An analysis of Neogene climates in Beringia

Abstract

A newly developed multivariate analysis of foliar physiognomy provides accurate (valid) and precise (repeatable) data for nonmarine climates in Beringia. During the mid-Miocene thermal maximum, both summers and especially winters were warmer than now. A temperature decline at about 12–13 Ma involved decreases in both summer and winter temperatures, but summer temperatures appear to have decreased more than winter temperatures. During the interval from about 12 Ma to about 8 Ma, winter temperatures fluctuated, resulting in two apparent increases in mean annual temperature. When the counter-clockwise rotation of North America during this interval is factored in, overall mean annual temperature declined. Decrease in summer and winter temperatures at about 12–13 Ma can also be documented in the west Beringian (northeast Siberian) region. Although small size of known Beringian leaf assemblages younger than about 7 or 8 Ma precludes multivariate physiognomic analysis, general floristic analyses concomitant with inferences based on the sedimentary record suggest that, whereas summer temperatures had approximately reached their present-day levels by 5–6 Ma, winter temperatures continued to decline during the Pliocene.