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

_________________________________________________________________________________________________________________________除了多年冻土融化对基础设施的威胁外，了解多年冻土对过去变暖的反应也是至关重要的。洞穴(石笋和钟乳石)只有在覆盖的永久冻土融化，不再构成从地表渗入洞穴的不透水屏障时，才有望在北极洞穴中生长。该项目将记录洞穴在北极洞穴中生长的时间，以及在过去的气候条件下，持续多年冻土融化的情况。主要研究人员将开发一个网站，旨在教育非专业观众如何利用洞穴研究过去的气候。他们将参加剑桥科学节的街头科学计划，该计划为科学家提供了一个渠道，让他们与参加社区活动的公众受众就他们的研究进行接触。该项目将通过帮助启动三名职业早期科学家的研究计划，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。这项拟议的研究代表了一种新的方法，可以通过测定现在冻结地区的洞穴来重建过去的永久冻土融化时期。洞穴需要液态水才能生长，因此它们在沉积时意味着地面条件已经解冻。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群收集资料，这些地区横跨17°纬度，范围从孤立到连续的永久冻土带，以记录过去600KYR多变的间冰期条件下洞穴群生长的程度，从而记录永久冻土融化的程度，其中一些条件比今天更温暖。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。准确、高分辨率的陆地古气候记录在北极也很少见，尽管这对于了解该地区对辐射强迫的反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异性。虽然这些记录可能是零碎的，仅限于暖期，但这些记录基本上将提供格陵兰冰芯𝛿18O记录的地下延伸，延伸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.