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

山顶的火山口。南极洲西部的莫尔顿有一个600米厚的水平暴露的冰段，中间有来自附近柏林山的火山灰层。氩-40/氩-39对厚的近源火山灰的测年表明，水平冰段的年龄在15，000到492，000年之间。因此，莫尔顿山遗址提供了一个无与伦比的古代西南极雪和被困空气的储存库，可以用来调查过去50万年的大部分时间里西南极的气候。火山灰层的平面性质和一致的倾角表明，尽管冰层变薄了，但它没有变形。山脉在1999/2000年的野外考察季节，考察了莫尔顿遗址，当时收集了一个代表约400米冰的水平冰芯，年龄从15，000年到480，000多年不等。除了这个水平的冰芯外，还收集了不同深度的冰样本，以测试冰中气候记录的质量。还收集了40层镶嵌在冰中的火山灰层，以提供冰段的年代学。这一初步努力的结果极为令人鼓舞。根据D？18 O的冰，例如，有一个明确的可用记录过去的气候在山。莫尔顿可以追溯到14万年前。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，被困气体的元素和同位素组成表明，现代空气中存在一些污染。由于冰芯的气体交叉年代测定是目前比较气候记录的标准，因此在将莫尔顿加入我们的冰芯古气候记录库之前，我们需要了解气体记录为什么以及如何受到损害。该奖项支持三个机构之间的合作努力，其目标如下：1）通过对蓝冰区以及蓝冰上坡的雪场进行浅钻，更彻底地评估气候记录的完整性; 2）改进特定火山灰层的放射性同位素测年;（3）获得现代降雪沉积、年平均气温和山顶周围的风泵的基线信息。莫尔顿;和4）研究如何积雪致密化的不同时，表面积累从净积累到净消融。

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.