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On the subtropical Northeast Pacific mixed layer depth and its influence on the subduction

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Abstract

The present climate simulations of the mixed layer depth (MLD) and the subduction rate in the subtropical Northeast Pacific are investigated based on nine of the CMIP5 models. Compared with the observation data, spatial patterns of the MLD and the subduction rate are well simulated in these models. The spatial pattern of the MLD is nonuniform, with a local maximum MLD (>140 m) region centered at (28°N, 135°W) in late winter. The nonuniform MLD pattern causes a strong MLD front on the south of the MLD maximum region, controls the lateral induction rate pattern, and then decides the nonuniform distribution of the subduction rate. Due to the inter-regional difference of the MLD, we divide this area into two regions. The relatively uniform Ekman pumping has little effect on the nonuniform subduction spatial pattern, though it is nearly equal to the lateral induction in values. In the south region, the northward warm Ekman advection (–1.75×10–7 K/s) controls the ocean horizontal temperature advection (–0.85×10–7 K/s), and prevents the deepening of the MLD. In the ensemble mean, the contribution of the ocean advection to the MLD is about–29.0 m/month, offsetting the sea surface net heat flux contribution (33.9 m/month). While in the north region, the southward cold advection deepens the MLD (21.4 m/month) as similar as the heat flux (30.4 m/month). In conclusion, the nonuniform MLD pattern is dominated by the nonuniform ocean horizontal temperature advection. This new finding indicates that the upper ocean current play an important role in the variability of the winter MLD and the subduction rate.

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Acknowledgments

The authors appreciate World Climate Research Programme’s Working Group on Coupled Modeling, which is responsible for CMIP5, and thank the climate modeling groups (listed in Table 1) for producing and making available their model output.

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Authors and Affiliations

  1. Polar Climate System and Global Change Laboratory, Nanjing University of Information Science & Technology, Nanjing, 210044, China

    Ruibin Xia, Chengyan Liu & Chen Cheng

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  1. Ruibin Xia
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  2. Chengyan Liu
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  3. Chen Cheng
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Correspondence to Ruibin Xia.

Additional information

Foundation item: The National Natural Science Foundation of China under contract Nos 41606217, 41675064 and 41406214; the Scientific Research Foundation for the Talent Start-Up of University of Information Science and Technology under contract No. 2015r043; the Open Fund of the Key Laboratory of Research on Marine Hazards Forecasting under contract No. LOMF1702; the China Scholarship Council under contract No. 201708320046.

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Xia, R., Liu, C. & Cheng, C. On the subtropical Northeast Pacific mixed layer depth and its influence on the subduction. Acta Oceanol. Sin. 37, 51–62 (2018). https://doi.org/10.1007/s13131-017-1102-3

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  • DOI: https://doi.org/10.1007/s13131-017-1102-3

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