TRANSGRESSIVE BARRIER MOVEMENT DURING THE LITTLE ICE AGE: CONFIRMATION OF A MAJOR LAKE ATHABASCA (ALBERTA, CANADA) HIGH-WATER STAND THAT INUNDATED THE PEACE-ATHABASCA DELTA

The Peace-Athabasca Delta (PAD), located at the termini of the Peace and Athabasca rivers in northern Alberta, Canada, is a Ramsar wetland of international significance and UNESCO World Heritage Site. Paleoenvironmental investigations, ongoing since 2000, aim to reconstruct hydroecological variability of this complex northern freshwater ecosystem. Extended temporal perspectives are necessary for effective ecosystem management in light of multiple potential stressors, ranging from climate variability to discharge alteration of major rivers due to natural resource development. Previous studies, incorporating archival maps and multi-proxy paleolimnological data from a small, central low-lying basin in the PAD, document a high-water stand on Lake Athabasca during the Little Ice Age (LIA) possibly driven by snowmelt-enhanced summer discharge of the Athabasca River. Here we present supporting geophysical and paleolimnological results from a preserved barrier beach complex on Bustard Island in western Lake Athabasca. Profiles generated from ground-penetrating radar transects define a transgressive barrier including lagoonal, washover fan (horizontal and delta forests) and dune facies. A 5,300 year-long sedimentary record from the lagoon contains multiple sand lenses interpreted to reflect washover fans deposited from episodic barrier movement toward the lagoon, with the most recent having occurred during the LIA (~1600-1850 AD). The oldest cored living tree on the barrier crest was established at the end of the LIA suggesting reduced vegetative cover may have aided barrier mobilization. The LIA stratigraphic interval in the sedimentary record is also defined by an increase in the abundance of submerged and emergent plant macrofossils as well as epiphytic diatoms consistent with higher water levels. Aeolian deposition of the sand lenses is unlikely because the orientation of the beach-barrier-lagoon is opposite to the prevailing wind direction and the elevation of the barrier exceeds the historical range in Lake Athabasca water level fluctuations. Thus, results confirm a multi-centennial high-stand and associated storm related events characterized Lake Athabasca during the LIA, and was one of several such high-stands to have occurred during the late Holocene.