Organic Carbon-14 in the Amazon River System

Hedges, John I.; Ertel, John R.; Quay, Paul D.; Grootes, Pieter Meiert; Richey, Jeffrey E.; Devol, Allan H.; Farwell, George; Schmidt, Fred W.; Salati, Enéas

doi:10.1126/science.231.4742.1129

Cited by 176 publications

(104 citation statements)

References 20 publications

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“…1 caption) is present in the HMW fraction of colloidal material (COM~0), and also in COMI from near-shore environments. The presence of contemporary fractions of DOM in freshwater endmembers has been previously observed by Hedges et al (1986) for the Amazon River. Our results indicate that Gulf of Mexico colloids have 113-57% modern ~4C (i.e., apparent ages of --<40 to 4.5 x 103 years aP, or A 14C of 126 to -432%0; note that 100% = pre-bomb = pre-1950, and 114% = 1992 value).…”

Section: C Evidence For Differential Ages Of Comsupporting

confidence: 53%

Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments

Santschi

Guo

Baskaran

et al. 1995

Geochimica et Cosmochimica Acta

178

100

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Abstract--Previous work has suggested that apparent old ~4C ages for oceanic DOC are the result of mixing of different organic carbon fractions. This report provides direct evidence for a contemporary ~4C age of a high-molecular-weight (HMW) fraction of colloidal organic carbon (-> 10 kD). Colloidal organic matter, COM~0 (from 10 kDaltons (kD) to 0.2/zm), isolated from the upper water column of the Gulf of Mexico and the Middle Atlantic Bight (MAB) region, generally has a contemporary age (i.e., younger than a few decades), while COMI (from 1 kD to 0.2 pm), is apparently old: 380-4500 y BP. Thus, HMW COM~0 (3-5% of DOC) from the upper water column is derived from living particulate organic matter (POM) and cycles rapidly, while a significant fraction of low-molecular-weight (-< 1 kD) DOM is likely more refractory, and cycles on much longer time scales. The presence of pigment biomarker compounds in COMI from the upper water column points to selected phytoplankton species as one of the sources of COM. Terrestrial carbon as another source of COM is suggested from the inverse correlation between A ~4C and 6 ~3C values, as well as the increasing 613C values with increasing salinity. 2~l'h-derived turnover times of COM~0 and COM~ from both the Gulf of Mexico and MAB are consistently short, 1-20 and 3-30 days, respectively. These short residence times support the hypothesis that ~4C ages of colloidal fractions of DOC are the result of COM fractions being a mixture of several endmembers with fast and slow turnover rates.

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Section: C Evidence For Differential Ages Of Comsupporting

confidence: 53%

Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments

Santschi

Guo

Baskaran

et al. 1995

Geochimica et Cosmochimica Acta

178

100

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“…A model describing the composition and fate of particulate organic matter in large tropical rivers [1] was developed from a series of studies of the major rivers of the Amazon basin [2][3][4][5][6]. These authors used 13 C analyses to show that leaves of C3 plants are the ultimate source of carbon in coarse particulate organic material (CPOM, >63 mm), fine particulate organic material (FPOM, 63-0.1 mm), and ultrafiltered dissolved organic matter (UDOM; o0.1 mm and >100 kDa).…”

Section: Introductionmentioning

confidence: 99%

Composition of particulate and dissolved organic matter in a disturbed watershed of southeast Brazil (Piracicaba River basin)

Krusche

2002

Water Research

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The elemental and isotopic composition of particulate and dissolved organic matter was investigated in the Piracicaba River basin, S* ao Paulo State, Brazil. Comparison of riverine organic matter from the Piracicaba River basin, a region where rivers and streams receive urban sewage and industrial effluents, with data reported for the pristine Amazon system revealed significant differences associated with anthropogenic impacts. One important difference was N enrichment in the particulate organic material of the Piracicaba basin rivers, due to (a) urban and industrial effluents, and (b) enhanced phytoplankton growth, which results from the combination of nutrient enrichment and damming of sections of the rivers. Radiocarbon concentrations were overall more depleted (older 14 C age) in the Piracicaba basin rivers than in the Amazon, which may reflect the importance of soil erosion in the former. Analyses of stable and radioactive carbon isotopes and lignin-derived compounds indicated that coarse particulate organic material is composed of a mixture of soil particles and degraded organic matter from C3 and C4 vascular plants. Fine particulate organic material was composed mainly of soil particles and phytoplankton cell remains, the latter especially during low water. Ultrafiltered dissolved organic matter was the most degraded fraction according to its lignin oxidation products, and showed the greatest influence of C4 plant sources. r

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“…This approach is especially relevant given the extensive organic geochemical studies conducted on the modern Amazon River (Ertel et al, 1986;Hedges et al, 1986aHedges et al, , 1986b1992;Quay et al, 1992;Richey et al, 1990) and Amazon shelf (Showers and Angle, 1986;Aller et al, 1991;Blair and Aller, 1995;Goñi et al, 1995). In addition, organic analyses provide data that are independent and complementary information to palynological and inorganic geochemical studies of the Amazon Fan .…”

Section: Introductionmentioning

confidence: 99%

Record of terrestrial organic matter composition in Amazon Fan sediments

Goñi¹

1997

Proceedings of the Ocean Drilling Program, 155 Scientific Results

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Elemental, stable carbon isotope, and lignin analyses were carried out to characterize the organic matter in sediments from Site 932 on the Amazon Fan. The lignin compositions of sedimentary organic matter in Subunits IIA and IIB at this site resembled those of fine-and coarse-suspended particles from the present-day Amazon River. The lignin concentrations and isotopic composition of organic carbon suggest that the organic matter in Subunit IIA sediments is composed of varying amounts of marine (85% to 20%) and terrestrial (15% to 80%) contributions, whereas in Subunit IIB, it is exclusively terrestrial in origin. The compositions of lignin phenols indicate that the vegetation of the Amazon Basin did not change appreciably during the period represented by the sediments in Site 932. The data also illustrate the depositional differences that were responsible for the formation of the various lithologic units at the site.

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Organic Carbon-14 in the Amazon River System

Cited by 176 publications

References 20 publications

Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments

Isotopic evidence for the contemporary origin of high-molecular weight organic matter in oceanic environments

Composition of particulate and dissolved organic matter in a disturbed watershed of southeast Brazil (Piracicaba River basin)

Record of terrestrial organic matter composition in Amazon Fan sediments

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