Islands of proglacial lake Ojibway acted as outposts favoring postglacial forest migration in northwestern Québec

• Main Authors: Vogel, Marianne, Ali, Adam, Joannin, Sébastien, Bergeron, Yves, Asselin, Hugo
• Other Authors: Institut des Sciences de l'Evolution de Montpellier (UMR ISEM), Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Montpellier (UM)-Institut de recherche pour le développement IRD : UR226-Centre National de la Recherche Scientifique (CNRS), Université du Québec en Abitibi-Témiscamingue (UQAT), Centre d'étude de la forêt (CEF), Université de Sherbrooke (UdeS)-Université Laval Québec (ULaval)-McGill University = Université McGill Montréal, Canada -Université du Québec à Chicoutimi (UQAC)-Université de Montréal (UdeM)-Université Téluq (TELUQ)-Université du Québec en Abitibi-Témiscamingue (UQAT)-Université du Québec à Rimouski (UQAR)-Concordia University Montreal -Université du Québec à Montréal = University of Québec in Montréal (UQAM)-Université du Québec en Outaouais (UQO)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2022
• Subjects: [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces; environment; [SDE.MCG]Environmental Sciences/Global Changes; Ice Sheet; James Bay
• Online Access: https://hal.science/hal-03846635; https://doi.org/10.5194/egusphere-egu22-2701

International audience At the beginning of the Holocene, the Laurentide Ice Sheet was progressively melting and liberating Canadian landscapes. Proglacial Lake Ojibway formed at the contact of the glacier and covered western Québec and eastern Ontario for approximately 2000 years before flushing into James Bay around 8,200 years ago. Lake Ojibway could have limited the afforestation of newly liberated landscapes but could have also provided migratory outposts on its islands. Indeed, several islands were present on Lake Ojibway which could have been colonized by forests before the drainage of lake Ojibway. We studied lake sediments from a small lake located on a paleo-island of Lake Ojibway in Aiguebelle National Park, in order to test the outpost hypothesis. Radiocarbon dating, XRF analysis and charcoal analysis reveal that organic matter (gyttja) started to accumulate around 9,626 years before today (i.e., 1400 years before Lake Ojibway retreat). The signatures of Ca, Sr and Si indicate that soil erosion declined between 9500 and 9000 years before present, meaning this paleo-island was probably colonized during this interval as vegetation stabilizes the soils. Moreover, K (an indicator of vegetation extension) also suggests that afforestation occurred around 9,250 years before present. Macroscopic charcoal particles reveal that one local fire likely occurred 9239 years before present. Burned conifer needle fragments were found among the fossil charcoals, lending support to the hypothesis of wildfire occurrence. All the studied indicators suggest paleo-island colonization around 9,250 years before present, more than 1,000 years before Lake Ojibway retreat.