An Atmospheric Constraint on the Seasonal Air-Sea Exchange of Oxygen and Heat in the Extratropics Journal of Geophysical Research: Oceans

The air-sea exchange of oxygen (O2) is driven by changes in solubility, biological activity, and circulation. The total air-sea exchange of O2 has been shown to be closely related to the air-sea exchange of heat on seasonal timescales, with the ratio of the seasonal flux of O2 to heat varying with latitude, being higher in the extratropics and lower in the subtropics. This O2/heat ratio is both a fundamental biogeochemical property of air-sea exchange and a convenient metric for testing earth system models. Current estimates of the O2/heat flux ratio rely on sparse observations of dissolved O2, leaving it fairly unconstrained. From a model ensemble we show that the ratio of the seasonal amplitude of two atmospheric tracers, atmospheric potential oxygen (APO) and the argon-to-nitrogen ratio (Ar/O2), exhibits a close relationship to the O2/heat ratio of the extratropics (40–urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0001). The amplitude ratio, urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0002/urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0003, is relatively constant within the extratropics of each hemisphere due to the zonal mixing of the atmosphere. urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0004/urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0005 is not sensitive to atmospheric transport, as most of the observed spatial variability in the seasonal amplitude of urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0006APO is compensated by similar variations in urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0007(Ar/urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0008). From the relationship between urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0009/heat and urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0010/urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0011 in the model ensemble, we determine that the atmospheric observations suggest hemispherically distinct urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0012/heat flux ratios of 3.3 urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0013 0.3 and 4.7 urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0014 0.8 nmol urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0015 between 40 and urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0016 in the Northern and Southern Hemispheres respectively, providing a useful constraint for urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0017 and heat air-sea fluxes in earth system models and observation-based data products.

氧气（O₂）的海气交换由溶解度、生物活动与环流的变化驱动。研究表明，在季节尺度上，氧气总海气交换量与海气热交换密切相关；氧气季节通量与热通量的比率随纬度变化，在外热带（extratropics）较高，在亚热带（subtropics）较低。该氧热比率既是海气交换的核心生物地球化学属性，也是检验地球系统模式（earth system models）的便捷量化指标。当前氧热通量比率的估算依赖于稀疏的溶解氧（dissolved O₂）观测数据，导致该比率的约束性相对不足。基于模式集合（model ensemble）分析，我们发现两种大气示踪剂（atmospheric tracers）——大气潜在氧（APO）与氩氮比（Ar/O₂）——的季节振幅比率，与外热带（40–urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0001）的氧热比率存在密切关联。该振幅比率（urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0002/urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0003）因大气纬向混合作用，在各半球的外热带区域内相对恒定。（urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0004/urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0005）对大气输送并不敏感，这是因为观测到的大气潜在氧季节振幅空间变率（urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0006）大多可通过（Ar/urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0008）的相似变化得到补偿。基于模式集合中（urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0009/热）与（urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0010/urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0011）的关联关系，我们通过大气观测数据得出：南北半球40°~urn:x-wiley:21699275:media:jgrc24653:jgrc24653-math-0016纬度带内的氧热通量比率分别为3.3±0.3和4.7±0.8纳摩尔（nmol），该结果可为地球系统模式与观测驱动数据产品中的氧气与海气热通量提供有效的约束条件。