Palaeolimnological and sedimentary responses to Holocene forest retreat in the Scandes Mountains, west-central Sweden
Palaeolimnological and sedimentary responses to Holocene forest retreat in the Scandes Mountains, west-central Sweden
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瑞典中西部斯坎德斯山脉全新世森林退缩的古湖泊学和沉积响应
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发表时间：
2004
期刊：
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通讯作者：
G. Possnert
中科院分区：
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作者：
D. Hammarlund;G. Velle;B. Wolfe;T. Edwards;L. Barnekow;J. Bergman;Sofia Holmgren;Sara Lamme;I. Snowball;B. Wohlfarth;G. Possnert
研究人员对西班牙湖（Lake Spaime）过去10700年积累的沉积物进行了一系列分析。西班牙湖是瑞典中西部斯坎德斯山脉现代高山冻原地带的一个小型水文开放水体。本研究旨在评估：(1)气候变化迫使该地区晚全新世海拔树木极限降低的性质，其时间由先前基于亚化石木材放射性碳定年的研究得知；(2)这些植被变化对水生生态系统的影响。树花粉和植物大化石资料证实，至少从约9700 cal. BP到约3700 cal. BP，湖泊流域的树木持续存在。尽管生长季节的温度通常被认为是驱动该地区北方森林树木极限变化的主要因素，但基于chironomides的7月平均气温重建表明，全新世晚期的当地森林砍伐并未伴随着显著的降温。树限退缩更可能是由于有效水分的增加和生长季节长度的缩短引起的。Spaime湖对这种气候和植被变化组合的生态水文响应包括初级生产力的下降，如沉积物有机质含量的突然减少所表明的那样，而有机613C、615N和C/N的相关增加表明，森林砍伐后流域营养物质的通量减少和平衡改变。水生生产力的下降还表现为矿物磁性的明显变化，从以生物成因的细粒磁铁矿为主的高磁性浓度组合到以背景水平的粗粒碎屑磁铁矿为主的组合。
A suite of analyses was performed on sediments accumulated during the last 10 700 years in Lake Spaime, a small, hydrologically open water body in the modem alpine tundra zone of the Scandes Mountains, west-central Sweden. The study aimed to evaluate (1) the nature of climate changes that forced the late-Holocene lowering of altitudinal tree limit in the region, the timing of which is known from prior studies based on radiocarbon dating of subfossil wood, and (2) the impact of these vegetational changes on an aquatic ecosystem. Arboreal pollen and plant macrofossil data confirm the persistence of trees in the lake catchment at least from c. 9700 cal. BP until c. 3700 cal. BP. Although growing-season temperature is commonly believed to be the dominant factor driving boreal forest tree-limit variations in the region, a chironomid-based reconstruction of mean July air temperature suggests that local deforestation during the late Holocene was not accompanied by a significant cooling. The tree-limit retreat was more likely caused by increasing effective moisture and declining length of the growing season. The ecohydrological response of Lake Spaime to this combination of climate and vegetational changes included a decline in primary productivity, as indicated by an abrupt decrease in sediment organic matter content, while associated increases in organic 613C, 615N and C/N point to diminished fluxes and altered balance of catchment derived nutrients following deforestation. The decline in aquatic productivity is also marked by a distinct change in the mineral magnetic properties, from a high magnetic concentration assemblage dominated by fine-grained magnetite of biogenic origin to one dominated by background levels of coarse-grained detrital magnetite.