A quantitative midge-based reconstruction of mean July air temperature from a high-elevation site in central Colorado, USA, for MIS 6 and 5

Abstract

Sediments recovered from the Ziegler Reservoir fossil site (ZRFS) in Snowmass Village, Colorado (USA) were analyzed for subfossil chironomids (or midges). The midge stratigraphy spans~140-77 ka, which includes the end of Marine Oxygen Isotope Stage (MIS) 6 and all of MIS 5. Notable shifts in midge assemblages occurred during two discrete intervals: the transition from MIS 6 to MIS 5e and midway through MIS 5a. A regional calibration set, incorporating lakes from the Colorado Rockies, Sierra Nevada, and Uinta Mountains, was used to develop a midge-based mean July air temperature (MJAT) inference model (r 2 jack = 0.61, RMSEP = 0.97°C). Model results indicate that the transition from MIS 6 to MIS 5e at the ZRFS was characterized by an increase in MJAT from~9.0 to 10.5°C. The results also indicate that temperatures gradually increased through MIS 5 before reaching a maximum of 13.3°C during MIS 5a. This study represents the first set of quantitative, midge-based MJAT estimates in the continental U.S. that spans the entirety of MIS 5. Overall, our results suggest that conditions in the Colorado Rockies throughout MIS 5 were cooler than today, as the upper limit of the reconstructed temperatures is~2°C below modern July air temperatures.

Reconstruction of full glacial environments and summer temperatures from Lago della Costa, a refugial site in Northern Italy

“…However, chironomid-based temperature reconstructions which extend into the LGM and preceding periods are rare (e.g. Engels et al 2008, Haskett and Porinchu 2014, Helmens et al 2015 (Kaltenrieder et al 2009). On the basis of the chironomidinferred temperature reconstruction we address the question whether the climatic conditions around Lago della Costa were warm enough to support the survival of temperate trees (e.g.…”

Does glacial retreat impact benthic chironomid communities? A case study from Rocky Mountain National Park, Colorado

“…Protanypus has also been found in high elevation lakes in Canada and is associated with deep and cold lakes [35,80]. However, these taxa have not been identified in previous work done on modern chironomid distribution in the continental western USA [23,58,59,61,68]. Porinchu et al [59] did find Pseudodiamesa in sediment collected from California from the interval corresponding to ages between 14,800 and 13,700 cal yr BP.…”

“…Thus, the survival of chironomid egg masses is largely influenced by surface water temperature [72], the larval stage is influenced by bottom water temperature, and adult flies exist in environments dominated by air temperature [15]. Chironomids have been used as a biological proxy to model both surface water temperature [7,61,83] and air temperature [23,26,35,38] based on the assumption that a strong relationship exists between surface water temperature and air temperature. Eggermont and Heiri [15] caution that multiple factors such as depth, thermal stratification, and glacial melt may impact the relationship between air and surface water temperatures.…”