نتایج جستجو برای: geochemical tracers
تعداد نتایج: 20295 فیلتر نتایج به سال:
Time-series observations of geochemical tracers and diazotroph abundances in the northern subtropical gyres suggest variability in nitrogen fixation on interannual and longer timescales. Using a highly idealized model of the biogeochemistry and ecology of a subtropical gyre, we explore the previously proposed hypothesis that such variability is regulated by an internal “biogeochemical oscillato...
The composition and photochemical transformations of dissolved organic matter (DOM) in the northern North Pacific Ocean were investigated at the molecular level using ultrahigh resolution mass spectrometry and geochemical tracers. Analyses included vertical profiles and experiments in which deep sea DOM was exposed to sunlight and incubated in the dark. The composition of the deep sea DOM was f...
We present a methodology for calculating the conditional temporal moments of kinetically sorbing solutes based on the conditional temporal moments of non-reactive tracers. The methodology is based on a Lagrangian description of solute transport in heterogeneous media, and it can be applied to a large variety of flow configurations and mass-transfer ratelimited processes. A stochastic approach i...
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The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemica...
The positions of Laurentia and other landmasses in the Precambrian supercontinent of Rodinia are controversial. Although geological and isotopic data support an East Antarctic fit with western Laurentia, alternative reconstructions favor the juxtaposition of Australia, Siberia, or South China. New geologic, age, and isotopic data provide a positive test of the juxtaposition with East Antarctica...
the production and application of pet tracers has been a unique step in the progress of nuclear medicine in last two decades. the most important pet tracers include f-18, c-11 and n-13 radioisotopes and many nuclear medicine centers throughout the globe are using them. however some new tracers are under their way to the mass administration, currently being in the clinical trials or preliminary ...
The ratios of stable isotopes of certain elements in rocks and minerals have strong regional characteristics that are reflected in atmospheric components, in water, and in the living organisms that form Earth's surface environment as well as in agricultural and fishery products. Geologically derived stable isotope ratios can be used as a tracer for the source of many kinds of substances, with c...
Sediment sources fingerprinting is needed as an autonomous tool for erosion prediction, validation of soil erosion models, monitoring of sediment budget and consequently for selecting soil conservation practices and sediment control methods at the catchment scale. Apportioning of eroded-soil into multiple sources using natural tracers is an integrated approach in soil erosion and sediment studi...
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