Productivity and Biogeochemistry of terrestrial ice-bound ecosystems of the maritime Antarctic.

对南极洲陆地栖息地了解最少的是它的冰：这是一种重要的微生物资源，它们共同构成了地球表面最大的单一淡水细菌库。南极冰盖的细菌细胞总生物量被认为达到~ 2.44 Tg (Priscu和Christner， 2004)，因此南极西部和半岛的质量损失（~ 180 Gt冰a-1: Ringnot等人，in Press: Nature Letters）意味着主要的生物量和有机碳通量（~ 16 GgC a-1）正在发生，其生态影响被完全忽视了。此外，这些有活力的微生物在融化发生时非常活跃，它们吸收了50%至75%的无机积雪营养库（Hodson, 2006），并通过光合作用从大气中固定了约10毫克碳水化合物m-2 d-1 （Fogg, 1968）。因此，冰雪结合的微生物在向海岸运输的过程中，将大气中的大量无机营养物质和二氧化碳转化为有机生物质。在这里，现在有证据表明，冰川和融雪径流可以增加离岸100公里的海洋浮游生物大量繁殖（diersen等，2002年）。因此，对南极海洋冰雪栖息地的内部生物生产和生物地球化学的系统研究早就应该进行了。此外，由于对气候变化的极端反应已经在这里的土壤、湖泊和沿海生态系统中观察到，我们认为，迫切需要对这些变化与冰雪栖息地发生的变化之间的关系进行调查。在冰雪融化前对其养分含量的测量不能用于预测冰缘陆地、淡水和海洋生态系统产量的增加，因为这忽略了其自身生物生产所施加的内部养分需求。它也没有提供关于冰冻栖息地的生物二氧化碳泵的见解，这将主导陆地生态系统的二氧化碳预算，但从未被测量过。冰雪生物生产的净影响很可能是一个重要的区域二氧化碳源，但如果南极洲沿海的其他地区开始融化到与北部半岛和斯科舍弧线相同的程度，这种通量将变得大得多。因此，该项目将量化南极海洋冰雪表面栖息地在融化过程中的微生物学、营养经济和生产力。我们的方法是在西格尼岛（南奥克尼群岛）上建立横断面，这些横断面代表了南极半岛西海岸和相关群岛的广泛融化和营养梯度。这些地点将包括营养丰富、融化率高的沿海积雪和营养贫乏、融化零星且通常局限于地表的高海拔寒冷积雪。我们还将沿着我们的横断面跟随积雪的消退，并检查因此暴露的冰川表面栖息地。在每个站点，我们将建立整个夏季的微生物群落结构和生物量，并跟踪微生物从冰雪中融化时的命运。我们还将同时跟踪营养物质，并测量驱动整个系统的熔体能量通量。这种物理、化学和生物过程测量的紧密结合以及正在考虑的地点范围是重要的，因为它们将使我们能够评估南极半岛不受详细监测的其他部分。对于这些地区，我们将使用现有的气象数据和对融化程度的估计来计算在当前和未来融化情景下可能预期的向西融化通量、营养物质和微生物生物量。与此同时，我们将首次确定由于南极冰雪栖息地内的生物活动而产生的二氧化碳通量。

The most poorly understood terrestrial habitat in Antarctica is its ice: a significant microbial resource that collectively constitutes the largest single freshwater reservoir of bacteria on the Earth's surface. The total bacterial cell biomass in the Antarctic ice sheet is thought to amount to ~ 2.44 Tg (Priscu and Christner, 2004) and so mass losses from West Antarctic and the Peninsula (~ 180 Gt ice a-1: Ringnot et al, In Press: Nature Letters) mean major biomass and organic carbon fluxes (~ 16 GgC a-1) are taking place whose ecological implications have been completely overlooked. Furthermore, these are viable microorganisms that are so active when melting takes place that they sequester between 50% and 75% of the inorganic snowpack nutrient reservoir (Hodson, 2006) and fix ~ 10 mgC m-2 d-1 from the atmosphere by photosynthesis (Fogg, 1968). Thus snow and ice-bound microorganisms transform enormous quantities of inorganic nutrients and CO2 from the atmosphere into organic biomass while they are in transit to the coast. Here, there is now evidence that glacial and snowmelt runoff can increase marine plankton blooms up to 100 km offshore (Dierssen et al, 2002). A systematic study of the internal biological production and biogeochemistry of snow and ice habitats in the maritime Antarctic is therefore long overdue. Further, since extreme responses to climate change are already being observed here in its soil, lake and coastal ecosystems, we believe that an investigation of the relationship between these changes and those occurring in snow and ice habitats is urgently required. Measurements of the nutrient content of snow and ice prior to melt cannot be used to predict enhanced production in terrestrial, freshwater and marine ecosystems at the ice margin because this neglects the internal nutrient demands imposed by its own biological production. It also offers no insights into the biological CO2 pump in icy habitats, which will dominate the terrestrial ecosystem CO2 budget, yet has never been measured. The net impact of biological production within snow and ice is most likely a significant regional CO2 source, but this flux will become far greater if other parts of coastal Antarctica begin to melt to the same extent as the northern Peninsula and Scotia arc. This project will therefore quantify the microbiology, nutrient economy and productivity of snow and ice surface habitats as they melt in the maritime Antarctic. Our approach will be to establish transects upon Signy Island (South Orkney Islands) that are representative of the broad range of melting and nutrient gradients found along much of the Antarctic Peninsula's west coast and associated archipelagos. These sites will encompass nutrient-rich, high melt rate coastal snowpacks and nutrient impoverished, cold snowpacks at altitudes where melting is sporadic and typically restricted to the surface. We will also follow the retreat of the snowpack up our transects and examine the glacier surface habitats exposed as a consequence. At each site we will establish the microbial community structure and biomass throughout the summer and track the fate of microorganisms as melting removes them from the snow and ice. We will also track nutrients at the same time and measure the melt energy fluxes that drive the whole system. This tight integration of physical, chemical and biological process measurements and also the range of sites being considered are important because they will then enable us to assess other parts of the Antarctic Peninsula not subject to detailed monitoring. For these areas, we will use existing meteorological data and estimates of melt extent to calculate the westward flux of melt, nutrients and microbial biomass that might be expected under current and future melt scenarios. At the same time we will establish the CO2 fluxes as a result of biological activity within Antarctic snow and ice habitats for the first time.