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

________________________________________________________________________________________________________________________________考虑到在未来变暖的情况下，永久冻土融化可能会释放大量温室气体，以及永久冻土融化对基础设施的威胁，了解永久冻土对过去温暖的反应至关重要。只有当覆盖的永久冻土层融化，不再是从地表渗透到洞穴的不透水屏障时，洞穴沉积物（石笋和钟乳石）才会在北极洞穴中生长。该项目将记录北极洞穴中的洞穴沉积物何时生长，以及在过去的气候条件下连续的永久冻土融化的情况。主要研究人员将开发一个网站，旨在教育外行观众如何利用洞穴沉积物研究过去的气候。他们将参加剑桥科学基金会的“街头科学”项目，该项目为科学家提供了一个渠道，让他们与参加社区活动的公众接触。该项目将通过帮助启动三名早期职业科学家的研究计划，以及支持两名研究生和三名本科生的培训，为STEM劳动力发展做出贡献。这项研究提出了一种新的方法来重建过去的事件的永久冻土融化的约会洞穴洞穴从现在冻结的地区。洞穴沉积物需要液态水才能生长，因此意味着它们沉积时的地面条件已经解冻。这项工作将利用铀钍地质年代学的进展，并利用加拿大三个偏远地区现有的洞穴沉积物收集，跨越17°纬度，从孤立的到连续的永久冻土区，记录洞穴沉积物生长的程度，从而记录永久冻土融化，在过去60万年的不同间冰期条件下，其中一些比今天更温暖。他们还将对一些样本进行铀铅测年，将测年范围扩大到数百万年。在北极地区，关于陆地古气候的高分辨率、年代久远的记录也很罕见，尽管这对于理解该地区对辐射强迫的响应以及确定推动冰盖、永久冻土、海冰和植被过去变化的气候强迫至关重要。因此，他们将测量沿着洞穴沉积物的稳定同位素记录，以重建它们生长期间的气候变化。虽然这些记录可能是零碎的，并局限于温暖时期，但这些记录将基本上提供格陵兰冰芯180记录的地下延伸到过去的许多间冰期。𝛿

________________________________________________________________________________________________________________________________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.