A multi-proxy record of the Last Glacial Maximum and last 14,500 years of paleoenvironmental change at Lone Spruce Pond, southwestern Alaska
A multi-proxy record of the Last Glacial Maximum and last 14,500 years of paleoenvironmental change at Lone Spruce Pond, southwestern Alaska
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阿拉斯加西南部孤云杉池塘的末次盛冰期和过去 14,500 年古环境变化的多代理记录
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发表时间：
2012
影响因子：
2.1
通讯作者：
A. Werner
中科院分区：
文献类型：
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作者：
D. Kaufman;Y. Axford;R. Anderson;S. Lamoureux;D. Schindler;I. Walker;A. Werner
来自阿拉斯加西南部Lone Spruce Pond（60.007°N，159.143°W）的沉积物岩心记录了全球末次盛冰期（LGM）和过去14，500个日历年BP（14.5 cal ka）期间的古环境变化。我们分析了丰富的有机质，生物硅，碳，氮，碳和氮的同位素比和N，磁化率，和粒度分布的散装沉积物，丰富的桤木灌木（Alnus）花粉，和蚊（摇蚊科和Chaoboridae）组合在一个4.7米长的沉积序列在22米水深的沉积中心。基底单元包含可追溯到25-21 cal ka（全球LGM）的大型化石，并被解释为冰川-湖泊沉积物。开放水域要求阿克伦山冰盖的出口已经退到距离山脉顶峰6公里以内。除了枝角类和硅藻，冰川湖泥包含摇蚊符合深，贫营养条件;几个分类群与相对温暖的条件下存在，暗示全球末次盛冰期的相对温暖。冰湖单元与上覆的非冰川湖泊沉积物之间可能存在一个不整合面，这可能记录了冰川冰的再进。非冰川沉积物开始积累约14.5卡ka，高通量的矿物质和波动的物理和生物特性，通过全球冰消期，包括逆转的生物硅（BSi）含量在新仙女木（YD）。在全球冰消期，湖泊沉积物的δ 13 C值相对于其他时期更高，与低C：N比一致（8），并表明浮游植物的C的主要大气CO2来源。在整个冰消期，水生动物遗骸（摇蚊和枝角类）的浓度很低，多样性很低，没有温暖的指示类群。较高的生产和空气温度推断以下YD，当散装有机质（OM）含量（LOI 550 °C）大幅增加，并永久性地从10%增加到30%，增加的C和N丰度的趋势，增加C：N比（约12），并在沉积物的δ 13 C的减少。后YD变暖的标志是一个快速的转变，在摇蚊组合。在8.9和8.5 cal ka之间，Alnus花粉增加了两倍（25- 75%），随后BSi增加了近两倍（7- 19%），8.2 cal ka，δ 15 N开始稳步上升，反映了土壤中N的积累和反硝化作用的增加。几个摇蚊类群指示相对温暖的条件下，整个全新世。定量的摇蚊为基础的温度推断是复杂的赤杨属的扩张，并导致湖泊营养状况和生产的变化，这些变化与枝藻丰度的突然增加和持久的转变摇蚊组合。在过去的2,000年里，摇蚊组合的变化表明温度较低，BSi和OM值一般低于其最大全新世值，最小值在第七和第八世纪，并再次在十八世纪。
Sediment cores from Lone Spruce Pond (60.007°N, 159.143°W), southwestern Alaska, record paleoenvironmental changes during the global Last Glacial Maximum (LGM), and during the last 14,500 calendar years BP (14.5 cal ka). We analyzed the abundance of organic matter, biogenic silica, carbon, and nitrogen, and the isotope ratios of C and N, magnetic susceptibility, and grain-size distribution of bulk sediment, abundance of alder shrub (Alnus) pollen, and midge (Chironomidae and Chaoboridae) assemblages in a 4.7-m-long sediment sequence from the depocenter at 22 m water depth. The basal unit contains macrofossils dating to 25–21 cal ka (the global LGM), and is interpreted as glacial-lacustrine sediment. The open water requires that the outlet of the Ahklun Mountain ice cap had retreated to within 6 km of the range crest. In addition to cladocerans and diatoms, the glacial-lacustrine mud contains chironomids consistent with deep, oligotrophic conditions; several taxa associated with relatively warm conditions are present, suggestive of relative warmth during the global LGM. The glacial-lacustrine unit is separated from the overlying non-glacial lake sediment by a possible disconformity, which might record a readvance of glacier ice. Non-glacial sediment began accumulating around 14.5 cal ka, with high flux of mineral matter and fluctuating physical and biological properties through the global deglacial period, including a reversal in biogenic-silica (BSi) content during the Younger Dryas (YD). During the global deglacial interval, the δ13C values of lake sediment were higher relative to other periods, consistent with low C:N ratios (8), and suggesting a dominant atmospheric CO2 source of C for phytoplankton. Concentrations of aquatic faunal remains (chironomids and Cladocera) were low throughout the deglacial interval, diversity was low and warm-indicator taxa were absent. Higher production and air temperatures are inferred following the YD, when bulk organic-matter (OM) content (LOI 550 °C) increased substantially and permanently, from 10 to 30 %, a trend paralleled by an increase in C and N abundance, an increase in C:N ratio (to about 12), and a decrease in δ13C of sediment. Post-YD warming is marked by a rapid shift in the midge assemblage. Between 8.9 and 8.5 cal ka, Alnus pollen tripled (25–75 %), followed by the near-tripling of BSi (7–19 %) by 8.2 cal ka, and δ15N began a steady rise, reflecting the buildup of N and an increase in denitrification in soils. Several chironomid taxa indicative of relatively warm conditions were present throughout the Holocene. Quantitative chironomid-based temperature inferences are complicated by the expansion of Alnus and resulting changes in lake nutrient status and production; these changes were associated with an abrupt increase in cladoceran abundance and persistent shift in the chironomid assemblage. During the last 2,000 years, chironomid-assemblage changes suggest cooler temperatures, and BSi and OM values were generally lower than their maximum Holocene values, with minima during the seventh and eighth centuries, and again during the eighteenth century.