Lovvorn M B, Frison G C, Tieszen L L
Department of Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA.
Proc Natl Acad Sci U S A. 2001 Feb 27;98(5):2485-90. doi: 10.1073/pnas.041616098. Epub 2001 Feb 20.
Two Amerindian demographic shifts are attributed to climate change in the northwest plains of North America: at approximately 11,000 calendar years before present (yr BP), Amerindian culture apparently split into foothills-mountains vs. plains biomes; and from 8,000-5,000 yr BP, scarce archaeological sites on the open plains suggest emigration during xeric "Altithermal" conditions. We reconstructed paleoclimates from stable isotopes in prehistoric bison bone and relations between weather and fractions of C(4) plants in forage. Further, we developed a climate-change model that synthesized stable isotope, existing qualitative evidence (e.g., palynological, erosional), and global climate mechanisms affecting this midlatitude region. Our isotope data indicate significant warming from approximately 12,400 to 11,900 yr BP, supporting climate-driven cultural separation. However, isotope evidence of apparently wet, warm conditions at 7,300 yr BP refutes emigration to avoid xeric conditions. Scarcity of archaeological sites is best explained by rapid climate fluctuations after catastrophic draining of the Laurentide Lakes, which disrupted North Atlantic Deep Water production and subsequently altered monsoonal inputs to the open plains.
大约在距今11000个历年（yr BP）前，美洲印第安文化明显分化为山麓-山区与平原生物群落；在距今8000 - 5000年期间，开阔平原上稀少的考古遗址表明在干旱的“高温期”有移民现象。我们通过史前野牛骨骼中的稳定同位素以及气候与饲料中C4植物比例之间的关系重建了古气候。此外，我们开发了一个气候变化模型，该模型综合了稳定同位素、现有的定性证据（如孢粉学、侵蚀学证据）以及影响该中纬度地区的全球气候机制。我们的同位素数据表明，在距今约12400年至11900年期间有显著变暖，支持了气候驱动的文化分离。然而，距今7300年时明显湿润温暖的同位素证据反驳了为躲避干旱条件而移民的说法。考古遗址稀少的最佳解释是劳伦泰德湖灾难性排水后气候的快速波动，这扰乱了北大西洋深水的形成，随后改变了对开阔平原的季风输入。
