Understanding the Boundary Conditions of the Lake Vostok Environment: A Site Survey for Future Work

该奖项由极端环境生命(Lexen)计划下的极地计划办公室提供，支持对东南极冰盖下的大湖沃斯托克湖的地球物理研究。冰下生态系统，特别是冰下湖泊生态系统是极端的寡营养环境。这些环境及其内部可能存在的生态系统应能为关于地球和太阳系其他天体发展的一系列基本问题提供关键的见解，其中包括：1)广泛的新元古代冰川之后与快速演化辐射有关的过程；2)整个冰川和间冰期的碳循环；3)生物在木星的冰盖卫星欧罗巴等环境中繁衍生息可能需要的适应。在南极洲3-4公里厚的冰层下，已经发现了70多个冰下湖泊。沃斯托克湖是一个足够大的湖泊，可以通过卫星测高从太空中清楚地辨认出来。沃斯托克湖在面积上与安大略湖相似，但体积要大得多，包括测量的水深为600米。当冰盖流过湖面时，覆盖的冰盖充当了一条传送带，不断输送新的水、营养物质、天然气水合物、沉积物和微生物。这个项目的目标是确定这个冰下湖泊的基本边界条件，作为了解湖泊内部物理过程的必要的第一步。为实现这一目标，将在湖上和周围地区进行一次航空地球物理调查。该数据集包括重力、磁力、激光测高和冰层穿透雷达数据，并将用于编制一套基本的冰面高程、冰层下地形、重磁异常图。在石油工业中广泛使用的潜在野外方法将被修改，以根据重力数据估计冰下地形，在那里，冰穿透雷达将无法恢复湖泊的深度。一种类似的方法可以被修改，以根据磁性数据估计湖下沉积物的厚度。这些方法将在沃斯托克湖实地活动之前在南极附近的冰下湖泊进行测试和应用，并将与计划中的调查进行有价值的比较。一旦方法针对沃斯托克湖的应用进行了调整，将生成湖底水洞和沉积物厚度的地图。这些地图将成为探索该湖地质起源的工具。两种端元模式是，第一，该湖是一个活跃的构造裂谷，如贝加尔湖；第二，该湖是冰川冲刷的结果。伸展裂谷的明显特征可以很容易地通过我们的航空地球物理调查来识别。航空地球物理调查的地质解释将根据现代数据首次提供东南极大陆内部的地质约束。此外，下伏的地质条件将影响湖泊内的生态系统。对于湖泊内的生态系统来说，关键问题之一将是营养物质的流动。将根据雷达数据上观察到的不同内部层之间的距离对冻结和融化区域进行初步估计。这些基本边界条件将为旨在就地勘探该湖的潜在国际努力提供指导，并增进对南极东部地质结构的了解。

9978236BellAbstractThis award, provided by the Office of Polar Programs under the Life in Extreme Environments (LExEn) Program, supports a geophysical study of Lake Vostok, a large lake beneath the East Antarctic Ice Sheet. Subglacial ecosystems, in particular subglacial lake ecosystems are extreme oligotrophic environments. These environments, and the ecosystems which may exist within them, should provide key insights into a range of fundamental questions about the development of Earth and other bodies in the Solar System including: 1) the processes associated with rapid evolutionary radiation after the extensive Neoproterozoic glaciations; 2) the overall carbon cycle through glacial and interglacial periods; and 3) the possible adaptations organisms may require to thrive in environments such as on Europa, the ice covered moon of Jupiter. Over 70 subglacial lakes have been identified beneath the 3-4 kilometer thick ice of Antarctica. One lake, Lake Vostok, is sufficiently large to be clearly identified from space with satellite altimetry. Lake Vostok is similar to Lake Ontario in area but with a much larger volume including measured water depths of 600 meters. The overlying ice sheet is acting as a conveyer belt continually delivering new water, nutrients, gas hydrates, sediments and microbes as the ice sheet flows across the lake. The goal of this program is to determine the fundamental boundary conditions for this subglacial lake as an essential first step toward understanding the physical processes within the lake. An aerogeophysical survey over the lake and into the surrounding regions will be acquired to meet this goal. This data set includes gravity, magnetic, laser altimetry and ice penetrating radar data and will be used to compile a basic set of ice surface elevation, subglacial topography, gravity and magnetic anomaly maps. Potential field methods widely used in the oil industry will be modified to estimate the subglacial topography from gravity data where the ice penetrating radar will be unable to recover the depth of the lake. A similar method can be modified to estimate the thickness of the sediments beneath the lake from magnetic data. These methods will be tested and applied to subglacial lakes near South Pole prior to the Lake Vostok field campaign and will provide valuable comparisons to the planned survey. Once the methods have been adjusted for the Lake Vostok application, maps of the water cavity and sediment thickness beneath the lake will be produced.These maps will become tools to explore the geologic origin of the lake. The two endmember models are, first, that the lake is an active tectonic rift such as Lake Baikal and, second, the lake is the result of glacial scouring. The distinct characteristics of an extensional rift can be easily identified with our aerogeophysical survey. The geological interpretation of the airborne geophysical survey will provide the first geological constraints of the interior of the East Antarctic continent based on modern data. In addition, the underlying geology will influence the ecosystem within the lake. One of the critical issues for the ecosystem within the lake will be the flux of nutrients. A preliminary estimation of the regions of freezing and melting based on the distance between distinctive internal layers observed on the radar data will be made. These basic boundary conditions will provide guidance for a potential international effort aimed at in situ exploration of the lake and improve the understanding of East Antarctic geologic structures.