SAGE: Attribution of Biomass Burning Tracers sampled on the Greenland Ice Sheet in 2013

The SAGE team traversed and sampled the snow stratigraphy representing 2012-2014 snow accumulation in the northwest sector of the Greenland Ice Sheet (GrIS) and found evidence of aerosol deposition that originated from biomass burning (BB). Black carbon (BC) concentrations (range 2.8-43 ng/g) were closely correlated with ammonium (NH4), both of which are tracers that are indicative of BB events. Data indicated the strongest deposition events occurred in July and August of 2013. Using a combination of these in-situ samples, modeling and satellite data, the transport and attribution of deposited smoke is back-traced from the GrIS to particular fires. The Langley Research Center Trajectory Model (LaTM) is used to track deposition events from pit locations on the GrIS to particular source fires from June through August 2013, which includes 2 months when smoke is known to have strongly impacted the GrIS (July August 2013) and 1 month (June 2013) of relatively low smoke impact. Simulated smoke is injected every 100 vertical meters to 2km ( boundary layer) in the LaTM and run backwards in time and space from sample sites until coincident with fire (MODIS data). Ground-based and satellite data are used to verify transport. As an example, we focus on one case study that traces smoke from fires that started burning on July 22nd and continued to burn through July 26-29. A river of smoke crosses Canada and is transported to the GrIS, arriving August 1st-2nd. Overall, we find the largest BB events do not equate to the largest deposition events, rather this process requires a combination of: intense fires; conducive transport paths; and deposition and preservation opportunities (snowfall). Intensely burning fires produce thick smoke, which is less likely to be dispersed or diluted in transport, and the smoke is injected to higher altitudes, which ensure a faster transport. Because fire severity, extreme fire seasons, general circulation patterns and precipitating snowfall are all under the control of climate, this work has significance for understanding past, current and future BB deposition on the ice sheet and surface melt.