Collaborative Research: Speleothem records of permafrost thaw and paleoclimate in the North American Arctic

________________________________________________________________________________________________________________________________ 鉴于大量温室气体释放的可能性永久冻土融化在温暖的未来,以及基础设施从永久冻土融化,威胁了解冻土过去温暖的反应是基本的重要性。只有当覆盖在北极洞穴上的永久冻土融化，不再形成从表面渗透到洞穴的不透水屏障时，洞穴中才会生长石笋和钟乳石。该项目将记录洞穴动物在北极洞穴中生长的时间，以及在过去的气候条件下持续的永久冻土融化的情况。主要研究人员将开发一个网站，旨在教育非专业观众如何使用洞穴主题来研究过去的气候。他们将参加剑桥科学节的“街头科学”项目，该项目为科学家提供了一个与参加社区活动的公众交流他们研究的渠道。该项目将通过帮助启动三名早期职业科学家的研究项目，以及支持两名研究生和三名本科生的培训，为STEM劳动力的发展做出贡献。这项提议的研究代表了一种新的方法，通过对现在冻结地区的洞穴洞穴进行测年，来重建过去的永久冻土解冻时期。洞穴化石需要液态水才能生长，因此它们沉积时的地面条件是解冻的。这项工作将利用铀钍地质年代学方面的进展，并利用加拿大三个偏远地区现有的洞穴标本，跨越17°纬度，从孤立的永久冻土带到连续的永久冻土带，记录洞穴生长的程度，从而记录过去600年不同间冰期条件下的永久冻土带解冻程度，其中一些比今天更温暖。他们还将对选定的样品进行铀铅测年，将测年范围扩大到数百万年。尽管对于了解该地区对辐射强迫的响应以及确定过去驱动冰盖、永久冻土、海冰和植被变化的气候强迫至关重要，但在北极地区，准确、精确的陆地古气候记录也很少见。因此，他们将沿着洞穴测量稳定的同位素记录，以重建它们生长期间的气候变化。虽然这些记录很可能是零碎的，而且仅限于温暖时期，但它们基本上提供了格陵兰冰芯的地下延伸𝛿18O记录，可以追溯到许多过去的间冰期。

________________________________________________________________________________________________________________________________Given the possibility of substantial greenhouse gas release from thawing permafrost in a warmer future, as well as the threats to infrastructure from thawing permafrost, understanding the response of permafrost to past warmth is of fundamental importance. Speleothems (stalagmites and stalactites) are expected to grow in Arctic caves only when the overlying permafrost has thawed and no longer presents an impermeable barrier to seepage from the surface into the cave. This project will develop a record of when speleothems grew in Arctic caves and, consequently, under what past climatic conditions continuous permafrost thawed. The principal investigators will develop a website designed to educate lay audiences on how speleothems are used to study past climate. They will participate in the Cambridge Science Festivals’ Science on the Street program, which provides an outlet for scientists to engage with public audiences attending community events on their research. This project will contribute to STEM workforce development by helping launch the research programs of three early-career scientists, as well as supporting the training of two graduate and three undergraduate students. The proposed study represents a novel approach to reconstruct past episodes of permafrost thaw by dating cave speleothems from now-frozen areas. Speleothems require liquid water to grow and thus imply thawed ground conditions when they were deposited. This work will take advantage of advances in uranium-thorium geochronology and use existing speleothem collections from three remote areas of Canada, spanning 17° of latitude and range from isolated to continuous permafrost zones to document the extent of speleothem growth, and thus permafrost thaw, across variable interglacial conditions of the past 600 kyr some of which were warmer than today. They will also apply uranium-lead dating to a selection of samples to extend the dating range to millions of years. Well-dated, high-resolution records of terrestrial paleoclimate are also rare in the Arctic, though critical for understanding the response of this region to radiative forcings and determining the climate forcing that drove past changes in ice sheets, permafrost, sea ice, and vegetation. Therefore, they will measure stable isotope records along the speleothems to reconstruct climate variability over the intervals during which they grew. While likely fragmentary and confined to warm periods, these records will essentially provide underground extensions of the Greenland ice core 𝛿18O record to numerous past interglacial periods.