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.

scholarly journals Historic carbon burial spike in an Amazon floodplain lake linked to riparian deforestation near Santarem, Brazil

2017 ◽  
Author(s):  
Luciana M. Sanders ◽  
Kathryn Taffs ◽  
Debra Stokes ◽  
Christian J. Sanders ◽  
Alex Enrich-Prast ◽  
...  
Keyword(s):  
Amazon Basin ◽  
Sediment Accumulation ◽  
Lacustrine Sediments ◽  
Open Water ◽  
Depositional Environments ◽  
Floodplain Lake ◽  
Δ13c And Δ15n ◽  
Amazon Floodplain ◽  
Carbon Burial ◽  
Deforestation Rates

Abstract. The forests along the Amazon Basin produce significant quantities of organic material, a portion of which is deposited in floodplain lakes. However, potentially important effects of ongoing deforestation in the watershed on these carbon fluxes is still poorly understood. Here, a sediment core was extracted from an Amazon floodplain lake to examine the relationship between carbon burial and land cover/use. Historical records from 1942 and satellite data from 1975 were used to calculate deforestation rates between 1942 and 1975, and 1975 to 2008 in four zones with different distances from the margins of the lake and its tributaries (100, 500, 1000 and 6000-m buffers). Sediment accumulation rates were determined from the 240+239Pu signatures and the excess 210Pb method, reaching near 3.8 and 4.2 mm year−1 in the last 60 and 120 years respectively. The average carbon burial rates ranged between 100 and 350 g C m−2 year−1, with pulses of high carbon burial derived from the forest vegetation, as indicated by δ13C and δ15N signatures, which corresponded to heavy deforestation in the 1940 and 50s. Finally, our results revealed a potentially important spatial dependence of the OC burial in Amazon lacustrine sediments in relation to deforestation rates in the catchment. These deforestation rates were more intense in the riparian vegetation (100-m buffer) during the period 1942–1975 and the larger open water areas (500, 1000 and 6000-m buffer) during 1975–2008. The continued removal of vegetation from the interior of the forest was not related to the peak of OC burial in the lake, but only the riparian deforestation around 1950. Our novel findings suggest the importance of abrupt and temporary events in which some of the biomass released by the deforestation, especially restricted to areas along open water edges, might reach the depositional environments in the floodplain of the Amazon Basin.

Radiometric dating of the United Kingdom SWAP sites

1990 ◽  
Vol 327 (1240) ◽  
pp. 233-238 ◽  
Keyword(s):  
Sediment Cores ◽  
Radiometric Dating ◽  
Recent Sediment ◽  
Accumulation Rates ◽  
Water Acidification ◽  
Sediment Record ◽  
The United Kingdom ◽  
Surface Water Acidification ◽  
Study Sites ◽  
Gamma Assay

Measurements of 210 Pb by direct gamma assay have been used to date sediment cores from Surface Water Acidification Project (SWAP) study sites in the U.K. The results were checked against additional dating evidence from the artificial fallout isotopes 137 Cs and 241 Am. At one of the sites, Devoke Water in Cumbria, the 137 Cs and 241 Am data were crucial in identifying a recent sediment hiatus. At sites with recently afforested catchments the sediment record indicated substantial increases in accumulation rates.

Reconstructing the Rate of Accumulation of Lake Sediment: The Effect of Sediment Focusing

1975 ◽  
Vol 5 (4) ◽  
pp. 541-550 ◽  
Author(s):  
John T. Lehman
Keyword(s):  
Temporal Variation ◽  
Lake Sediment ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Maximum Depth ◽  
Accumulation Rates ◽  
Sediment Focusing ◽  
Regional History ◽  
Rate Of Accumulation

Use of accumulation rates of pollen or minerals to infer regional history is complicated by nonuniform deposition of lake sediment. Sediment focusing, direction of sediment to the deepest part of a basin, can introduce a discrepancy between changes in accumulation rates measured directly from sediment cores and actual changes in influx of sediment or pollen to a lake. This difference depends on values and temporal variation of the ratio of mean depth to maximum depth in a basin as it fills. Several models of sediment accumulation show how measurements from a single core can be transformed to yield basinwide influx rates, and how the distortion due to sediment focusing can be assessed. Basins shaped like hyperboloids or frustums may introduce much greater distortions than basins conforming to ellipsoid or sinusoid shapes.

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 Vertical and lateral flux on the continental slope off Pakistan: correlation of sediment core and trap results

2014 ◽  
Vol 11 (12) ◽  
pp. 3107-3120 ◽  
Author(s):  
H. Schulz ◽  
U. von Rad
Keyword(s):  
Continental Slope ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Lower Boundary ◽  
Distribution Patterns ◽  
Sediment Traps ◽  
Accumulation Rates ◽  
Fine Grained ◽  
Minimum Zone ◽  
The Individual

Abstract. Due to the lack of bioturbation, the varve-laminated muds from the oxygen minimum zone (OMZ) off Pakistan provide a unique opportunity to precisely determine the vertical and lateral sediment fluxes in the nearshore part of the northeastern Arabian Sea. West of Karachi (Hab area), the results of two sediment trap stations (EPT and WPT) were correlated with 16 short sediment cores on a depth transect crossing the OMZ. The top of a distinct, either reddish- or light-gray silt layer, 210Pb-dated as AD 1905 ± 10, was used as an isochronous stratigraphic marker bed to calculate sediment accumulation rates. In one core, the red and gray layer were separated by a few (5–10) thin laminae. According to our varve model, this contributes < 10 years to the dating uncertainty, assuming that the different layers are almost synchronous. We directly compared the accumulation rates with the flux rates from the sediment traps that collected the settling material within the water column above. All traps on the steep Makran continental slope show exceptionally high, pulsed winter fluxes of up to 5000 mg m−2 d−1. Based on core results, the flux at the seafloor amounts to 4000 mg m−2 d−1 and agrees remarkably well with the bulk winter flux of material, as well as with the flux of the individual bulk components of organic carbon, calcium carbonate and opal. However, due to the extreme mass of remobilized matter, the high winter flux events exceeded the capacity of the shallow traps. Based on our comparisons, we argue that high-flux events must occur regularly during winter within the upper OMZ off Pakistan to explain the high accumulations rates. These show distribution patterns that are a negative function of water depth and distance from the shelf. Some of the sediment fractions show marked shifts in accumulation rates near the lower boundary of the OMZ. For instance, the flux of benthic foraminifera is lowered but stable below ~1200–1300 m. However, flux and sedimentation in the upper eastern Makran area are dominated by the large amount of laterally advected fine-grained material and by the pulsed nature of the resuspension events at the upper margin during winter.

scholarly journals Radiocarbon Dating, Chronologic Framework, and Changes in Accumulation Rates of Holocene Estuarine Sediments from Chesapeake Bay

2002 ◽  
Vol 57 (1) ◽  
pp. 58-70 ◽  
Author(s):  
Steven M. Colman ◽  
Pattie C. Baucom ◽  
John F. Bratton ◽  
Thomas M. Cronin ◽  
John P. McGeehin ◽  
...  
Keyword(s):  
Chesapeake Bay ◽  
Deep Water ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Complex Mixture ◽  
Estuarine Sediments ◽  
Accumulation Rates ◽  
Pollen Stratigraphy ◽  
Mass Accumulation Rates ◽  
Mass Accumulation

AbstractRapidly accumulating Holocene sediments in estuaries commonly are difficult to sample and date. In Chesapeake Bay, we obtained sediment cores as much as 20 m in length and used numerous radiocarbon ages measured by accelerator mass spectrometry methods to provide the first detailed chronologies of Holocene sediment accumulation in the bay. Carbon in these sediments is a complex mixture of materials from a variety of sources. Analyses of different components of the sediments show that total organic carbon ages are largely unreliable, because much of the carbon (including coal) has been transported to the bay from upstream sources and is older than sediments in which it was deposited. Mollusk shells (clams, oysters) and foraminifera appear to give reliable results, although reworking and burrowing are potential problems. Analyses of museum specimens collected alive before atmospheric nuclear testing suggest that the standard reservoir correction for marine samples is appropriate for middle to lower Chesapeake Bay. The biogenic carbonate radiocarbon ages are compatible with 210Pb and 137Cs data and pollen stratigraphy from the same sites.Post-settlement changes in sediment transport and accumulation is an important environmental issue in many estuaries, including the Chesapeake. Our data show that large variations in sediment mass accumulation rates occur among sites. At shallow water sites, local factors seem to control changes in accumulation rates with time. Our two relatively deep-water sites in the axial channel of the bay have different long-term average accumulation rates, but the history of sediment accumulation at these sites appears to reflect overall conditions in the bay. Mass accumulation rates at the two deep-water sites rapidly increased by about fourfold coincident with widespread land clearance for agriculture in the Chesapeake watershed.

scholarly journals Comparative 210Pb, 137Cs, and Pollen Geochronologies of Sediments from Lakes Ontario and Erie

1978 ◽  
Vol 10 (2) ◽  
pp. 256-278 ◽  
Author(s):  
J.A. Robbins ◽  
D.N. Edgington ◽  
A.L.W. Kemp
Keyword(s):  
Lake Erie ◽  
Sediment Cores ◽  
Sediment Accumulation ◽  
Radioactive Decay ◽  
Storm Surges ◽  
Accumulation Rates ◽  
Near Surface ◽  
Western Lake ◽  
Physical Mixing ◽  
Regional Forest

The distribution of 210Pb, 137Cs, and Ambrosia (ragweed) pollen in two sediment cores from Lake Ontario and in three cores from Lake Erie provides independent estimates of sediment accumulation rates. Geochronology with 210Pb is based on radioactive decay of the isotope following burial in sediments. The method can reveal with precision changes in sedimentation occurring over the past 100 yr or so. Geochronologies with 137Cs and Ambrosia are based on the occurrence of a horizon corresponding, respectively, to the onset of nuclear testing 25 yr ago and to regional forest clearance in the middle 1800s. These methods provide estimates of long-term average sediment accumulation rates. In all but one core, the distributions of 137Cs and 210Pb indicate no physical mixing of near-surface sediments. In two cores, including one from central Lake Erie collected by diver, all three estimates of sedimentation rates are in excellent agreement. In two other cores, rates based on 210Pb are significantly higher than those inferred from Ambrosia pollen profiles. Lower average rates appear to result from occasional massive losses of sediments. Such events, apparent in the distribution of 210Pb but not in pollen records, correlate with the occurrence of major storm surges on the lakes during this century. In one core from western Lake Erie, exponential distributions of both 210Pb and Ambrosia appear to be artifacts which may result from extensive biological or physical reworking of sediments in shallow water (11 m). Previous indications of increased sedimentation in Lake Erie since about 1935 based on Castanea (chestnut) pollen data are not substantiated.

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