, which are most likely due to enhanced burial under euxinic (anoxic and sulfidic) conditions. Independently, I/(Ca+Mg) values point to locally anoxic bottom waters in the distal and deeper basinal setting in Nevada before, during, and after the Ireviken positive δ13C excursion. I/(Ca+Mg) values in the proximal shelf setting in Tennessee show relatively oxic waters during the onset of peak δ13C values, after which bottom-water oxygen concentrations dropped throughout the remainder of the excursion. This multiproxy paleoredox dataset provides the first direct evidence for local and global expansion of reducing marine conditions coincident with the Silurian biotic event and positive δ13C excursion. Integration of these geochemical data for local- and global-scale changes in marine redox conditions with the paleontological data and evidence for eustatic sea-level rise points toward a shoaling of anoxic and/or euxinic waters onto the shelf as a driver for the Ireviken extinction event.

Deep‐Sea Oxygen Depletion and Ocean Carbon Sequestration During the Last Ice Age

AbstractEnhanced ocean carbon storage during the Pleistocene ice ages lowered atmospheric CO2 concentrations by 80 to 100 ppm relative to interglacial levels. Leading hypotheses to explain this phenomenon invoke a greater efficiency of the ocean's biological pump, in which case carbon storage in the deep sea would have been accompanied by a corresponding reduction in dissolved oxygen. We exploit the sensitivity of organic matter preservation in marine sediments to bottom water oxygen concentration to constrain the level of dissolved oxygen in the deep central equatorial Pacific Ocean during the last glacial period (18,000–28,000 years BP) to have been within the range of 20–50 μmol/kg, much less than the modern value of ~168 μmol/kg. We further demonstrate that reduced oxygen levels characterized the water column below a depth of ~1,000 m. Converting the ice age oxygen level to an equivalent concentration of respiratory CO2, and extrapolating globally, we estimate that deep‐sea CO2 storage during the last ice age exceeded modern values by as much as 850 Pg C, sufficient to balance the loss of carbon from the atmosphere (~200 Pg C) and from the terrestrial biosphere (~300–600 Pg C). In addition, recognizing the enhanced preservation of organic matter in ice age sediments of the deep Pacific Ocean helps reconcile previously unexplained inconsistencies among different geochemical and micropaleontological proxy records used to assess past changes in biological productivity of the ocean.

Centennial OMZ changes in the NW Mexican Margin from geochemical and foraminiferal sedimentary records

Oxygen minimum zones (OMZs) are predicted to expand in the near future due to continued global warming, with largest declines in oxygen occurring within the strong tropical OMZs. In this study, shifts in the position and intensity of the OMZ in the Eastern Tropical North Pacific (ETNP) were examined using three 210Pb-dated sediment cores collected along the continental shelf and slope of the NW Mexican Margin (southwest of Mazatlán). Using a suite of redox sensitive elements, bulk element and physical analyses, three main factors were identified as driving the geochemical signatures of trace elements across the NW Mexican Margin: 1) terrigenous input, 2) organic matter scavenging and 3) bottom water oxygen content. Downcore trends in benthic foraminiferal assemblages and authigenic concentrations of Mo and U suggest that dysoxic conditions were more intense and covered a larger depth range prior to the 20th century followed by a reduction in both size and strength of the OMZ over the last century.

Organic matter content and type variation in the sequence stratigraphic context of the Upper Devonian New Albany Shale, Illinois Basin

Organic matter quantity and type are important parameters in conventional source rock evaluation and unconventional shale oil/gas reservoir characterization. Understanding the stratigraphic distribution of organic matter content and type in black shale successions is critical for identifying potentially productive intervals, because organic matter can adsorb large amounts of oil and gas. Detailed examination of total organic carbon content, organic petrographic composition, and high-resolution (8 cm spacing) geochemical proxies in a sequence stratigraphic framework were conducted on an early mature (0.55% Ro) New Albany Shale core of the Illinois Basin to study the influence of relative sea-level fluctuations on paleoproductivity, clastic supply, bottom-water redox conditions, and their combined control on total organic carbon distribution pattern and organic maceral variation.Marine organic matter including amorphous organic matter and alginite (mainly derived from Tasmanites cysts) is the dominant organic matter in the New Albany Shale. Terrestrial organic matter accounts for <10% of total organic matter. Within a sequence stratigraphic context, total organic carbon content increases in transgressive systems tracts, reaches a maximum before the maximum flooding surface, and shows relatively low values in highstand systems tracts. Comparatively, low total organic carbon contents at maximum flooding surfaces reflect a combination of low sedimentation rates, elevated bottom-water oxygenation, and high biogenic silica dilution.Stratigraphically, amorphous organic matter content increases in transgressive systems tracts, reaches a maximum near the maximum flooding surface, and decreases in highstand systems tracts. Enrichment of broken Tasmanites cysts and their detrital infills are an indicator of high-energy environments and could possibly indicate lowstand systems tracts. The stratigraphic distribution of organic matter content and type may result in cyclic stratigraphic variations of hydrocarbon generation potential and oil saturation, and influence the development of secondary organic pores when the New Albany Shale is within the oil and gas windows.

Variations in trace metal concentrations and Sr, Nd isotopic compositions in sediments from two contrasting settings in the Eastern Arabian Shelf: Implications for provenance and paleoclimate reconstruction

Major and trace elements concentrations as well as Nd and Sr isotopic ratios were measured in sediments from two gravity cores (GC17 and GC19) deposited in the high-sediment flux regime of the Eastern Arabian Shelf (EAS). The core-sampling locations are close to the mouths of the geochemically and isotopically well-characterized Rivers Mandovi and Zuari and are overlain by water columns of contrasting redox conditions. Given the available knowledge of bottom water oxygen concentrations in the studied locations, the compositions of the Mandovi and Zuari sediments as well as the lithology of the drainage basin, the goal of this study was to test the efficacy of different paleo-redox proxies and provenance indicators in a high-sediment flux regime of the ocean.The variations of immobile elements like Al, Ti, Th, and Zr in the studied samples suggest lack of sediment reworking and sorting. Provenance proxies such as Th/Co, La/Sc ratios and variations in La-Th-Sc concentrations suggests a dominantly silicic source rock of granitic to granodioritic composition for these sediments, which is consistent with the dominant lithology of the drainage basins of the Mandovi and Zuari Rivers. Minor contributions from a mafic source (basalt or metabasalt) cannot be ruled out. The chemical index of alteration (CIA) and plagioclase index of alteration (PIA) values of the samples suggest low to moderate weathering of the source rocks. While the Sr isotopic compositions of the GC17 and GC19 sediments overlap with that of the gneissic basement rocks from the Mandovi and Zuari drainage basins, the εNd(0) of the sediments (average −13.72) show significantly more radiogenic values compared to the gneissic basement rocks (average −36). This difference in the Nd isotopic compositions is explained by early selective weathering and removal of rock-forming minerals like plagioclase in the source rocks which results in the supply of radiogenic Nd isotopic composition bearing sediments to the ocean. This argument is consistent with the overlapping εNd(0) of the GC17 and GC19 sediments and suspended particulate matter (SPM) of the Mandovi and Zuari Rivers. Although, the Nd isotopic compositions overlap, the less radiogenic Sr isotopic compositions of the GC17 and GC19 sediments compared to the SPM of the Mandovi and Zuari Rivers suggests the influence of organic matter, formation of authigenic clay and carbonates, as well as the contribution of Sr from submarine groundwater discharge.Trace metal concentrations and ratios were measured in the bulk sediments as well as in the leached authigenic and residual detrital-rich fractions of selected samples. For the GC19 sediments overlain by oxygenated waters, these geochemical proxies correctly infer their deposition under oxic conditions. In contrast, most of these proxies, barring those involving U and Mo, erroneously infer oxic depositional conditions for the GC17 sediments which are overlain by an oxygen minimum zone (OMZ) of the eastern Arabian Sea. We believe that the high sedimentation rate and large terrigenous flux possibly prohibits the equilibration of some of these trace metals in the sediments with the ambient seawater. Our study suggests that U and Mo-based proxies for inferring paleo-redox conditions are robust even under high sedimentation conditions. Overall, this study provides useful insights into the behaviour of redox-sensitive elements and provenance indicators in a continental margin setting impinged by an OMZ.

Benthic fluxes from hypoxia-influenced Gulf of Mexico sediments: Impact on bottom water acidification

Benthic fluxes are reported from 8 sites on the shelf and slope of the Gulf of Mexico (GoM) in the region near the Mississippi River delta. Benthic landers, with the capability to incubate 3 chambers simultaneously, were deployed in August 2011 to establish the rate of phosphate, nitrate, ammonium, dissolved Si, Dissolved Inorganic Carbon (DIC) and alkalinity concentration change vs. incubation time (7–50 h) thereby providing flux estimates for these parameters. Stations located within 350 km of the Mississippi River mouth have nutrient and DIC fluxes that vary by a factor of 10 but show no longitudinal trends. Chambers deployed in low oxygen bottom water (<4 μM) do not have different flux values compared to chambers deployed in settings with higher bottom water oxygen (160 μM). At some stations, ammonium shows a change in flux with incubation time, yet no other species shows this change; hence neither a change in transport mechanism or reaction rate can explain the non-steady state behavior of ammonium. A positive correlation (r2 = 0.91) between the fluxes of dissolved Si and DIC imply a linkage between the diagenesis of biogenic Si and organic C throughout this region. The efflux of DIC and alkalinity in a ratio > 1 drives GoM bottom waters to a lower calcite and aragonite saturation state. Carbon isotopes of the DIC were measured on chamber waters and the calculated δ13C of the DIC source at 4 stations was similar, between −14 to −17‰ compared to typical δ13C values of bulk organic carbon in the GoM of −22‰. At a fifth station, the DIC added was calculated to have an isotope value of −31‰. Dissolved inorganic carbon isotope compositions that are significantly heavier or lighter than particulate organic carbon are unexpected and may be explained by a combination of inputs: the oxidation of average marine organic carbon and calcium carbonate dissolution, methanogenesis, and/or from oxidation of terrestrial lignin fractions.

High-resolution bio- and chemostratigraphy of an expanded record of Oceanic Anoxic Event 2 (Late Cenomanian–Early Turonian) at Clot Chevalier, near Barrême, SE France (Vocontian Basin)

A newly located exposure of the Niveau Thomel, an organic-­‐rich level at the Cenomanian–Turonian boundary, provides a highly expanded record of Oceanic Anoxic Event (OAE) 2, excepted for the lower relatively condensed glauconite-­rich part of the section. The new locality, close to Barreme in the Vocontian Basin, SE France, is developed in deep-­water hemi-­pelagic facies (shales, marls, marly limestones, variably enriched in organic matter) and provides an improved understanding of palaeoceanographic events associated with OAE 2. Investigation of the biostratigraphy (nannofossils and planktonic foramininfera), organic and inorganic geochemistry (bulk carbonate δ18O, total organic carbon (TOC), bulk organic, biomarker-specific and carbonate δ13C, major and trace elements, and Rock-­Eval data) has allowed characterization of the sediments in great detail. The combined study further constrains the detailed relationship between bio-­ and chemostratigraphy (particularly with respect to the details of the well-­displayed positive carbon-­‐isotope excursion) for this interval. The section also provides new evidence, in the form of a positive oxygen-­isotope excursion and an offset between carbonate and organic-­carbon carbon-­isotope records, which confirms the importance of cooling accompanied by a drop in dissolved CO2 in near-­surface waters during the Plenus Cold Event that characterized the early part of OAE 2. Evidence for increased oxygenation of bottom waters, together with elevated concentrations of redox-­sensitive and chalcophilic elements registered elsewhere through the level of the Plenus Cold Event, may be reflected in enhanced concentrations of iron (in glauconite) and nickel in coeval strata from the Clot Chevalier section.

EARLY TITHONIAN DEEP-WATER COLONIZATION BY BENTHIC FORAMINIFERA IN THE MAGURA BASIN (PIENINY KLIPPEN BELT, WESTERN CARPATHIANS): A CLUE TO THE ORIGINS OF DEEP-WATER FORAMINIFERA.

Deep-water benthic foraminifera were reported from lower Tithonian abyssal deposits lying above a barren interval of radiolarites in the Magura Basin (Western Carpathians). The analysis of morphogroups shows that the assemblage is represented by increased globular chambered morphogroups of both agglutinated and calcareous benthic foraminifera and planoconvex calcareous benthic foraminifera. The composition of the benthic foraminiferal assemblage points to a stressed setting particularly occurring in environments with increased organic flux and depleted oxygen in bottom and pore waters, as indicated by the scarcity of strictly epifaunal agglutinated foraminifera and the absence of strictly epifaunal calcareous benthic foraminifera. The assemblage is compared with Oxfordian – Tithonian assemblages reported from deep-water facies and shelf assemblages from the Boreal, Tethys and Atlantic realms.

The Influence of Sediment‐Derived Dissolved Organic Matter in the Vistula River Estuary/Gulf of Gdansk

AbstractDissolved organic matter (DOM) concentrations in sediment porewaters are often orders of magnitude higher than in the overlying water column resulting in a diffusive flux of DOM from sediments. The intensity and fate of this DOM flux is poorly understood. The Gulf of Gdansk in the Southern Baltic Sea is dominated by the Vistula River, one of the largest and most anthropogenically impacted rivers in the Baltic Sea catchment. The sediment characteristics of the region are varied, from mixed sandy conditions near shore to mud sediments in the Gdansk Deep. We investigated the significance of sediment‐derived DOM in the Gulf of Gdansk in comparison to that supplied by the river. Sediment‐derived DOM in the region was found to have an organic matter fluorescence signature distinct from the DOM in the water column. The visible wavelength fluorescence could be used to distinguish organic matter from near shore sediments influenced by riverine sources and organic matter from deeper offshore sediments, influenced by more pelagic sources. Ultraviolet‐A wavelength fluorescence dominated the sediment flux but was rapidly removed in bottom waters suggesting that it may contribute to bottom water oxygen consumption. While there is potential for DOM fluxes from sediments in the Gulf of Gdansk, the high background pelagic concentration of DOM in these waters and the much stronger influence of the Vistula River can mask the contributions from sediments.

An integrated approach to understanding the depositional environment and organic matter enrichment factor in Carboniferous source rocks, Junggar Basin, NW China

Multiple indicators (trace fossils, trace metals, and δ13Corg) are used to assess the depositional environments and controls on organic carbon accumulation in the Lower Carboniferous Nanmingshui Formation, Junggar Basin, NW China. The majority of trace fossils belong to the Nereites ichnofacies, representing low energy, oxygen‐poor, and relatively quiet bottom water environments. However, the shallow water trace fossil Planolites also appears in the strata, possibly reflecting variations in the bottom water oxygen contents of the turbidite succession. Redox proxies Th/U, V/Sc, and V/(V + Ni) reveal variable redox conditions; most of the samples are in the range from suboxic to anoxic depositional conditions. Ni and Cu show a positive correlation with TOC, but U and V have no correlation with TOC, also suggesting the redox conditions were mainly suboxic. The P/Al and Cu/Al ratios of all samples are higher than those of Post‐Archean Australian Shales (PAAS), and about two‐thirds of the samples' Ba/Al and Ni/Al ratios are close to or higher than PAAS, suggesting the Early Carboniferous Junggar Basin had relatively high palaeo‐productivity levels. δ13Corg values average − 23.75‰, reflecting a mixture of terrestrial organic and marine organic matter. The indexes of Ba/Al, Cu/Al, Ni/Al, and δ13Corg show good positive correlations with TOC, indicating the palaeo‐productivity played an important role for the organic matter accumulation. On the other hand, the TOC correlates inversely with redox proxies (Th/U, V/Sc, and V/(V + Ni)), suggesting the preservation conditions (anoxia) are not the control factor of organic matters accumulation. Using these multiple approaches, our results indicate that productivity was the primary factor controlling organic matter accumulation.

Dissolved benthic phosphate, iron and carbon fluxes in the Mauritanian upwelling system and implications for ongoing deoxygenation

Benthic fluxes of total dissolved phosphate (TPO43-), dissolved iron (Fe2+), and dissolved inorganic carbon (DIC) were determined in situ using benthic chambers at nine stations along a depth transect between 47 and 1108 m water depth at 18°N off Mauritania (NW Africa) during the upwelling season in 2014 (RV Meteor cruise M107). Bottom water oxygen (O2) concentrations were always ≥ 25 µM, and all fluxes (TPO43-, Fe2+, DIC) were consistently directed from the sediments into the bottom water. The highest benthic TPO43- release of 0.2 ± 0.07 mmol m2 d−1 was found at 47 m water depth (50 µM O2). The highest diffusive Fe2+ flux of 0.03 mmol m2 d−1, determined from porewater Fe2+ concentrations, occurred at 67 m water depth (27 µM O2). This was much lower than the detrital Fe supply as indicated by constant Fe/Al ratios along the depth transect. TPO43- release rates decreased concurrently with DIC flux and water depth. A difference of up to one order of magnitude between benthic chamber and diffusive TPO43- fluxes indicated that the total TPO43- release was strongly enhanced by bioirrigation.The observed fluxes were similar to those measured during an earlier cruise in 2011, generally indicating comparable release rates during both upwelling seasons. Furthermore, ex situ oxygen manipulation experiments showed an increase of the nutrient release (e.g. TPO43-, Fe2+) after seven days of anoxic bottom water conditions. The fluxes were enhanced by a factor of 1.4 for P and 7.3 for Fe compared to the measured release under natural conditions and reached values as high as those measured in the anoxic oxygen minimum zone off Peru. Our observations support the hypothesis that increasing deoxygenation of the oceans will likely enhance sedimentary TPO43- and Fe2+ release and thus contribute to a positive feedback mechanism with increasing nutrient levels and increased ocean productivity.

The impact of declining oxygen conditions on pyrite accumulation in shelf sediments (Baltic Sea)

Deterioration of oxygen conditions in water below the halocline has been observed in the Baltic Sea. Deoxygenation is linked to the reduced frequency and volume of inflows of highly saline surface water from the North Sea (major Baltic inflows—MBIs) in the second half of the twentieth century and the increased organic matter respiration due to eutrophication. In the present study, the impact of worsening oxygen conditions on pyrite content in the Gdańsk Deep (max. depth of 118 m, southern Baltic Sea) sediments was determined. Geochemical parameters (acid volatile sulfides, pyrite sulfur, reactive iron, organic carbon, sedimentation rate and sediment age) were analyzed in relation to the variation in bottom water oxygen concentration and the occurrence of MBI. The obtained results demonstrate that pyrite content in the study area decreased after 1960. The declining pyrite content coincided with the deterioration of oxygen conditions (concentration < 2 ml l−1) in bottom water. In the same period, reactive iron concentration decreased and organic carbon increased in sediment. In the period 1616–1960, average pyrite accumulation rate was 322 µmol m−2 day−1. In the subsequent years, its average accumulation rate decreased to 210 µmol m−2 day−1. Fluctuations of oxygenation of bottom water in the study area were manifested by highly variable degree of pyritization (36 ± 11%) and particulate organic carbon to pyrite sulfur ratio (2.8–37).

Deep-sea ostracod faunal dynamics in a marginal sea: biotic response to oxygen variability and mid-Pleistocene global changes

AbstractDeep-sea benthic ostracod assemblages covering the last 2 Myr were investigated in Integrated Ocean Drilling Program Site U1426 (at 903 m water depth) in the southern Sea of Japan. Results show that (1) orbital-scale faunal variability has been influenced by eustatic sea-level fluctuations and oxygen variability and (2) secular-scale faunal transitions are likely associated with the mid-Brunhes event (MBE, ~0.43 Ma) and the onset of the Tsushima Warm Current (TWC, ~1.7 Ma).Krithe,Robertsonites, andAcanthocythereisare the three most abundant genera throughout the core, accounting for 78.5% of total specimens. Multiple-regression tree analysis indicated that the TWC, the MBE, and oxygen content are the significant controlling factors of ostracod dominance. Changes in assemblages exhibit decline and recovery patterns corresponding to orbital-scale cyclicity of sea-level changes. In the Sea of Japan marginal ocean setting, this cyclicity shows a close relationship with bottom-water oxygen variability since the onset of the TWC influx. The MBE amplified the influence of the TWC and oxygen variability to the deep-sea ecosystem through larger sea-level fluctuations.Acanthocythereis dunelmensis, a circumpolar species, dominates before the TWC onset. After the TWC onset and during the mid-Pleistocene transition (MPT, ~1.2–0.7 Ma)Krithespp., known for their low-oxygen tolerance, substantially increase under moderate oxygen depletion. At the end of the MPT,Krithedominance diminishes and is replaced byRobertsonites hanaiiandPropontocyprisspp. after the MBE. The post-MBE assemblage, characterized byR. hanaii, suggests a slightly warmer environment under the development of the TWC. In addition, the post-MBE high-amplitude climate system may have caused the increased abundance of active-swimmingPropontocyprisspp. due to their superior migration ability. Benthic ecosystems in marginal seas are sensitive and vulnerable to both short- and long-term climatic changes, and the MBE is suggested to be a global biotic event affecting benthic ecosystems substantially.