Subglacial Chemical Weathering under East Antarctica

非技术性描述化学风化是岩石和矿物转变为粘土、氧化物和化学营养物的过程。大多数这些风化反应消耗大气气体，如氧气和二氧化碳，因此化学风化可以驱动大气化学的自然，长期变化。化学风化作用从岩石中释放出的营养物质被输送到海洋，是维持地球生命所必需的。该项目的主要目的是评估南极洲最大的冰盖下发生了多少化学风化。在世界其他地方，化学风化是通过分析河流的流出来评估的，但这种直接测量化学流出是不可能的，因为几乎所有的南极洲都被冰覆盖。在南极洲，研究人员使用来自南极洲外山脉的样本，在那里，流动的冰与山峰的相互作用导致岩石和矿物材料从冰川底部出现。该项目将评估这种新出现的矿物材料与底层岩石相比被化学风化的程度以及这种风化发生的时间尺度。技术说明来自一个横贯南极山脉遗址的初步数据有力地表明，化学风化的矿物产品（粘土和氧化物）在新出现的物质中比在下层岩石中更丰富。然而，这种物质的化学变化可能发生在最近或南极洲冰川形成之前。为了限制风化的时间轴，从而评估南极洲现代风化速率，该项目将分析风化矿物中的两种稀有放射性同位素。由于这些同位素会通过放射性衰变而丢失，它们就像时钟一样，可以为化学风化过程中形成的粘土和氧化物的形成计时。早于冰的矿物将有这些同位素附着在它们的表面，但不在它们的晶体结构中。通过首先化学去除粘土和氧化物表面的元素，然后分析矿物本身，项目调查人员将确定这些矿物是最近在冰下形成的，还是之前在无冰环境中形成的。通过计算这些矿物形成的时间，并分析冰将它们运离大陆的速度，他们将能够计算出跨南极山脉上下位置的化学风化速率。其结果将是估计东南极冰盖下的风化对地球海洋营养物质化学性质的影响。这项研究将为下一代极地科学家提供宝贵的培训。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical DescriptionChemical weathering is the process by which rocks and minerals are turned to clay, oxides, and chemical nutrients. Most of these weathering reactions consume atmospheric gases, such as oxygen and carbon dioxide, and therefore chemical weathering can drive natural, long-term changes in atmosphere chemistry. The nutrients released from rocks by chemical weathering are transported to the oceans and are necessary for the maintenance of life on Earth. The principal aim of this project is to assess how much chemical weathering occurs beneath Antarctica's largest ice sheet. Elsewhere in the world, chemical weathering is assessed by analyzing the outflow of rivers, but such direct measurements of chemical outflow are not possible because nearly all of Antarctica is covered by ice. In Antarctica investigators use samples from the Transantarctic Mountains where the interaction of flowing ice with mountain peaks causes rock and mineral material to emerge from the glacier base. This project will assess the degree to which this emerging mineral material has been chemically weathered compared to the underlying rock and the time scale at which such weathering occurs. Technical DescriptionPreliminary data from a Transantarctic Mountain site strongly suggests that the mineral products of chemical weathering (clays and oxides) are more abundant in the emerging material than in the underlying rocks. However, the chemical alteration of this material could have occurred recently or prior to glaciers forming in Antarctica. To constrain the timeline of weathering and thereby assess modern rates of weathering in Antarctica, this p[project will analyze two rare, radioactive isotopes within the weathered minerals. Because these isotopes are lost through radioactive decay, they act as clocks that can time the formation of the clays and oxides that form during chemical weathering. Minerals that pre-date the ice will have these isotopes clinging to their surface but not in their crystal structure. By first chemically removing the elements on the surface on the clays and oxides and then analyzing the minerals themselves, the project investigators will determine whether the minerals formed recently under the ice or beforehand in an ice-free environment. By calculating how recently these minerals formed and by analyzing the rate at which ice transports them off the continent, they will be able to calculate chemical weathering rates at locations up and down the Transantarctic Mountains. The result will be an estimate the impact of weathering under the East Antarctic ice sheet on the chemistry of the Earth's ocean nutrients. This research will provide valuable training for the next generation of polar scientists.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.