Abstract. Oxygen minimum zones (OMZs) are characterized by enhanced carbon dioxide (CO₂) levels and low pH and are being further acidified by uptake of anthropogenic atmospheric CO₂. With ongoing intensification and expansion of OMZs due to global warming, carbonate chemistry conditions may become more variable and extreme, particularly in the Eastern Boundary Upwelling Systems. In austral summer (Feb–Apr) 2017, a large-scale mesocosm experiment was conducted in the coastal upwelling area off Callao (Peru) to investigate the impacts of on-going ocean deoxygenation on biogeochemical processes, coinciding with a rare coastal El Niño event. Here we report on the temporal dynamics of carbonate chemistry in the mesocosms and surrounding Pacific waters over a continuous period of 50 days with high temporal resolution observations (every 2^nd day). The mesocosm experiment simulated an upwelling event in the mesocosms by addition of nitrogen (N)-deficient and CO₂-enriched OMZ water. Surface water in the mesocosms was acidified by the OMZ water addition, with pHT lowered by 0.1–0.2 and pCO₂ elevated to above 900 μatm. Thereafter, surface pCO₂ quickly dropped to near or below the atmospheric level (405.22 μatm in 2017, NOAA/GML) mainly due to enhanced phytoplankton production with rapid CO₂ consumption. Further observations revealed that the dominance of dinoflagellate Akashiwo sanguinea and contamination of bird excrements played important roles in the dynamics of carbonate chemistry in the mesocosms. Compared to the simulated upwelling, natural upwelling events in the surrounding Pacific waters occurred more frequently with sea-to-air CO₂ fluxes of 4.2–14.0 mmol C m⁻² d⁻¹. The positive CO₂ fluxes indicated our site was a local CO₂ source during our study, which may have been impacted by the coastal El Niño. However, our observations of DIC drawdown in the mesocosms suggests that CO₂ fluxes to the atmosphere can be largely dampened by biological processes. Overall, our study characterized carbonate chemistry in near-shore Pacific waters that are rarely sampled in such temporal resolution and hence provided unique insights into the CO₂ dynamics during a rare coastal El Niño event.

中文翻译：

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秘鲁卡亚奥附近2017年沿海厄尔尼诺现象期间，地面海洋碳酸盐化学对自然和模拟上升事件的响应的时间动态

摘要。最低氧区（OMZ）的特征在于二氧化碳（CO ₂）含量提高和pH值低，并且由于人为吸收大气中的CO ₂而被进一步酸化。随着全球变暖对OMZ的持续加剧和扩展，碳酸盐化学条件可能变得更加可变和极端，特别是在东部边界上升流系统中。在2017年的夏季（二月至四月），在卡亚俄（秘鲁）附近的沿海上升流地区进行了大规模的中观试验，研究正在进行的海洋脱氧对生物地球化学过程的影响，同时也发生了罕见的沿海厄尔尼诺事件。 。在这里，我们在生物群落碳酸盐化学的时空动态报告和周围的太平洋水域超过50天，高时间分辨率观测（每2个连续的时间段^次天）。中膜实验通过添加氮（N）不足和CO _2来模拟中膜的上升流事件富含OMZ水。中膜的地表水通过添加OMZ水而被酸化，pHT降低0.1-0.2，pCO ₂升高至900μatm以上。此后，表面pCO ₂迅速下降至接近或低于大气水平（2017年为405.22μatm，NOAA / GML），这主要是由于浮游植物的产量增加和CO _2的快速消耗所致。进一步的观察表明，鞭毛藻的赤藻的优势地位和鸟类排泄物的污染在中膜的碳酸盐化学动力学中起着重要的作用。与模拟上升流相比，周围太平洋水域的自然上升流事件发生的频率更高，海对空CO ₂通量为4.2–14.0 mmol C m^-2  d ^-1。CO ₂的正通量表明我们的站点是我们研究期间的本地CO ₂来源，这可能已受到沿海厄尔尼诺现象的影响。但是，我们对中膜DIC下降的观察表明，生物过程可以大大抑制通向大气的CO ₂通量。总的来说，我们的研究描述了近岸太平洋水域中碳酸盐化学的特征，这些碳酸盐化学很少以这种时间分辨率进行采样，因此，对于罕见的沿海厄尔尼诺事件，CO ₂动力学具有独特的见解。