Range of mean annual temperatures of the past million years inferred from properties of relict paleosols and periglacial features, Glacier Park area, Montana
Dr. Eric T. Karlstrom
Emeritus Professor of Geography, California State University, Stanislaus
Particular kinds of soils and periglacial features form under particular climatic regimes. Thus, magnitude of past climate fluctuations can be estimated in areas where these features record environmental conditions significantly different from those of the present. Relict interglacial paleosols (less than a miiion years old based on paleomagnetic analyses) near Glacier National Park, Montana resemble fersiallitic soils (Paleudalfs, Palustalfs, and Paleudolls) of the southeastern U.S., where mean annual temperature (MAT) is at least 6 to 8°C warmer and mean average precipitation (MAP) is at least 40 cm greater than present in the Glacier Park area, where MAT is 4.2°C and MAP is 50 cm. Relict periglacial features in this area, including ice-wedge casts, record radically colder glacial conditions. Because active ice-wedges form in continuous permafrost where MAT is -6°C or less, their occurrence here suggests MAT in the Glacier Park area during full glacial conditions was at least 10°C colder than today. Thus, these data suggest that over the past ~ million years, MAT fluctuated between -6C or colder during full glacial conditions to 10 to 12C or warmer during interglacials. Distribution of plant and animal fossils in mid-continental Eurasia and North America record a similar (extreme) range of average annual temperatures (at least 16-18°C or 29-32°F). Applying Milankovitch’s concept of “equivalent latitude” to estimate displacement of climate zones, “equivalent latitude” here during the past million years apparently shifted at least 8 to 11southward during interglacial maxima and 16 northward during glacial maxima in this extremely continental locale.
Rocky Mountain Geological Society of America Section Meeting, 9-11 May, 2012, Vol. 44, No. 6, p. 84.