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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Glacial effects on weathering processes: New insights from the elemental and lithium isotopic composition of West Greenland rivers
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Glacial effects on weathering processes: New insights from the elemental and lithium isotopic composition of West Greenland rivers

机译：冰川对风化过程的影响：西格陵兰河流的元素和锂同位素组成的新见解

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摘要

Greenland is by far the dominant source of glacial runoff to the oceans but the controls on the chemical and isotopic composition of this runoff are poorly known. To better constrain glacial effects on weathering processes, we have conducted elemental and lithium isotope analyses of glacial and non-glacial rivers in gneiss catchments in West Greenland. The glacial rivers have high total suspended solids (0.5 g l(-1)) and low total dissolved solids (12 mu Scm(-1)) relative to the non-glacial rivers, and they contain a higher proportion of dissolved Ca2+ and K+ because of subglacial, preferential, weathering of trace carbonates and biotite. The glacial rivers also have high SO42- because of the oxidation of trace sulphides under the ice. Both glacial and non-glacial rivers have high delta Li-7 (respectively, similar to 26 parts per thousand and similar to 30 parts per thousand) relative to the rocks from which the Li is derived (similar to 8 parts per thousand). Saturation state modelling suggests that this is due to the formation of Fe-oxyhydroxides in the non-glacial rivers, with preferential uptake of Li-6 during inner sphere sorption of Li+ on the Fe-oxyhydroxide surface. Glacial rivers, however, are undersaturated with respect to clay minerals and Fe-oxyhydroxides. Nevertheless, leaching of suspended sediments indicates that similar to 65% of the Li in these sediments is associated with Fe-oxyhydroxide phases, and the delta Li-7 value of this Li is low, similar to 5 parts per thousand. These results suggest that these Fe-oxyhydroxides formed under the ice, as a product of sulphide oxidation, with preferential uptake of Li-6 onto the mineral surface. Solubilisation of Li from these Fe-oxyhydroxide phases is unlikely to represent a significant flux of Li to the oceans. Moreover, because the difference between the 67 Li values of glacial vs non-glacial rivers is small, glaciation has not had a significant impact on the Li isotopic composition of the riverine flux delivered to the oceans in the past, even at the height of the last deglaciation.
机译：到目前为止，格陵兰是海洋冰川径流的主要来源，但对该径流的化学和同位素组成的控制知之甚少。为了更好地限制冰川对风化过程的影响，我们对西格陵兰片麻岩流域的冰川和非冰川河流进行了元素和锂同位素分析。相对于非冰川河流，冰川河流的总悬浮固体含量高（0.5 gl（-1）），总溶解固体含量低（12 mu Scm（-​​1）），并且它们含有较高比例的溶解的Ca2 +和K +，因为次冰期，优先风化的微量碳酸盐和黑云母。由于冰下微量硫化物的氧化，冰河中的SO42也很高。相对于产生锂的岩石（分别为千分之八），冰川河和非冰川河都具有较高的三角洲Li-7（分别约等于千分之26和千分之三十）。饱和状态模拟表明，这是由于在非冰川河流中形成了Fe-羟基氢氧化物，并且在Fe +羟基氧化物表面上的Li +内球吸附过程中，Li-6被优先吸收。然而，冰川河相对于粘土矿物和羟基氧化铁而言却不饱和。但是，悬浮沉积物的浸出表明，这些沉积物中约65％的Li与羟基氧化铁相相关，并且该Li的δLi-7值较低，约为千分之五。这些结果表明，在冰下形成的这些Fe-羟基氧化物是硫化物氧化的产物，优先吸收Li-6到矿物表面。从这些羟基氧化铁中溶解出的Li不太可能代表大量的Li流入海洋。此外，由于冰川河和非冰川河的67 Li值之间的差异很小，因此冰川作用对过去输送到海洋的河流通量的Li同位素组成没有显着影响，即使在高海拔地区也是如此。最后冰消。

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