During the summer of 2018, a widespread drought developed over Northern and Central Europe. The increase in temperature and the reduction of soil moisture have influenced carbon dioxide (CO₂) exchange between the atmosphere and terrestrial ecosystems in various ways, such as a reduction of photosynthesis, changes in ecosystem respiration, or allowing more frequent fires. In this study, we characterize the resulting perturbation of the atmospheric CO₂ seasonal cycles. 2018 has a good coverage of European regions affected by drought, allowing the investigation of how ecosystem flux anomalies impacted spatial CO₂ gradients between stations. This density of stations is unprecedented compared to previous drought events in 2003 and 2015, particularly thanks to the deployment of the Integrated Carbon Observation System (ICOS) network of atmospheric greenhouse gas monitoring stations in recent years. Seasonal CO₂ cycles from 48 European stations were available for 2017 and 2018. Earlier data were retrieved for comparison from international databases or national networks. Here, we show that the usual summer minimum in CO₂ due to the surface carbon uptake was reduced by 1.4 ppm in 2018 for the 10 stations located in the area most affected by the temperature anomaly, mostly in Northern Europe. Notwithstanding, the CO₂ transition phases before and after July were slower in 2018 compared to 2017, suggesting an extension of the growing season, with either continued CO₂ uptake by photosynthesis and/or a reduction in respiration driven by the depletion of substrate for respiration inherited from the previous months due to the drought. For stations with sufficiently long time series, the CO₂ anomaly observed in 2018 was compared to previous European droughts in 2003 and 2015. Considering the areas most affected by the temperature anomalies, we found a higher CO₂ anomaly in 2003 (+3 ppm averaged over 4 sites), and a smaller anomaly in 2015 (+1 ppm averaged over 11 sites) compared to 2018.

This article is part of the theme issue ‘Impacts of the 2018 severe drought and heatwave in Europe: from site to continental scale'.

2018 年夏季，北欧和中欧出现大面积干旱。温度升高和土壤湿度降低以各种方式影响了大气和陆地生态系统之间的二氧化碳 (CO ₂ ) 交换，例如光合作用减少、生态系统呼吸变化或导致火灾更频繁。在这项研究中，我们描述了大气 CO ₂季节性循环的由此产生的扰动。2018 年覆盖了受干旱影响的欧洲地区，可以调查生态系统通量异常如何影响空间 CO ₂站之间的梯度。与之前的 2003 年和 2015 年干旱事件相比，这种站点密度是前所未有的，这尤其要归功于近年来部署的大气温室气体监测站综合碳观测系统 (ICOS) 网络。2017 年和 2018 年来自 48 个欧洲站的季节性 CO ₂循环可用。从国际数据库或国家网络中检索早期数据以进行比较。在这里，我们表明，对于位于受温度异常影响最严重的地区（主要在北欧）的 10 个站点，由于表面碳吸收，CO _{2 中}通常的夏季最小值在2018 年减少了 1.4 ppm。尽管如此，CO ₂与 2017 年相比，2018 年 7 月前后的过渡阶段较慢，表明生长季节延长，光合作用持续吸收CO ₂和/或前几个月遗传的呼吸底物消耗导致呼吸减少由于干旱。对于时间序列足够长的站点，将2018 年观测到的 CO ₂异常与之前 2003 年和 2015 年的欧洲干旱进行了比较。考虑到受温度异常影响最大的地区，我们发现2003 年的CO ₂异常更高（平均为 +3 ppm超过 4 个站点），与 2018 年相比，2015 年的异常值较小（11 个站点的平均值为 +1 ppm）。

本文是主题问题“2018 年欧洲严重干旱和热浪的影响：从场地到大陆尺度”的一部分。