Late glacial and Holocene mean annual temperature changes in the south-central Chile using a chironomid-based inference model

MARTEL CEA,A; ABARZUA, A; HERNANDEZ, M; MASSAFERRO, J

Dublin

Congreso; INQUA; 2018

INQUA

The use of non-biting midges as a tool for inferring past environmental conditions in south America has grown in the recent years. However, the lack of modern ecological and taxonomic information at spatial scale difficult to state if the main forcing factor that control chironomid assemblages are the same across the continent. Here we present a chironomid training set from 24 lakes located in the south-central Chile between 37°S and 41°S. Multivariate analyses indicate that mean annual temperature (MAT) is the main driver that controls the chironomid distribution (12,8% of total variance and MAT gradient 7-13°C). Based on these results, a temperature inference model is developed using the weighted average partial least square technique, achieving a performance of R2jack=0.64, RMSEPjack=1.15°C, Max.Biasjack=1.38°C. A transfer function was applied to infer quantitative MAT changes in the fossil record from Laguna Las Ranas (39.2°S, 72.1°W, 389m asl, modern MAT=10.2°C) spanning the last 18,6 ka BP. The results suggest the major MAT increment occurred during the late glacial between 18,6 and 13,5 cal ka BP, from 7.6°C to 9.5°C, and then, the rising temperature trend stopped and fluctuated around 10.5°C until 10.8 cal ka BP. From the early to mid-Holocene (10.8 and 6.5 cal ka BP) an increase and high variability of MAT values are recorded (peak MAT=12.3°C around 9 cal ka BP), and associated to important changes in the chironomid assemblages suggest environmental instability around Laguna Las Ranas. Less extent MAT fluctuations are observed in the last 7 cal ka BP, however, comparing to modern values, relative cold periods are inferred around 7-4.2 cal ka BP and 0.25 cal ka BP (ca. 9.7°C), whereas warm periods occurred around 4.2-3.6 cal ka BP and 0.8-0.25 cal ka BP (10.6°C). Despite to relative low coefficient of determination of the inference model and the short environmental gradient of sampled lakes, the chironomid-based MAT reconstruction follows the main climatological patterns occurred in the southern South America during the late Quaternary.