Master of Science
Longstaffe, Fred J.
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.
Summary for Lay Audience
Records of past interglacial (warm) and glacial (cold) stages during the last ice age are rare. Samples comprising these records are also commonly difficult to date. This study improves our knowledge of Ice Age climatic conditions in northern Canada through analysis of sub-fossil wood from the Quaternary Missinaibi Formation sediments of the James Bay Lowland, Canada. All samples were too old (> 50,000 kya) to date using radiocarbon methods. Nonetheless, most other data suggest that these trees grew between the retreat and advancement of the Laurentide Ice Sheet during a warm interval (interglacial) that peaked at ~82 kya, although some consider them to have been younger (71-57 kya). Tree rings are sensitive bioindicators of local environmental change and hence ideal for reconstructing past growing-season climate. Every year, trees form early-wood in the spring to early summer and late-wood from mid-summer to autumn. The cellulose in this wood systematically records growing-season carbon and oxygen-isotope compositions, which respond to changes in temperature and water availability. At the specific site studied here (Adam Creek, Ontario), these data suggest that growing-season conditions during the MIS 5a interglacial were similar to slightly warmer and/or less humid conditions than is the case today. However, the trees from Adam Creek at MIS 5a were still growing within the range of favourable conditions with temperature and water availability.
Lee, Jumin, "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" (2020). Electronic Thesis and Dissertation Repository. 7191.
Available for download on Thursday, September 01, 2022