Stable oxygen isotopes in chironomid and cladoceran remains as indicators for lake-water delta O-18

An understanding of modern relationships between the stable oxygen isotope composition (delta O-18) of lake water and aquatic invertebrates is essential for the interpretation of paleoclimate records based on delta O-18 of organic remains of these organisms. We analyzed delta O-18 of lake water and invertebrate remains, including head capsules of chironomid larvae and resting eggs (ephippia) of planktonic Cladocera, in surface sediments from 31 large, deep, and stratified lakes along a latitudinal transect through Europe. The delta O-18 values measured for both lake water and aquatic invertebrate remains were compared to estimated delta O-18 in precipitation. A strong linear relationship between mean annual air temperature and delta O-18 of precipitation was observed along the north-south transect (r = 0.97), whereas the relationship between precipitation delta O-18 and lake-water delta O-18 was weaker (r = 0.80). A strong positive correlation was observed between delta O-18 in lake water and aquatic invertebrates (r = 0.95 and 0.94 for chironomids and cladocerans, respectively). Although slopes of linear regressions between lake-water delta O-18 and delta O-18 of both aquatic invertebrate groups are similar, a systematic offset between the absolute delta O-18 values of chironomids and cladocerans was observed; chironomids were on average 2.4 parts per thousand heavier than Cladocera. We attribute this offset to differences in ecology, metabolism, and/or behavior between benthic chironomid larvae and planktonic Cladocera. delta O-18 records based on subfossil chironomid and cladoceran remains have the potential to quantitatively characterize past lake-water delta O-18 and, indirectly, past climatic changes.