Moisture and temperature changes associated with the mid-Holocene Tsuga decline in the northeastern United States
Moisture and temperature changes associated with the mid-Holocene Tsuga decline in the northeastern United States
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DOI：
10.1016/j.quascirev.2013.09.001
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发表时间：
2013-11-15
影响因子：
4
通讯作者：
Oswald, W. Wyatt
中科院分区：
文献类型：
--
作者：
Marsicek, Jeremiah P.;Shuman, Bryan;Oswald, W. Wyatt
铁杉(Tsuga)种群的下降约为5.5ka(公元1950年前的数千个校准放射性碳年)，是北美全新世最突然的植被变化，但经过数十年的研究，人们对此仍知之甚少。最近对化石花粉的分析表明，在马萨诸塞州东部的科德角，橡树(Quercus)的数量同时急剧下降，而山毛榉(Fagus)和松树(Pinus)的丰度增加，但耐旱性较强的橡树被对水分敏感的山毛榉所取代，似乎与该地区的低湖泊水位在同一时间不一致。橡木和山毛榉的变化也仅限于沿海地区，沿海和内陆的差异需要解释。在这里，我们开发了一个新的湖平面重建从科德角深池通过使用横断面的沉积物岩芯和探地雷达(GPR)剖面，以限制过去的高程沙质，沿岸带的池塘。重建表明，几个世纪以来的一系列低水位事件与铁杉和橡树的突然下降相吻合，并中断了铁杉恢复的后续阶段。湖面的变化相当于类似于100毫米的降水赤字叠加在全新世长达400毫米的水分增加之上。然而，由于水分不足很难解释橡树和山毛榉的变化，我们还通过将深池的化石花粉组合与现代花粉组合进行匹配，评估了该地区植被的气候偏好是如何随着时间的推移而变化的。植被降水需求的重建甚至与湖平面记录(深池的r=0.88)有很好的相关性，并表明尽管物种突然减少，但植被对有效水分(降水减去蒸散)的密切跟踪，这可能会使气候和植被趋势脱钩。植被温度偏好的重建表明，在约5.5ka之后，沿海地点可能冷却了0.5-2.5摄氏度，而内陆地点则变暖了0.5-1摄氏度。海岸温度偏好的变化与大西洋西部海面冷却>；1℃相一致。因此，美国东北部在5.5ka后铁杉种群持续低丰度的原因可能是海洋变化导致了长达数世纪的干旱，从而推迟了铁杉种群下降后的恢复。(C)2013爱思唯尔有限公司。保留所有权利。
A decline of hemlock (Tsuga) populations at ca 5.5 ka (thousands of calibrated radiocarbon years before 1950 AD) stands out as the most abrupt vegetation change of the Holocene in North America, but remains poorly understood after decades of study. Recent analyses of fossil pollen have revealed a concurrent, abrupt oak (Quercus) decline and increases in the abundance of beech (Fagus) and pine (Pinus) on Cape Cod in eastern Massachusetts, but the replacement of drought-tolerant oaks by moisture-sensitive beeches appears inconsistent with low lake levels in the region at the same time. The oak and beech changes are also limited to coastal areas, and the coastal-inland differences require an explanation. Here, we develop a new lake-level reconstruction from Deep Pond, Cape Cod by using a transect of sediment cores and ground-penetrating radar (GPR) profiles to constrain the past elevations of the sandy, littoral zone of the pond. The reconstruction shows that a series of multi-century episodes of low water coincide with the abrupt hemlock and oak declines, and interrupt subsequent phases of hemlock recovery. The lake-level variations equal precipitation deficits of similar to 100 mm superimposed on a Holocene long moisture increase of >400 mm. However, because moisture deficits do not easily explain the oak and beech changes, we also evaluate how the climate preferences of the regional vegetation changed over time by matching the fossil pollen assemblages from Deep Pond with their modern equivalents. Reconstructions of the precipitation requirements of the vegetation correlate well even in detail with the lake-level record (r = 0.88 at Deep Pond), and indicate close tracking of effective moisture (precipitation minus evapotranspiration) by the vegetation despite the abrupt species declines, which could have decoupled climate and vegetation trends. Reconstructions of the temperature preferences of the vegetation indicate that coastal sites may have cooled by 0.5-2.5 degrees C after ca 5.5 ka, while inland sites warmed by 0.5-1 degrees C. The change in coastal temperature preferences agrees with sea surface cooling in the western Atlantic Ocean of >1 degrees C. Consequently, the persistence of low hemlock abundance after 5.5 ka in the northeast U.S. may have resulted from oceanic changes that produced multi-century droughts and thus delayed the post-decline recovery of hemlock populations. (C) 2013 Elsevier Ltd. All rights reserved.