科研之友
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摘要
Understanding the mechanism associated with rates of weathering and evolution of rockssedimentsoilpaleosol in alpine environments raises questions related to the impact of microbial mediation versus various diverse abiotic chemical/physical processes, even including the overall effect of cosmic impact/airburst during the early stage of weathering in Late Glacial (LG) deposits. This study is of a chronosequence of soils/paleosols, with an age range that spans the post-Little Ice Age (post-LIA; <150 yr), the Little Ice Age (LIA; AD 1500-1850), the middle Neoglacial (approximate to 3 ka)-Younger Dryas (YD; <12.8 ka), and the LG (<15 ka). The goal is to elicit trends in weathering, soil morphogenesis, and related eubacterial population changes over the past 13-15 k.yr. The older LG/YD paleosols in the sequence represent soil morphogenesis that started during the closing stage of Pleistocene glaciation. These are compared with undated soils of mid- to late Neoglacial age, the youngest of LIA and post-LIA age. All profiles formed in a uniform parent material of metabasalt composition and in moraine, rockfall, protalus, and alluvial fan deposits. Elsewhere in Europe, North America, and Asia, the cosmic impact/airburst event at 12.8 ka often produced a distinctive, carbon-rich black mat layer that shows evidence of high-temperature melting. At this alpine site, older profiles of similar LG age contain scorched and melted surface sediments that are otherwise similar in composition to the youngest/thinnest profiles developing in the catchment today. Moreover, microbial analysis of the sediments offers new insight into the genesis of these sediments: the C and Cu (u = unweathered) horizons in LG profiles present at 12.8 ka (now Ah/Bw) show bacterial population structures that differ markedly from recent alluvial/protalus sample bacterial populations. We propose here that these differences are, in part, a direct consequence of the age/cosmic impact/weathering processes that have occurred in the chronosequence. Of the several questions that emerge from these sequences, perhaps the most important involve the interaction of biotic-mineral factors, which need to be understood if we are to generally fully appreciate the role played by microbes in rock weathering.
- 出版日期2016-3
