Younger Dryas and early Holocene climate in south Greenland inferred from oxygen isotopes of chironomids, aquatic Moss, and Moss cellulose
Younger Dryas and early Holocene climate in south Greenland inferred from oxygen isotopes of chironomids, aquatic Moss, and Moss cellulose
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DOI：
10.1016/j.quascirev.2022.107810
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发表时间：
2022-11
影响因子：
4
通讯作者：
P. Puleo;A. Masterson;A. Medeiros;G. Schellinger;Regan Steigleder;S. Woodroffe;M. Osburn;Y. Axford
中科院分区：
文献类型：
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作者：
P. Puleo;A. Masterson;A. Medeiros;G. Schellinger;Regan Steigleder;S. Woodroffe;M. Osburn;Y. Axford
冰芯记录长期以来表明，新仙女木期开始和结束时格陵兰岛气候发生了巨大而突然的变化。主要气候特征仍然未知，包括新仙女木-全新世过渡期间变暖的幅度以及格陵兰岛新仙女木气候变化的季节性和空间变异性。在这里，我们利用格陵兰岛南部 N14 湖沉积物的地球化学和古生态学指标来解决这些悬而未决的问题。放射性碳测年和硅藻组合证实了 N14 湖在距今 13,600 年之前的早期冰消和隔离，这与之前的工作一致。摇蚊头囊、散装水生苔藓和水生苔藓衍生纤维素的氧同位素比 (δ18O) 用于重建过去湖水和年降水的氧同位素。氧同位素代理表明，新仙女木期末年降水量 δ18O 值增加了 5.9–7.7‰。新仙女木期之后，苔藓和纤维素 δ18O 值显示降水 δ18O 值从约 11,540–11,340 卡路里年BP 明显下降 2–3‰，这可能与北方振荡相对应。重建的降水 δ18O 值随后从 11,300–10,100 cal yr BP 逐渐增加。随着时间的推移，所有三种水生有机物质都记录了类似的降水 δ18O 值变化，并且它们与在冰芯中观察到的 δ18O 变化非常相似。这一证据有力地支持了这些方法可用于重建湖水 δ18O 以及湖水反映降水的降水 δ18O 值。 N14湖降水同位素组成相对较大的变化表明，新仙女木期结束时格陵兰岛南部的温度、降水季节性和/或水分来源的变化甚至比格陵兰岛中部更大，很可能是因为靠近北大西洋环流的重大变化。与之前根据摇蚊物种组合推断的夏季变暖（~6°C）相比，新仙女木期末期 N14 湖的年气温变化估计也非常大（~18±7°C）。这表明新仙女木期结束时最强烈的变暖发生在冬季，这与过去对 N14 湖和格陵兰其他地方新仙女木期季节性加剧的观察结果一致。
Ice core records have long indicated that the Younger Dryas began and ended with large, abrupt climate shifts over Greenland. Key climatic features remain unknown, including the magnitude of warming during the Younger Dryas-Holocene transition along with the seasonality and spatial variability of Younger Dryas climate changes across Greenland. Here, we use geochemical and paleoecological proxies from lake sediments at Lake N14 in south Greenland to address these outstanding questions. Radiocarbon dating and diatom assemblages confirm early deglaciation and isolation of Lake N14 before ∼13,600 cal yr BP, consistent with previous work. Oxygen isotope ratios (δ18O) of chironomid head capsules, bulk aquatic moss, and aquatic moss-derived cellulose are used to reconstruct oxygen isotopes of past lake water and annual precipitation. Oxygen isotope proxies indicate annual precipitation δ18O values increased by 5.9–7.7‰ at the end of the Younger Dryas. Following the Younger Dryas, moss and cellulose δ18O values show a clear decline in precipitation δ18O values of 2–3‰ from ∼11,540–11,340 cal yr BP that may correspond with the Preboreal Oscillation. Reconstructed precipitation δ18O values then gradually increased from 11,300–10,100 cal yr BP. All three aquatic organic materials register similar shifts in precipitation δ18O values over time, and they closely parallel the δ18O shifts observed in ice cores. This evidence strongly supports the utility of these methods for reconstructing lake water δ18O, and furthermore precipitation δ18O values where lake water reflects precipitation. The relatively large shift in isotopic composition of precipitation at Lake N14 suggests that shifts in temperature, precipitation seasonality, and/or moisture sources at the end of the Younger Dryas were even larger in south Greenland than they were in central Greenland, most likely because of the proximity to major changes in North Atlantic Ocean circulation. The annual air temperature change estimated at Lake N14 at the end of the Younger Dryas is also very large (∼18 ± 7 °C) compared to the summer warming previously inferred from chironomid species assemblages there (∼6 °C). This indicates that the strongest warming at the end of the Younger Dryas occurred in the winter season, consistent with past observations of intensified Younger Dryas seasonality at Lake N14 and elsewhere in Greenland.