The Stage 3 interstadial complex (Karginskii/middle Wisconsinan interval) of Beringia: variations in paleoenvironments and implications for paleoclimatic interpretations
Questionable chronologies have limited detailed reconstructions of past vegetation and climate trends for the Karginskii/Middle Wisconsinan interstade (abbreviated here as MW). However, recent results from continuous lake records, while not resolving all the dating issues, do provide a new framework within which to examine this intriguing period. Paleobotanical data suggest significant regional variations in the interstadial vegetation of Beringia. Larix forests were relatively common in central and western areas of western Beringia through much of the middle and late MW, whereas tundra dominated most eastern Beringian landscapes. During relatively warm intervals within the interstade, western Beringia was more extensively forested (at times achieving modern forest distribution) than was eastern Beringia, where Picea forests were limited to lowlands of interior Alaska and the Yukon Territory. A period of maximum tree-cover occurred between ca. 35 and 33 ka BP, but forests were also present in western Beringia and the Yukon Territory between ca. 39 and 33 ka BP. Although a period of maximum warmth probably occurred throughout Beringia between ca. 35 and 33 ka BP, significant regional variability characterized other intervals, with differences not only in the timing of climatic changes but also in their trends (e.g., warming in the upper Kolyma region, cooling in interior Alaska). The paleovegetational data suggest that the greatest interstadial warming occurred in far eastern and far western regions of Beringia, with areas that are now closest to Bering Strait showing more moderate climatic fluctuations. The causes for either the long-term or the rapid climatic variations within interstadial Beringia do not seem to relate simply to either Milankovitch or sub-Milankovitch scale forcings.