DROUGHT HISTORY OF SCOUT LAKE DURING THE HOLOCENE BASED ON SEDIMENT LIGHTNESS

Scout Lake is a shallow, hydrologically closed, thermally-stratified, lake in the rain shadow of the St. Elias Mts. in SW Yukon Territory, Canada. Sources of precipitation, in order of importance include NE-moving weather patterns (warm Pacific air masses), weather patterns interfering from the north (Arctic air masses), or in extreme cases southern continental air masses (from the Gulf of Mexico). By using reflectance of finely laminated lacustrine sediments, we seek to determine if Scout Lake shows influences of Holocene variability in NE-moving weather patterns, from the deglaciation to present. The sediment lightness, L*, with 0 indicating black and 100 indicating diffuse white can be related to the carbonate content of the sediment core. The detrended L* record decreases in brightness from the base of the core to the top. We can determine evaporative-intensive periods by observing the changes in brightness. Increased brightness (L*) indicates greater carbonate presence in the sediment. During the early Holocene, this system had intensive drought as indicated by elevated L* levels.

Time series analysis by wavelet transformation of the detrended L* record, interpolated to 15-year resolution, demonstrates that there are times of increased variability at clearly defined periodicities. The record has quasi-cyclic periodicities centered at several hundred years, and multi-millennial intervals. A greater variance occurs at end of the Holocene interglacial period at 12 ka. There are three distinct intervals of high variability throughout the record, centered on 2 ka, 6 ka, and 10 ka with periods of ~1 kyr. Low-frequency temporal variability is demonstrated by the plotted L* trend throughout the length of the record at a period of ~10 kyr. Increasing variance is prominent in the record in three distinct peaks under the cone of influence. We infer the data represents a period of regionally colder temperatures at this time. The Younger Dryas, often indentified as a Heinrich event (H₀) lasted around 1,300 ± 70 years beginning at 12,800 ka and ending 11,500 ka may coincide with the interval of elevated L* at the base of the core.

Our data provides insights into changes in the timing and periodicity of Holocene droughts in the Yukon. Further analyses of the sediment core must be made to evaluate the potential sources which cannot be differentiated by L* analysis alone.