Multidecadal-scale freshening at the salinity minimum in the western part of North Pacific: Importance of wind-driven cross-gyre transport of subarctic water to subtropical gyre
Multidecadal-scale freshening at the salinity minimum in the western part of North Pacific: Importance of wind-driven cross-gyre transport of subarctic water to subtropical gyre
复制标题
北太平洋西部盐度最低点的数十年尺度淡水化：风驱动的亚北极水跨环流输送到副热带环流的重要性
DOI：
10.1175/jpo-d-13-0274.1
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发表时间：
2015
影响因子：
3.5
通讯作者：
M. Wakatsuchi
中科院分区：
文献类型：
--
作者：
Nakanowatari;T.;H. Mitsudera;T. Motoi;I. Ishikawa;K.-I. Ohshima;M. Wakatsuchi
利用1955 - 2004年的海洋观测资料和涡分辨冰-海耦合模式模拟，研究了20世纪70年代末北太平洋中层水（NPIW）在盐度最低密度（~26.8σθ）下的多年尺度淡化过程中，风驱动的海洋环流变化的影响。对观测资料的分析表明，在包括混合水域在内的西副热带环流区，盐度在26.6-26.8σθ的密度范围内显著下降。盐度的时间变化主要是在20世纪70年代后期的显着变化。该模型的结果与观测结果相似，选择性地受风力驱动的海洋环流的年际变化的影响，模拟了副热带环流上空中间层的显着淡化。这一显著的增淡现象与阿留申低压加强导致的俄亥俄向南输送的增加有关。伴随着这些变化，入侵的淡水和低位涡水，起源于鄂霍次克海，MWR增加，并在随后的6年中，在西副热带环流进一步向南传播的清新信号，穿过黑潮延伸区。这些结果表明，NPIW的数十年尺度的清新部分是由加强风驱动的副北极水的副热带环流的交叉环流输送。
Using oceanographic observations and an eddy-resolving ice–ocean coupled model simulation from 1955 to 2004, the effects of the wind-driven ocean circulation change that occurred in the late 1970s during multidecadal-scale freshening of the North Pacific Intermediate Water (NPIW) at salinity minimum density (~26.8σθ) were investigated. An analysis of the observations revealed that salinity decreased significantly at the density range of 26.6–26.8σθin the western subtropical gyre, including the mixed water region (MWR). The temporal variability of the salinity is dominated by the marked change in the late 1970s. With results similar to the observations, the model, selectively forced by the interannual variability of the wind-driven ocean circulation, simulated significant freshening of the intermediate layer over the subtropical gyre. The significant freshening is related to the increase in southward transport of the Oyashio associated with the intensification of the Aleutian low. Accompanying these changes, the intrusion of fresh and low potential vorticity water, originating in the Okhotsk Sea, to the MWR increased, and the freshening signal propagated farther southward in the western subtropical gyre during the subsequent 6 yr, crossing the Kuroshio Extension. These results indicate that the multidecadal-scale freshening of the NPIW is partly caused by intensification of the wind-driven cross-gyre transport of the subarctic water to the subtropical gyre.