Department of Earth Sciences, ETH Zurich, 8092, Switzerland;
Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.
Proc Natl Acad Sci U S A. 2021 Feb 23;118(8). doi: 10.1073/pnas.2011585118.
Terrestrial vegetation and soils hold three times more carbon than the atmosphere. Much debate concerns how anthropogenic activity will perturb these surface reservoirs, potentially exacerbating ongoing changes to the climate system. Uncertainties specifically persist in extrapolating point-source observations to ecosystem-scale budgets and fluxes, which require consideration of vertical and lateral processes on multiple temporal and spatial scales. To explore controls on organic carbon (OC) turnover at the river basin scale, we present radiocarbon (C) ages on two groups of molecular tracers of plant-derived carbon-leaf-wax lipids and lignin phenols-from a globally distributed suite of rivers. We find significant negative relationships between the C age of these biomarkers and mean annual temperature and precipitation. Moreover, riverine biospheric-carbon ages scale proportionally with basin-wide soil carbon turnover times and soil C ages, implicating OC cycling within soils as a primary control on exported biomarker ages and revealing a broad distribution of soil OC reactivities. The ubiquitous occurrence of a long-lived soil OC pool suggests soil OC is globally vulnerable to perturbations by future temperature and precipitation increase. Scaling of riverine biospheric-carbon ages with soil OC turnover shows the former can constrain the sensitivity of carbon dynamics to environmental controls on broad spatial scales. Extracting this information from fluvially dominated sedimentary sequences may inform past variations in soil OC turnover in response to anthropogenic and/or climate perturbations. In turn, monitoring riverine OC composition may help detect future climate-change-induced perturbations of soil OC turnover and stocks.
陆地植被和土壤中储存的碳是大气中碳含量的三倍。人类活动将如何干扰这些地表碳库，从而可能加剧正在进行的气候系统变化，这是一个备受争议的问题。在将点源观测值外推到生态系统尺度的收支和通量时，特别存在不确定性，这需要考虑多个时间和空间尺度上的垂直和水平过程。为了探索在流域尺度上控制有机碳（OC）转化的因素，我们对来自全球分布的一系列河流中的两组植物衍生碳示踪剂——叶蜡脂和木质素酚——的放射性碳（C）年龄进行了研究。我们发现这些生物标志物的 C 年龄与年均温度和降水量呈显著负相关。此外，河流生物群系碳年龄与流域范围内土壤碳周转时间和土壤 C 年龄成比例，这表明土壤中 OC 循环是控制输出生物标志物年龄的主要因素，并揭示了土壤 OC 反应性的广泛分布。普遍存在的长寿命土壤 OC 库表明，全球土壤 OC 易受未来温度和降水增加的干扰。河流生物群系碳年龄与土壤 OC 周转的比例表明，前者可以约束碳动态对广泛空间尺度上环境控制的敏感性。从河流主导的沉积序列中提取这些信息可以为响应人为和/或气候干扰的土壤 OC 周转的过去变化提供信息。反过来，监测河流 OC 组成可能有助于发现未来气候变化引起的土壤 OC 周转和储量的变化。
