Distinct Permafrost Conditions Across the Last Two Glacial Periods in Midlatitude North America
Distinct Permafrost Conditions Across the Last Two Glacial Periods in Midlatitude North America
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DOI：
10.1029/2019gl083951
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发表时间：
2019-11-28
影响因子：
5.2
通讯作者：
Cheng, Hai
中科院分区：
文献类型：
--
作者：
Batchelor, Cameron J.;Orland, Ian J.;Cheng, Hai
在过去的冰川时期，北美的大部分地区都被永久冻土覆盖。然而，这些古冻土条件的时间和范围仍然模糊不清。在这里，我们提出了一个250,000年的记录，从中纬度的北美洞穴的洞穴沉积物的增长，并报告141 U-Th年龄与间断的增长，反映了发展的时间连续的永久冻土。结合U-Th年龄从其他洞穴沉积物的研究，我们表明，区域冻土条件发生在前两次冰期的最大值，但在倒数第二（海洋同位素阶段6，MIS 6）与最后（MIS 2）冰期的持续时间明显较短。值得注意的是，海洋表面温度网络表明，在MIS 6的高潮期间，中低纬度温度比MIS 2高0.9摄氏度+/- 0.2摄氏度。我们的研究结果说明了发展区域古冻土记录的重要性，并强调了冰川期的冻土条件相对较小的差异，在全球范围的temperature.Plain语言摘要冻土是一个重要的水库的碳在冰川期。然而，由于缺乏古冻土指标，我们对最近冰川作用期间冻土条件的时间和空间范围的了解还很缺乏。在这里，我们提出了一个新的，高精度的洞穴沉积物生长在威斯康星州（美国）洞穴，在过去的两个冰川期约束冻土条件年表。新的记录表明，永久冻土条件持续了18万年的最后一个冰期的高潮，但在倒数第二个冰期短暂。我们的发现得到了海面温度重建的支持，表明倒数第二次冰期比末次冰期温暖近1摄氏度。这些结果为定量研究多年冻土对过去温度变化的敏感性提供了有用的信息。
During past glacial periods, extensive areas of North America were covered by permafrost. The timing and extent of these paleo-permafrost conditions, however, remains ambiguous. Here we present a 250,000-year record of speleothem growth from a midlatitude North American cave and report 141 U-Th ages with hiatuses in growth that reflect the development of temporally continuous permafrost. Combined with U-Th ages from other speleothem studies, we demonstrate that regional permafrost conditions occurred during both of the prior two glacial maxima but were markedly shorter in duration during the penultimate (Marine Isotope Stage 6, MIS 6) versus the last (MIS 2) glacial period. Notably, a network of sea surface temperatures indicates that mid- and low-latitude temperatures were 0.9 degrees C +/- 0.2 degrees C warmer during the culmination of MIS 6 versus MIS 2. Our results illustrate the importance of developing regional paleo-permafrost records and highlight the sensitivity of permafrost conditions during glacial periods to relatively small differences in global-scale temperature.Plain Language Summary Permafrost is an important reservoir of carbon during glacial periods. Our understanding of the timing and spatial extent of permafrost conditions during recent glaciations, however, is lacking because of a paucity of paleo-permafrost indicators. Here we present a new, high-precision chronology of speleothem growth in a Wisconsin (USA) cave that constrains permafrost conditions during the last two glacial periods. The new record suggests that permafrost conditions endured for 18 ka during the culmination of the last glacial period but were ephemeral during the penultimate glacial period. Our findings are supported by sea surface temperature reconstructions that indicate the penultimate glaciation was nearly 1 degrees C warmer than the last glacial period. These results provide useful information for quantifying the sensitivity of permafrost to past temperature changes.