Formation and transport of intermediate water masses in a model of the Pacific Ocean
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Formation and transport of intermediate water masses in a model of the Pacific Ocean LI Yangchun1, XU Yongfu1* 1
State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
Received 11 December 2012; accepted 1 July 2013 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2014
Abstract A basin-wide ocean general circulation model of the Pacific Ocean was used to investigate how the interior restoration in the Okhotsk Sea and the isopycnal diffusion affect the circulation and intermediate water masses. Four numerical experiments were conducted, including a run with the same isopycnal and thickness diffusivity of 1.0×103 m2/s, a run employing the interior restoration of temperature and salinity in the Okhotsk Sea with a time scale of 3 months, a run that is the same as the first run except for the enhanced isopycnal mixing, and a final run with the combination of the restoration in the Okhotsk Sea and large isopycnal diffusivity. Simulated results show that the intermediate water masses reproduced in the first run are relatively weak. An increase in isopycnal diffusivity can improve the simulation of both Antarctic and North Pacific intermediate waters, mainly increasing the transport in the interior ocean, but inhibiting the outflow from the Okhotsk Sea. The interior restoration generates the reverse current from the observation in the Okhotsk Sea, whereas the simulation of the temperature and salinity is improved in the high latitude region of the Northern Hemisphere because of the reasonable source of the North Pacific Intermediate Water. A comparison of vertical profiles of temperature and salinity along 50°N between the simulation and observations demonstrates that the vertical mixing in the source region of intermediate water masses is very important. Key words: intermediate water mass, Okhotsk Sea, isopycnal diffusivity, interior restoration Citation: Li Yangchun, Xu Yongfu. 2014. Formation and transport of intermediate water masses in a model of the Pacific Ocean. Acta Oceanologica Sinica, 33(5): 8–16, doi: 10.1007/s13131-014-0480-z
1 Introduction The formation and transport pathways of water masses have a great influence on the oceanic uptake of passive tracers such as carbon dioxide. In the Pacific Ocean, besides Antarctic Bottom Water (AABW), both Antarctic Intermediate Water (AAIW) and North Pacific Intermediate Water (NPIW) play an important role in the uptake of anthropogenic gases. Many studies on the formation and transport of NPIW have been made (Talley, 1993; Yamanaka et al., 1998a, b; You et al., 2000; You, 2003a, b). Those studies indicated that the Okhotsk Sea is important to the formation of NPIW, while in the ocean models, especially in the relatively coarse models, the formation and transport of NPIW are always underestimated because of the weak simulated source of fresh water from the Okhotsk Sea and weak eddy transport. In order to accurately simulate these
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