Interactions between riverine inputs, internal cycling, and oceanic exchange result in dynamic variations in the partial pressure of carbon dioxide (pCO₂) in large estuaries. Here, we report the first bay‐wide, annual‐scale observations of surface pCO₂ and air–water CO₂ flux along the main stem of the Chesapeake Bay, revealing large annual variations in pCO₂ (43–3408 μatm) and a spatial‐dependence of pCO₂ on internal and external drivers. The low salinity upper bay was a net source of CO₂ to the atmosphere (31.2 mmol m⁻² d⁻¹) supported by inputs of CO₂‐rich Susquehanna River water and the respiration of allochthonous organic matter, but part of this region was also characterized by low pCO₂ during spring and fall phytoplankton blooms. pCO₂ decreased downstream due to CO₂ ventilation supported by long water residence times, stratification, mixing with low pCO₂ water masses, and carbon removal by biological uptake. The mesohaline middle bay was a net CO₂ sink (−5.8 mmol m⁻² d⁻¹) and the polyhaline lower bay was nearly in equilibrium with the atmosphere (1.0 mmol m⁻² d⁻¹). Although the main stem of the bay was a weak CO₂ source (3.7 ± 3.3 × 10⁹ mol C) during the dry hydrologic (calendar) year 2016, our observations showed higher river discharge could decrease CO₂ efflux. In contrast to many other estuaries worldwide that are strong sources of CO₂ to the atmosphere, the Chesapeake Bay and potentially other large estuaries are very weak CO₂ sources in dry years, and could even turn into a CO₂ sink in wet years.

中文翻译：

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切萨皮克湾的表面pCO2和空气-水CO2通量的季节性和空间变化

河流输入，内部循环和海洋交换之间的相互作用导致大河口二氧化碳分压（p CO ₂）的动态变化。在这里，我们报告的第一隔间全，表面的年度尺度观测p CO ₂和空气-水CO ₂通量沿Chesapeake湾的主茎，在揭示大年变化p CO ₂（43-3408  μ大气压）以及p CO ₂对内部和外部驱动器的空间依赖性。低盐度上海湾是大气中CO ₂的净来源（31.2 mmol m ^-2 d^-1）得到了富含CO _2的萨斯奎哈纳河水的输入和异源有机物的呼吸的支持，但该地区的一部分还以春季和秋季浮游植物开花期间的低p CO ₂为特征。由于长时间的水停留时间，分层，低p CO ₂水量的混合以及通过生物吸收去除碳，支持了CO ₂通风，因此下游的p CO ₂减少。中盐间海湾是一个净CO ₂汇（-5.8 mmol m ^-2 d ^-1），而多盐水下部湾与大气（1.0 mmol m ^-2 d ^-1）几乎处于平衡状态。尽管在 2016年干旱水文（日历）年期间，海湾的主要茎为弱CO ₂来源（3.7±3.3×10 ⁹ mol C），但我们的观察结果表明，较高的河流排放量可能会降低CO _2的流出量。相较于全球其他许多河口是二氧化碳的强光源₂到大气中，切萨皮克湾和潜在的其他大型河口是非常弱的CO ₂源在干旱年份，甚至可能变成CO ₂片在丰水年。