Collaborative Research: Refining a 500-kyr Climate Record From the Mt. Moulton Blue Ice Field in West Antarctica

位于南极洲西部的莫尔顿山的山顶火山口，包含了一段600米厚的水平暴露的冰，其中穿插着来自附近柏林山的冰层。用氩-40/氩-39测年法测定厚的近源冰原，表明水平冰原的年龄在15000年到492000年之间。因此，莫尔顿山遗址提供了一个无与伦比的古南极西部积雪和被困空气的储存库，可以用来研究过去50万年中大部分时间里南极西部的气候。冰层的平面性质和一致的倾斜表明，尽管冰部分变薄了，但它在其他方面没有变形。在1999/2000年的野外季节，人们访问了莫尔顿山遗址，当时收集了一个水平冰芯，代表了大约400米的冰，年龄从15,000年到480,000年不等。除了这个水平的核心外，还收集了一定深度的冰样本，以测试冰中气候记录的质量。还收集了嵌入冰中的40个温层，以便为冰段提供年代学。这第一次努力的结果是极其令人鼓舞的。基于d？例如，在莫尔顿山，有一份可追溯至14万年前的可用的过去气候记录。然而，要实现这个水平冰芯的全部潜力，还有很多工作要做。例如，捕获气体的元素和同位素组成表明现代空气受到了污染。由于冰芯的气体交叉定年是目前比较气候记录的标准，我们需要在将莫尔顿的气体记录添加到我们的冰芯古气候记录库之前，了解气体记录被破坏的原因和方式。该奖项支持三个机构之间的合作努力，其目标如下：1)通过对蓝冰地区的浅层钻探，以及蓝冰上坡的雪原，更彻底地评估气候记录的完整性；2)改进了特定温度层的放射性同位素定年；3)获取现代降雪量、年平均气温和莫尔顿峰顶附近风泵的基线信息；4)研究表面堆积从净堆积到净烧蚀变化过程中硬化密度的变化。

The summit crater of Mt. Moulton, in West Antarctica, contains a 600-m thick horizontally-exposed section of ice with intercalated tephra layers from nearby Mt Berlin. Argon-40/Argon-39 dating of the thick, near-source tephra indicates that the age of the horizontal ice section ranges between 15,000 and 492,000 years. Thus, the Mt Moulton site offers an unparalleled repository of ancient West Antarctic snow and trapped air that can be used to investigate West Antarctic climate over much of the past 500,000 years. The planar nature and consistent dips of the tephra layers suggests that, although the ice section has thinned, it is otherwise undeformed. The Mt. Moulton site was visited during the 1999/2000 field season, at which time a horizontal ice core representing approximately 400 meters of ice was collected, ranging in age from 15,000 to older than 480,000 years. In addition to this horizontal core, samples of ice at a range of depths were collected in order to test the quality of the climate record in the ice. Forty tephra layers intercalated in the ice were also collected in order to provide chronology for the ice section. The results of this first effort are extremely encouraging. Based on the d?18 O of ice, for example, there is clearly a useable record of past climate at Mt. Moulton extending back beyond 140,000 years. There is work to do, however, to realize the full potential of this horizontal ice core. The elemental and isotopic composition of trapped gases suggest some contamination with modern air, for example. As gas cross-dating of ice cores is the current standard by which climate records are intercompared, we need to understand why and how the gas record is compromised before adding Moulton to our arsenal of ice core paleoclimate records. This award supports a collaborative effort between three institutions with following objectives: 1) to evaluate more thoroughly the integrity of the climatic record through shallow drilling of the blue ice area, as well as the snow field upslope from the blue ice; 2) to improve the radioisotopic dating of specific tephra layers; 3) to obtain baseline information about modern snowfall deposition, mean annual temperature, and wind pumping around the summit of Mt. Moulton; and 4) to study how firn densification differs when surface accumulation changes from net accumulation to net ablation.