|Title||Holocene investigations of three lakes in the central Northwest Territories: climate change across ecotone gradients and implications for future change|
|Author||Galloway, J M; Sulphur, K C; Goldsmith, S A; Trainor, P; Patterson, R T; Hills, L V; Roe, H M; Swindles, G T; Crann, C; Macumber, A L; Falck, H|
|Source||41st Annual Yellowknife Geoscience Forum Abstracts; by Irwin, D; Northwest Territories Geoscience Office, Yellowknife Geoscience Forum Abstracts Volume 2013, 2013 p. 22-23|
|Links||Online - En ligne|
|Alt Series||Earth Sciences Sector, Contribution Series 20130446|
|Meeting||41st Annual Yellowknife Geoscience Forum; Yellowknife; CA; 2013|
|NTS||85I; 85J; 85P; 75M; 76D|
|Area||Waite Lake; Danny's Lake; Horseshoe Lake|
|Lat/Long WENS||-115.0000 -110.0000 65.0000 62.5000|
|Subjects||geochronology; lake sediments; Holocene; climatic fluctuations; palynomorphs; radiocarbon dates; cores; Quaternary|
|Program||environmental impacts and adaptation in the northern environment, Environmental Geoscience|
|Abstract||The continued success of the natural resource based economy of the Northwest Territories depends on the use of winter roads. A 568 km long winter road, the Tibbitt to Contwoyto Winter Road (TCWR), is
the only ground transportation route that services mines in the central NWT, including the Ekati Diamond Mine, the Snap Lake Mine, and the Diavik Diamond Mine. Cold winter temperatures are necessary for the continued viability of the TCWR because
87% of its length is built over frozen lakes. Changing ice stability, thickness, and duration of cover associated with recent climate variability have impacted the use of the road.|
The purpose of this project is to analyze lake sediments,
natural archives of past climate change, to better understand climate variability and terrestrial ecosystems response to those changes. This information may be used by stakeholders in adaption planning for current and forecasted climate change.
Three lakes were studied along the latitudinal gradient of the TCWR. Waite Lake is located 75 km northeast of Yellowknife and within boreal forest. The late freezing and early ice breakup of this lake is a concern for winter road operation. Danny¿s
Lake is located 30 km south of treeline and Horseshoe Lake is located 60 km north of treeline.
Sediments were obtained from the lakes using a freeze-coring device and analyzed for palynomorphs and microscopic charcoal at 2-cm intervals.
Age-depth relationships of the sediments show decreasing sedimentation rates northward. Based on AMS 14C dating, the Waite Lake record extends to ~2500 BP and is analyzed at a ~30-yr resolution, the Danny¿s Lake record extends to ~8610 BP and is
analyzed at a ~160-yr resolution, and the Horseshoe Lake record extends to ~8866 BP and is analyzed at a ~ 215 to ~860-yr resolution. The longer Danny¿s and Horseshoe lake records capture a warming event at ~7000 BP when Picea (spruce) replaced
shrub tundra and tundra vegetation. The frequency and severity of regional fires decreased at this time, suggesting climate also became moister. At ~1730 BP fires increased and warmer temperatures resulted in the expansion of Pinus (probably jack
pine) at Danny¿s and Horseshoe lakes. Picea glauca (white spruce) and Cupressaceae (probably juniper) expanded at this time at Waite Lake. Palynomorph abundances in Waite Lake document additional variability at ~1300 BP and ~120 BP, using the
higher resolution analysis that was possible with this core.
Time series analyses of the accumulation rate of charcoal in the Waite Lake core show a significant (>95% C.I.) ~99-yr periodicity between ~1500 and ~1720 BP and between ~2050 and
~2350 BP. In the Danny¿s Lake record, significant ~430-yr and ~2610-yr (>90% C.I.) and ~980-yr (>95% C.I.) signals are present in the frequency of charcoal. The ~430-yr signal is significant between~4950 and ~5550 BP, the ~980-yr signal between
~3850 and ~6650 BP and the ~2610-yr signal is significant throughout the record. These signals suggest that solar variability may have influenced regional fire regimes in the NWT at various times in the Holocene.
|Summary||(Plain Language Summary, not published)|
We use pollen, spores, and microscopic charcoal preserved in the sediments of three lakes, Waite Lake, Danny's Lake, and Horseshoe Lake, located along
the latitudinal gradient of the Tibbitt to Contwoyto Winter Road in the central NWT, to show that climate, vegetation, and fire regimes have changed throughout the Holocene. The longer Danny¿s and Horseshoe lake records capture a warming event at
~7000 BP when spruce expanded northward. Regional fires decreased at this time. At ~1730 BP fires increased and warmer temperatures resulted in the expansion of pine at Danny¿s and Horseshoe lakes. White spruce and juniper expanded at this time at
Waite Lake. Time series analysis of microscopic charcoal in the cores show a ~99 yr periodicity (in the Waite Lake core) and ~430 yr and ~2610 yr periodicities (in the Danny's Lake core). These signals suggest that solar variability may have impacted
fire regimes in the NWT at various times in the Holocene.