scholarly journals Evidence for Highly Complex Redox Conditions and Strong Water-Column Stratification in an Early Cambrian Continental-Margin Sea

2018 ◽  
Vol 19 (8) ◽  
pp. 2397-2410 ◽  
Author(s):  
Zihu Zhang ◽  
Chao Li ◽  
Meng Cheng ◽  
Thomas J. Algeo ◽  
Chengsheng Jin ◽  
...  
Keyword(s):  
Water Column ◽  
Continental Margin ◽  
Redox Conditions ◽  
Early Cambrian ◽  
Water Column Stratification

scholarly journals Bacteriohopanepolyols record stratification, nitrogen fixation and other biogeochemical perturbations in Holocene sediments of the central Baltic Sea

2013 ◽  
Vol 10 (4) ◽  
pp. 2725-2735 ◽  
Author(s):  
M. Blumenberg ◽  
C. Berndmeyer ◽  
M. Moros ◽  
M. Muschalla ◽  
O. Schmale ◽  
...  
Keyword(s):  
Baltic Sea ◽  
Water Column ◽  
Stable Stratification ◽  
The Baltic Sea ◽  
Allochthonous Input ◽  
The North ◽  
Water Column Stratification ◽  
Gotland Deep ◽  
History Of ◽  
The Baltic

Abstract. The Baltic Sea, one of the world's largest brackish-marine basins, established after deglaciation of Scandinavia about 17 000 to 15 000 yr ago. In the changeable history of the Baltic Sea, the initial freshwater system was connected to the North Sea about 8000 yr ago and the modern brackish-marine setting (Littorina Sea) was established. Today, a relatively stable stratification has developed in the water column of the deep basins due to salinity differences. Stratification is only occasionally interrupted by mixing events, and it controls nutrient availability and growth of specifically adapted microorganisms and algae. We studied bacteriohopanepolyols (BHPs), lipids of specific bacterial groups, in a sediment core from the central Baltic Sea (Gotland Deep) and found considerable differences between the distinct stages of the Baltic Sea's history. Some individual BHP structures indicate contributions from as yet unknown redoxcline-specific bacteria (bacteriohopanetetrol isomer), methanotrophic bacteria (35-aminobacteriohopanetetrol), cyanobacteria (bacteriohopanetetrol cyclitol ether isomer) and from soil bacteria (adenosylhopane) through allochthonous input after the Littorina transgression, whereas the origin of other BHPs in the core has still to be identified. Notably high BHP abundances were observed in the deposits of the brackish-marine Littorina phase, particularly in laminated sediment layers. Because these sediments record periods of stable water column stratification, bacteria specifically adapted to these conditions may account for the high portions of BHPs. An additional and/or accompanying source may be nitrogen-fixing (cyano)bacteria, which is indicated by a positive correlation of BHP abundances with Corg and δ15N.

scholarly journals Diatoms as a paleoproductivity proxy in the NW Iberian coastal upwelling system (NE Atlantic)

2017 ◽  
Vol 14 (5) ◽  
pp. 1165-1179 ◽  
Author(s):  
Diana Zúñiga ◽  
Celia Santos ◽  
María Froján ◽  
Emilia Salgueiro ◽  
Marta M. Rufino ◽  
...  
Keyword(s):  
Water Column ◽  
Surface Sediment ◽  
Sediment Trap ◽  
Coastal Upwelling ◽  
Late Summer ◽  
Early Summer ◽  
Marine Diatom ◽  
Photic Zone ◽  
Upwelling System ◽  
Water Column Stratification

Abstract. The objective of the current work is to improve our understanding of how water column diatom's abundance and assemblage composition is seasonally transferred from the photic zone to seafloor sediments. To address this, we used a dataset derived from water column, sediment trap and surface sediment samples recovered in the NW Iberian coastal upwelling system. Diatom fluxes (2.2 (±5.6) 106 valves m−2 d−1) represented the majority of the siliceous microorganisms sinking out from the photic zone during all studied years and showed seasonal variability. Contrasting results between water column and sediment trap diatom abundances were found during downwelling periods, as shown by the unexpectedly high diatom export signals when diatom-derived primary production achieved their minimum levels. They were principally related to surface sediment remobilization and intense Minho and Douro river discharge that constitute an additional source of particulate matter to the inner continental shelf. In fact, contributions of allochthonous particles to the sinking material were confirmed by the significant increase of both benthic and freshwater diatoms in the sediment trap assemblage. In contrast, we found that most of the living diatom species blooming during highly productive upwelling periods were dissolved during sinking, and only those resistant to dissolution and the Chaetoceros and Leptocylindrus spp. resting spores were susceptible to being exported and buried. Furthermore, Chaetoceros spp. dominate during spring–early summer, when persistent northerly winds lead to the upwelling of nutrient-rich waters on the shelf, while Leptocylindrus spp. appear associated with late-summer upwelling relaxation, characterized by water column stratification and nutrient depletion. These findings evidence that the contributions of these diatom genera to the sediment's total marine diatom assemblage should allow for the reconstruction of different past upwelling regimes.

scholarly journals Geochemical features, sources and geodynamic settings of accumulation of the cambrian sedimentary rocks of the Mel’gin trough (Bureya continental massif)

2019 ◽  
Vol 64 (5) ◽  
pp. 503-519
Author(s):  
R. O. Ovchinnikov ◽  
A. A. Sorokin ◽  
V. P. Kovach ◽  
A. B. Kotov
Keyword(s):  
Continental Margin ◽  
Active Continental Margin ◽  
Sedimentary Rocks ◽  
Detrital Zircons ◽  
Igneous Rocks ◽  
Early Cambrian ◽  
Relative Probability ◽  
Early Proterozoic ◽  
Geodynamic Settings ◽  
Probability Plots

The first data about geochemical features of the Cambrian sedimentary rocks of the Mel’gin trough of the Bureya continental Massif, as well as ages of detrital zircons of them are obtained. It is established, that among the detrital zircons from the sandstones of the Chergilen and Allin formations of the Mel’gin trough zircons with Late Riphean (peaks on relative probability plots – 0.78, 0.82, 0.94, 1.04 Ga) and Early Riphean (peaks on relative probability plots – 1.38, 1.45, 1.64 Ga) ages predominate. The single grains have a Middle Riphean, Early Proterozoic and Late Archean ages. We can suppose, that the sources of Late Riphean detrital zircons from sandstones of the Chergilen and Allin formations are igneous rocks of gabbro-granitoids (940–933 Ma) and granite- leucogranites (804–789 Ma) association, identified in the Bureya continental Massif. We can`t assume, what kind of rocks were the source for Middle Riphean and older detrital zircons from the Cambrian sedimentary rocks of the Bureya continental Massif, because in this massif still do not identified complexes older Late Riphean age. The most probable geodynamic conditions of accumulation of the Cambrian deposits of the Mel’gin trough is the conditions of active continental margin, which is corresponding to of Early Cambrian granitoids magmatism.

scholarly journals The response of water column and sedimentary environments to the advent of the Messinian salinity crisis: insights from an onshore deep-water section (Govone, NW Italy)

2020 ◽  
pp. 1-17
Author(s):  
Mathia Sabino ◽  
Francesco Dela Pierre ◽  
Marcello Natalicchio ◽  
Daniel Birgel ◽  
Susanne Gier ◽  
...  
Keyword(s):  
Water Column ◽  
Deep Water ◽  
Bottom Layer ◽  
Messinian Salinity Crisis ◽  
Sedimentary Environments ◽  
Water Column Stratification ◽  
Stratigraphic Architecture ◽  
Spatial Changes ◽  
Oxygen Stable Isotope ◽  
Nw Italy

Abstract During Messinian time, the Mediterranean underwent hydrological modifications culminating 5.97 Ma ago with the Messinian salinity crisis (MSC). Evaporite deposition and alleged annihilation of most marine eukaryotes were taken as evidence of the establishment of basin-wide hypersalinity followed by desiccation. However, the palaeoenvironmental conditions during the MSC are still a matter of debate, chiefly because most of its sedimentary record is buried below the abyssal plains of the present-day Mediterranean Sea. To shed light on environmental change at the advent and during the early phase of the MSC, we investigated the Govone section from the Piedmont Basin (NW Italy) using a multidisciplinary approach (organic geochemical, petrographic, and carbon and oxygen stable isotope analyses). The Govone section archives the onset of the crisis in a succession of organic-rich shales and dolomite-rich marls. The MSC part of the succession represents the deep-water equivalent of sulphate evaporites deposited at the basin margins during the first phase of the crisis. Our study reveals that the onset of the MSC was marked by the intensification of water-column stratification, rather than the establishment of widespread hypersaline conditions. A chemocline divided the water column into an oxygen-depleted, denser and more saline bottom layer and an oxygenated, upper seawater layer influenced by freshwater inflow. Vertical oscillations of the chemocline controlled the stratigraphic architecture of the sediments pertaining to the first stage of the MSC. Accordingly, temporal and spatial changes of water masses with different redox chemistries must be considered when interpreting the MSC event.

scholarly journals Assessing the utility of Fe/Al and Fe-speciation to record water column redox conditions in carbonate-rich sediments

2014 ◽  
Vol 382 ◽  
pp. 111-122 ◽  
Author(s):  
M.O. Clarkson ◽  
S.W. Poulton ◽  
R. Guilbaud ◽  
R.A. Wood
Keyword(s):  
Water Column ◽  
Redox Conditions ◽  
Fe Speciation

scholarly journals Chromium isotope cycling in the water column and sediments of the Peruvian continental margin

2019 ◽  
Vol 257 ◽  
pp. 224-242 ◽  
Author(s):  
S. Bruggmann ◽  
F. Scholz ◽  
R.M. Klaebe ◽  
D.E. Canfield ◽  
R. Frei
Keyword(s):  
Water Column ◽  
Continental Margin

scholarly journals Phytoplankton bloom phenomena in the North Atlantic Ocean and Arabian Sea

2015 ◽  
Vol 72 (6) ◽  
pp. 2021-2028 ◽  
Author(s):  
John F. Marra ◽  
Tommy D. Dickey ◽  
Albert J. Plueddemann ◽  
Robert A. Weller ◽  
Christopher S. Kinkade ◽  
...  
Keyword(s):  
Water Column ◽  
Mixed Layer ◽  
Arabian Sea ◽  
Phytoplankton Bloom ◽  
Mixed Layer Depth ◽  
Ocean Dynamics ◽  
Layer Depth ◽  
Diurnal Variability ◽  
Water Column Stratification ◽  
Iceland Basin

Abstract We review bio-optical and physical data from three mooring experiments, the Marine Light–Mixed Layers programme in spring 1989 and 1991 in the Iceland Basin (59°N/21°W), and the Forced Upper Ocean Dynamics Experiment in the central Arabian Sea from October 1994 to 1995 (15.5°N/61.5°E). In the Iceland Basin, from mid-April to mid-June in 1989, chlorophyll-a concentrations are sensitive to small changes in stratification, with intermittent increases early in the record. The spring increase occurs after 20 May, coincident with persistent water column stratification. In 1991, the bloom occurs 2 weeks earlier than in 1989, with a background of strong short-term and diurnal variability in mixed layer depth and minimal horizontal advection. In the Arabian Sea, the mixing response to the northeast and southwest monsoons, plus the response to mesoscale eddies, produces four blooms over the annual cycle. The mixed layer depth in the Arabian Sea never exceeds the euphotic zone, allowing interactions between phytoplankton and grazer populations to become important. For all three mooring experiments, change in water column stratification is key in producing phytoplankton blooms.

Sign in / Sign up

Export Citation Format

Share Document