Evidence of multiple thermokarst lake generations from an 11800-year-old permafrost core on the northern Seward Peninsula, Alaska
Evidence of multiple thermokarst lake generations from an 11800-year-old permafrost core on the northern Seward Peninsula, Alaska
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DOI：
10.1111/bor.12186
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发表时间：
2016-10-01
期刊：
影响因子：
2.2
通讯作者：
Grosse, Guido
中科院分区：
文献类型：
--
作者：
Lenz, Josefine;Wetterich, Sebastian;Grosse, Guido
永久冻土退化在一定时间尺度上影响北极景观的形态、生物地球化学循环和水文。为了重建早至晚全新世永久冻土和热喀斯特动力学的时间模式，需要特定地点的古记录。在这里，我们对阿拉斯加苏厄德半岛北部一个干涸湖盆的 350 厘米长的永久冻土核心进行了多代理研究，揭示了白令陆桥中心位置的晚冰期到全新世热岩溶湖泊动态。利用放射性碳测年、微型古生物学（介形类和甲壳动物）、沉积学（粒度分析、磁化率、火山灰分析）、地球化学（总氮和碳、总有机碳、C-13(org)）和地面冰的稳定水同位素（O-18、D、右）可以重建几个不同的热喀斯特湖阶段。其中包括位于核心底部的前湖泊环境，其特征是魔鬼山玛珥火山灰（22800 +/- 280cal.a BP，A 单元），由于随后在 11800cal 左右开始形成深热喀斯特湖，该环境已在某些地方垂直下沉。 BP（B 单元）。大约9000cal。 a BP 该湖泊从稳定的沉积环境转变为非常动态的湖泊系统（C 单元），其特征是湖泊水位波动、潜在的中间湿地发育以及岸沉积物的扩张和侵蚀。该湖在 1060cal 时完全排水。 a BP，包括排水后沉积物从顶部向下冻结至154cm和陆地泥炭的逐渐积累（D单元），以及均匀向上的talik再冻结。这是自 11800cal 以来多代热喀斯特湖的基于岩心的重建。 a BP 提高了我们对热喀斯特湖泊从起始到排水的时间尺度的理解，展示了晚冰期和全新世期间白令海峡中部富含冰的永久冻土地区复杂的景观演化，并增强了我们对北极受热喀斯特影响地区的生物地球化学循环的理解。
Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site-specific palaeo-records are needed. Here we present a multi-proxy study of a 350-cm-long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial toHolocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain-size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, C-13(org)) and stable water isotopes (O-18, D, dexcess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre-lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22800 +/- 280cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11800cal. a BP (Unit B). At about 9000cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060cal. a BP, including post-drainage sediment freezing from the top down to 154cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core-based reconstruction of multiple thermokarst lake generations since 11800cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice-rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst-affected regions of the Arctic.