Continuous, diurnally fluctuating turbidity currents in Kluane Lake, Yukon Territory

Abstract

Modern sedimentary processes were studied in Kluane Lake, Yukon Territory, to determine the spatial and temporal patterns of sediment distribution in a large, dynamic, glacier-fed lake. Data from a river monitoring station, moored instruments, sediment traps, and water-column profiles in the lake were used to document lacustrine sedimentary processes in 2006 and 2007. During the peak melt season, the suspended sediment concentration of Slims River is weakly dependent on river discharge and can reach up to 5 g L–1, although a diurnal range between 1 and 2 g L–1 is more commonly observed. The high suspended sediment load in the river generates continuous, diurnally fluctuating turbidity currents in Kluane Lake with maximum velocities up to 0.6 m s–1. During times of peak flow, variations in velocity can be traced to beyond 4 km from the river mouth. The vertical concentration profiles, mass accumulation rates, and suspended sediment loads show distinctive longitudinal variations; the highest rate of accumulation occurs ∼1 km from the point of inflow, which is concurrent with a distinct change in flow structure. Diurnal laminations are apparent in sediment traps close to the point of inflow and can be directly linked to variations in current velocity; however, these laminations do not occur consistently over space or time. These results suggest that long-term measurement records of lacustrine turbidity currents provide valuable insights regarding the multiple scales of environmental variability and have important implications for paleoenvironmental reconstruction using lacustrine sediments.

How are subaqueous sediment density flows triggered, what is their internal structure and how does it evolve? Direct observations from monitoring of active flows

“…Crookshanks and Gilbert (2008) show that flows can sometimes be continuous over several weeks, with diurnal fluctuation mimicking change in meltwater river discharge. In some locations, tens of flow events have occurred during a single year.…”

“…In lakes and reservoirs, river flood discharge is often sustained for several days, and can be sustained for weeks (Crookshanks and Gilbert, 2008), generating prolonged turbidity currents ( Table 2). The volume concentrations of suspended sediment in river flood water are typically between 0.01 (Umeda et al, 2006) Table 2).…”

“…Density flows along the floor or lakes and reservoirs are typically dilute with maximum measured volume concentrations of 0.07% to 0.001% for suspended sediment (Table 2), with sediment concentrations increasing progressively towards the bed (e.g. Chikita, 1990;Best et al, 2005;Umeda et al, 2006;Crookshanks and Gilbert, 2008).…”

“…The relative importance of hyperpycnal river discharge, or other processes such as delta-front slope failure, for triggering turbidity currents remains a key question for this contribution. Sediment density flows play an important role in the dispersal of sediment within freshwater lakes (Lambert and Hsu, 1979;Gilbert et al, 2006;Crookshanks and Gilbert, 2008), and lacustrine turbidites can form hydrocarbon reservoirs (Feng et al, 2010). These flows can also play an important part in the delivery of organic matter and nutrients within lakes (De Cesare et al, 2006).…”

Characterizing and Monitoring the Water Properties and Dynamics of Lhù’ààn Mǟn (Kluane Lake), Yukon, in the Face of Climate Change

“…comm. 2014), and limited point sampling has been completed by the Fish and Wildlife Branch, Government of Yukon, during routine fish surveys (Barker et al, 2014), as well as by university-based researchers (Crookshanks and Gilbert, 2008). Over the course of 2013 -14, Dr. David Hik and I met several times with representatives of the Kluane First Nation (KFN), the Dän Keyi Renewable Resources Council (DKRRC), and local community members to identify common research interests.…”