NOAA/WDS Paleoclimatology - Kirk Lake, Northern Brooks Range Foothills, Alaska: Chronology and Charcoal Data 760 years BP to present - IMPD USANS002

Charcoal particles in lake sediments can reveal past fires and linkages to climate and vegetation change. We use analyses of charcoal accumulation rates from two lakes on the Alaskan North Slope to reconstruct past fire activity, and charcoal morphology to identify changes in fuel sources. Charcoal peak analyses were used to calculate individual fire-return intervals (FRIs; years between fire) and mean FRIs (mFRIs) with 95% confidence intervals at local and regional scales. The Lake I4 core (RTS7U2, basal age 7046 cal year B.P.) shows shorter FRIs after ∼3000 cal year B.P. based on the >90 µm charcoal size fraction (regional burning), which coincides with Neoglacial cooling and decreasing moisture. A second higher-resolution core from nearby Kirk Lake (RTS5U3, basal age 743 years) captures short FRIs (mFRI = 198 (105–133) years), suggesting frequent burning compared to the late Holocene portion of Lake I4 core (mFRI = 378 (294–455) years). mFRIs from the larger charcoal size fractions (>125 µm; local burning) at both sites overlap with modern fire cycles observed in the region over the past 82 years. However, the Kirk Lake watershed burned more frequently than other sites in the region, likely related to abundant local shrub cover. These analyses suggest that tundra fires are related to climate variability, but local-scale feedbacks with vegetation can result in heterogenous burning, with implications for ongoing Arctic greening and warming.

湖泊沉积物中的炭粒可揭示过去的火灾事件，并阐明火灾与气候变化及植被变化之间的关联。本研究通过分析阿拉斯加北坡两处湖泊的炭粒堆积速率，重建区域过去的火灾活动历史；同时借助炭粒形态学分析，识别火灾燃料源的变化情况。研究采用炭粒峰值分析方法，计算了局地与区域尺度下的单次火灾轮回期（fire-return intervals，简称FRIs，即两次火灾间的间隔年数）与平均火灾轮回期（mean FRIs，简称mFRIs），并给出95%置信区间。I4湖岩芯（编号RTS7U2，基底年代为7046个校准年BP）基于>90μm粒径的炭粒组分（代表区域尺度火灾），显示约3000个校准年BP之后火灾轮回期更短，这与新冰期降温及湿度降低的时期相吻合。邻近的柯克湖（Kirk Lake）另有一根更高分辨率的岩芯（编号RTS5U3，基底年代为743个校准年BP），其记录的平均火灾轮回期为198年（置信区间105–133年），相较I4湖岩芯的全新世晚期部分（平均火灾轮回期为378年，置信区间294–455年），火灾发生更为频繁。两处岩芯基于较大粒径炭粒组分（>125μm，代表局地尺度火灾）得到的平均火灾轮回期，与该区域过去82年间观测到的现代火灾周期基本重合。但柯克湖流域的火灾发生频率高于区域内其他点位，这可能与当地丰富的灌丛覆盖有关。本研究的分析结果表明，苔原火灾与气候变化存在关联，但局地尺度的植被反馈机制可导致火灾分布呈现异质性，这对当前正在发生的北极绿化与气候变暖研究具有重要启示意义。