Investigating seasonal deposition of dust along arctic rivers

 

Submitter:

de Boer, Gijs - University of Colorado

Area of research:

Radiation Processes

Journal Reference:

de Boer G, C Cox, and J Creamean. 2019. "Accelerated Springtime Melt of Snow on Tundra Downwind from Northern Alaska River Systems Resulting from Niveo-aeolian Deposition Events." ARCTIC, 72(3), 10.14430/arctic68654.

Science

This study investigates the seasonal appearance of dark material along river beds in northern Alaska, which reduces the surface reflectivity in these areas, enhancing absorption of solar radiation. This deposition is demonstrated to be associated with high-wind events and is shown to accelerate seasonal snow melt over and around the river beds.

Impact

This accelerated melt of snow results in early river breakup, increased water flow, and potential downstream flooding.  It kicks off a positive feedback loop, with enhanced snow melt revealing the darker underlying tundra, which subsequently absorbs more solar radiation and warms the snow around the areas of initial deposition.  Future changes in the frequency of high-wind events may further alter the net impact of these deposition events on an Arctic-wide scale.

Summary

In this study, we combine various observational tools to demonstrate that aeolian deposition of PM along fluvial features on the North Slope of Alaska resulted in a notable reduction of surface albedo in the spring of 2016, from values typical for snow (∼0.8) to around 0.35 on average.  This reduction resulted in accelerated snow and ice melt by up to three weeks compared to unaffected areas. This phenomenon was observed to some degree in 12 other years dating back to 2003. Deposition generally was found to occur near particular sections of the rivers, with several areas affected by events in multiple years. In all years, the deposition is attributed to high-wind events. The extreme case in 2016 is linked to unusually strong and extraordinarily persistent winds during April.  The deposited material is thought to be the natural sediment carried by the rivers, resulting in a seasonally replenished source of PM. These findings indicate a previously unreported impact of both fluvial and atmospheric processes on the seasonal melt of northern Alaska rivers.