scholarly journals Neodymium Isotopes in Glauconite for Palaeoceanographic Reconstructions at Continental Margins: A Preliminary Investigation From Demerara Rise

2021 ◽  
Vol 9 ◽  
Author(s):  
Pierre Giresse ◽  
Germain Bayon ◽  
Cedric Tallobre ◽  
Lies Loncke
Keyword(s):  
Water Depth ◽  
Bottom Water ◽  
French Guiana ◽  
Preliminary Investigation ◽  
Water Circulation ◽  
Continental Margins ◽  
Isotopic Signatures ◽  
Neodymium Isotopes ◽  
Isotopic Compositions ◽  
Sediment Redistribution

Contourite sediment accumulations at continental margins are related to strong bottom water circulation, where intense winnowing can result in neoformation of authigenic grains of glauconite at the seafloor. In this study, we investigated whether such glauconite grains could faithfully record ambient bottom-water neodymium (Nd) isotopic compositions, and hence be used as paleoceanographic archives. To this purpose, we measured Nd isotopic compositions (εNd) in a series of glauconitic grains, foraminiferal assemblages, leached Fe-Mn oxyhydroxide phases, and detrital clays separated from a contourite sediment record at the Demerara slope off French Guiana (IG-KSF-11; 2370 m water depth), at a location where the present-day εNd distribution along the water column is well characterised. We show that the εNd composition of core-top glauconite grains (−12.0 ± 0.5) agrees with the expected NADW-like seawater signature at the same location and water depth (−11.6 ± 0.3), while departing from measured εNd values for corresponding detrital clays (−11.3 ± 0.2), foraminiferal (−10.9 ± 0.2), and Fe-Mn oxyhydroxide fractions (−9.2 ± 0.2). This finding indicates that glauconitic grains at this particular location are probably best suited for paleoceanographic reconstructions than foraminifera and leached Fe-oxyhydroxide fractions, which appear to be influenced by sediment redistribution and the presence of terrestrial continental Fe-oxides, respectively. Using rare earth elements (REE), we tentatively propose that the acquisition of seawater Nd isotopic signatures by glauconite is controlled by the presence of authigenic REE-bearing phosphate-rich phases intertwined within clay mineral sheets, while confirming previous findings that the process of glauconitisation results in the progressive loss of REE within glauconitic grains. Preliminary paleoceanographic implications suggest strengthened bottom-water circulation of the glacial analogue of NADW at this particular location and water depth, with a εNd signature (between −10.8 and −11.5) similar to that of modern NADW.

scholarly journals Trophic state of benthic deep-sea ecosystems from two different continental margins off Iberia

2013 ◽  
Vol 10 (5) ◽  
pp. 2945-2957 ◽  
Author(s):  
A. Dell'Anno ◽  
A. Pusceddu ◽  
C. Corinaldesi ◽  
M. Canals ◽  
S. Heussner ◽  
...  
Keyword(s):  
Organic Matter ◽  
Water Depth ◽  
Surface Waters ◽  
Deep Sea ◽  
Nutritional Value ◽  
Trophic State ◽  
Phytoplankton Bloom ◽  
Continental Margins ◽  
Organic C ◽  
Deep Sea Sediments

Abstract. The bioavailability of organic matter in benthic deep-sea ecosystems, commonly used to define their trophic state, can greatly influence key ecological processes such as biomass production and nutrient cycling. Here, we assess the trophic state of deep-sea sediments from open slopes and canyons of the Catalan (NW Mediterranean) and Portuguese (NE Atlantic) continental margins, offshore east and west Iberia, respectively, by using a biomimetic approach based on enzymatic digestion of protein and carbohydrate pools. Patterns of sediment trophic state were analyzed in relation to increasing water depth, including repeated samplings over a 3 yr period in the Catalan margin. Two out of the three sampling periods occurred a few months after dense shelf water cascading events. The benthic deep-sea ecosystems investigated in this study were characterized by high amounts of bioavailable organic matter when compared to other deep-sea sediments. Bioavailable organic matter and its nutritional value were significantly higher in the Portuguese margin than in the Catalan margin, thus reflecting differences in primary productivity of surface waters reported for the two regions. Similarly, sediments of the Catalan margin were characterized by significantly higher food quantity and quality in spring, when the phytoplankton bloom occurs in surface waters, than in summer and autumn. Differences in the benthic trophic state of canyons against open slopes were more evident in the Portuguese than in the Catalan margin. In both continental margins, bioavailable organic C concentrations did not vary or increase with increasing water depth. Overall, our findings suggest that the intensity of primary production processes along with the lateral transfer of organic particles, even amplified by episodic events, can have a role in controlling the quantity and distribution of bioavailable organic detritus and its nutritional value along these continental margin ecosystems.

Recent sedimentation in the southeast Indian Ocean with special reference to the effects of Antarctic Bottom Water circulation

1978 ◽  
Vol 27 (1-2) ◽  
pp. 1-17 ◽  
Author(s):  
Venkatarathnam Kolla ◽  
Lawrence Henderson ◽  
Lawrence Sullivan ◽  
Pierre E. Biscaye
Keyword(s):  
Indian Ocean ◽  
Special Reference ◽  
Bottom Water ◽  
Water Circulation ◽  
Antarctic Bottom Water

Bottom water circulation in Cascadia Basin

2009 ◽  
Vol 56 (10) ◽  
pp. 1688-1707 ◽  
Author(s):  
Susan L. Hautala ◽  
H. Paul Johnson ◽  
Douglas E. Hammond
Keyword(s):  
Bottom Water ◽  
Water Circulation

Variability of surface sediments in the Peru basin: dependence on water depth, productivity, bottom water flow, and seafloor topography

2000 ◽  
Vol 163 (1-4) ◽  
pp. 169-184 ◽  
Author(s):  
M.E Weber ◽  
U von Stackelberg ◽  
V Marchig ◽  
M Wiedicke ◽  
B Grupe
Keyword(s):  
Water Flow ◽  
Water Depth ◽  
Bottom Water ◽  
Surface Sediments ◽  
Seafloor Topography

scholarly journals Late- and Post-glacial sediments in the Randers fjord area. Geochemical, sedimentological, and geoelectric investigations

1976 ◽  
Vol 107 ◽  
pp. 1-124
Author(s):  
Arne Villumsen ◽  
Holger Lykke Andersen
Keyword(s):  
Marine Sediments ◽  
Water Depth ◽  
Groundwater Level ◽  
Bottom Water ◽  
Sedimentary Facies ◽  
Late Glacial ◽  
Supplementary Information ◽  
Specific Resistivity ◽  
Glacial Sediments ◽  
New System

Thickness and distribution of Late- and Post-glacial sediments in an Eastern Jutland valley system have been mapped, and their sedimentogenetic and diagenetic relations have been studied. The chemical and sedimentological methods used are discussed in detail. Post-glacial marine sediments formed in a tidal fjord environment are the most important deposits in the area, and it is shown that river supplies of freshwater control the salinity of the environment and were responsible for the rather high content of allochthonous material in the sediment. The marine sediments rest on Late-glacial sand, whose surface topography indicates that the valleys were formed by subglacial erosion. Local occurrences of dead ice were present at least until the Littorina sea (Atlantic) transgression. Depth conditions for Early Post-glacial peat are used to estimate the groundwater level and the course of the river Gudenå in the Continental Period. Sedimentary facies in the Atlantic Littorina sea are discussed, including salinity, tidal activity, water depth, nutrient conditions, and exchange of stagnant bottom water from the deepest parts of the fjord area. The sequence seems to have been influenced only by minor syndiagenetic and weathering processes.With the intention of providing supplementary information to that obtained from mapping of the Post-glacial sediments of the region 161 electric soundings have been carried out in the Randers fjord area. The specific resistivity of the sediments has been determined and the principle limitations of the methods applied have been investigated. Interpretation of the electric soundings has been done using a new system of computer programs. Maps showing the thickness relationships and variations in specific resistivity in the uppermost, largely Post-glacial deposits in the area have been prepared, and a map showing the location of the surface of the Danian limestone and occurrence of Tertiary clay is also presented.

scholarly journals Also tropical freshwater ostracods show a seasonal life cycle

2017 ◽  
Author(s):  
Juliane Meyer ◽  
Claudia Wrozyna ◽  
Albrecht Leis ◽  
Werner Piller
Keyword(s):  
Life Cycle ◽  
Environmental Factors ◽  
Isotopic Composition ◽  
Temporal Variations ◽  
South Florida ◽  
Population Variation ◽  
Instrumental Data ◽  
Mean Values ◽  
Isotopic Signatures ◽  
Isotopic Compositions

Abstract. Isotopic signatures of ostracod shells became common proxies for the reconstruction of paleo-environmental conditions. Their isotopic composition is the result of the composition of their host water and the phenology and ecology of the target species. The sum of spatial and temporal variations from environmental factors in the species habitat defines the maximum isotopic variation of a population during the time of their shell formation. Here we present isotopic signatures (δ18O, δ13C) of living Cytheridella ilosvayi (Ostracoda) and chemical and isotopic compositions of 14 simultaneously sampled freshwater habitats in South Florida and instrumental data of the region. The chemical and isotopic compositions of the selected sites characterize the different habitats and show the influence of the source water, biological activity and the duration of exposure to the surface. Isotopic signatures of C. ilosvayi shells correlate well with the isotopic composition of their host waters. Within-sample variability of repeated isotopic measurements of ostracod shells reflect habitat dependent ranges and indicate temperature and the δ18O composition of precipitation (δ18Oprec) as regional environmental factors responsible for the population variation. Instrumental data of water temperature and δ18Oprec were used to calculate the monthly variation of a theoretical calcite in rivers of Florida showing distinct seasonal variations in values and ranges. Different configurations of the theoretical calcite were compared to the within-sample variability to identify possible calcification periods of C. ilosvayi. For a plausible calcification period the ostracod isotopic range has to correlate with mean values of the theoretical calcite with a slight positive offset (vital effect) and the extension of the theoretical calcite range. The tested model suggests a seasonal calcification period of C. ilosvayi in early spring. The surprising seasonality of a tropical ostracod life cycle is probably coupled to the hydrologic cycle of Florida. The results of this study contribute to the application of ostracod isotopes in modern calibration studies and their potential use in paleontology.

Mo isotope records from Lower Cambrian black shales, northwestern Tarim Basin (China): Implications for the early Cambrian ocean

2021 ◽  
Author(s):  
Guangyou Zhu ◽  
Tingting Li ◽  
Kun Zhao ◽  
Chao Li ◽  
Meng Cheng ◽  
...  
Keyword(s):  
Lower Cambrian ◽  
Bottom Water ◽  
Black Shales ◽  
Early Cambrian ◽  
Middle Portion ◽  
Isotopic Compositions ◽  
Tarim Block ◽  
Time Period ◽  
Fe Speciation ◽  
Marine Areas

The widely developed black shales deposited during the early Cambrian recorded paleoenvironmental information about coeval seawater. Numerous studies have been conducted on these shales to reconstruct the paleomarine environment during this time period. However, most research has been conducted on stratigraphic sections in South China, and equivalent studies of sections from other cratons are relatively rare. Here, we report Mo isotopic compositions as well as redox-sensitive trace-element and iron (Fe) speciation data for black shales of the Lower Cambrian Yuertusi Formation from the Tarim block (i.e., a small craton). The Fe speciation data show high FeHR/FeT and Fepy/FeHR ratios, indicating roughly sustained euxinic bottom-water conditions during their deposition. Based on Mo isotopic compositions (δ98/95Mo), we further classified the euxinic black shales into two intervals: a lower interval (0−21.3 m) and an upper interval (21.3−32.3 m). The lower interval is characterized by variable Mo isotopic compositions (−2.12‰ to +0.57‰, mean = −0.52‰ ± 0.72‰), with an obvious negative excursion in its middle portion. The overlying upper interval has relatively heavy δ98/95Mo values up to +1.42‰ (mean = +0.62‰ ± 0.37‰). We ascribe δ98/95Mo differences in the lower and upper intervals to inadequate aqueous H2S concentrations for quantitative thiomolybdate formation under euxinic conditions. The most negative Mo isotope excursion may have been caused by upwelling hydrothermal inputs during a transgression, consistent with significantly elevated total organic carbon (TOC) contents, Mo and U enrichments, and Fe supply. Relatively positive δ98/95Mo values in the upper interval have roughly similar variations with other coeval sections, indicating such variations were common for early Cambrian euxinic deposits, and they were most likely caused by local differences in [H2S]aq. Compilation of Mo isotope data from the early Cambrian and earlier times further indicates relatively oxygenated seawater, especially the deep-marine areas during the early Cambrian before reaching a state like modern seawater.

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