Permafrost at the time of the Last Glacial Maximum (LGM) in North America

This paper presents three maps that summarize current knowledge as to the extent of P ast permafrost and R elict permafrost in N orth A merica at approximately the time of the Last Glacial Maximum ( LGM ; c . 25–17 ka BP ) and during subsequent deglaciation until c . 10 ka BP . Analysis of the post‐1983 literature suggests that the extent of P ast permafrost south of the LGM limit was broader in eastern N orth A merica and slightly narrower in the I nterior G reat P lains than previously mapped. The recognition and dating of R elict permafrost in the nonglaciated terrain of the northwestern A rctic suggests that permafrost may be of great antiquity and can persist under changing climatic conditions. The formation of permafrost features during deglaciation suggests that ice‐proximal climatic conditions remained cold at least long enough for short‐lived permafrost aggradation; a latitudinal gradient is evident in the timing of its development as the L aurentide I ce S heet retreated.