scholarly journals 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 the Subtropical Gyre

2015 ◽  
Vol 45 (4) ◽  
pp. 988-1008 ◽  
Author(s):  
Takuya Nakanowatari ◽  
Humio Mitsudera ◽  
Tatsuo Motoi ◽  
Ichiro Ishikawa ◽  
Kay I. Ohshima ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
North Pacific ◽  
Model Simulation ◽  
Kuroshio Extension ◽  
Marked Change ◽  
Coupled Model ◽  
Subtropical Gyre ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
The North

AbstractUsing 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 (~26.8 σθ) were investigated. An analysis of the observations revealed that salinity decreased significantly at the density range of 26.6–26.8 σθ in 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.

scholarly journals Assessment of the Effects of Tidal Mixing in the Kuril Straits on the Formation of the North Pacific Intermediate Water

2010 ◽  
Vol 40 (12) ◽  
pp. 2569-2574 ◽  
Author(s):  
Yuki Tanaka ◽  
Toshiyuki Hibiya ◽  
Yoshihiro Niwa
Keyword(s):  
North Pacific ◽  
Kuroshio Extension ◽  
Tidal Mixing ◽  
Tuning Parameter ◽  
Intermediate Water ◽  
Low Resolution ◽  
North Pacific Intermediate Water ◽  
The North ◽  
Diapycnal Diffusivity ◽  
The North Pacific

Abstract To assess accurately the effect of tidal mixing in the Kuril Straits on the formation of the North Pacific Intermediate Water (NPIW), the spatial distribution of diapycnal diffusivity recently obtained by the present authors is incorporated into an eddy-permitting OGCM. It is shown that the NPIW is successfully reproduced, although the diapycnal diffusivity averaged over the entire Kuril Straits is an order of magnitude less than has previously been assumed as a tuning parameter to reproduce the NPIW in low-resolution OGCMs. This strongly suggests that the effect of tidal mixing in the Kuril Straits on the formation of the NPIW is relatively minor and that the physical processes omitted by the low-resolution OGCMs, such as isopycnal mixing along the Kuroshio Extension region, are much more important. This suggestion gives warning of the danger that some misleading conclusions might be derived from OGCMs that employ diapycnal diffusivity just as a tuning parameter to reproduce the observed features.

Changes of North Pacific Intermediate Water properties in the subtropical gyre

2007 ◽  
Vol 34 (2) ◽  
Author(s):  
Shinya Kouketsu ◽  
Ikuo Kaneko ◽  
Takeshi Kawano ◽  
Hiroshi Uchida ◽  
Toshimasa Doi ◽  
...  
Keyword(s):  
North Pacific ◽  
Subtropical Gyre ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
Water Properties

A modelling perspective of North Pacific Intermediate water in the future

2020 ◽  
Author(s):  
Xun Gong ◽  
Lars Ackermann ◽  
Gerrit Lohmann
Keyword(s):  
Pacific Ocean ◽  
North Pacific ◽  
Carbon Sink ◽  
North Pacific Ocean ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
The North ◽  
The Future ◽  
Near Future ◽  
The North Pacific

<p>North Pacific Intermediate water (NPIW) is a dominant water mass controlling ~400-1200m depth North Pacific Ocean, characterized by its low salinities and relatively lower temperatures. In the modern climate, the interplay between NPIW-related physical and biogeochemical processes among seasons determines annual-mean budget and efficiency of carbon sink into the North Pacific Ocean. Thus, to understand the NPIW physics is key to project roles of the North Pacific Ocean in changing Earth climate and carbon systems in the future. In this study, we provide a modelling view of the NPIW history since Yr 1850 (historical experiment) and its projection to near future (IPCC-defined RCP 4.2 and 8.5 experiments until Yr 2100), using new-generation Alfred Wegener Institute Earth System Model (AWI-ESM). Our results suggest an important role of regional hydroclimate feedback over the NW Pacific and Sea of Okhotsk in determining the NPIW from recent past to near future.</p>

scholarly journals Roles of the Okhotsk Sea and Gulf of Alaska in forming the North Pacific Intermediate Water

2000 ◽  
Vol 105 (C2) ◽  
pp. 3253-3280 ◽  
Author(s):  
Yuzhu You ◽  
Nobuo Suginohara ◽  
Masao Fukasawa ◽  
Ichiro Yasuda ◽  
Ikuo Kaneko ◽  
...  
Keyword(s):  
North Pacific ◽  
Gulf Of Alaska ◽  
Intermediate Water ◽  
Okhotsk Sea ◽  
North Pacific Intermediate Water ◽  
The North ◽  
The North Pacific

Persistent millennial-scale links between North Pacific intermediate-water ventilation and North Atlantic Climate during the deglaciation and last glaciation

2020 ◽  
Author(s):  
Jianjun Zou ◽  
Xuefa Shi ◽  
Aimei Zhu ◽  
Yuan-Pin Chang ◽  
Min-Te Chen ◽  
...  
Keyword(s):  
North Atlantic ◽  
North Pacific ◽  
North Pacific Ocean ◽  
Meridional Overturning Circulation ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
The North ◽  
Last Glaciation ◽  
The North Pacific ◽  
Millennial Scale

<p>The deep ocean carbon cycle, especially carbon sequestration and outgassing, is one of the mechanisms to explain variations in atmospheric CO<sub>2</sub> concentrations on millennial and orbital timescales. However, the potential role of subtropical North Pacific subsurface waters in modulating atmospheric CO<sub>2</sub> levels on millennial timescales is poorly constrained. Here, we investigate a suite of geochemical proxies in a sediment core from the northern and middle Okinawa Trough to understand variations in intermediate-water ventilation of the subtropical North Pacific over the last 50,000 years (50 ka). Our results suggest that enhanced mid-depth western subtropical North Pacific (WSTNP) sedimentary oxygenation occurred during cold intervals during the last deglaciation and last glaciation, while oxygenation decreased during the Bölling-Alleröd (B/A) and warm interstadials. The enhanced oxygenation during cold spells is linked to the intensified North Pacific Intermediate Water (NPIW), while interglacial increase after 8.5 ka is linked to an intensification of the Kuroshio Current due to strengthened northeast trade winds over the tropics. The enhanced formation of NPIW during Heinrich Stadials was likely driven by the perturbation of sea ice formation and sea surface salinity oscillations in high-latitude North Pacific. The diminished sedimentary oxygenation during the B/A and interstadials due to decreased NPIW formation and enhanced export production, indicates an expansion of oxygen minimum zone in the North Pacific and enhanced CO<sub>2</sub> sequestration at mid-depth waters. We attribute the millennial-scale changes to intensified NPIW and enhanced abyss flushing during deglacial cold and warm intervals, respectively, closely related to variations in North Atlantic Deep Water formation. Out study extends the millennial-scale links between ventilation in the subtropical North Pacific Ocean and the Atlantic Climate into the last glaciations, highlighting the key roles of Atlantic Meridional Overturning Circulation in regulating the North Pacific environment at millennial timescales. Note: Financial support was provided by the National Program on Global Change and Air-Sea Interaction (GASI-GEOGE-04) and by the National Natural Science Foundation of China (Grant Nos.: 41876065, 41476056, and U1606401).</p>

scholarly journals Sensitivity of the Simulated Distributions of Water Masses, CFCs, and Bomb 14C to Parameterizations of Mesoscale Tracer Transports in a Model of the North Pacific

2006 ◽  
Vol 36 (3) ◽  
pp. 273-285 ◽  
Author(s):  
Yongfu Xu ◽  
Shigeaki Aoki ◽  
Koh Harada
Keyword(s):  
North Pacific ◽  
General Circulation ◽  
Western North Pacific ◽  
North Pacific Ocean ◽  
Circulation Model ◽  
Water Masses ◽  
Intermediate Water ◽  
North Pacific Intermediate Water ◽  
The North ◽  
The North Pacific

Abstract A basinwide ocean general circulation model of the North Pacific Ocean is used to study the sensitivity of the simulated distributions of water masses, chlorofluorocarbons (CFCs), and bomb carbon-14 isotope (14C) to parameterizations of mesoscale tracer transports. Five simulations are conducted, including a run with the traditional horizontal mixing scheme and four runs with the isopycnal transport parameterization of Gent and McWilliams (GM). The four GM runs use different values of isopycnal and skew diffusivities. Simulated results show that the GM mixing scheme can help to form North Pacific Intermediate Water (NPIW). Greater isopycnal diffusivity enhances formation of NPIW. Although greater skew diffusivity can also generate NPIW, it makes the subsurface too fresh. Results from simulations of CFC uptake show that greater isopycnal diffusivity generates the best results relative to observations in the western North Pacific. The model generally underestimates the inventories of CFCs in the western North Pacific. The results from simulations of bomb 14C reproduce some observed features. Greater isopycnal diffusivity generates a longitudinal gradient of the inventory of bomb 14C from west to east, whereas greater skew diffusivity makes it reversed. It is considered that the ratio of isopycnal diffusivity to skew diffusivity is important. An increase in isopycnal diffusivity increases storage of passive tracers in the subtropical gyre.

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