ICE PATCHES AND RELICT WOOD: A PALEOCLIMATE PROXY FOR THE ROCKY MOUNTAIN WEST

Climate scientists need multiple archives to identify and corroborate long term paleoclimatic trends. Surveys in the Greater Yellowstone Area (GYA) have identified numerous ice patches where the remains of large timber trees are preserved above modern treeline, including in the Absaroka and Gallatin Mountains. Samples of wood from such locations range in age between 7955 ± 15 and 640 ± 15 radiocarbon years BP. In September 2013 six slabs/cookies ranging in diameter between 30 and 50 cm were recovered from a cluster of 20+ exceptionally well-preserved trees in the Beartooth Mountains. Radiocarbon dates are pending. Radial growth (the addition of new rings) in most trees in the GYA is limited by soil moisture, which is controlled mainly by precipitation. Patterns of wide and narrow rings are highly replicated between trees because they are driven by a common climate signal. This makes them readily amenable to cross-dating through ring width comparisons. Analysis of the ring profile in these trees should reveal interannual to possibly centennial variability. These unique records are collocated with other paleobiological materials (e.g., bighorn sheep and bison remains), as well as archaeological material. The stable ice in these features exhibits little internal deformation or movement and can preserve otherwise perishable materials for millennia. The exposure of ancient archaeological and paleobiological materials by the retreat of moisture-starved and heat-ravaged ice patches in the GYA is a tangible indication of climate change in the Rocky Mountain West. The impacts transcend the divide between the cultural and natural world. Archaeological remains identified to date include ancient wooden dart shafts and fragments, wooden artifacts of unknown function, a wrapped leather object of unknown function, a woven basket, butchered animal remains, and chipped stone artifacts.