Holocene and Recent Paleoclimate Investigations Using Carbon and Nitrogen Isotopes from Bulk Sediment of Two Subarctic Lakes, Central Northwest Territories

• Main Author: Griffith, Fritz
• Format: Thesis
• Language: English
• Published: Université d'Ottawa / University of Ottawa 2013
• Subjects: isotopes; carbon; nitrogen; paleoclimate; arctic; subarctic; sediment; lake sediment; northwest territories; paleoclimatology; paleolimnology; Arctic; Canada; Northwest Territories; Pacific; Yellowknife; Subarctic; Tundra
• Online Access: https://dx.doi.org/10.20381/ruor-3393; http://www.ruor.uottawa.ca/handle/10393/30197

The Tibbitt-to-Contwoyto Winter Ice Road (TCWR) is the sole overland route servicing diamond mines north of Yellowknife, Northwest Territories (NWT), Canada. The road is 568 km long, 85% of which extends over frozen lakes. As such, its operational season is highly dependent upon the length of the winter season. This was exemplified in 2006, when an El Niño event caused an unusually short ice road season and resulted in a costly reduction of shipments to the mines. For future use and development of the TCWR, a comprehensive understanding of past regional climate variability is required. This study is an integral component of a larger-scale study designed to develop a comprehensive database of high-resolution paleoclimate data for the NWT, using a variety of proxies. As part of the larger study, freeze cores were taken from numerous lakes along the TCWR and sliced at 1-mm intervals using a custom-designed sledge microtome. Bulk 13C and 15N isotope analysis was completed at preliminary 1-cm intervals through the cores of two lakes on opposite sides of the tree line. Results from this analysis show clear trends with distinct transitions in both cores, whose closely-matched timing suggests regional-scale climate events. These results indicate that the Early Holocene was warm and dry, with a sudden shift to wetter conditions around 7200-6900 cal yr BP. Another shift to cooler conditions occurred at 4000 cal yr BP, and a final transition to even cooler temperatures occurred around 755-715 cal yr BP, coinciding with the Little Ice Age. Additionally, a modern lake survey was completed using surface sediments of numerous lakes throughout the Arctic and Subarctic. This survey verifies the strong influence of boreal forest vs. tundra conditions in affecting various environmental properties within lakes, including carbon and nitrogen isotopes. Lastly, time-series analysis was completed on two sections of Danny’s Lake core at high resolution (up to 2 mm), in order to determine short-term climate cycles. These results highlight specific climate frequencies which may be related to the Pacific Decadal Oscillation. These results offer insight to short-term climate phenomena in the Northwest Territories which will allow future climate modellers to make more accurate predictions of future climate and its impact on the ice road.