Increased Fire Activity in Alaska Since the 1980s: Evidence From an Ice Core‐Derived Black Carbon Record

Abstract

AbstractWildfires emit large quantities of particles that affect Earth's climate and human health. Black carbon (BC), commonly known as soot, is directly emitted to the atmosphere by wildfires and other processes and can be transported and deposited in remote regions including high‐altitude glaciers and the polar regions. Here, we present a continuous, high‐resolution record of BC and ammonium (NH4+) from 1933 to 2001 extracted from two ice cores retrieved in 2002 from the col between Mt. Bona and Mt. Churchill in the Wrangell‐St. Elias Mountain Range, southeast Alaska. Despite the substantial increase of BC from fossil fuels in the Arctic since the Industrial Revolution, BC at Bona‐Churchill originates primarily from biomass burning and thus provides a record reflecting a fire history for Alaska. The BC record from Bona‐Churchill reveals that high fire activity became more frequent after 1984 in agreement with Alaska fire records. Most years associated with high BC or high NH4+ before 1984 occurred during El Niño events when precipitation in Alaska was below “normal,” suggesting that precipitation played an important role in modulating fire activity in Alaska prior to the 1980s. Conversely, years with high BC or NH4+ after 1984 coincided with years with “normal” and low precipitation, but elevated temperatures, strongly suggesting that temperature became a more dominant factor influencing fire activity in Alaska after the 1980s as suggested by other studies. Recent Alaska fire records and temperatures indicate that this trend has continued in the 21st century.