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Si element active isotopes active8/18/2023 There is no correlation between δ7Li values and uranium activity ratios for the dissolved load for non-glacial rivers, but for glacier-fed rivers there is an increase in δ7Li with increasing (234U/238U), suggesting that where physical comminution of mineral grains by glaciers is high, chemical weathering is suppressed, and vice-versa. δ7Li for the dissolved load decreases with increasing levels of dissolved silicon, and the saturation index of secondary minerals, which suggests that δ7Li decreases with increasing chemical weathering. Silicon (z 14, atomic mass 28.0855) has three stable isotopes of atomic mass units (AMU) 28Si (27.976927), 29Si (28.976495) and 30Si (29.973770), with. In turn, the δ7Li value of the dissolved load is always greater than that of the bedload, ranging from 17.0 to 43.7‰. The δ7Li value of the suspended load is always lower than that of the bedload due to preferential retention of 6Li in secondary minerals during weathering. In contrast, in non-glacial rivers, uranium activity ratios increase with distance downstream due to continued weathering in soils and of bedrock. Activity ratios in glacial rivers decrease with distance from the glacial source due to input from non-glacial tributaries which have high levels of dissolved uranium and lower activity ratios. ![]() The highest (234U/238U) values are found in glacier-fed rivers, and can be attributed to α-recoil effects, as grinding by glaciers locally enhances rates of physical weathering. Uranium activity ratios, (234U/238U), are close to secular equilibrium in the suspended and bedloads, but all dissolved load samples show values greater than unity, ranging from 1.13 to 2.41. Some elements have no stable isotopes and eventually decay to other elements. Chemical erosion rates range from 45 to 91 t/km2/yr, with lower rates being associated with glacier-fed rivers. Although most of the known elements have at least one isotope whose atomic nucleus is stable indefinitely, all elements have isotopes that are unstable and disintegrate, or decay, at measurable rates by emitting radiation. Physical erosion rates range from 920 to 2084 t/km2/yr, with the higher values associated with glacier-fed rivers. This study presents U and Li isotope and major and trace element data for the dissolved load, suspended particulates and bedload for Icelandic rivers draining predominantly basaltic catchments. Earth and Planetary Science Letters, 251(1-2) pp. Of the first 82 elements in the periodic table, 80 have isotopes considered to be stable. Riverine behaviour of uranium and lithium isotopes in an actively glaciated basaltic terrain.
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