Refractory Black carbon (rBC) variability in a 47-year West Antarctic Snow and Firn core

Abstract

Abstract. Black carbon (BC) is an important climate-forcing agent that affects snow albedo. In this work, we present a record of refractory black carbon (rBC) variability, measured from a 20-meter deep snow and firn core drilled in West Antarctica (79°55'34.6"S, 94°21'13.3"W) during the 2014–2015 austral summer. The core was analyzed using a Single Particle Soot Photometer (SP2) coupled to a CETAC Marin-5 nebulizer. Results show a well-defined seasonality with geometric mean concentrations of 0.015 µg L−1 for the wet season (summer/fall) and 0.057 µg L−1 for the dry season (winter/spring). The core was dated to 47 years (1968–2015) using rBC seasonality as the main parameter, along with Na, S and Sr variations. The annual rBC concentration geometric mean was 0.03 µg L−1, the lowest of all rBC cores in Antarctica referenced in this work, while the annual rBC flux was 6.25 µg m−2 a−1, the lowest flux in West Antarctica records so far. No long-term trend was observed. Snow albedo changes in the site due to BC were simulated using SNICAR-online and found to be very low comparing to clean snow (−0.48 %). Fire spots inventory and BC emission estimates from the Southern Hemisphere suggest Australia and Southern Hemisphere South America as the most probable emission sources of BC to the drilling site. Spectral analysis (REDFIT method) of the BC record showed cycles related to the Antarctic Oscillation (AAO) but not to El Niño Southern Oscillation ENSO, and comparison with time series of co-registered Na record suggest BC transport to the site not to be related to the intrusion of marine air masses.