Glacial–interglacial environmental changes inferred from molecular and compound-specific δ13C analyses of sediments from Sacred Lake, Mt. Kenya
Glacial–interglacial environmental changes inferred from molecular and compound-specific δ13C analyses of sediments from Sacred Lake, Mt. Kenya
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DOI：
10.1016/s0016-7037(99)00074-5
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发表时间：
1999-05
影响因子：
5
通讯作者：
Y. Huang;F. Street-Perrott;R. Perrott;P. Metzger;G. Eglinton
中科院分区：
文献类型：
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作者：
Y. Huang;F. Street-Perrott;R. Perrott;P. Metzger;G. Eglinton
分子地层分析，包括脂质分布和化合物特异性 δ13C 测量，已在肯尼亚山圣湖沉积物岩心的 15 个水平上进行，圣湖是一个高海拔（海拔 2350 米）淡水湖，其记录从末次冰期（>40,000 卡年BP）一直延伸到目前的间冰期。使用特定来源的生物标志物独立评估陆地和水生有机物来源。陆生高等植物的长链正烷基脂质的 δ13C 值表现出较大的冰期到间冰期的转变：来自末次盛冰期 (LGM) 的值（-20 至 -18%）表明陆地植被以 C4 草或莎草为主，而来自全新世早期的值（-34% 至 -27%）则反映了 C3 植物对集水区的重新定植，这与植被的快速上升一致。上部林线。扫描电子显微镜 (SEM) 证实，特定的藻类生物标志物非常丰富，包括微藻 Botryococcus braunii 的五种新颖结构的不饱和烃。藻类生物标志物显示出超过 25‰ 的极端 δ13C 变化，末次盛冰期 (LGM) 的升高值为 -5.1‰，而全新世初期的最小值为 -30.3‰。藻类生物标志物分子分布的重大变化与这种大的 δ13C 变化平行，无环类异戊二烯烃在最后一次冰期中占主导地位，环状类异戊二烯烃在全新世占主导地位。末次盛冰期的低大气 CO2 (pCO2) 分压有利于具有 CO2 浓缩机制的光合生物，包括陆地 C4 草和淡水绿藻。因此，除了气候和当地环境因素的影响外，冰期/间冰期 pCO2 的变化，特别是 CO2:O2 比率的变化，对肯尼亚山的陆地和水生生态系统也产生了重大影响。
Molecular stratigraphic analyses, including lipid distributions and compound-specific δ13C measurements, have been performed at 15 levels in a sediment core from Sacred Lake, Mt. Kenya, a high-altitude (2350 m a.s.l.) freshwater lake with a record extending from the last glacial (>40,000 cal. yr BP) through the present interglacial. Terrestrial and aquatic organic-matter sources were independently assessed using source-specific biomarkers. δ13C values of long-chain n-alkyl lipids from terrestrial higher plants exhibit large glacial to interglacial shifts: those from the last glacial maximum (LGM) (−20 to −18‰) indicate a terrestrial vegetation dominated by C4grasses or sedges, whereas those from the early Holocene (−34 to −27‰) reflect recolonization of the catchment area by C3plants, consistent with a rapid rise in the upper treeline. Specific algal biomarkers, including five unsaturated hydrocarbons of novel structure ascribed to the microalga Botryococcus braunii, were abundant, as confirmed by scanning electronic microscopy (SEM). An extreme δ13C shift of over 25‰ is displayed by the algal biomarkers, an elevated value of −5.1‰ at the last glacial maximum (LGM) contrasting with a minimum value of −30.3‰ at the beginning of the Holocene. A major change in the molecular distributions of the algal biomarkers parallels this large δ13C shift, with acyclic isoprenoid hydrocarbons dominating the last glacial and cyclic isoprenoid hydrocarbons the Holocene. The low atmospheric partial pressure of CO2(pCO2) at the LGM would favour photosynthetic organisms possessing CO2-concentrating mechanisms, including terrestrial C4grasses and freshwater green algae. Hence, glacial/interglacial changes in pCO2, and in the CO2:O2ratio in particular, had a significant impact on both terrestrial and aquatic ecosystems on Mt. Kenya, in addition to the effects of climate and local environmental factors.