Chironomid thermometry of MIS 3 in the Northern Alps

The study of ancient climates (palaeoclimatology) provides an essential perspective on what causes climate change and the potential range and effects of future climate change on natural systems. High climate variability during the period between ~60 and 30 thousand years ago (referred to Marine Isotope Stage (MIS) 3 in oxygen isotope records in North Atlantic deep-sea sediments and Greenland ice cores) is of special interest because frequent rapid shifts from cold to warm conditions may be a model for the climatic conditions that determined environmental processes during much of the late-Quaternary period (past 0.51.0 million years). The generally discontinuous nature of sedimentation and repeated erosion combined with a scarcity of high-resolution records, however, hamper a detailed study of climate changes during MIS 3 in the Alps and in Europe as a whole. As such, the magnitude of climate change on the continent through MIS 3 remains mostly unknown. Given the remaining controversy and uncertainties regarding MIS 3 climate in the Alps, we will test two competing hypotheses: i) summers in the Northern Limestone Alps were as warm as today at least during warm sub-periods of MIS 3, and ii) summers in the Northern Limestone Alps were substantially cooler than today during the entire MIS 3. The goal will be achieved by means of an analysis of chironomid subfossils (remains of non-biting midges) in the recently discovered 21 m-long sediment sequence covering the entire MIS 3 from a small ancient lake in the Northern Limestone Alps, SE Germany. Quantitative estimates of MIS 3 summer temperature variability will be produced by applying a quantitative approach to a high-resolution subfossil chironomid record from the ancient lake deposit. This study will offer new insights into the climate history of the region during the prominent period of climate variability in the middle of the last glacial period. For the first time in the Alps and in Europe as a whole, changes in summer air temperature during the entire MIS 3 will be quantified with a high temporal resolution by subfossil chironomid analysis. Results of the temperature reconstruction will be relevant not only to climatologists, but also to a variety of ecologists studying effects of climate change on ecosystems in the past.

The study of ancient climates (palaeoclimatology) provides an essential perspective on what causes climate change and the potential range and effects of future climate change on natural systems. High climate variability during the period between ~60 and 30 thousand years ago (referred to Marine Isotope Stage (MIS) 3 in oxygen isotope records in North Atlantic deep-sea sediments and Greenland ice cores) is of special interest because frequent rapid shifts from cold to warm conditions may be a model for the climatic conditions that determined environmental processes during much of the late-Quaternary period (past 0.5-1.0 million years). The generally discontinuous nature of sedimentation and repeated erosion combined with a scarcity of high-resolution records, however, hamper a detailed study of climate changes during MIS 3 in the Alps and in Europe as a whole. As such, the magnitude of climate change on the continent through MIS 3 remains mostly unknown. Given the remaining controversy and uncertainties regarding MIS 3 climate in the Alps, we tested two competing hypotheses: i) summers in the Northern Limestone Alps were as warm as today at least during warm sub-periods of MIS 3, and ii) summers in the Northern Limestone Alps were substantially cooler than today during the entire MIS 3. The goal was achieved by means of an analysis of chironomid subfossils (remains of non-biting midges) in the recently discovered 21 m-long sediment sequence covering the entire MIS 3 from a small ancient lake in the Northern Limestone Alps, SE Germany. Quantitative estimates of MIS 3 summer temperature variability were produced by applying a quantitative approach to a high-resolution subfossil chironomid record from the ancient lake deposit. The results of our study indicate that summer air temperatures were 2-6 C lower than present day (16.3 C) during the entire MIS 3, the lowest temperatures between 40 and 44 thousand years ago and the highest temperatures ca. 36 and ca. 38 thousand years ago. This study offers new insights into the climate history of the region during the prominent period of climate variability in the middle of the last glacial period. For the first time in the Alps and in Europe as a whole, changes in summer air temperature during the entire MIS 3 were quantified with a high temporal resolution by subfossil chironomid analysis. Results of the temperature reconstruction will be relevant not only to climatologists, but also to a variety of ecologists studying effects of climate change on ecosystems in the past.