The North Brazil Current (NBC) flows offshore of the mouth of the Amazon River and seasonally sheds anticyclonic rings (NBC rings) that propagate northwestward and interact with the Amazon River plume (ARP). Mesoscale features have a high temporal variability that is hard to monitor from current weekly and monthly sea surface salinity (SSS) satellite fields. Novel SSS fields with a higher temporal resolution analyzed together with satellite geostrophic currents, chlorophyll-a, and wind speed and in-situ data from the “Microbiomes cruise” on the SV in August–September 2021 revealed a late summer freshwater pathway, which was not well documented in earlier studies. By combining these datasets, we improved the characterization of summer ARP pathways. In 2021, the ARP was a succession of freshwater patches cut off from the main plume by the NBC rings. A patch of about 200.000 km with salinity <33.5 pss was observed in September 2021, bringing 0.5 Sv of Amazon water northwestward in a period where the mean ocean currents lead to eastward transport. This patch was shallow, very stratified, and it created a surface steric-height anomaly that was identified as an anticyclonic feature in altimetric sea level products. Once separated from the NBC retroflection, it was mainly driven by Ekman currents. Other similar patches were observed during the 2021 summer, leading to a strong intermittency of the ARP transport. They strongly contributed to make 2021 the year with the largest northwestward freshwater transport in late summer within the 2010–2021 time-period investigated. This freshwater transport pathway is important for all plume-related phenomena, and show the ability of combined SMOS and SMAP data to accurately represent the day-to-day SSS variability.

中文翻译：

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夏末北巴西洋流环作用下的亚马逊西北羽流路径

北巴西洋流 (NBC) 在亚马逊河河口近海流动，季节性地脱落反气旋环 (NBC 环)，向西北传播并与亚马逊河羽流 (ARP) 相互作用。中尺度特征具有较高的时间变化，很难从当前每周和每月的海面盐度（SSS）卫星场进行监测。具有更高时间分辨率的新型 SSS 场与卫星地转流、叶绿素 a 和风速以及 2021 年 8 月至 9 月 SV 上的“微生物组巡航”的现场数据一起分析，揭示了一条夏末淡水路径，早期研究中没有详细记录。通过结合这些数据集，我们改进了夏季 ARP 路径的表征。 2021 年，ARP 是一系列被 NBC 环与主羽流隔断的淡水斑块。 2021 年 9 月，观测到一片长约 20 万公里、盐度 <33.5 pss 的区域，在平均洋流向东输送的时期，将 0.5 Sv 的亚马逊水带向西北方向。该斑块很浅，分层程度很高，并且产生了表面空间高度异常，该异常被认为是测高海平面产品中的反气旋特征。一旦与 NBC 逆反射分离，它主要由艾克曼电流驱动。 2021 年夏季还观察到了其他类似的补丁，导致 ARP 传输出现强烈的间歇性。在 2010 年至 2021 年调查期间，它们为使 2021 年成为夏末向西北淡水输送最多的一年做出了巨大贡献。这种淡水输送路径对于所有与羽流相关的现象都很重要，并且显示了结合 SMOS 和 SMAP 数据准确表示日常 SSS 变化的能力。