Local glaciers record delayed peak Holocene warmth in south Greenland
Local glaciers record delayed peak Holocene warmth in south Greenland
复制标题
DOI：
10.1016/j.quascirev.2020.106421
复制
发表时间：
2020-08
影响因子：
4
通讯作者：
L. Larocca;Y. Axford;A. Bjørk;G. Lasher;Jeremy P. Brooks
中科院分区：
文献类型：
--
作者：
L. Larocca;Y. Axford;A. Bjørk;G. Lasher;Jeremy P. Brooks
当地的冰川和冰盖(GIC)对气候变化做出了敏感而迅速的反应，反应范围从几十年到几个世纪。对过去GIC大小波动的连续记录提供了关于全新世气候变化的时间和幅度的信息，以及对21世纪冰川消退的更长期的展望。尽管在全新世气候变异性和格陵兰当地GIC波动的千禧年尺度趋势上存在广泛的共识，但区域差异仅受到松散的限制。在这里，我们介绍了来自格陵兰南部的三个全新世前冰期湖泊沉积记录，该地区拥有丰富的当地冰川，但几乎没有全新世长度的古气候记录。此外，我们使用地理空间分析来模拟过去的平衡线高度(ELA)，从而限制在全新世最热和最冷的时期消融季节温度变化的幅度。物理和地球化学沉积特征表明，两个前冰期湖泊继续接受冰川融水输入，直到∼7.3ka BP和∼7.1ka BP。当地冰川的存活意味着南格陵兰保持相对凉爽，夏季气温逐渐变暖，但远未超过全新世早期1.2摄氏度的温度。在全新世中期，从∼7.1ka BP到5.5ka BP，这两个地点的有机沉积表明，当地的冰川变得非常小，或者更有可能完全融化。第三湖集水区内的冰川在∼5.2ka BP之前融化，因为在全新世早期沉积的沉积物不能在这个地点确定年代。我们估计夏季气温比现在至少升高了1.2-1.8摄氏度，增加了∼7.3-7.1ka BP。我们的结果与其他观察结果一致，这些观察表明，全新世最高温度条件的时间存在从北到南的梯度，相对于格陵兰其他地区，格陵兰南部经历了延迟的变暖。随着夏季新冰川温度的下降，我们的记录显示，冰川的持续再生开始于∼3.1ka BP，最南端的集水区的冰川目前接收的降水量最多。在另外两个冰川集水区，冰川的再生开始于∼1.3ka BP和∼1.2ka BP，这与北冰洋地区的其他冰川记录一致。当地冰川在小冰河时代(LIA)∼0.2-0.1ka BP较凉爽的第二阶段达到最大程度的晚全新世，我们估计比现在至少低0.4-0.9摄氏度。总体而言，这些发现提高了对格陵兰全新世冰川和气候变化的时空动态的理解，可能为它们未来的反应提供有价值的信息。
Local glaciers and ice caps (GICs) respond sensitively and quickly, on the scale of decades to centuries, to climate variations. Continuous records of past fluctuations in GIC size provide information on the timing and magnitude of Holocene climate shifts, and a longer-term perspective on 21st century glacier retreat. Although there is broad-scale agreement on millennial-scale trends in Holocene climate variability and fluctuations in local GICs in Greenland, regional variations are only loosely constrained. Here we present three Holocene proglacial lake sediment records from South Greenland, an area with abundant local glaciers but few Holocene-length paleoclimate records. In addition, we use geospatial analysis to model past equilibrium-line altitudes (ELAs) and thereby constrain the magnitude of ablation-season temperature change during the warmest and coolest periods of the Holocene. Physical and geochemical sedimentary characteristics show that two of the proglacial lakes continued to receive glacial meltwater input until ∼7.3 and ∼7.1 ka BP. The survival of local glaciers implies that South Greenland remained relatively cool, and that summer temperatures gradually warmed, but did not warm well beyond 1.2 °C above present in the early Holocene. In the mid-Holocene, from ∼7.1 to 5.5 ka BP, organic sedimentation at these two sites indicates that local glaciers became very small, or more likely melted away completely. The glaciers within the third lake’s catchment melted away prior to ∼5.2 ka BP, as sediments deposited earlier in the Holocene could not be dated at this site. We estimate that summer temperatures increased by at least 1.2–1.8 °C above present by ∼7.3–7.1 ka BP. Our results are consistent with other observations that suggest a north-to-south gradient in the timing of Holocene thermal maximum conditions, with southern Greenland experiencing a delayed warming relative to other regions in Greenland. As summer temperatures cooled in the Neoglacial, our records show that sustained glacier regrowth began ∼3.1 ka BP with glaciers in the southernmost catchment, which at present, receive the most precipitation. In the other two catchments, which host smaller glaciers in a drier environment, regrowth began at ∼1.3 and ∼1.2 ka BP, the timing of which is in agreement with other glacial records from the Arctic Atlantic region. Local glaciers reached their maximum late Holocene extents during a cooler, second phase of the Little Ice Age (LIA) ∼0.2-0.1 ka BP, that we estimate was at least 0.4–0.9 °C cooler than present. Overall, these findings improve understanding of the spatio-temporal dynamics of Holocene glacier and climate change in Greenland, potentially yielding valuable information about their future response.