The early Eocene (~56-53 Ma) polar forests of Ellesmere Island: quantitative analyses of diversity and floristic change

Please join us for a graduate student seminar this Friday March 22 at 3:30 pm in rm 155 Geology presented by Christopher West, PhD candidate:

The early Eocene (~56-53 Ma) polar forests of Ellesmere Island: quantitative analyses of diversity and floristic change

Late Paleocene-early Eocene deposits belonging to the Eureka Sound Group on Ellesmere Island in northern Canada preserves fossil evidence of diverse mesothermal deciduous forests of ferns, conifers (e.g., the Dawn Redwood), and broad-leaved trees (e.g., horse chestnut, alder, hazel, walnut, and elms); and a unique polar fauna (e.g., tapirs, alligators, and terror birds). These polar forests proliferated at a time when global temperatures were much higher than modern values, and were exacerbated by a series of superimposed short-lived hyperthermal events (e.g., the Paleocene-Eocene Thermal Maximum (PETM) ca. 56 Ma, and the Eocene Thermal Maximum 2 (ETM-2) ca. 53.7 Ma) ─ intense episodes of global warming that punctuated the early Eocene.

Multiple proxies provide evidence for the warm and wet climate, and frost-free winters (e.g., mean annual temperature ≥ 12 °C, cold month mean temperature ≥ 0 °C, and mean annual precipitation ≥ 150 cm/yr), that characterized the high latitudes at that time. Furthermore, these forests would have endured extended periods of continuous day and night during the respective polar summer and winter, in what could be characterized as extreme photic seasonality, coupled with an otherwise warm equable climate.

Previous palynological research from Stenkul Fiord has shown that the polar forests on Ellesmere Island were of similar diversity to modern mid-latitude temperate deciduous forests; however, pooled samples and the potential for fossil pollen to undergo reworking and significant transport may have artificially inflated or confounded the diversity of the palynoflora. Fossil megaflora, however, allows for examination of diversity and floristic change at a lower taxonomic level without concern of time-averaging or reworking.

Presented here are the first quantitative analyses of polar floral diversity based on census collected leaf compression fossils from Stenkul Fiord, southern Ellesmere Island, Nunavut. These collections were sampled stratigraphically above and below horizons identified as recording both the PETM and ETM-2 hyperthermal events. Site-specific palynological data is also evaluated to provide a more robust interpretation of local and regional floral diversity. These data and the taxonomic composition of the fossil flora is discussed in terms of floristic change as a potential response to the hyperthermal events. The results of these analyses substantiate previous studies that showed that the early Eocene polar forests of the Canadian Arctic were similar in diversity to modern mid-latitude temperate deciduous forests. Floral diversity appears to remain stable through time, whereas taxonomic composition of the floras appears to change following the hyperthermal events.