Simulation and future projection of the mixed layer depth and subduction process in the Subtropical Southeast Pacific

Ruibin Xia Yijun He Tingting Yang

Ruibin Xia, Yijun He, Tingting Yang. Simulation and future projection of the mixed layer depth and subduction process in the Subtropical Southeast Pacific[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-021-1877-0
Citation: Ruibin Xia, Yijun He, Tingting Yang. Simulation and future projection of the mixed layer depth and subduction process in the Subtropical Southeast Pacific[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-021-1877-0

doi: 10.1007/s13131-021-1877-0

Simulation and future projection of the mixed layer depth and subduction process in the Subtropical Southeast Pacific

Funds: The National Natural Science Foundation of China under contract Nos 41606217, 41620104003; the Open Fund of Key Laboratory for Polar Science, Polar Research Institute of China, Ministry of Natural Resources, under contract No. KP201702; the Open Fund of the Key Laboratory of Ocean Circulation and Waves, Chinese Academy of Sciences, under contract No. KLOCW1903.
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  • Figure  1.  The September mean mixed layer depth (MLD, shading) based on ARGO (a), SODA (b), ECCO2 (c), and GFDL-ESM2M (d–f, with different MLD definition). The MLD in a–d is defined by $ \Delta \rho =0.1 $ kg/m3, and the MLD in e and f are defined by $\Delta \rho=0.125 $ kg/m3 and $\Delta T=0.5 $ °C, respectively. The bold black contours (100 m MLD) represent the MLD front roughly.

    Figure  2.  Monthly mean mixed layer depth (MLD, shading) in May (a, g), June (b, h), July (c, i), August (d, j), September (e, k), and October (f, l) based on ARGO (a–f), and GFDL-ESM2M (g–l). The bold black contours (100 m MLD) represent the MLD front roughly.

    Figure  3.  The mean mixed layer depth (MLD, contours, interval 20 m) and subduction rate (shading, positive means subduction) in September in historical simulation (a) and RCP8.5 experiment (b); and the differences of MLD (contours, interval: 20 m) and subduction rate (shading) between two scenarios (RCP 8.5 minus historical) (c). Magenta frames in c represent the three key regions where subduction increases significantly in the SEP, marked as K1, K2 and K3, respectively. In c, positive subduction rate means subduction increases.

    Figure  4.  The mean mixed layer depth (MLD, contours, interval 20 m), wind stress (vectors), and Ekman pumping (shading, downward is positive, contribute to deepening the MLD) in September in historical simulation (a) and RCP8.5 experiment (b); and the differences of wind stress (vectors) and Ekman pumping (shading) between two scenarios (RCP 8.5 minus historical) (c). Magenta frames in c represent the three key regions defined in Fig. 3. In a and b, positive subduction rate means subduction, and in c, postive Ekman pumping means the downward Ekman pumping increasing.

    Figure  5.  The mean mixed layer depth (MLD, contours, interval 20 m) and net heat flux from the atmosphere to ocean (shading) in September in historical simulation (a) and RCP8.5 experiment (b); and the differences of MLD and net heat flux (shading, unit: W·m−2) between two scenarios (RCP 8.5 minus historical) (c). Magenta frames in c represent the three regions defined in Fig. 3. In a and b, positive net heat flux means ocean get heat and helps to shallow the MLD, and in c positive difference of netheat flux means ocean get more heat.

    Figure  6.  The mean mixed layer depth (MLD, contours, interval 20 m) and EP flux (evaporation minus precipitation) from the atmosphere to ocean (shading) in September in historical simulation (a) and RCP8.5 experiment (b); and the differences of MLD and E-P flux (shading) between two scenarios (RCP 8.5 minus historical) (c). Magenta frames in c represent the three regions defined in Fig. 3. In a and b, positive EP flux means the upper ocean salinity increasing and helps to deepen the MLD, and in c, positive difference of EP flux means ocean becomes saltier.

    Figure  7.  The mean mixed layer depth (MLD, contours, interval 20 m), the vertical average velocity (vectors), and the PDHA (shading, vertical integration above 100 m, positive values help MLD shoals) in September in historical simulation (a) and RCP8.5 experiment (b); and the differences of MLD, the vertical average velocity, and the PDHA (shading) between two scenarios (RCP 8.5 minus historical) (c). Magenta frames in c represent the three regions defined in Fig. 3.

    Figure  8.  The mean mixed layer depth (MLD, contours, interval 20 m), the vertical average geostrophic velocity (vectors) and the $ {\mathrm{P}\mathrm{D}\mathrm{H}\mathrm{A}}_{\mathrm{g}} $ (shading, vertical integration above 100 m, positive values help MLD shoals) in September in historical simulation (a) and RCP8.5 experiment (b); and the differences of MLD, the vertical average geostrophic velocity and the $ {\mathrm{P}\mathrm{D}\mathrm{H}\mathrm{A}}_{\mathrm{g}} $ (shading) between two scenarios (RCP 8.5 minus historical) (c). Magenta frames in c represent the three regions defined in Fig. 3.

    Figure  9.  The mean mixed layer depth (MLD, contours, interval 20 m), the vertical average Ekman horizontal velocity (vectors) and the $ {\mathrm{P}\mathrm{D}\mathrm{H}\mathrm{A}}_{\mathrm{e}} $ (shading, vertical integration above 100 m, positive values help MLD shoals) in September in historical simulation (a) and RCP8.5 experiment (b); and the differences of MLD, the vertical average Ekman horizontal velocity and the $ {\mathrm{P}\mathrm{D}\mathrm{H}\mathrm{A}}_{\mathrm{e}} $ (shading) between two scenarios (RCP 8.5 minus historical) (c). Magenta frames in c represent the three regions defined in Fig. 3.

    Figure  10.  Depth-latitude section of PDHA (shading) along 140°W to 130°W in (a, b) and along 87°W to 85°W (c, d). a and c represent the present climate, and b and d represent the change after global warming (RCP8.5 minus historical). Superimposed are the MLD in historical (black lines) and RCP8.5 (dashed lines). We check the PDHA in the Region K1 from a and b, and the Regions K2 and K3 from c and d.

    Table  1.   Qualitative comparison of the contributions of major factors to the MLD change after global warming

    VariableRegion K1Region K2Region K3
    NorthSouthNorthSouthNorthSouth
    ΔMLD
    $ \Delta {w}_{\mathrm{e}} $
    ΔQ
    Δ(EP)
    ΔPDHA
    ΔPDHAg
    ΔPDHAe
    Note: Regions K1, K2 and K3 are the three key regions defined in Fig. 3c. ΔMLD, $ {\Delta w}_{\mathrm{e}} $, ΔQ, Δ(EP), ΔPDHA represent the changes of mixed layer depth, Ekman pumping (positive values help the MLD deepening), net heat flux from the atmosphere to the ocean (positive values help the MLD shoaling), freshwater flux (evaporation minus precipitation, positive helps the MLD deepening) and upper-ocean potential-density horizontal advection (positive helps the MLD shoaling) after global warming, respectively. $ \Delta {\mathrm{P}\mathrm{D}\mathrm{H}\mathrm{A}}_{\mathrm{e}} $ and $ {\Delta \mathrm{P}\mathrm{D}\mathrm{H}\mathrm{A}}_{\mathrm{g}} $ are the two components of $ \Delta $PDHA: Ekman advection and geostrophic advection change. ↑ means the factor increases after global warming, while ↓ means the factor decreases. The red color represents that factor provides a positive contribution to the regional MLD change.
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出版历程
  • 收稿日期:  2021-03-20
  • 录用日期:  2021-06-15
  • 网络出版日期:  2021-09-03

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