The Atlantic Meridional Overturning Circulation (AMOC) drives northward Meridional Heat Transport (MHT) and affects climate and weather patterns, regional sea levels, and ecosystems. This study uses a methodology recently applied in 22.5°S to estimate the strength and structure of the AMOC, MHT and freshwater (FWT) transports at 34.5°S since 2005. For this, temperature and salinity profiles from sustained observations were used in conjunction with satellite and reanalysis data under two mapping methodologies: (i) an optimized mapping and (ii) a two-layer feed-forward neural network approach. There is strong agreement between both methods for AMOC, MHT and FWT estimates, thus showing the mapping methodologies are robust. In addition, the AMOC variability estimate is significantly correlated with the monthly SAMBA array data (correlation of 0.41). The mean AMOC transport of 17.0 ± 1.6 Sv, a MHT of 0.6 ± 0.1 PW, and a FWT of -0.02 ± 0.01 Sv are estimated between January 2005 and May 2023 at 34.5°S. The MHT and FWT are analyzed in terms of their horizontal (Hhor and Fhor) and overturning contributions (Hov and Fov), and vertical structures. The MHT is dominated by the overturning contribution (correlation of 0.92), while the FWT is controlled by the overturning contribution driven by the wind via Ekman transport at seasonal timescale, and by horizontal contribution at longer timescales. Both horizontal heat (Hhor) and freshwater (Fhor) components are mostly confined to the upper 500 m, with the geostrophic Fov and Fhor offsetting each other between 50 m and 500 m, and the Ekman Fov in the upper 50 m determining the negative FWT. Finally, the estimated mean Fov of -0.15 Sv agrees with previous estimates that the AMOC exports freshwater in the South Atlantic, and suggests that the AMOC is unstable. Although a long-term trend in the Fov was not detected in the past 20 years, there is a salinification trend (0.05 ± 0.01 PSU/decade) in the upper 300 m near 34.5°S since 2005.

中文翻译：

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南大西洋经向翻转环流及其各自的热和淡水输送来自南纬 34.5°附近持续观测


大西洋经向翻转环流 （AMOC） 推动经向热输送 （MHT） 向北移动，并影响气候和天气模式、区域海平面和生态系统。本研究使用最近在南纬 22.5°应用的方法来估计自 2005 年以来南纬 34.5°的 AMOC、MHT 和淡水 （FWT） 传输的强度和结构。为此，在两种绘图方法下，将持续观测的温度和盐度曲线与卫星和再分析数据结合使用：（i） 优化绘图和 （ii） 两层前馈神经网络方法。两种方法对 AMOC、MHT 和 FWT 估计有很强的一致性，因此表明映射方法是稳健的。此外，AMOC 变异性估计值与每月 SAMBA 阵列数据显著相关（相关性为 0.41）。在 2005 年 1 月至 2023 年 5 月期间，估计在 34.5°S 的平均 AMOC 传输为 17.0 ± 1.6 Sv，MHT 为 0.6 ± 0.1 PW，FWT 为 -0.02 ± 0.01 Sv。 根据其水平 （Hhor 和 Fhor） 和翻转贡献 （Hov 和 Fov） 以及垂直结构分析 MHT 和 FWT。MHT 以翻转贡献为主（相关性为 0.92），而 FWT 在季节性时间尺度上受风通过 Ekman 传递驱动的翻转贡献控制，在较长时间尺度上由水平贡献控制。水平热 （Hhor） 和淡水 （Fhor） 分量大多局限于上部 500 m，地转视场和 Fhor 在 50 m 到 500 m 之间相互抵消，而上部 50 m 的 Ekman 视场决定了负 FWT。最后，估计的平均 Fov 为 -0。15 Sv 同意之前关于 AMOC 在南大西洋出口淡水的估计，并表明 AMOC 不稳定。尽管在过去 20 年中没有检测到 Fov 的长期趋势，但自 2005 年以来，在 34.5°S 附近的上部 300 m 存在盐碱化趋势（0.05 ± 0.01 PSU/十年）。