NOAA/WDS Paleoclimatology - Sedimentological Data from Lake Midsommer, Northern Greenland during the last 8 ka

Reconstructing past ice extent and climate at the margins of the Greenland Ice Sheet (GrIS) offers important insights into the sensitivity of the ice sheet and its peripheral regions to climate forcing. Wandel Dal is a valley in northern Greenland that drains the northern margin of the GrIS as well as several ice caps. The valley was also an important landscape corridor for Inuit cultures beginning in the mid-Holocene. Here we examine the Holocene deglaciation and climate history of Wandel Dal based on analysis of sediment cores from Lake Midsommer (Midsommersø). We analyzed physical sediment properties, carbon and nitrogen content, grain size, diatom assemblages, and scanning X-ray fluorescence profiles to reconstruct physical and biological changes in the lake that were influenced by variations in glacier meltwater input, snowpack melt, precipitation, and lake primary productivity over the last c. 8.2 kyr. We find evidence that meltwater input to the lake was highest from at least c. 8.2 to c. 6.5 cal ka BP, delivering highly minerogenic sediments characterized by dense clay with frequent coarse layers. At c. 6.5 cal ka BP, there was an abrupt transition to sediment that is less dense, more organic rich, and where diatoms first appear. We interpret these changes to represent a significant reduction of meltwater input due to reduced ice extent within the catchment. These conditions lasted until c. 3.9 cal ka BP when we infer a shift to colder and drier conditions based on diatom and grain size data, which suggest longer periods of ice cover and reduced runoff to the lake. These conditions persisted until c. 50 years ago when diatom diversity dramatically increased due to recent climate warming. Our results add new constraints to the climate and deglaciation history of Inutoqqat Nunaat (Peary Land) and provide context for the Paleo-Inuit settlement history of Wandel Dal.

重建格陵兰冰盖（Greenland Ice Sheet, GrIS）边缘的古冰范围与气候记录，可为理解冰盖及其周边区域对气候强迫的敏感性提供关键认知。万德尔谷（Wandel Dal）地处格陵兰北部，汇聚格陵兰冰盖北缘及数处冰帽的融水径流。自全新世中期以来，该河谷亦是因纽特文化的重要景观通道。本研究基于对米德瑟默湖（Lake Midsommer, Midsommersø）沉积物岩芯的分析，探讨万德尔谷的全新世冰消历史与气候演化过程。我们通过分析沉积物物理性质、碳氮含量、粒度、硅藻组合及扫描X射线荧光剖面，重建了过去约8200年以来，受冰川融水输入、积雪消融、降水及湖泊初级生产力变化影响的湖泊物理与生物过程演变。研究发现，至少在距今约8200年至6500年校正后距今千年（calibrated kiloyears before present, cal ka BP）期间，湖泊冰川融水输入量达到峰值，沉积了以致密黏土为主且夹有频繁粗粒层的高矿质沉积物。在约6500 cal ka BP时，沉积物特征发生突变：从致密高矿质类型转变为密度更低、有机质含量更高的类型，且硅藻首次出现。我们将该变化归因于汇水区内冰盖范围缩减，导致冰川融水输入大幅减少。该环境状态持续至约3900 cal ka BP，此时基于硅藻与粒度数据，我们推断区域气候转向冷干——具体表现为湖泊冰盖期更长、入湖径流减少。该冷干环境持续至约50年前，受近代气候变暖影响，湖泊硅藻多样性显著提升。本研究结果为伊努托克夸特·努纳特（Inutoqqat Nunaat，即佩里兰Peary Land）的气候与冰消历史提供了新的约束条件，并为万德尔谷的古因纽特定居历史提供了重要背景参考。