The interplay of global climate change and anthropogenic activities has significantly affected the carbon cycle in coastal ocean environments. Consequently, further investigation into the carbonate system, carbon source and sink processes, and acidification mechanisms is essential. This study examined the surface carbonate system offshore of Qingdao, utilizing data from nine spring cruises in 2011–2019. The inter-annual variations in sea surface temperature revealed a gradual upward trend, whereas chlorophyll a (Chl-a) and apparent oxygen utilization (AOU) exhibited alternating trends of increase and decrease. Over the period from 2011 to 2019, pH levels ranged from 8.00 to 8.19, partial pressure of CO2 (pCO2) values varied between 187.8 and 364.1 μatm, and calcium carbonate saturation (Ωarag) ranged from 3.22 to 4.79. From 2011 to 2017, both pH and Ωarag showed a decreasing trend, attributed to the increasing influence of respiration. In contrast, an upward trend was observed for both parameters during 2018 and 2019, indicating a decline in respiration's contribution. Biological processes, especially the increase in respiration caused by the nutrients and organic matter released through human activities, were pivotal in determining spatial variations in pCO2 and Ωarag offshore, while the impact of mixing processes and temperature was comparatively negligible. Furthermore, the Ulva prolifera bloom event in July 2015 significantly affected the coastal waters of Qingdao's carbonate system when compared to the no-bloom period in March 2015. Overall, the study area functioned as a sink for atmospheric CO2 in the spring. The fluctuations in air-sea CO2 fluxes corresponded with changes in ΔpCO2 and wind speeds, with surface seawater air-sea CO2 fluxes ranging from −17.7 to 12.2 mmol m−2 d−1 between 2011 and 2019, yielding an average flux of −9.4 ± 5.3 mmol m−2 d−1.

中文翻译：

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2011—2019 年青岛市近海海气 CO2 通量年际变化和酸化机制


全球气候变化和人为活动的相互作用对沿海海洋环境的碳循环产生了重大影响。因此，必须进一步研究碳酸盐系统、碳源和碳汇过程以及酸化机制。本研究利用 2011 年至 2019 年九次春季游轮的数据检查了青岛近海的表面碳酸盐系统。海表温度的年际变化呈逐渐上升的趋势，而叶绿素 a （Chl-a） 和表观氧利用率 （AOU） 呈上升和下降的交替趋势。在 2011 年至 2019 年期间，pH 值在 8.00 到 8.19 之间，CO2 分压 （pCO2） 值在 187.8 到 364.1 μatm 之间变化，碳酸钙饱和度 （Ωarag） 在 3.22 到 4.79 之间。从 2011 年到 2017 年，由于呼吸的影响越来越大，pH 和 Ωarag 均呈下降趋势。相比之下，在 2018 年和 2019 年期间，这两个参数都呈上升趋势，表明呼吸的贡献有所下降。生物过程，尤其是由人类活动释放的营养物质和有机物引起的呼吸作用增加，在决定 pCO2 和 Ωarag 近海空间变化方面起着关键作用，而混合过程和温度的影响相对可以忽略不计。此外，与 2015 年 3 月的不开花期相比，2015 年 7 月的石莼增殖水华事件对青岛碳酸盐系统沿海水域产生了重大影响。总体而言，研究区域在春季起到了大气 CO2 汇的作用。海气 CO2 通量的波动与 ΔpCO2 和风速的变化相对应，表层海水气海 CO2 通量范围为 -17.7 至 12。2011 年至 2019 年间为 2 mmol m-2 d-1，产生的平均通量为 -9.4 ± 5.3 mmol m-2 d-1。