scholarly journals Distribution of Natural Radioactivity,137Cs,90Sr, and Plutonium Isotopes in a Water Column and Sediment Core along the Algerian Coast

2007 ◽  
Vol 2007 ◽  
pp. 1-6 ◽  
Author(s):  
A. Noureddine ◽  
M. Benkrid ◽  
R. Maoui ◽  
M. Menacer ◽  
R. Boudjenoun

Concentrations of natural (40K,210Pb, uranium, and thorium series) and artificial radioelements (137Cs,90Sr,239+240Pu) were determined in seawater and sediment samples collected from stations along the Algerian coast. Seawater was collected from the surface to a maximum depth of 2000 m; the sediment cores were sampled from a depth of around 1500 m. This work was carried out in August 2001, in the framework of the Regional African project /7/004 (RAF), by the accomplishment of an oceanographic campaign organized by the International Atomic Energy Agency (IAEA) in collaboration with Commissariat à l'Energie Atomique (COMENA) and L'Institut des Sciences de la Mer et de L'Amenagement du Littoral (ISMAL), on board of the research vessel of M.S. Benyahia of ISMAL. In addition to the record of the conductivity (mS) and temperature (°C) data at each station, seawater samples were treated and preconcentrated on board, those of sediment cores were divided into different layers in order to undergo analyses in the laboratory of radiological impact studies of Algiers. Concentration results were obtained for137Cs and90Sr in mBq/L and239+240Pu inμBq/L in seawater, and also for natural and artificial radionuclides in Bq/kg dry weight in the layers of the sediment cores. The different profiles of137Cs,239+240Pu,90Sr, and210Pb concentrations against depth were presented to show artificial radioactivity distribution in the water column and sediment core. Concentrations of137Cs in the sediment core were also used to identify the137Cs peak in the area of interest.

2007 ◽  
Vol 2007 ◽  
pp. 1-5
Author(s):  
M. Benkrid ◽  
A. Noureddine

The International Atomic Energy Agency has organised in the framework of the regional project RAF/7/004, in collaboration with “Commissariat à l'Energie Atomique” (COMENA) and “Institut des Sciences de la Mer et de l'Aménagement du Littoral” (ISMAL), during August 2001, a scientific campaign along the Algerian coast, on board of the research vessel M.S. Benyahia of ISMAL is. Three stations, at the centre, east and west, were selected to collect five seawater samples for each water column reaching a maximum depth of 2000 m, using a stainless-steel water sampler of a volume of 250 litres. After recording the marine environment parameters (temperature and conductivity), seawater samples were conditioned and preconcentrated to precipitate plutonium isotopes usingMnCl2in the form ofMnO2in order to proceed to plutonium extraction by radiochemical separation and prepare the source by coprecipitation using neodymium fluoride (NdF3) by vacuum filtration and an evaluation of the activity by alpha spectrometry. Concentration results in units ofμBq/l of plutonium isotopes were obtained in the range of 6.7±1.00 to 25.5±3.70 forP239+240uand 0.21±0.04 to 0.77±0.15 forP238u. Distribution of Pu through the plot of its profile was studied and the concentration was estimated. The obtained results were compared toC137sand those found by other authors in the same Mediterranean area.


1985 ◽  
Vol 42 (7) ◽  
pp. 1249-1254 ◽  
Author(s):  
Stephen A. Norton ◽  
Charles T. Hess ◽  
Geneva M. Blake ◽  
Marilyn L. Morrison ◽  
Jill Baron

Sediment cores from four high-altitude (approximately 3200 m) lakes in Rocky Mountain National Park, Colorado, were dated by 210Pb chronology. Background (supported) 210Pb activities for the four cores range from 0.26 to 0.93 Beq/g dry weight, high for typical oligotrophic lakes, integrated unsupported 210Pb ranges from 0.81 (a typical value for most lakes) to 11.0 Beq/cm2. The 210Pb activity in the surface sediments ranges from 1.48 to 22.2 Beq/g dry weight. Sediment from Lake Louise, the most unusual of the four, has 22.2 Beq/g dry weight at the sediment surface, an integrated unsupported 210Pb = 11.0 Beq/cm2, and supported 210Pb = 0.74 Beq/g dry weight. 226Ra content of the sediment is insufficient to explain either the high unsupported 210Pb or the Rn content of the water column of Lake Louise, which averaged 96.2 Beq/L. We concluded that 222Rn-rich groundwater entering the lake is the source of the high 222Rn in the water column. This, in turn, is capable of supporting the unusually high 210Pb flux to the sediment surface. Groundwater with high 222Rn may control the 210Pb budget of lakes where sediment cores have integrated unsupported 210Pb greater than 2 Beq/cm2.


2021 ◽  
Author(s):  
Melanie Münch ◽  
Rianne van Kaam ◽  
Karel As ◽  
Stefan Peiffer ◽  
Gerard ter Heerdt ◽  
...  

<p>The decline of surface water quality due to excess phosphorus (P) input is a global problem of increasing urgency. Finding sustainable measures to restore the surface water quality of eutrophic lakes with respect to P, other than by decreasing P inputs, remains a challenge. The addition of iron (Fe) salts has been shown to be effective in removing dissolved phosphate from the water column of eutrophic lakes. However, the resulting changes in biogeochemical processes in sediments as well as the long-term effects of Fe additions on P dynamics in both sediments and the water column are not well understood.</p><p>In this study, we assess the impact of past Fe additions on the sediment P biogeochemistry of Lake Terra Nova, a well-mixed shallow peat lake in the Netherlands. The Fe-treatment in 2010 efficiently reduced P release from the sediments to the surface waters for 6 years. Since then, the internal sediment P source in the lake has been increasing again with a growing trend over the years.</p><p>In 2020, we sampled sediments at three locations in Terra Nova, of which one received two times more Fe during treatment than the other two. Sediment cores from all sites were sectioned under oxygen-free conditions. Both the porewaters and sediments were analysed for their chemical composition, with sequential extractions providing insight into the sediment forms of P and Fe. Additional sediment cores were incubated under oxic and anoxic conditions and the respective fluxes of P and Fe across the sediment water interface were measured.</p><p>The results suggest that Fe and P dynamics in the lake sediments are strongly coupled. We also find that the P dynamics are sensitive to the amount of Fe supplied, even though enhanced burial of P in the sediment was not detected. The results of the sequential extraction procedure for P, which distinguishes P associated with humic acids and Fe oxides, as well as reduced flux of Fe(II) across the sediment water interface in the anoxic incubations, suggest a major role of organic matter in the interaction of Fe and P in these sediments.</p><p>Further research will include investigations of the role of organic matter and sulphur in determining the success of Fe-treatment in sequestering P in lake sediments. Based on these data in combination with reactive transport modelling we aim to constrain conditions for successful lake restoration through Fe addition.</p>


2008 ◽  
Vol 21 (2) ◽  
pp. 131-134 ◽  
Author(s):  
Tao Huang ◽  
Liguang Sun ◽  
Yuhong Wang ◽  
Renbin Zhu

AbstractDuring CHINARE-22 (December 2005–March 2006), we investigated six penguin colonies in the Vestfold Hills, East Antarctica, and collected several penguin ornithogenic sediment cores, samples of fresh guano and modern penguin bone and feather. We selected seven penguin bones and feathers and six sediments from the longest sediment core and performed AMS14C dating. The results indicate that penguins occupied the Vestfold Hills as early as 8500 calibrated years before present (cal. yrbp), following local deglaciation and the formation of the ice free area. This is the first report on the Holocene history of penguins in the Vestfold Hills. As in other areas of Antarctica, penguins occupied this area as soon as local ice retreated and the ice free area formed, and they are very sensitive to climatic and environmental changes. This work provides the foundation for understanding the history of penguins occupation in Vestfold Hills, East Antarctica.


1982 ◽  
Vol 39 (5) ◽  
pp. 748-759 ◽  
Author(s):  
J. Bloesch

From June through October 1978 sediment traps were moored at three stations in an inshore–offshore transect in the Eastern Basin of Lake Erie. Settling fluxes measured with the traps exposed close to lake bottom were rather similar at all three stations during summer stratification, averaging 6.1 g∙m−2∙d−1 for dry weight, 293 mg∙m−2∙d−1 for particulate organic carbon (POC), 38 mg∙m−2∙d−1 for particulate nitrogen (PN), and 5.44 mg∙m−2∙d−1 for particulate phosphorus (PP). A comparison of the hypolimnetic traps with the epilimnetic traps at the offshore station indicated that considerable resuspension takes place even in summer. During fall, however, the nearshore sedimentation rates were markedly increased because of storm-induced bottom resuspension. By comparing the trap catches with sediment cores taken at all three stations, a resuspension model for dry weight, POC, and PN was developed. The calculations showed that newly formed organic material is resuspended and redeposited more frequently at nearshore locations than offshore. This repeated nearshore resuspension enhances decomposition of detritus, as shown by low relative phytoplankton activity in the hypolimnetic traps, and results in horizontal transport of fine-grained organic matter in the offshore direction. The significant POC and PN concentration differences found in the inshore–offshore transect of the bottom sediments can be explained by these two processes.Key words: sedimentation, sediment traps, sediment cores, resuspension, inshore–offshore differences


2014 ◽  
Vol 41 (4) ◽  
pp. 369-376 ◽  
Author(s):  
Omorotionmwan Omokheyeke ◽  
Francis Sikoki ◽  
Abdelmourhit Laissaoui ◽  
David Akpuluma ◽  
Peter Onyagbodor ◽  
...  

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.


Author(s):  
David Lazarus ◽  
Johan Renaudie

Paleontology lies at the interface of earth sciences, biology and geologic time. When matched to histories of environmental change, such data is ideally suited to understanding how climate/environmental change affects biodiversity, and even how biodiversity change affects climate. Paleontologic and earth science collections, the data derived from them, and the global data infrastructures used in research are distinctively different than those in biology. Geologic time-linked earth science collections are found in geologic surveys, the oil industry and in museums as rock samples and sediment cores; paleontologic collections in museums and (via the microscopic fossils they contain) in sediment core repositories. Much published geologic time-linked earth science data is not tied to any collection material, and collected fossils are mostly only loosely linked to earth science collections or data. The exception is sediment cores and microfossils, where both earth science data and microfossil specimens are taken from the same cores and are thus tightly linked to each other. Lastly, most paleobiodiversity data used in research, even if derived from collection material, is compiled from the published literature rather than from collection databases. Three major types of linked earth science-paleontology data exist, each with its own data infrastructure. Very long time scale (Phanerozoic: 600 million years [myr]-Recent) but low time resolution (ca 10 myr) published fossil data is held in the Paleobiology Database [PBDB] and/or the Geobiodiversity Database [GBDB], together with very limited earth science data (mostly general rock type and approximate rock layer where found). PBDB in particular has been very successful in documenting the history of biodiversity over the last 600 my, and how a few major environmental events have affected it (mass extinctions and recoveries). Poor time resolution, taxonomic coarseness (most records are only for genera, not species) and poor links to earth science data have limited using this type of data for detailed studies of paleodiversity-environmental change. The NSB (formerly 'Neptune') database of deep-sea marine microfossils holds published fossil species occurrence data for the last ca 100 myr from the earth science sediment core collections of the deep-sea drilling programs [DSDP, ODP, IODP] together with detailed geochronologic data used to assign precise geologic ages to samples [.2-.02 myr resolution]. Species names are mostly linked to the separate community taxonomic catalog Mikrotax. All fossil occurrence data is also linked by sample name to the geologic core section material it was derived from. Earth history data from these core sections is not held in a central database, but a significant fraction is archived in the Pangea database, part of the ICSU World Data Center system. Biodiversity and environmental data can be linked directly via their shared sediment core sample locations, and/or by the high precision geologic ages for data in the systems. This type of data has been used to study biodiversity response to environmental change on many time and geographic scales, including rapid warming or cooling events, and response to major environmental catastrophes, e.g. the meteorite impact at the end of the Cretaceous. Lastly, very high temporal resolution (.01-.0001 my), mostly microfossil, plus earth-science data from land sections is held in the Neotoma system. This covers the last few my and is mostly used in local or regional studies of biodiversity and environmental change. New global data networking initiatives such as the Digital Deep Earth [DDE] initiative will create new opportunities to link earth science and biodiversity data to each other.


2021 ◽  
Author(s):  
Jose A. Corcho Alvarado ◽  
Misael Diaz-Asenciuo ◽  
Stefan Röllin ◽  
Juan Carlos Herguera

Abstract Here we report on new data on plutonium (Pu) isotopes to elucidate activity concentrations, inventories, sources and their transport from the ocean surface to the sea floor from a collection of deep-sea sediment cores (depths ranging from 257 to 3739 m) in the Gulf of Mexico (GoM). Sediment cores collected from the continental shelf and upper slope region of the GoM consistently showed 240Pu/239Pu ratios of 0.15 to 0.26 and Pu-inventories ranging from 15 to 35 Bq m− 2. Inventories and ratios are consistent with global fallout Pu for this tropical region. In the continental shelf and upper slope regions, higher particle concentrations close to the margins favor significant scavenging and removal of Pu from the water column; in contrast with the deep-sea cores that show low 240Pu/239Pu ratios (0.07–0.13) and a much lower Pu inventory (< 7 Bq m-2) implying a small fraction of the expected global fallout inventory has reached into the lower slopes and abyssal plain of the GoM. Low values and a progressive decrease of 240Pu/239Pu ratios and Pu inventories with increasing water depth have been previously reported for the GoM. The low Pu ratios indicate that Nevada tests fallout was an important source of Pu to deep-sea sediments, and that this source was likely more efficiently removed from the water column than global fallout Pu. Analysis of Pu isotopes in two sediment traps from the upper slope regions show 240Pu/239Pu ratios comparable to the ones observed in the global fallout. These results indicate that global fallout Pu is currently the main source of Pu in water column particles. Therefore, a significant fraction of global fallout Pu must still be present; either in a dissolved phase, or as biologically recycled material in the water column, or scavenged on the shelf and shelf break. Our results bring to light important questions on the application of Pu isotopes to establish sediment chronologies, since these radionuclides are shown to be tracers of bioturbation rather than accumulation processes in deep-sea sediments of the GoM, similar to previously reported results from excess 210Pb.


2021 ◽  
Vol 8 ◽  
Author(s):  
Qiang Ma ◽  
Yusheng Qiu ◽  
Run Zhang ◽  
E Lv ◽  
Yipu Huang ◽  
...  

The 210Po/210Pb disequilibrium was attempted to reveal the small-scale particle dynamics in the eastern tropical North Pacific. Seawater samples in the full water column were collected from three sites in the Tehuantepec bowl near the East Pacific Ridge for determination of dissolved and particulate 210Po and 210Pb. Our results show that TPo/TPb activity ratios in the full water column at the three sites are less than 1, with an average of 0.56, indicating that the total 210Po in the oligotrophic sea is significantly deficient. The activity ratios of DPo/DPb in the dissolved phase are less than 1, while those in the particulate phase are greater than 1 (except for the bottom 300 m), indicating fractionation between 210Po and 210Pb in the scavenging process. A negative linear relationship between 210Po deficit and silicate proves that biological activities are responsible for 210Po deficiency in the upper 200 m. However, the deficit of 210Po in the bottom 300 m may be caused by the horizontal transport of the hydrothermal plume. After correcting the horizontal contribution, the removal rates of 210Po for the 200–1,500 m and the bottom 300 m layers increased by 7.5–21 and 26.1–29.5%, respectively. Correspondingly, the variation range of the residence time of a total 210Po became smaller. Our calculations suggest that horizontal transport is acting as a stabilizer for small-scale variation in the 210Po deficit in the eastern tropical North Pacific. Our study highlights the need to pay more attention to the small-scale variation of 210Po deficit when applying 210Po/210Pb disequilibria to trace biogeochemical processes, and the mechanism responsible for this variation deserves further study.


2021 ◽  
Vol 40 (1) ◽  
pp. 15-35 ◽  
Author(s):  
Romana Melis ◽  
Lucilla Capotondi ◽  
Fiorenza Torricella ◽  
Patrizia Ferretti ◽  
Andrea Geniram ◽  
...  

Abstract. During the Late Pleistocene–Holocene, the Ross Sea Ice Shelf exhibited strong spatial variability in relation to the atmospheric and oceanographic climatic variations. Despite being thoroughly investigated, the timing of the ice sheet retreat from the outer continental shelf since the Last Glacial Maximum (LGM) still remains controversial, mainly due to a lack of sediment cores with a robust chronostratigraphy. For this reason, the recent recovery of sediments containing a continuous occurrence of calcareous foraminifera provides the important opportunity to create a reliable age model and document the early deglacial phase in particular. Here we present a multiproxy study from a sediment core collected at the Hallett Ridge (1800 m of depth), where significant occurrences of calcareous planktonic and benthic foraminifera allow us to document the first evidence of the deglaciation after the LGM at about 20.2 ka. Our results suggest that the co-occurrence of large Neogloboquadrina pachyderma tests and abundant juvenile forms reflects the beginning of open-water conditions and coverage of seasonal sea ice. Our multiproxy approach based on diatoms, silicoflagellates, carbon and oxygen stable isotopes on N. pachyderma, sediment texture, and geochemistry indicates that abrupt warming occurred at approximately 17.8 ka, followed by a period of increasing biological productivity. During the Holocene, the exclusive dominance of agglutinated benthic foraminifera suggests that dissolution was the main controlling factor on calcareous test accumulation and preservation. Diatoms and silicoflagellates show that ocean conditions were variable during the middle Holocene and the beginning of the Neoglacial period at around 4 ka. In the Neoglacial, an increase in sand content testifies to a strengthening of bottom-water currents, supported by an increase in the abundance of the tycopelagic fossil diatom Paralia sulcata transported from the coastal regions, while an increase in ice-rafted debris suggests more glacial transport by icebergs.


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