From 2015 to 2019 we installed high-frequency (HF) sea surface temperature (SST), salinity, fluorescence, dissolved oxygen (DO) and partial pressure of CO2 (pCO2) sensors on a cardinal buoy of opportunity (ASTAN) at a coastal site in the southern Western English Channel (sWEC) highly influenced by tidal cycles. The sensors were calibrated against bimonthly discrete measurements performed at two long-term time series stations near the buoy, thus providing a robust multi-annual HF dataset. The tidal transport of a previously unidentified coastal water mass and an offshore water mass strongly impacted the daily and seasonal variability of pCO2 and pH. The maximum tidal variability associated to spring tides (>7 m) during phytoplankton blooms represented up to 40% of the pCO2 annual signal at ASTAN. At the same time, the daily variability of 0.12 pH units associated to this tidal transport was 6 times larger than the annual acidification trend observed in the area. A frequency/time analysis of the HF signal revealed the presence of a day/night cycle in the tidal signal. The diel biological cycle accounted for 9% of the annual pCO2 amplitude during spring phytoplankton blooms. The duration and intensity of the biologically productive periods, characterized by large inter-annual variability, were the main drivers of pCO2 dynamics. HF monitoring enabled us to accurately constrain, for the first-time, annual estimates of air-sea CO2 exchanges in the nearshore tidally-influenced waters of the sWEC, which were a weak source to the atmosphere at 0.51 mol CO2 m–2 yr–1. This estimate, combined with previous studies, provided a full latitudinal representation of the WEC (from 48°75′ N to 50°25′ N) over multiple years for air-sea CO2 fluxes in contrasted coastal ecosystems. The latitudinal comparison showed a clear gradient from a weak source of CO2 in the tidal mixing region toward sinks of CO2 in the stratified region with a seasonal thermal front separating these hydrographical provinces. In view of the fact that several continental shelf regions have been reported to have switched from sources to sinks of CO2 in the last century, weak CO2 sources in such tidal mixing areas could potentially become sinks of atmospheric CO2 in coming decades.

中文翻译：

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基本浮标：研究沿海生态系统中海气二氧化碳通量的机会

从 2015 年到 2019 年，我们在沿海站点的主要机会浮标 (ASTAN) 上安装了高频 (HF) 海面温度 (SST)、盐度、荧光、溶解氧 (DO) 和 CO2 分压 (pCO2) 传感器在受潮汐周期影响很大的西英吉利海峡南部 (sWEC)。传感器根据在浮标附近的两个长期时间序列站进行的双月离散测量进行校准，从而提供了强大的多年度 HF 数据集。以前未知的沿海水团和近海水团的潮汐传输强烈影响了 pCO2 和 pH 值的日常和季节性变化。浮游植物大量繁殖期间与大潮 (>7 m) 相关的最大潮汐变化代表了 ASTAN 每年 pCO2 信号的 40%。同时，日变化为0。与这种潮汐传输相关的 12 个 pH 单位比在该地区观察到的年度酸化趋势大 6 倍。HF 信号的频率/时间分析揭示了潮汐信号中存在昼/夜循环。在春季浮游植物大量繁殖期间，昼夜生物循环占每年 pCO2 振幅的 9%。以年际变化大为特征的生物生产期的持续时间和强度是 pCO2 动态的主要驱动因素。HF 监测使我们第一次能够准确地限制对 sWEC 近岸潮汐影响水域的海气 CO2 交换的年度估计，这些水域是 0.51 mol CO2 m–2 yr– 大气的弱源1. 这个估计，结合之前的研究，提供了多年的 WEC（从北纬 48°75' 到北纬 50°25'）的完整纬度表示，用于对比沿海生态系统中的海气二氧化碳通量。纬度比较显示从潮汐混合区的弱 CO2 源到分层区的 CO2 汇有明显的梯度，季节性热锋将这些水文省分开。鉴于上世纪几个大陆架区域已被报道从 CO2 的源转换为汇，这种潮汐混合区的弱 CO2 源可能在未来几十年成为大气 CO2 的汇。纬度比较显示从潮汐混合区的弱 CO2 源到分层区的 CO2 汇有明显的梯度，季节性热锋将这些水文省分开。鉴于上世纪几个大陆架区域已被报道从 CO2 的源转换为汇，这种潮汐混合区的弱 CO2 源可能在未来几十年成为大气 CO2 的汇。纬度比较显示，从潮汐混合区的弱 CO2 源到分层区的 CO2 汇有明显的梯度，季节性热锋将这些水文省分开。 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 鉴于上世纪几个大陆架区域已被报道从 CO2 的源转换为汇，这种潮汐混合区的弱 CO2 源可能在未来几十年成为大气 CO2 的汇。