Last interglacial plant macrofossils and climates from Ziegler Reservoir, Snowmass Village, Colorado, USA

Abstract

Ninety plant macrofossil taxa from the Ziegler Reservoir fossil site near Snowmass Village, Colorado, record environmental changes at high elevation (2705 m asl) in the Rocky Mountains during the Last Interglacial Period. Present-day vegetation is aspen forest (Populus tremuloides) intermixed with species of higher (Picea, Abies) and lower (Artemisia, Quercus) elevations. Stratigraphic units 4–13 contain montane forest taxa found near the site today and several species that today generally live at lower elevations within (Abies concolor, Lycopus americanus) and outside Colorado (Najas flexilis). These data suggest near-modern climatic conditions, with slightly warmer summer and winter temperatures. This montane forest period was succeeded by a shorter treeless interval (Unit 14) representing colder and/or drier conditions. In units 15–16, conifer trees reoccur but deciduous and herb taxa are lacking, suggesting a return to warmer conditions, although cooler than during the earlier forest period. Comparison of these inferred paleoclimatic changes with the site's geochronologic framework indicates that the lower interval of sustained warmth correlates with late MIS 6–early 5b (~138–94 ka), the cold interval with MIS 5b (~94–87 ka), and the uppermost cool assemblages with MIS 5a (~87–77 ka).

Wetter Summers Mitigated Temperature Stress on Rocky Mountain Forests During the Last Interglacial Warm Period

“…Earlier analyses on these samples showed the wood assemblage contained Abies and Picea (like today) and that growing conditions were similar, but more favorable in terms of moisture stress, relative to modern (Brown et al, 2014). This interpretation of a similar climate to today based on the subfossil wood is consistent with plant macrofossil (Strickland et al, 2014) and insect assemblage (Elias, 2014) from the same site. These proxy records were used to conclude that growing season temperatures were similar or warmer than modern.…”

The influence of orbital parameters on the North American Monsoon system during the Last Interglacial Period

“…Pigati et al ., 2014). Particularly, the data provide background to consider how global carbon cycle dynamics and ecological systems in the southwestern US might have responded to recent periods in Earth history when summer temperatures exceeded those of today (Brown et al ., 2014; Elias, 2014; Strickland et al ., 2014). Understanding these variations is critical to the seasonal supply of water to, and habitat changes in, the southwestern US under warming conditions.…”

Mountain lion genomes provide insights into genetic rescue of inbred populations

“…North American mountain lions were successful throughout MIS 5, a warm interglacial period during which forests were prevalent across much of the continent 28 . As the climate cooled into the MIS 4 ice age, forests were replaced by more open and exposed grasslands, and megafaunal prey decreased in abundance 29 .…”