Abstract
We observed a subthermocline eddy (STE) with a cold and fresh core during an observation cruise along a transect of 10°S in the southeastern tropical Indian Ocean (SETIO) in December 2017. The vertical scale, speed radius, and maximum swirl velocity of the STE were about 200 m, 55 km, and 0.5 m/s, respectively. The mean Rossby number and Burger number of the STE were then estimated to be about −0.7 and 2.4, indicating the STE was a submesoscale coherent vortex. The STE core water had characteristics of the Indonesian Throughflow (ITF) water and was distinct from that of surrounding areas. By examining Argo float data, another STE was well captured by five successive profiles of the same Argo float. Both STEs showed significant temperature and salinity anomalies at the σ0=26.0–26.5 kg/m3 surfaces. With the assumption that the low-salinity ITF water parcels could be carried only by surface eddies and the STEs, the Argo profiles, which detected low-salinity ITF water and were located outside a surface eddy, were believed to be inside an STE and were used to analyze the distribution, origin, and generation mechanism of the STE. The results suggested that the STEs carrying ITF water may be generated under topography-current interaction at the eastern coastal waters or under front-induced subduction in the area away from coastal waters. Those STEs may be widely distributed in the SETIO and may play a role in ITF water parcel transport.
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Acknowledgements
We thank all onboard crews of R/V Xiangyanghong 18 and the two anonymous reviewers. The cruise data can be obtained at this website (https://jmp.sh/wWLYFUk). The sources of other data are provided in Section 2.
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Foundation item: The Shandong Provincial Natural Science Foundation under contract No. ZR2022MD080; the Basic Scientific Fund for National Public Research Institutes of China under contract No. 2017Q01; the National Natural Science Foundation of China (NSFC) under contract Nos 41706038, 41576027, 41376038, and 40406009; the NSFC-Shandong Joint Fund for Marine Science Research Centers under contract Nos U1406405 and U1606405; the International Cooperation Project of Indo-Pacific Ocean Environment Variation and Air-Sea Interaction under contract No. GASI-03-IPOVAI-05; the National Programme on Global Change and Air-Sea Interaction under contract Nos GASI-03-01-01-02 and GASI-IPOVAI-01-05; the Public Science and Technology Research Funds Projects of Ocean under contract No. 2009050240; the National Key Scientific Instrument and Equipment Development Projects under contract No. 2012YQ12003908; the National Science and Technology Major Project under contract No. 2016ZX05057015.
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Yang, G., Zheng, Q. & Xiong, X. Subthermocline eddies carrying the Indonesian Throughflow water observed in the southeastern tropical Indian Ocean. Acta Oceanol. Sin. 42, 1–13 (2023). https://doi.org/10.1007/s13131-022-2085-2
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DOI: https://doi.org/10.1007/s13131-022-2085-2