Disentangling the relative contributions of vertical pumping and horizontal transport to water-property anomalies within eddy cores in the southern Indian Ocean

The eddies in the southernmost southern Indian Ocean exert major dynamical and biogeochemical influences on the Earth system. Therefore, disentangling the relative contributions of vertical pumping and horizontal transport to water-property anomalies in the eddy cores is of fundamental importance. Here, the authors introduce a temperature–salinity gradient-ratio approach (the “ R -method”) that compares vertical and meridional gradients to quantitatively separate the two processes. Application of the R-method to three-dimensional Argo observations reveals that horizontal transport, rather than vertical pumping, predominantly governs the observed temperature and salinity anomalies within eddy cores in the SIO. Independent theoretical estimations based on background meridional gradients, together with composites formed on isopycnal surfaces, further corroborate this conclusion. The results challenge the conventional assumption that vertical pumping invariably controls eddy-core property anomalies and demonstrate the utility of the R -method for diagnosing eddy impacts in climate and biogeochemical studies. 摘要 南印度洋最南端的涡旋对整个地球系统的动力学和生物地球化学过程具有重大影响. 因此, 厘清垂直抽吸与水平输送对涡旋中心水体性质异常的相对贡献具有重要意义. 本研究提出了一种温-盐梯度比值方法 (“ R 方法”), 即通过比较海水温盐的垂向梯度比值与经向梯度比值, 可定量区分垂直抽吸与水平输送对温盐异常的相对贡献. 本研究将该方法应用于三维 Argo 观测资料后发现, 在南印度洋最南端区域内, 观测到的涡旋中心温盐异常主要由水平输送而非垂直抽吸所主导. 基于背景经向梯度的理论估算, 以及按等密度面合成的结果, 进一步验证了这一结论. 本研究结果表明, 传统假设“涡旋中心的温盐异常始终由垂直抽吸控制”并不成立. 研究结果还展示了利用 R 方法诊断涡旋水平和垂向贡献在气候与海洋生态研究中的应用前景.