NOAA/WDS Paleoclimatology - Higuera fire data from Poktovik Lake, Noatak River Valley, Northwestern Alaska - IMPD USPO-001

Tundra fires have important ecological impacts permafrost, and carbon cycling, but the on vegetation, wildlife, pattern and controls of historic tundra fire regimes are fire and vegetation history poorly understood. We use sediment records from four lakes to in a highly flammable tundra region develop a 2000-yr and compare this history with previously published fire records to examine spatial across Arctic Alaska. The four sites span and temporal variability a modern climatic gradient of tundra burning in the Noatak National Preserve, from warmer, drier down-valley locations. Modern vegetation valley sites, and pollen data past two millennia. Peaks in event return intervals (FRIs), locations to cooler, generally moister up-valley varies from herb- to shrub-dominated tundra from down- to up- suggest that this spatial pattern in macroscopic charcoal accumulation which did not vary significantly vegetation persisted over the provide estimates of fire- at millennial time scales but did vary across space. Down-valley with median FRIs of 150 years (95% sites burned relatively frequently CI 101-150) over the past similar to those from ancient shrub tundra and modern boreal forest. At significantly longer than those at 128-285). These differences evaporative demand at shaped tundra fire two millennia, and FRI distributions statistically up-valley sites FRIs were down-valley sites, with a median FRI of 218 likely reflect the cooler up-valley sites, but local-scale regimes. Comparisons with other that the tundra biome can sustain a wide range years (95% CI growing-season temperatures and lower variability in vegetation may have also long-term fire records in Alaska reveal of burning, with individual FRIs from as low as 30 years to more than 5000 burning has occurred under a years. These records range of climatic and fire histories within Alaska suggests together indicate that vegetation scenarios. The that the ecological impacts frequent tundra variety of tundra of tundra burning likewise vary widely, for wildlife-habitat maintenance and for the responses with important implications of tundra biophysical and biogeochemical processes Key words: Alaska; Arctic; charcoal analysis; climatic to climatic change.

苔原火对多年冻土（permafrost）、碳循环（carbon cycling）以及植被与野生动物具有重要生态影响，但目前对历史苔原火格局的模式、调控机制，乃至相关火与植被历史的认知仍较为匮乏。
本研究选取火频发的苔原区域内的4个湖泊沉积物记录（sediment records），重建了过去2000年的火与植被历史，并将其与已发表的火记录进行对比，以探究阿拉斯加北极地区苔原燃烧的空间与时间变异特征。
4个研究点位均位于诺阿塔克国家保留地（Noatak National Preserve），沿现代苔原燃烧的气候梯度分布，从温暖干燥的谷地下游点位延伸至凉爽湿润的谷地上游点位；植被类型也从草本占优逐渐过渡到灌丛占优的苔原，且孢粉数据（pollen data）覆盖了过去两千年的时间跨度。
本研究结合宏观木炭（macroscopic charcoal）积累量与孢粉数据，估算火间隔期（fire-return interval, FRI）。结果显示，宏观木炭积累量在千年尺度上无显著变化，但空间差异显著：谷地下游点位的燃烧频率相对更高，中位FRI为150年（95%置信区间（confidence interval, CI）：101–150年），这与古代灌丛苔原以及现代北方针叶林（boreal forest）的火间隔期相近；而谷地上游点位的FRI则显著更长，中位FRI为218年（95%置信区间（confidence interval, CI）：128–285年）。
这种空间格局的差异可能源于谷地上游更低的生长季温度（growing-season temperatures）与蒸发需求（evaporative demand），同时局地尺度的植被变异也可能对苔原火动态产生调控作用。
与阿拉斯加其他长期火记录的对比表明，苔原生物群系可维持广泛的燃烧模式，单个FRI可低至30年，甚至超过5000年；在阿拉斯加多样的气候与火历史背景下，苔原均可发生持续燃烧。本研究的多项记录共同揭示，苔原燃烧的生态影响同样存在显著差异，这对野生动物栖息地维持以及苔原生物物理与生物地球化学过程的气候变化响应具有重要启示。
关键词：阿拉斯加；北极；木炭分析（charcoal analysis）；气候变化（climatic change）