Orbital-scale climate forcing of grassland burning in southern Africa
Orbital-scale climate forcing of grassland burning in southern Africa
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DOI：
10.1073/pnas.1214292110
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发表时间：
2013-03
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通讯作者：
A. Daniau;M. F. Sánchez Goñi;P. Martinez;D. Urrego;V. Bout‐Roumazeilles;S. Desprat;J. Marlon
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作者：
A. Daniau;M. F. Sánchez Goñi;P. Martinez;D. Urrego;V. Bout‐Roumazeilles;S. Desprat;J. Marlon
尽管草原和稀树草原只占世界植被的四分之一，但这些生态系统的燃烧约占全球火灾碳排放量的一半。然而，人们对控制草原燃烧变化的过程知之甚少，特别是在超出卫星记录的时间尺度上。我们分析了纳米比亚近海高分辨率海洋沉积物岩芯中的微炭、沉积物和地球化学，以确定在大的、多年尺度的气候变化下控制南部非洲草原生态系统生物质燃烧的过程。在过去170000年期间，南部非洲发生了六个火灾周期，在时间和强度上都与热带辐合带南北变化的进动强迫相一致。与传统的随着气温升高和干旱加剧而增加火灾的预期相反，我们发现，由于降雨量和季节性的变化(从而导致植被易燃性)，更潮湿和更凉爽的气候导致研究地区的燃烧增加。我们还表明，木炭形态(即颗粒的长宽比)可以用来重建火灾活动以及生物群随时间移动的变化。我们的结果为理解当前和未来的草原火灾动态及其相关的碳排放提供了必要的背景。
Although grassland and savanna occupy only a quarter of the world's vegetation, burning in these ecosystems accounts for roughly half the global carbon emissions from fire. However, the processes that govern changes in grassland burning are poorly understood, particularly on time scales beyond satellite records. We analyzed microcharcoal, sediments, and geochemistry in a high-resolution marine sediment core off Namibia to identify the processes that have controlled biomass burning in southern African grassland ecosystems under large, multimillennial-scale climate changes. Six fire cycles occurred during the past 170,000 y in southern Africa that correspond both in timing and magnitude to the precessional forcing of north–south shifts in the Intertropical Convergence Zone. Contrary to the conventional expectation that fire increases with higher temperatures and increased drought, we found that wetter and cooler climates cause increased burning in the study region, owing to a shift in rainfall amount and seasonality (and thus vegetation flammability). We also show that charcoal morphology (i.e., the particle's length-to-width ratio) can be used to reconstruct changes in fire activity as well as biome shifts over time. Our results provide essential context for understanding current and future grassland-fire dynamics and their associated carbon emissions.