High Organic Carbon Accumulation Research Articles

Biotic response of plankton communities to Middle to Late Miocene monsoon wind and nutrient flux changes in the Oman margin upwelling zone

Abstract. Understanding past dynamics of upwelling cells is an important aspect of assessing potential upwelling changes in future climate change scenarios. Our present understanding of nutrient fluxes throughout the world's oceans emphasizes the importance of intermediate waters transporting nutrients from the Antarctic divergence into the middle and lower latitudes. These nutrient-rich waters fuel productivity within wind-driven upwelling cells in all major oceans. One such upwelling system is located along the Oman margin in the western Arabian Sea (WAS). Driven by cross-hemispheric winds, the WAS upwelling zone's intense productivity led to the formation of one of the most extensive oxygen minimum zones known today. In this study covering the Middle to Late Miocene at Ocean Drilling Program (ODP) Site 722, we investigate the inception of upwelling-derived primary productivity. This study presents new plankton assemblage data in the context of existing model- and data-based evidence constraining the tectonic and atmospheric boundary conditions for upwelling in the WAS. With this research, we build upon the original planktonic foraminifer-based research by Dick Kroon in 1991 as part of his research based on the ODP LEG 117. We show that monsoonal winds likely sustained upwelling since the emergence of the Arabian Peninsula after the Miocene Climatic Optimum (MCO) ∼ 14.7 Ma, with fully monsoonal conditions occurring since the end of the Middle Miocene Climatic Transition (MMCT) at ∼ 13 Ma. However, changing nutrient fluxes through Antarctic Intermediate and sub-Antarctic Mode Waters (AAIW/SAMW) were only established after ∼ 12 Ma. Rare occurrences of diatom frustules correspond to the maximum abundances of Reticulofenestra haqii and Reticulofenestra antarctica, indicating higher upwelling-derived nutrient levels. By 11 Ma, diatom abundance increases significantly, leading to alternating diatom blooms and high-nutrient-adapted nannoplankton taxa. These changes in primary producers are also well reflected in geochemical proxies with increasing δ15Norg. values (> 6 ‰) and high organic carbon accumulation. These proxies provide further independent evidence for high productivity and the onset of denitrification simultaneously. Our multi-proxy-based evaluation of Site 722 primary producers provides evidence for a stepwise evolution of Middle to Late Miocene productivity in the western Arabian Sea for the first time. The absence of a clear correlation with existing deep marine climate records suggests that both local wind patterns and intermediate water nutrient changes likely modulated productivity in the western Arabian Sea during the Middle to Late Miocene. Finally, we show that using a multi-proxy record provides novel insights into how plankton responded to changing nutrient conditions through time in a monsoon-wind-driven upwelling zone.

Unexpected high alkyl carbon contents in organic matter-rich sandy agricultural soils of Northwest Central Europe

Carbon sequestration in Plaggic Anthrosols is most often investigated by bulk soil carbon inventories, without considering the form in which the carbon is stored (e.g., particulate or mineral-associated organic matter (OM), its capacity, or its chemical composition). Here, we focus on the unusual high organic carbon (OC) accumulation in sandy Plaggic Anthrosols and adjacent reference soils under agricultural use. In these soils, the mineral fraction ≤20 µm which is commonly assumed to be the major factor for OC stabilization, are very low in mass proportion. Soil organic matter (SOM) physical fractionation was done to evaluate the quantity and quality of OC in the topsoil (Ap horizon). For the fraction ≤20 µm (medium and fine silt-, and clay-sized particles), we measured the concentration of OC and calculated its OC storage capacity and contribution. The OC of the fraction ≤20 µm was radiocarbon-dated and analyzed for its chemical composition by solid-state 13C NMR spectroscopy. The highly sandy (∼90 % sand and coarse silt) soils showed an accumulation of OC much higher than the conventionally calculated saturation level controlled by the proportion of the fraction ≤20 µm. Unexpectedly, Plaggic Anthrosols and the respective reference soils showed similar fractional OC concentrations, radiocarbon ages, and OM composition. The isolated fraction ≤20 µm contained, on average, 81 % of the total soil OC in only 9 % of the corresponding soil mass. All soil fractions ≤20 µm are characterized by a high mean OC concentration in the topsoil (reference soils: 226 ± 66.5 mg OC g−1, Plaggic Anthrosols: 202 ± 59.0 mg OC g−1) with a C/N ratio of 15 on average for both soils. The OM composition of the fraction ≤20 µm was specifically rich in alkyl-C, with unusually low proportions of O-alkyl-C and low contents of aryl-C. The radiocarbon concentration (F14C) indicated that topsoil OM of the ≤20 µm fraction is stored for long time periods with high mean conventional radiocarbon ages (14C) not only for Plaggic Anthrosols (F14C: 0.92 ± 0.04; 14C: 639 yBP) but also for the reference soils (F14C: 0.93 ± 0.04; 14C: 575 yBP) and received low inputs of OC derived from recent photosynthesis. Our data indicate the existence of specific SOM accumulation processes in the investigated sandy agricultural soils, resulting particularly large SOM stocks which cannot be explained by mechanistic association of OM with mineral surfaces. It is not clear, if this inherited OM is stable under present-day soil and management conditions.

The high organic carbon accumulation in estuarine wetlands necessarily does not represent a high CO2 sequestration capacity

Estuarine wetlands with high organic carbon (OC) accumulation rates due to their high plant biomass and interception of tide-derived OC are generally considered as large CO2 sinks. However, our previous study found that tidal OC input seems to stimulate soil CO2 emissions, potentially weakening CO2 sequestration in estuarine wetlands. To further verify this phenomenon, we first established a structural equation model, which confirmed a positive correlation between tidal OC input and soil organic carbon (SOC) and soil respiration. We then performed trace analysis to determine the stability of SOC derived from different sources and its effect on soil CO2 emissions by analyzing the input and retention of OC derived from tides and plants in the Yangtze Estuary wetlands. From upstream to downstream, as tidal OC input decreased, the relative retention ratio of the tidal OC in wetland soil increased from 1.259 to 2.148, whereas the relative retention ratio of plant OC in the soil decreased from 61.5% to 14.8%. Our findings indicated that the degradability of tidal OC was higher upstream than that downstream, but both inhibited plant OC degradation, thus providing an important reason for the higher CO2 emissions upstream of wetlands (with higher tidal OC input). In addition, the primarily contributor to CO2 (δ13) emissions’ transforming from plant SOC (81.35%) to tidal SOC (91.18%) was an increase in organic matter input from the tide in a microcosm system. Consequently, a higher CO2 output than CO2 input (plant OC) due to the ready degradation of tidal OC consequently weakens the CO2 sequestration capacity of the estuarine wetlands. This phenomenon is cause for concern regarding the CO2 sink function of estuarine wetlands intercepting large amounts of organic matter.

Soils, Geoenvironments and Ecosystem Services of a Protected Area in Western Brazilian Amazonia.

The Serra do Divisor National Park (SDNP) in the Westernmost Brazilian Amazonia possesses unique Mountain landscapes of sub-andean nature, with high geo-biodiversity and pristine environments, with a potential high contribution in ecosystems services. We studied and mapped the basic geo-environmental units of the main sector of the Park, evaluating soil carbon stocks as a key ecosystem service provided by the Protected Area. For the identification, characterization and mapping of the geoenvironmental units, we integrated pedological, geomorphological and vegetation data obtained by local soil survey and field campaigns, as well as secondary data. Eight geoenvironmental units were identified and mapped, distributed in three main compartments: the Serra do Divisor (SD) the upper Moa River and the medium Moa River. This region presents similar environments to the sub-Andean region, notably the Ceja Forest at the top surface of the SD. Soils at the SD have high organic carbon accumulation, with close association with the nutrient-poor, quartz-rich rocks, and shows organic matter illuviation indicating active podzolization. The SDNP encompasses important ecosystems and services linked with high geo-biodiversity, and high soil carbon stocks, representing a new frontier for scientific research in the only area of transitional sub-andean forested landscape in Brazil.

The High Organic Carbon Accumulation in Estuarine Wetlands Necessarily Does Not Represent a High Co2 Sequestration Capacity

The High Organic Carbon Accumulation in Estuarine Wetlands Necessarily Does Not Represent a High Co2 Sequestration Capacity

Evidence for high organic carbon export to the early Cambrian seafloor

Oxygenation of the early Cambrian ocean is commonly ascribed to high organic export to the sediment due to the rise of algae and filter-feeding animals, but direct evidence of elevated export fluxes has been lacking to date. Here, we report an integrated proxy dataset (U-Mo isotopes, Fe speciation, and major and trace elements) for lower Cambrian black shales at Yuanjia on the Yangtze Platform (South China). These shales are characterized by high iron speciation ratios and Mo and U enrichments, indicating persistently euxinic water conditions during their deposition, but a broad range of δ98Mo values (−0.10‰ to +1.94‰) implies strongly variable watermass sulfidity. High and variable nutrient element (Cu, Zn, Ni, Cd) enrichments at Yuanjia are consistent with elevated and variable organic productivity and export fluxes from the euphotic zone to the early Cambrian seafloor. The Yuanjia shales also exhibit super-heavy δ238U values (to +0.84‰) that cannot be explained by U reduction in sediment porewaters. We hypothesize that these values record a U reduction process within the water column, where U isotope fractionation can be much larger than in sediment porewaters. Such processes may have operated within a benthic organic flocculent layer at the sediment-water interface, a feature that is characteristic of high productivity systems with anoxic bottom waters. Furthermore, the coupling between δ238U, nutrient elements, and δ98Mo suggests that elevated productivity levels were driven likely by episodic upwelling in early Cambrian oceans, supplying abundant nutrients for productivity and influencing H2S concentrations in the water column. These observations, along with high organic carbon accumulation rates (5600 mg cm−2 kyr−1), are direct evidence of high organic export fluxes to the early Cambrian seafloor, thus providing key support for the hypothesis that enhanced organic export and burial triggered a major atmospheric-oceanic oxygenation event that stimulated the subsequent explosion of Cambrian life.

Integrated co-cultured bacterial strains capabilities to aqueous sulfide and chemical oxygen demand mitigation from high-strength petroleum refinery wastewater

The heterogeneous nature of petroleum refinery based wastewater (PRW) couple with the documented paucity of the classical physicochemical mitigation approaches were behind the quest for a cost-effective and ecofriendly alternative with minimum negative effects. The toxic and inhibitory substances contained in PRW have made its treatment strenuous using a simple pure culture. A novel integrated bacterial mixed culture (BMC), Pseudomonas putida (ATCC 49128) and Bacillus cereus (ATCC 14579) with traceable imprints in biodegradation of high-strength PRW was proposed as a suitable alternative for sulfide oxidation and COD reduction with a potential alternative to classical physicochemical mitigation approaches. Comparative biodegradation potential of two acclaimed bacteria mixed-culture regimen was evaluated. The degree of inhibition cast was assessed based on the effectiveness of BMC to remove the targeted compounds (aqueous hydrogen sulfide and COD) within the assigned period of 8 hours hydraulic retention time (HRT). The PRW was found to contained initial concentration of 8,155 ppm COD, and 500 ppm sulfide, coupled with other refractory substances. The experiment was repeated batch-wise under defined optimal conditions of 0.25 L/min O2, the temperature of 30oC, agitation of 140 rpm at 8 hours retention time. The results obtained indicated 97.47±1.7 % (mg/L) COD reduction and 99.75±1.8 (ppm) sulfide removal efficiency (RE). In addition, the SEM analysis revealed further the potential of BMC to degrade sulfide from PRW to economically feasible elemental sulfur species, while EDXS demonstrated a proportionate elemental composition revealing appreciable sulfur content and high organic carbon accumulation. Despite the expected toxicity and inhibitory effect of the medium, an overwhelming biodegradation was achieved disproportionately, hence the model can be suggested for further research of repulsive wastewaters.Keywords: Biodegradation, petroleum refinery wastewater, mixed-culture, Batch culture

Origin and fate of sedimentary organic matter in the northern Bay of Bengal during the last 18 ka

The Northern Bay of Bengal (NBoB) is a globally important region for deep-sea organic matter (OM) deposition due to massive fluvial discharge from the Ganges-Brahmaputra-Meghna (G-B-M) rivers and moderate to high surface productivity. Previous studies have focused on carbon burial in turbiditic sediments of the Bengal Fan. However, little is known about the storage of carbon in pelagic and hemipelagic sediments of the Bay of Bengal over millennial time scales. This study presents a comprehensive history of OM origin and fate as well as a quantification of carbon sediment storage in the Eastern Bengal Slope (EBS) during the last 18ka. Bulk organic proxies (TOC, TIC, TN, δ13CTOC, δ15NTN) and content and composition of total hydrolysable amino acids (THAA) in a sediment core (SO188-342KL) from the EBS were analyzed. Three periods of high OM accumulation were identified: the Late Glacial (LG), the Bölling/Alleröd (B/A), and the Early Holocene Climatic Optimum (EHCO). Lower eustatic sea level before 15ka BP allowed a closer connection between the EBS and the fluvial debouch, favoring high terrestrial OM input to the core site. This connection was progressively lost between 15 and 7ka BP as sea level rose to its present height and terrestrial OM input decreased considerably. Export and preservation of marine OM was stimulated during periods of summer monsoon intensification (B/A and EHCO) as a consequence of higher surface productivity enhanced by cyclonic-eddy nutrient pumping and fluvial nutrient delivery into the photic zone. Changes in the THAA composition indicate that the marine plankton community structure shifted from calcareous-dominated before 13ka BP to siliceous-dominated afterwards. They also indicate that the relative proportion of marine versus terrestrial OM deposited at site 342KL was primarily driven by relative sea level and enlarged during the Holocene. The ballasting effect of lithogenic particles during periods of high coastal proximity and/or enhanced fluvial discharge promoted the export and preservation of OM. The high organic carbon accumulation rates in the EBS during the LG (18–17ka BP) were 5-fold higher than at present and comparable to those of glacial upwelling areas. Despite the differences in sediment and OM transport and storage among the Western and Eastern sectors of the NBoB, this region remains important for global carbon sequestration during sea level low-stands. In addition, the summer monsoon was a key promotor of terrestrial and marine OM export to the deep-ocean, highlighting its relevance as regulator of the global carbon budget.

Role of alternating redox conditions in the formation of organic-rich interval in the Middle Devonian Marcellus Shale, Appalachian Basin, USA

Geochemical, isotopic and petrographic analyses were performed on a 30-m core of the Marcellus Shale obtained from Greene County, Pennsylvania, to understand the dominant controls on organic matter deposition in the black shale study units. Our study suggests that the regeneration of nutrients, such as nitrogen (N) and phosphorous (P), may have played a key role in the formation of organic carbon (OC)-rich intervals in the Marcellus Shale. The decomposition of organic matter is likely to have released N and P into the water column, and the episodic upward mixing of these nutrient-enriched waters enhanced primary production. The ratios of Corg/Nbulk and Corg/Ptot are significantly higher in the OC-rich zone of the core (i.e., defined as TOC>4% and located between 2393 and 2406.5m depth). The high Corg/Ptot and Corg/Nbulk ratios of the preserved organic matter may reflect the release of N and P by microbial processes, indicating the recycling of nutrients during deposition of the OC-rich interval. In addition, our data show a positive relationships between the Corg/Ptot and Corg/Nbulk ratios and the organic carbon content, which indicate that the recycled nutrients may have promoted primary productivity, resulting in higher OC accumulation in some intervals. The geochemical and stable isotopic results also suggest that the alternating redox conditions in the water mass were favorable for nutrient regeneration. Highly variable trace metal concentrations (e.g., U, Mo, and V) in the OC-rich zone and a wide range of δ15N and δ34Spyr values towards the top of the OC-rich zone suggest fluctuations between anoxic and suboxic water conditions. Finally, sedimentary features and agglutinated benthic foraminifera in the OC-rich zone support the existence of short-term fluctuations between suboxic and anoxic conditions near the sediment–water interface. Multiple lines of evidence suggest that nutrient regeneration due to alternating redox conditions may have played an important role in the formation of OC-rich intervals in the Marcellus Shale.

Seasonal Dynamics of Soil Labile Organic Carbon and Enzyme Activities in Relation to Vegetation Types in Hangzhou Bay Tidal Flat Wetland.

Soil labile organic carbon and soil enzymes play important roles in the carbon cycle of coastal wetlands that have high organic carbon accumulation rates. Soils under three vegetations (Phragmites australis, Spartina alterniflora, and Scirpusm mariqueter) as well as bare mudflat in Hangzhou Bay wetland of China were collected seasonally. Seasonal dynamics and correlations of soil labile organic carbon fractions and soil enzyme activities were analyzed. The results showed that there were significant differences among vegetation types in the contents of soil organic carbon (SOC) and dissolved organic carbon (DOC), excepting for that of microbial biomass carbon (MBC). The P. australis soil was with the highest content of both SOC (7.86 g kg-1) and DOC (306 mg kg-1), while the S. mariqueter soil was with the lowest content of SOC (6.83 g kg-1), and the bare mudflat was with the lowest content of DOC (270 mg kg-1). Soil enzyme activities were significantly different among vegetation types except for urease. The P. australis had the highest annual average activity of alkaline phosphomonoesterase (21.4 mg kg-1 h-1), and the S. alterniflora had the highest annual average activities of β-glycosidase (4.10 mg kg-1 h-1) and invertase (9.81mg g-1 24h-1); however, the bare mudflat had the lowest activities of alkaline phosphomonoesterase (16.2 mg kg-1 h-1), β-glycosidase (2.87 mg kg-1 h-1), and invertase (8.02 mg g-1 24h-1). Analysis also showed that the soil labile organic carbon fractions and soil enzyme activities had distinct seasonal dynamics. In addition, the soil MBC content was significantly correlated with the activities of urease and β-glucosidase. The DOC content was significantly correlated with the activities of urease, alkaline phosphomonoesterase, and invertase. The results indicated that vegetation type is an important factor influencing the spatial-temporal variation of soil enzyme activities and labile organic carbon in coastal wetlands.

Soil microbiological variability under different successional stages of the Chongming Dongtan wetland and its effect on soil organic carbon storage

Estuarine wetlands undergoing rapid succession have high organic carbon accumulation rates due to their high primary productivity. A previous study indicated that organic carbon storage in soil differed among successional stages of the Chongming Dongtan tidal wetland due to differences in soil microbial respiration (SMR) and plant biomass. To investigate the mechanisms underlying the differences in SMR, variability in microbial and physicochemical characteristics of soil from different successional stages was studied. Bacterial community composition varied among the successional stages. Some dominant and site-specific bacteria inhabiting the tidal flat may have influenced SMR and soil carbon storage capability. Uncultured members of the Cytophagales and Pseudomonas genera, which include efficient degraders of complex organic compounds, were found primarily in the high tidal flat where the highest SMR and relatively low soil organic carbon storage were observed. Soil environment factors such as particle size, salinity, and total nitrogen (TN) may have affected microbial community composition, in particular the dominant bacterial species, and hence, SMR. The relatively small particle size, low salinity, and high TN in the high tidal flat provided suitable conditions for chemoorganotrophic bacteria such as Cytophagales and Pseudomonas species, which are specialized in the degradation of organic matter.

Seasonal export fluxes of particulate organic carbon from 234Th/238U disequilibrium measurements in the Ulleung Basin1 (Tsushima Basin) of the East Sea1 (Sea of Japan)

Export fluxes of particulate organic carbon (POC) were estimated from the 234Th/238U disequilibrium in the Ulleung Basin1 (UB) of the East/Japan Sea1 (EJS) over four seasons. The fluxes were calculated by multiplying the average POC/234Th ratio of sinking particles larger than 0.7 μm at 100- and 200-m water depths to 234Th fluxes by the integrated 234Th/238U disequilibrium from the surface to 100-m water depth. In spring, the 234Th profiles changed dramatically with sampling time, and hence a non-steady-state 234Th model was used to estimate the 234Th fluxes. The 234Th flux estimated from the non-steady-state model was an order of magnitude higher than that estimated from the steady-state model. The 234Th fluxes estimated using the steady-state model showed distinct seasonal variation, with high values in summer and winter and low values in autumn. In spring, the phytoplankton biomass had the highest value, and primary production was higher than in summer and autumn, but the 234Th fluxes were moderate. However, these values might have been significantly underestimated, as the 234Th fluxes were estimated using the steady-state model. The POC export fluxes estimated in autumn were about four times lower than those in other seasons when they were rather similar. The annually averaged POC flux was estimated to be 161 ± 76 mgC m−2 day−1, which was somewhat lower than that in highly productive coastal areas, and higher than that in oligotrophic regions. The export/primary production (ThE) ratios ranged from 7.0 to 56.1%, with higher values in spring and summer and lower values in autumn and winter. In summer, a high ThE ratio of 48.4 ± 7.0% was measured. This may be attributed to the mass diatom sinking event following nitrate depletion. In the UB1, the annually averaged ThE ratio was estimated to be 34.4 ± 12.9%, much higher than that in oligotrophic oceans. The high ThE ratio may have contributed to the high organic carbon accumulation in the UB1.

Oxygen and carbon isotope analysis of the Mooreville Chalk and late Santonian-early Campanian sea level and sea surface temperature changes, northeastern Gulf of Mexico, U.S.A.

Oxygen and carbon isotope profiles for strata of the Mooreville Chalk (upper Santonian-lower Campanian) of the eastern Gulf Coastal Plain, U.S.A., show correlations with published curves for these isotopes. The δ 18O curve exhibits a strong similarity to the Exmouth Plateau δ 18O curve from ODP drilling sites offshore northwestern Australia, and the δ 13C curve can be correlated with the δ 13C curve from the English Chalk Trunch section. A thermal maximum probably occurred in the northeastern Gulf of Mexico during the latest Santonian (∼83.8 Ma), as evidenced by the minimum δ 18O values in the lower Mooreville beds. A δ 13C positive excursion occurs at the same stratigraphic level, which has been recognized as the “Santonian/Campanian boundary event” worldwide. After this event, ocean surface water temperature decreased throughout the early Campanian. This carbon isotope excursion is followed by a plateau in δ 13C values with a peak value occurring in a condensed section (∼80 Ma), which has been correlated to a downlap or maximum flooding surface on seismic data from offshore Alabama. The section characterized by increasing δ 13C values corresponds to a marine transgression. The interval characterized by decreasing δ 13C values corresponds to regression and progradation. The maximum flooding event occurred ∼0.8 Ma later than the thermal maximum event. The Mooreville chalk/marl cycles are most likely a product of fluctuations in siliciclastic sediment influx into the northeastern Gulf of Mexico modulated by the precession band of the Earth's orbital cycles. Higher carbon isotope values occur in the marl beds indicating that these beds were formed in a more anoxic/dysoxic environment characterized by higher clay, silt input and higher organic carbon accumulation.

Surface water productivity and paleoceanographic implications in the Cenozoic Arctic Ocean

Study of bulk nitrogen contents and isotopic composition in Arctic Ocean sequences (Integrated Ocean Drilling Program Expedition 302) over the past 60 Ma revealed changes in the export flux and sources of sedimentary nitrogen. The paleoproductivity calculated from the fraction of organic nitrogen to total nitrogen is distinctly lower (<20 g C m−2 a−1) during the ice‐covered Neogene compared to the ice‐free, warm, and biologically active early Paleogene (∼50–100 g C m−2 a−1). Nitrogen isotope measurements from late Paleocene to early Eocene sediments provide evidence for a stepwise stratification and nutrient depletion in surface water masses. Cyanobacterial nitrogen fixation appeared to be the main source of nutrient N in the Arctic Ocean during the early‐middle Eocene characterized by conditions of strong oxygen depletion, high nutrient N losses, and high organic carbon accumulation rates. We speculate that biological CO2 sequestration in the Arctic Ocean and enhanced organic carbon burial rates may have contributed to lower atmospheric CO2 subsequent to the early Eocene climate optimum.

Organic carbon accumulation and sulfate reduction rates in slope and basin sediments of the Ulleung Basin, East/Japan Sea

This study investigated the organic carbon accumulation rates (OCARs) and sulfate reduction rates (SRRs) in slope and basin sediments of the Ulleung Basin, East/Japan Sea. These sediments have high organic contents at depths greater than 2,000 m; this is rare for deep-sea sediments, except for those of the Black Sea and Chilean upwelling regions. The mean organic carbon to total nitrogen molar ratio was estimated to be 6.98 in the Ulleung Basin sediments, indicating that the organic matter is predominantly of marine origin. Strong organic carbon enrichment in the Ulleung Basin appears to result from high export production, and low dilution by inputs of terrestrial materials and calcium carbonate. Apparent sedimentation rates, calculated primarily from excess 210Pb distribution below the zone of sediment mixing, varied from 0.033 to 0.116 cm year−1, agreeing well with previous results for the basin. OCARs fluctuated strongly in the range of 2.06–12.5 g C m−2 year−1, these rates being four times higher at the slope sites than at the basin sites. Within the top 15 cm of the sediment, the integrated SRRs ranged from 0.72 to 1.89 mmol m−2 day−1, with rates approximately twice as high in the slope areas as in the basin areas. SRR values were consistently higher in areas of high sedimentation and of high organic carbon accumulation, correlating well with apparent sedimentation rates and OCARs. The sulfate reduction rates recorded in the basin and slope sediments of the Ulleung Basin are higher than those reported for other parts of the world, with the exception of the Peruvian and Chilean upwelling regions. This is consistent with the high organic carbon contents of surface sediments of the Ulleung Basin, suggesting enhanced organic matter fluxes.

Palaeoenvironmental information gained from calcareous dinoflagellates: the late Quaternary eastern and western tropical Atlantic Ocean in comparison

The environmental preferences of calcareous dinoflagellates have been investigated over the last 140 ka by comparing material from two sediment cores: one from the highly productive equatorial divergence of the eastern Atlantic Ocean and the other from the low productivity western tropical Atlantic Ocean. Pronounced differences in palaeoproductivity between the two sediment cores are indicated by high and variable organic carbon accumulation rates in the east, in contrast to relatively constant and low values in the west. Calcareous dinoflagellates show just the opposite pattern: high accumulation rates in the west and lower in the east. At the equatorial divergence, temporal variations of calcareous dinoflagellate and organic carbon accumulation rates show, for the most part, an inverse relationship. High calcareous dinoflagellate content coincides with low organic carbon accumulation rates and vice versa. In the investigated region and time interval, enhanced production of calcareous dinoflagellates can be correlated to periods of reduced palaeoproductivity probably related to relatively stratified conditions of the upper water column.

Sampling the oxygen minimum zone off Pakistan: glacial-interglacial variations of anoxia and productivity (preliminary results, sonne 90 cruise)

During cruise sonne 90 the well developed oxygen minimum zone (OMZ) in the northeastern Arabian Sea was sampled in great detail to study surface ocean productivity and organic carbon accumulation/preservation during the last hundred to hundred thousands of years. Nearly anoxic conditions on and below the seafloor are indicated by the lack of macrobenthos and nekton, absence of bioturbation, high marine organic carbon accumulation and preservation of laminated sediments between about 300 and 1000 m water depth on the steep continental slope. This pattern approximately coincides with the zone of extremely low O 2 concentrations presently observed in the water column. Accumulation of organic material on the deeper slope near the lower boundary of the OMZ is enhanced by downslope transport. Downcore we observe a complex alternation of dark-colored, laminated, and light-colored, homogeneous facies. In general, laminated, organic carbon-rich intervals were deposited under suboxic bottom water and enhanced productivity conditions, mainly during warm stages (e.g., Bölling/Alleröd and Holocene from 8000 yrs B.P. to Recent). The homogeneous, bioturbated intervals indicate normal bottom water oxygen levels and reduced productivity during or just after cold stages (e.g. Terminations IA and B, and Younger Dryas). The striking facies similarities of the sedimentary record in cores collected from different areas and water depths suggest a unique pattern of late Pleistocene C org accumulation in the northeastern Arabian Sea which depends mainly on regional surface ocean productivity and intermediate water oxygenation. However, the sedimentary record is also influenced by variations in sediment supply from the Makran and Karachi shelf and from Indus River discharge during rapid sea-level changes.

Low organic carbon accumulation rates in Black Sea sediments

THE Black Sea, the world's largest anoxic marine basin, is frequently used as a modern analogue for the formation of organic-rich sediments and carbonaceous rocks1–3, on the widely held assumption that anoxic conditions promote the preferential preservation of organic matter in sediments. Data for testing this hypothesis have so far been equivocal4–7, but here we use radiocarbon ages obtained using accelerator mass spectrometry for the organic fraction of recent Black Sea sediments to estimate the organic carbon accumulation rates. These range from 0.69 to 2.09 g C m−2 yr−1 and are significantly lower than earlier estimates based on varve counting6. Depending on the value taken for the rate of primary production in the Black Sea4,8, between 0.7 and 2.1% of the organic carbon is preserved in the bottom sediments. When compared with carbon accumulation rates in equivalent oxygenated environments9, these results indicate that the modern Black Sea is not a site of anomalously high organic carbon accumulation. This suggests that anoxic conditions in the water column may not be a prerequisite for the preservation of organic matter in marine sediments, and that models of the origin of carbonaceous facies in the geological record may therefore need to be modified.

Faunal fluctuations related to oceanographical changes in the Vocontian Basin (S-E France) during Aptian-Albian Time

Planktonic foraminifera and ammonites containedin mid-Cretaceous sediments of the blue marls Formation of the Vocontian basin (S-E France) display a marked evolution in populations from the base to the top of the series. Planktonic foraminifera undergo a positive shift in their production, diversity, size and morphology: from only primitive minute globular forms of “shallow water” present in poor associations to well developped keeled forms of “deep water” dwelling that complete rich associations. Ammonite fauna displays an important increase of cosmopolitan forms at the expense of tethyan ones. Such a pattern is to be parallelized with the general mid-Cretaceous sea level rise. Beside this broad trend, small scale fluctuations of shorter duration occur; they result from changes in oceanographic parameters. Peculiarly, the fauna provide some elements that allow to characterize to a certain extent the conditions of settling of the different horizons deposited at the time of high organic carbon accumulation. Consideration of benthic organisms helps in deciphering environmental conditions of bottom water oxygenation. So moderately organic carbon-rich horizons may be interpreted as corresponding to a marked decrease in dissolved oxygen of the water column (hypoxia) that affects both pelagic and benthic biota. This may be a consequence of the weakness of convective water movement. The well laminated horizons, rich in organic matter, present a variety of characters. The general lack of benthic fauna may be ascribed to a density stratification of water mass, and a consecutive anoxia, but due to specific patterns, the plankton production may be enhanced as for the Paquier event (Lower Albian) or on the contrary strongly inhibited as for the Goguel event (upper part of the Lower Aptian). Furthermore a single model is not reliable to explain all cases of anoxia generation.

Upwelling in Cretaceous Western Interior Seaway: Sharon Springs Member, Pierre Shale: ABSTRACT

Upwelling zones are characterized by the following features: (1) facies distribution, which is related to oxygenation of bottom waters, of laminated, organic-rich sediment, phosphate, and glauconite; (2) abundant organic-rich fecal pellets; (3) abundant marine biota at all trophic levels; (4) high organic carbon accumulation rates, with predominance of marine organic matter; and (5) a distribution of the anoxic facies that is not controlled by bathymetry. By contrast, stratified stagnant basins characteristically (1) lack significant phosphate; (2) show little or no evidence of high biologic productivity; (3) have high organic carbon accumulation rates with significant influx of terrestrial organic matter; and (4) have an anoxic facies that is confined to the deepest part of the basin. The Sharon Springs Member of the Pierre Shale, usually described as a stagnant-basin deposit, shares more features in common with upwelling zones than with stratified stagnant basins. Specifically, the overall facies distribution of the Sharon Springs includes a basinward zone of laminated, highly organic-rich strata bounded on the west by phosphate, which is, in turn, bounded at the western shoreline by glauconitic sandstone. The same facies distribution might be expected on the eastern shoreline, but the Sharon Springs is truncated there by erosion. The organicmore » matter in the Sharon springs is almost entirely contained in fecal pellets and is predominantly marine in origin, organic carbon accumulation rates are comparable to those of upwelling zones. Finally, the Sharon Springs is noted for high concentrations of bones of marine reptiles. These bones occur in a band that may mark the zone of highest biologic productivity.« less