Trend in seasonal amplitude of northern net ecosystem production: Simulated results from IAP DGVM in CAS-ESM2

Abstract

Net ecosystem production (NEP) over northern latitudes has an obvious seasonal variation, which dominantly drives the seasonal variation in atmospheric CO2. Investigating these carbon processes and understanding the underlying drivers is a key issue of climate research. This study focuses on the seasonal amplitude of northern NEP (40°–90°N) and investigates its trend in the period 1990–2014 by using the dynamic global vegetation model (IAP DGVM) in the second version of the Chinese Academy of Sciences Earth System Model (CAS-ESM2). Basing on a spin-up simulation, the authors conduct a control simulation to evaluate the modeled trend in the seasonal amplitude of northern NEP, and three sensitivity simulations to detect the contributions of the climate and atmospheric CO2. The results show that the modeled seasonal amplitude of northern NEP increases significantly from 1990 to 2014, with a trend of 9.69 TgC month−1 yr−1, which is mainly because of the increasing maximum NEP. The positive trend is largely reduced when CO2 fertilization effects and climatic effects are separately excluded. These significant reductions suggest important effects of atmospheric CO2 and climate change on the seasonal amplitude of northern NEP. Even though model uncertainties remain, the results favor further development of IAP DGVM in accurately simulating the terrestrial carbon cycle, and also provide an important reference for the application of CAS-ESM in further investigating carbon–climate interactions.摘要北方陆地净生态系统生产力(NEP)具有明显的季节变化特征, 这是大气CO2季节变化的关键驱动. 研究这些碳循环过程并理解潜在的驱动因素是气候研究的一个关键问题. 本文利用第二代中国科学院地球系统模式(CAS-ESM2)中的全球植被动态模型(IAP DGVM), 研究了1990−2014年北方NEP(40°−90°N)的季节振幅及其变化趋势. 在初始化试验的基础上, 本文开展了一个控制试验来评估模拟的北方NEP季节幅度的变化趋势, 同时开展了三个敏感性试验来研究气候和大气CO2的贡献. 结果表明: 1990−2014年, 模拟的北方NEP季节振幅显著增加, 趋势为9.69 万吨碳/月/年, 这主要是由于最大NEP增加所致. 当分别排除CO2施肥效应和气候效应时, 上述增加趋势大大减弱.这些显著的减少表明大气CO2和气候变化对北方NEP的季节性振幅有重要影响. 尽管模式存在不确定性, 但这些结果有利于进一步提升IAP DGVM对陆地碳循环的精确模拟, 也为CAS-ESM研究碳-气候相互作用的应用提供了重要参考.