Stable carbon and oxygen isotope investigation of Pleistocene growing-season paleoclimate using tree-ring cellulose from the Missinaibi Formation, Adam Creek, James Bay Lowland, Canada

The isotopic compositions of cellulose in tree rings provide a record of seasonal and annual climatic conditions such as precipitation and temperature. We analyzed stable isotopes of carbon (δ13Ccellulose) and oxygen (δ18Ocellulose) in early-wood and late-wood of five conifer sub-fossil wood samples from the Missinaibi Formation, which likely grew during the peak of Marine Isotope Substage (MIS) 5a (~82 kya) at Adam Creek, Ontario. There was no systematic difference between early-wood and late-wood for either δ13Ccellulose or δ18Ocellulose, suggesting similar climatic conditions throughout the growing season. A shift to lower δ13Ccellulose with growth age in most samples indicated rising water availability. The estimated value of δ18Oprecipitation was similar or slightly higher than modern δ18Oprecipitation. Hence, the area may have experienced similar to slightly warmer and/or less humid conditions than today, which is in agreement with the few other studies of MIS 5a climate in this region