Late Pleistocene vegetation and climate history of northern Vancouver Island, Canada: spatiotemporal variation in deglacial ecology along the Pacific margin of the Cordilleran Ice Sheet

Palaeoecological analysis of six cores on northern Vancouver Island, Canada, reveals asynchronous vegetation responses to climatic changes at the interface of the Cordilleran Ice Sheet and the Pacific Ocean during the terminal Pleistocene and earliest Holocene. We describe rapid vegetation shifts and define them in a regional palynostratigraphic sequence: the Non-Arboreal Herb-Shrub Zone, the Pinus (pine) Zone, the Mixed Alnus-Picea (alder-spruce) Zone, the Tsuga (hemlock) Zone, and the Alnus (alder) and Conifer Zone. On the outer west coast, cold and dry non-arboreal steppe-tundra was established first by ∼18,000 years ago, appearing later to the east and persisting there as late as ∼14,100 years ago. Pine dominated briefly in the west at ∼16,000 years ago under cool and relatively dry conditions, spreading progressively eastward and predominating at most sites by ∼14,300–14,100 years ago. Precipitation subsequently increased, with red/green alder and Sitka spruce (Picea sitchensis) as key species in the west from ∼15,700 years ago under moderate and moist conditions before spreading to eastern sites by ∼13,900–13,600 years ago. Western hemlock dominated under moist and cooler conditions by ∼13,800 years ago in the west and ∼13,200–12,900 years ago in the east as temperatures declined ∼1–2 °C. By ∼12,200 years ago at most sites, moist and increasingly warm conditions resulted in Sitka spruce forest with red alder and western hemlock across most of the region. Diachronous vegetation development may have resulted from an eastward-shifting band of precipitation and oceanic influence as ice retreated inland and climate stabilized at the end of the Pleistocene. We show that varied ecosystems existed across short distances throughout the late-glacial interval on northern Vancouver Island. Furthermore, we corroborate the timing and character of deglacial climatic episodes in the North Pacific Ocean, including Siku Event 1 and the early onset of a mild cooling event which pre-dated North Atlantic Younger Dryas by at least 200-600 years—here assigned the provisional name “Quatsino Event”. Our results demonstrate the importance of understanding regional vegetation and climatic histories at coast-continent interfaces adjacent to major components of global climate such as the North Pacific Ocean when investigating the teleconnections of oceanic and atmospheric systems.