Sediment accumulation and bio-diffusion mixing rates derived from excess 210Pb and 137Cs profiles in sediment cores of Mumbai Harbor Bay

2016 ◽  
Vol 20 (4) ◽  
pp. 289-297 ◽  
Author(s):  
Ajay Kumar ◽  
Sabyasachi Rout ◽  
R. K. Singhal ◽  
P. M. Ravi ◽  
R. M. Tripathi
Keyword(s):  
Sediment Cores ◽  
Sediment Accumulation ◽  
210Pb And 137Cs ◽  
Excess 210Pb ◽  
Mixing Rates ◽  
Diffusion Mixing

scholarly journals Evaluating the historical sedimentation patterns in two different Mediterranean deep environments (Sardinia and Sicily Channels)

2019 ◽  
Vol 20 (3) ◽  
pp. 542 ◽  
Author(s):  
NOUR EL HOUDA HASSEN ◽  
NAFAÂ REGUIGUI ◽  
MOHAMED AMINE HELALI ◽  
NEZHA MEJJAD ◽  
ABDELMOURHIT LAISSAOUI ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Water Depth ◽  
Accumulation Rate ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Inverse Correlation ◽  
Accumulation Rates ◽  
Deep Sediment ◽  
210Pb And 137Cs ◽  
Excess 210Pb

The sediment accumulation rate in the Sardinia and Sicily channels in the central part of the Mediterranean Sea was studied by using short-lived radionuclides (210Pb and 137Cs) in two deep sediment cores. Different sedimentation regimes were identified indicating substantial differences in accumulation rates and historical patterns. The 210Pb-derived mean accumulation rate found in the Strait of Sardinia was 0.05 g.cm-2.y-1, lower than that in Sicily Channel (0.1 g.cm-2.y-1) suggesting an inverse correlation with water depth. Excess 210Pb inventories were 24 ± 1 and 6.0 ± 0.4 kBq.m-2, while the fluxes to the sediment were 745 ± 31 and 188 ± 11 Bq.m-2.y-1 in Sicily and Sardinia channels, respectively. 137Cs failed to use for the validation of the established chronologies, while its inventories found 450 Bq.m-2 and 355 Bq.m-2 in the Sicily and Sardinia channel, respectively.

scholarly journals Sediment geochronology and spatio-temporal and vertical distributions of radionuclides in the Upper Bonny Estuary (South Nigeria)

2014 ◽  
Vol 41 (4) ◽  
pp. 369-376 ◽  
Author(s):  
Omorotionmwan Omokheyeke ◽  
Francis Sikoki ◽  
Abdelmourhit Laissaoui ◽  
David Akpuluma ◽  
Peter Onyagbodor ◽  
...  
Keyword(s):  
Sediment Cores ◽  
Sediment Accumulation ◽  
Dry Weight ◽  
Radiometric Dating ◽  
Layer By Layer ◽  
Excess 210Pb ◽  
Radio Nuclide ◽  
Vertical Distributions ◽  
Southwest Nigeria ◽  
Spatio Temporal

Abstract Surface deposits and sediment cores were collected from the Upper Bonny Estuary, located in Southwest Nigeria, and analyzed to determine spatio-temporal and vertical distributions of radio-nuclide activities expressed in Bq·kg−1 dry weight. The results of activities of naturally occurring radionuclides of 226Ra (15 ± 2–34 ± 3 Bq·kg−1), 228Ra (32 ± 5–48 ± 6 Bq·kg−1), 40K (264 ± 29–462 ± 36 Bq·kg−1) were found to be all within the range of typical values reported for coastal regions. Ratios of 226Ra to 228Ra suggested accretion for all samples with low sediment accumulation registered during rainy months. In addition, vertical distributions at the three sampling sites were also studied with the initial aim of establishing chronologies from the decay of excess 210Pb. In two cores, excess 210Pb, estimated by subtracting 226Ra from total 210Pb on a layer-by-layer basis, exhibit relatively constant activity with discrete minima and maxima. Therefore, these cores were excluded from radiometric dating. Only the third core could be dated by the constant rate of supply model, and 137Cs was utilized to validate the 210Pb chronology.

Use of excess 210Pb and 228Th to estimate rates of sediment accumulation and bioturbation in Port Phillip Bay, Australia

1999 ◽  
Vol 50 (6) ◽  
pp. 533 ◽  
Author(s):  
G. J. Hancock ◽  
J. R. Hunter
Keyword(s):  
Water Column ◽  
Accumulation Rate ◽  
Sediment Accumulation ◽  
Sediment Accumulation Rate ◽  
Mixing Coefficient ◽  
Excess 210Pb ◽  
Suspended Particulate ◽  
Mixing Rates ◽  
Diffusive Mixing ◽  
Upper Estimate

Rates of sediment accumulation, sediment mixing and depositional particle fluxes were estimated by use of excess 210Pb and 228Th. In central Port Phillip Bay, there was a rapidly mixed surface layer and two layers of different mixing rates at 2–20 cm and 21–45 cm depths. When the sediment profiles of excess 210Pb and 228Th were combined and diffusive mixing was assumed, the sediment accumulation rate in the 2–20 cm layer was constrained to be <0.15 cm year–1. The mixing coefficient in the 2–20 cm layer was 5.0 ± 0.1 cm2 year–1. Hence, mixing rather than sedimentation governs the distribution of 210Pb and 228Th in the surficial 20 cm. Below 20 cm, the different mixing regime may be due to the dominance of deposit-feeders at these depths. Evidence for bioturbation to a depth of 50 cm was obtained from profiles of excess 210Pb and 228Ra deficiency. The mean residence time of particles in the central bay water column was 10 ± 2 days (a normalized depositional particle flux of 0.16 ± 0.02 g cm–2 year–1). This flux is three times the upper estimate of the sediment accumulation rate, indicating that most of the suspended particulate matter in the water column is resuspended bottom sediment.

Pigment Preservation in Lake Sediments: A Comparison of Sedimentary Environments in Trout Lake, Wisconsin

1991 ◽  
Vol 48 (3) ◽  
pp. 472-486 ◽  
Author(s):  
James P. Hurley ◽  
David E. Armstrong
Keyword(s):  
Accumulation Rate ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Sediment Surface ◽  
Water Interface ◽  
Sedimentary Pigments ◽  
Sedimentary Environments ◽  
Trout Lake ◽  
Secondary Carotenoids ◽  
Β Carotene

Fluxes and concentrations of a phorbins and major algal carotenoids were quantified in sediment trap material and sediment cores from two basins of Trout Lake, Wisconsin (TrDH and TrAB). The basins were chosen to contrast the influence of oxygen content at the sediment–water interface (TrDH, oxic and TrAB, reducing), sediment accumulation rate, and focusing. Pigment diagenesis occurred in both basins, but transformations and destruction were more extensive in TrDH. Although untransformed chlorophyll a was the major phorbin deposited at the sediment surface of both basins (51–64 mol%), pigment destruction, coupled with transition to pheophytin, accounted for substantial losses, especially in oxic TrDH sediments. Fucoxanthin, peridinin, and diadinoxanthin, despite representing > 70% of the deposited carotenoid flux, were substantially degraded or transformed in both basins. However, preservation was relatively high for secondary carotenoids, such as diatoxanthin and β-carotene, and for a major cryptomonad pigment, alloxanthin. Residual profiles in sediments show that pigment sedimentation from the epilimnion and accumulation in the permanent sediments are not directly related and that diagenesis must be considered in interpreting sedimentary pigments.

The Toba Volcanic Event and Interstadial/Stadial Climates at the Marine Isotopic Stage 5 to 4 Transition in the Northern Indian Ocean

2002 ◽  
Vol 57 (1) ◽  
pp. 22-31 ◽  
Author(s):  
Hartmut Schulz ◽  
Kay-Christian Emeis ◽  
Helmut Erlenkeuser ◽  
Ulrich von Rad ◽  
Christian Rolf
Keyword(s):  
Arabian Sea ◽  
Water Productivity ◽  
Ice Core ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Sediment Supply ◽  
Volcanic Event ◽  
Additional Support ◽  
Marine Isotope Stage 5 ◽  
A Minor

AbstractThe Toba volcanic event, one of the largest eruptions during the Quaternary, is documented in marine sediment cores from the northeastern Arabian Sea. On the crest of the Murray Ridge and along the western Indian continental margin, we detected distinct concentration spikes and ash layers of rhyolithic volcanic shards near the marine isotope stage 5–4 boundary with the chemical composition of the “Youngest Toba Tuff.” Time series of the Uk′37-alkenone index, planktic foraminiferal species, magnetic susceptibility, and sediment accumulation rates from this interval show that the Toba event occurred between two warm periods lasting a few millennia. Using Toba as an instantaneous stratigraphic marker for correlation between the marine- and ice-core chronostratigraphies, these two Arabian Sea climatic events correspond to Greenland interstadials 20 and 19, respectively. Our data sets thus depict substantial interstadial/stadial fluctuations in sea-surface temperature and surface-water productivity. We show that variable terrigenous (eolian) sediment supply played a crucial role in transferring and preserving the productivity signal in the sediment record. Within the provided stratigraphic resolution of several decades to centennials, none of these proxies shows a particular impact of the Toba eruption. However, our results are additional support that Toba, despite its exceptional magnitude, had only a minor impact on the evolution of low-latitude monsoonal climate on centennial to millennial time scales.

scholarly journals 240+239Pu depositional signatures as a viable geochronological tool in the Amazon Basin

2017 ◽  
Vol 44 (1) ◽  
pp. 142-149 ◽  
Author(s):  
Luciana M Sanders ◽  
Kathryn H Taffs ◽  
Debra Stokes ◽  
Alex Enrich-Prast ◽  
Christian J Sanders
Keyword(s):  
Amazon Basin ◽  
Environmental Science ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Recent Sediment ◽  
Floodplain Lake ◽  
Accumulation Rates ◽  
Amazon Floodplain ◽  
Dating Methods ◽  
Lead 210

AbstractAnthropogenic radionuclide signatures associated with nuclear testing are increasingly utilized in environmental science to explore recent sedimentation. In this study, we assess the suitability of Pu radioisotope analysis in floodplain lake environments in the Amazon Basin to form geochronologies during the 20thcentury. The240Pu +239Pu (240+239Pu) signatures in six sediment cores indicate sediment accumulation rates in the floodplain lakes of the major rivers; Amazon (2.3 mm year-1), Tapajos (10.2 and 2.4 mm year-1) and Madeira (3.4, 4.2 and 6.2 mm year-1). The results from this study show that240+239Pu fallout activities, and the well documented (240Pu/239Pu) atomic ratios of the above ground nuclear tests which began in the 1950’s, are sufficient and well preserved in Amazon floodplain lake sediments to infer chronologies. Lead-210 dating analyses in the same sediment cores produced comparable sediment accumulation rates at three of the six sites. The differences between dating methods may be attributed to the different time scale these dating methods represent and/or in the solubility between Pb and Pu along the sediment column. The geochronologies derived from the240+239Pu and210Pb dating methods outlined in this work are of interest to identify the effects of changing sediment accumulation rates during the previous century as a result of development, including deforestation, along the Amazon Basin which increased towards the middle of the 20thcentury. This study shows that Pu dating provides a viable alternative geochronology tool for recent sediment accumulation (previous ~60 years) along the Amazon Basin.

3000-Year paleoseismological record from the region of the 1988 Saguenay, Quebec, earthquake

1998 ◽  
Vol 88 (5) ◽  
pp. 1198-1203
Author(s):  
Ronald Doig
Keyword(s):  
Active Region ◽  
Lake Sediment ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Recurrence Interval ◽  
Pattern Match ◽  
Local Origin ◽  
Organic Rich Sediment

Abstract The 1988, magnitude mb 5.9 (mbLg 6.5) Saguenay, Quebec, earthquake occurred in a region considered to be aseismic, but the epicenter was less than 100 km northwest of the seismically active region of Charlevoix. Lake sediment cores representing some 3000 yr of sediment accumulation contain abnormal silt layers attributed to seismic shaking events prior to the 1988 earthquake. The layers are formed by the relatively rapid settling of the silt portion of the seismically resuspended organic-rich sediment. Cores were obtained over a distance of 120 km, perpendicular to the Saguenay graben structure. Several silt layers are much thicker and more widely distributed than the effect of the 1988 earthquake and are comparable to those observed at Charlevoix that were produced by magnitude 6 to 7 events. The silting events do not correlate between the sampled lakes nor does the pattern match that at Charlevoix, so that the shaking events are interpreted to be of local origin. The recurrence interval for magnitude ≧6 earthquakes ranges from 350 to 1000 yr, in contrast to the roughly 75-yr historical recurrence of earthquakes of magnitude greater than 6 at Charlevoix.

Time averaging and stratigraphic unmixing: reconstructing ecological decline in molluscan production (Holocene, Brijuni, NE Adriatic)

2020 ◽  
Author(s):  
Adam Tomašových ◽  
Martin Zuschin ◽  
Ivo Gallmetzer ◽  
Alexandra Haselmair
Keyword(s):  
Accumulation Rate ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Coralline Algae ◽  
Time Averaging ◽  
Sedimentation Rates ◽  
Amino Acid Racemization ◽  
Ecological History ◽  
Shell Bed ◽  
Warm Temperate

&lt;p&gt;The northeastern Adriatic seafloor is formed by warm-temperate bioclastic carbonates with coralline algae, bryozoans and mollusks. These sediments represent a mixture of past and present-day production owing to low sedimentation rates and bioturbation. Although low sedimentation rates do not allow resolution of ecological history at centennial or even millennial scales on the basis of raw stratigraphic data, age unmixing based on radiocarbon-calibrated amino acid racemization shows that one of the major molluscan sediment producers &amp;#8211; the infaunal suspension-feeder Timoclea ovata &amp;#160;&amp;#8211; markedly peaked in production ~5,000 years during the maximum flooding and earliest highstand phase and significantly diminished in abundance during the late highstand phase at Brijuni, with a large proportion of dead shells now present in surface sediments representing shells that are several centuries old. This species still occurs in living assemblages but our analyses indicate that its former production was by several orders of magnitude higher. In contrast, stratigraphic trends in absolute and proportional abundance of this species in ~1.5 m-thick sediment cores show a gradual or a very mild upcore decline, indicating that raw stratigraphic data do not efficiently detect millennial-scale ecological dynamic. The temporal decline in production of Timoclea ovata is associated with an increase in water depth and an increase in sediment-accumulation rate, and led to a transition from molluscan oyster-scallop shell bed to late highstand bryomol sediments.&lt;/p&gt;

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