Subtropical seagrass meadows play a major role in the coastal carbon cycle, but the nature of air–water CO₂ exchanges over these ecosystems is still poorly understood. The complex physical forcing of air–water exchange in coastal waters challenges our ability to quantify bulk exchanges of CO₂ and water (evaporation), emphasizing the need for direct measurements. We describe the first direct measurements of evaporation and CO₂ flux over a calcifying seagrass meadow near Bob Allen Keys, Florida. Over the 78‐d study, CO₂ emissions were 36% greater during the day than at night, and the site was a net CO₂ source to the atmosphere of 0.27 ± 0.17 μmol m⁻² s⁻¹ (x̅ ± standard deviation). A quarter (23%) of the diurnal variability in CO₂ flux was caused by the effect of changing water temperature on gas solubility. Furthermore, evaporation rates were ~ 10 times greater than precipitation, causing a 14% increase in salinity, a potential precursor of seagrass die‐offs. Evaporation rates were not correlated with solar radiation, but instead with air–water temperature gradient and wind shear. We also confirm the role of convective forcing on night‐time enhancement and day‐time suppression of gas transfer. At this site, temperature trends are regulated by solar heating, combined with shallow water depth and relatively consistent air temperature. Our findings indicate that evaporation and air–water CO₂ exchange over shallow, tropical, and subtropical seagrass ecosystems may be fundamentally different than in submerged vegetated environments elsewhere, in part due to the complex physical forcing of coastal air–sea gas transfer.

中文翻译：

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大气涡动协方差揭示亚热带海草草甸水温对CO2通量和蒸发的控制

亚热带海草草甸在沿海碳循环中起着重要作用，但是在这些生态系统中空气-水CO ₂交换的性质仍然知之甚少。沿海水域空气-水交换的复杂物理强迫挑战了我们量化CO ₂和水的大量交换（蒸发）的能力，强调了直接测量的必要性。我们描述了在佛罗里达州鲍勃·艾伦·凯斯附近的钙化海草草甸上蒸发和CO ₂通量的首次直接测量。在78-d的研究中，CO ₂的排放量在白天比夜间分别为36％以上，该网站是一个CO净₂源的气氛0.27±0.17  μ摩尔米^-2小号^-1（x̅±标准偏差）。CO ₂通量日变化的四分之一（23％）是由于水温变化对气体溶解度的影响所致。此外，蒸发速率比降水高约10倍，导致盐度增加14％，这是海草死亡的潜在前兆。蒸发速率与太阳辐射无关，但与空气-水温梯度和风切变无关。我们还确认了对流强迫在夜间增强和白天抑制气体转移方面的作用。在这个地点，温度趋势受太阳能加热，浅水深度和相对稳定的气温的调节。我们的发现表明蒸发和空气-水CO ₂ 浅海，热带和亚热带海草生态系统的交换可能与其他地方的植被淹没环境有根本的不同，部分原因是沿海空气-海洋气体转移的物理强迫非常复杂。