N2O and CH4 underway measurements (atmosphere and ocean) during METEOR cruise M120@en

Upward transport and/or mixing of trace gas-enriched subsurface waters fosters the exchange of nitrous oxide (N2O) and methane (CH4) with the atmosphere in the Eastern-South Atlantic (ESA). To date, it is, however, unclear whether this source is maintained by local production or advection of trace-gas enriched water masses. So, the meridional and zonal variability of N2O and CH4 in the ESA were investigated to constrain the contributions of the major regional water masses to the overall budget of N2O and CH4. The fieldwork took place during the cruises M99 (July 31st - August 23rd, 2013) and M120 (October 17th - November 18th, 2015) onboard the R/V METEOR, which encompassed close-coastal and open ocean regions off Angola and Namibia. To investigate the regional concentration gradients of N2O and CH4 and corresponding sea-air fluxes, seven hydrographic sections (six zonal transects and one alongshore transect) were conducted between ~10°S and 26°S. Concentrations of dissolved N2O and CH4 in surface waters were continuously measured by using the Mobile Equilibrator Sensor System. To evaluate, the oceanic-atmospheric trace gas exchange, the atmospheric N2O and CH4 in ambient air were measured at several sporadic locations, with an inlet installed at 35 m height. The data were quality controlled by comparing with the data generated by NOAA in the nearest atmospheric sampling station (23.58° S, 15.03°E, Station NMB (Gobabeb, Namibia)). Also, to better understand the underlying patterns of the trace gas in the ESA, the vertical profiles were investigated by measuring discrete samples of N2O using the dynamic headspace method on M99. N2O and CH4 concentrations were also measured using a purge and trap system during M120 expedition.南大西洋东部（Eastern-South Atlantic, ESA）海域中，富集痕量气体的次表层水体通过向上输运或混合作用，推动了一氧化二氮（N₂O）与甲烷（CH₄）与大气的交换过程。然而迄今为止，尚不清楚该气体源是由局地生产过程维持，还是由富集痕量气体的水团平流输送所支撑。为此，本研究针对南大西洋东部海域的N₂O与CH₄经向及纬向变化特征展开调查，以限定主要区域水团对N₂O和CH₄总收支的贡献份额。本研究的野外调查依托“流星号”（R/V METEOR）科考船的两次航次开展：分别为2013年7月31日至8月23日的M99航次，以及2015年10月17日至11月18日的M120航次，调查覆盖安哥拉与纳米比亚周边的近岸及远洋海域。为探究N₂O与CH₄的区域浓度梯度及相应海-气通量，研究团队在南纬约10°至26°之间布设了7条水文断面，包括6条纬向断面与1条沿岸断面。研究采用移动平衡传感器系统（Mobile Equilibrator Sensor System）对表层海水溶解态N₂O与CH₄浓度进行连续监测。为评估海洋-大气痕量气体交换过程，研究团队在多个离散点位安装了高度为35米的进气口，对环境大气中的N₂O与CH₄浓度进行测定。本研究通过与最近的大气采样站（位于南纬23.58°、东经15.03°，纳米比亚戈巴布的NMB站）由美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）生成的观测数据进行比对，对所有数据开展质量控制。此外，为更好地解析南大西洋东部海域痕量气体的分布规律，M99航次采用动态顶空法对离散水样中的N₂O进行测定，以此获取其垂直剖面分布特征。而在M120航次中，研究团队采用吹扫捕集系统对N₂O与CH₄浓度进行测定。