ABSTRACT: Climate-driven shifts in quantity and seasonality of river discharge from the headwaters of the Mackenzie River basin over the past millennium: Implications for river-ocean interactions and natural resource management in the North.

CGRG Bibliography of Canadian Geomorphology
Search Results

Author :

Date :

Title :

Publication :

Issue :

Page(s) :

Abstract

Shrinking headwater glaciers, decreasing alpine snowmelt runoff, and declining river discharges at the headwaters of the Mackenzie River Basin (MRB) continue to alter the seasonal distribution and flux of water, materialsand heat to downstream landscapes and the Arctic Ocean. Rapidly increasing industrial development (e.g., Oil Sands) also raises concerns over the future availability of water resources for continued economic growth and to maintainintegrity of downstream ecosystems. Assessment of contemporary relations between climate and river discharge is limited by the short duration of meteorological and hydrometric records, and so longer hydrological recordsare needed to evaluate the responses of river discharge to a range of natural climatic conditions. Here, we assemble high-resolution 1,000 year paleohydrological records from multiple proxies measured in lake sediment cores obtained from a flood-prone oxbow lake, a climate-sensitive uplandperched basin, and two lowland basins in the Peace- Athabasca Delta adjacent to Lake Athabasca, as well as from a lagoonal pond on nearby Bustard Island in Lake Athabasca, to examine the effects of changing climateand runoff generation on the quantity and seasonality of river discharge at the headwaters of the MRB. Our reconstructions include a broad range of climatic conditions during the medieval (ca.1000 to 1530 CE), Little Ice Age (LIA; 1530 to 1890) and post-LIA intervals. As we will show, the site-specific paleohydrological trajectories are complex at the landscape scale, but can be reconciled by considering the quantity and seasonality of river discharge originating in the eastern Rocky Mountains in the context of climate and glacier mass balance variability over the past 1000 years. Glacier expansion in the Rocky Mountains during the medieval (mainly 1100-1380 and 1450-1505)created hydroclimatic conditions conducive for frequent, severe ice-jam flooding downstream, but that did not sustain river discharge and Lake Athabasca water levels beyond the spring melt period. Glacier advances during the LIA, in response to colder conditions between the sixteenth and nineteenth centuries, resulted in delayed generation of snowmelt runoff at the headwaters and reduced the frequency and magnitude of ice-jams downstream, but sustained higher river discharge that elevated water levels in Lake Athabasca despite locally arid conditions and reduced contributions from local precipitation. The hydrological conditions of the twentieth century are unique in the context of the past millennium, characterized by low frequency and magnitude of ice-jam floods and low Lake Athabasca levels -- a probable outcome of shrinking headwater glaciers and decreasing alpine snowmelt runoff since the conclusion of the LIA. The temporal perspective offered by these paleohydrological reconstructions indicates that climatic changes over the past millennium have led to characteristic responses in the quantity and seasonality of streamflow generated from the hydrographic apex of North America. A key feature is that the hydrograph of the twenty-first century may be evolving towards conditions unprecedented over the past 1000 years. Continuing reduction in both peak and total discharge clearly underscores the need for stringent allocation of freshwater resources in these watersheds, and effective management of downstream ecosystems and coastal areas.

Bibliography of Canadian Geomorphology