The Atmospheric Carbon Transport (ACT)-America Earth Venture mission conducted five airborne campaigns across four seasons from 2016 to 2019, to study the transport and fluxes of Greenhouse gases across the eastern United States. Unprecedented spatial sampling of atmospheric tracers (CO₂, carbon monoxide [CO], carbonyl sulfide [COS]) related to biospheric processes offers opportunities to improve our qualitative and quantitative understanding of seasonal and spatial patterns of biospheric carbon uptake. Here, we examine co-variation of boundary layer enhancements of CO₂, CO, and COS across three diverse regions: the crop-dominated Midwest, evergreen-dominated South, and deciduous broadleaf-dominated Northeast. To understand the biogeochemical processes controlling these tracers, we compare the observed co-variation to simulated co-variation resulting from model- and satellite- constrained surface carbon fluxes. We found indication of a common terrestrial biogenic sink of CO₂ and COS and secondary production of CO from biogenic sources in summer throughout the eastern US, driven by stomatal conductance. Upper Midwest crops drive CO₂ and COS depletion from early to late summer. Northeastern temperate forests drive CO₂ and COS depletion in late summer. The unprecedented ACT-America flask samples uncovered evidence that southern humid temperate forests photosynthesize and absorb CO₂ and COS, and emit CO precursors, deep into the growing season. Satellite- constrained carbon fluxes capture much of the observed seasonal and spatial variability, but underestimate the magnitude of net CO₂ and COS depletion in the South, indicating a stronger than expected net sink of CO₂ in late summer. Additional sampling of the South will more accurately constrain underlying biological processes and climate sensitivities governing southern carbon dynamics.

中文翻译：

---

机载生物示踪剂（CO2、COS 和 CO）的协变支持美国东南部生长季节光合吸收强于预期

大气碳传输 (ACT)-America Earth Venture 任务在 2016 年至 2019 年的四个季节进行了五次空中活动，以研究温室气体在美国东部的传输和通量。与生物圈过程相关的大气示踪剂（CO ₂、一氧化碳 [CO]、硫化羰 [COS]）的空前空间采样提供了机会，以提高我们对生物圈碳吸收的季节性和空间模式的定性和定量理解。在这里，我们检查了 CO ₂边界层增强的协变、CO 和 COS 跨越三个不同的区域：以作物为主的中西部、以常绿为主的南部和以落叶阔叶为主的东北部。为了了解控制这些示踪剂的生物地球化学过程，我们将观察到的协变与由模型和卫星约束的表面碳通量产生的模拟协变进行比较。我们发现了在整个美国东部夏季由气孔导度驱动的 CO ₂和 COS的共同陆地生物源汇和 CO二次生产的迹象。从夏初到夏末，中西部上部作物推动了CO ₂和COS 的消耗。东北温带森林驱动CO ₂和COS 在夏末耗尽。前所未有的 ACT-America 烧瓶样本揭示了南部潮湿温带森林光合作用和吸收 CO ₂和 COS，并在生长季节深处释放 CO 前体的证据。受卫星约束的碳通量捕获了大部分观测到的季节性和空间变化，但低估了南方净 CO ₂和 COS 消耗的幅度，表明夏末CO ₂净汇强于预期。南方的额外采样将更准确地限制控制南方碳动态的潜在生物过程和气候敏感性。