Advances in Earth Science ›› 2021, Vol. 36 ›› Issue (9): 883-898. doi: 10.11867/j.issn.1001-8166.2021.085

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Mesoscale Eddy Effects on Subduction and Transport of the North Pacific Subtropical Mode Water

Lixiao XU 1, 2( ),Qinyu LIU 1, 2( )   

  1. 1.Frontier Science Center for Deep Ocean Multispheres and Earth System (FDOMES) and Physical Oceanography Laboratory,Ocean University of China,Qingdao 266100,China
    2.Qingdao National Laboratory for Marine Science and Technology,Qingdao 266237,China
  • Received:2021-06-07 Revised:2021-08-25 Online:2021-09-10 Published:2021-10-15
  • Contact: Qinyu LIU E-mail:lxu@ouc.edu.cn;liuqy@ouc.edu.cn
  • About author:XU Lixiao (1985-), female, Laiwu County, Shandong Province, Associated Professor. Research areas include air-sea interaction. E-mail: lxu@ouc.edu.cn
  • Supported by:
    the Natural Science Foundation of China "Mesoscale eddy effect on the transport of the North Pacific Subtropical Mode Water"(41876006)

Lixiao XU, Qinyu LIU. Mesoscale Eddy Effects on Subduction and Transport of the North Pacific Subtropical Mode Water[J]. Advances in Earth Science, 2021, 36(9): 883-898.

Mode Mode water is important for the climate system as memories of climate variability and by 'breathing in' anthropogenic carbon dioxide. Due to the lack of subsurface observations, many fundamental questions remain regarding how it is subducted and transported by mesoscale eddies.

Results

from a field campaign from March 2014 that captured the eddy effects on mode water subduction and transport south of the Kuroshio Extension east of Japan are reviewed here. The experiment deployed 17 Argo floats in an Anticyclonic Eddy (AE) with enhanced daily sampling. Analysis of over 5 000 hydrographic profiles following the eddy reveals that: ①the eddy-induced North Pacific Subtropical Mode Water (STMW) subduction process is successfully captured for the first time, and the eddy subduction mechanism is revealed. We find potential vorticity and apparent oxygen utilization distributions are asymmetric outside the AE core, with enhanced subduction near the southeastern rim of the AE. There, the southward eddy flow advects newly ventilated mode water from the north into the main thermocline. Our results show that subduction by eddy lateral advection is comparable in magnitude to that by the mean flow—an effect that needs to be better represented in climate models. ②A new mode water transport pathway by anticyclonic eddies is found. AEs transport STMW westward across the Izu Ridge through a bathymetric gap between the Hachijojima and Bonin Islands, forming a cross-ridge pathway for STMW transport. Because of the eddy transport, the shallow STMW (< 400 m) intrudes through the gap westward, which is also observed in Argo climatology. ③the formation mechanism of STMW multicore structure is clarified. We find that AEs formed east of 150°E could trap the local cold and dense STMW and migrate westward. Since sea surface temperatures increase toward the west, warmer and lighter STMWs are formed during the winter ventilation process as the AEs move westward. The newly formed STMW ride on the preexisting cold and dense STMW inside the eddy core, forming a multicore structure in the STMW. These findings update the traditional understanding of mode water. Mesoscale eddies are usually accompanied by submesoscale processes, whose effects on mode water seems to be considerably significant as well and need to be studied in the future.

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