2 research outputs found
Lability of copper bound to humic acid
Geochemical speciation models generally include the assumption that all metal bound to humic acid and fulvic acid (HA, FA) is labile. However, in the current study, we determined the presence of a soluble ânon-labileâ Cu fraction bound to HA extracted from grassland and peat soils. This was quantified by determining isotopically-exchangeable Cu (E-value) and EDTA-extraction of HA-bound Cu, separated by size-exclusion chromatography (SEC) and assayed by coupled ICP-MS. Evidence of time-dependent Cu fixation by HA was found during the course of an incubation study (160 days); up to 50% of dissolved HA-bound Cu was not isotopically exchangeable. This result was supported by extraction with EDTA where approximately 40% of Cu remained bound to HA despite dissolution in 0.05 M Na2-EDTA. The presence of a substantial non-labile metal fraction held by HA challenges the assumption of wholly reversible equilibrium which is central to current geochemical models of metal binding to humic substances
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Solar Influence on Global and Regional Climates
The literature relevant to how solar variability influences climate is vastâbut
much has been based on inadequate statistics and non-robust procedures. The common
pitfalls are outlined in this review. The best estimates of the solar influence on the global
mean air surface temperature show relatively small effects, compared with the response to
anthropogenic changes (and broadly in line with their respective radiative forcings).
However, the situation is more interesting when one looks at regional and season variations
around the global means. In particular, recent research indicates that winters in Eurasia
may have some dependence on the Sun, with more cold winters occurring when the solar
activity is low. Advances in modelling ââtop-downââ mechanisms, whereby stratospheric
changes influence the underlying troposphere, offer promising explanations of the observed
phenomena. In contrast, the suggested modulation of low-altitude clouds by galactic
cosmic rays provides an increasingly inadequate explanation of observations