Interannual and Decadal Variabilities of NPIW Salinity Minimum Core Observed along JMA’s Hydrographic Repeat Sections

Nakano, Toshiya; Kaneko, Ikuo; Endoh, Masahiro; Kamachi, Masafumi

doi:10.1007/s10872-005-0076-5

Cited by 25 publications

(21 citation statements)

References 25 publications

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“…Changes on neutral density surfaces in the intermediate layers appear to be caused by “pure freshening” based on the relationships defined in and . The fresh tongue of NPIW, which extends from east to west in the western part of the section, stretches and shrinks annually [ Nakano et al , 2005]. The apparent freshening of this water mass (Figure 9) may result from such behavior of this tongue.…”

Section: Resultsmentioning

confidence: 99%

Changes in water properties and transports along 24°N in the North Pacific between 1985 and 2005

Kouketsu¹,

Fukasawa²,

Kaneko³

et al. 2009

J. Geophys. Res.

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[1] We conducted a trans-Pacific hydrographic section along 24°N in 2005 to investigate the ocean structure and its changes from previous observations in 1985. We detected significant basin-average water property changes from 1985 to 2005. Apparent oxygen utilization increased below the thermocline by up to 6 mmol kg À1 around the density of the central mode water (around 600 m). It appeared that the North Pacific intermediate water (around 800 m) was less dense in 2005 than in 1985 because of warming. From the decrease of the zonal gradient of the temperature and salinity around the North Pacific deep water (2500-4000 m) and lower circumpolar deep water (<4000 m), we suggest that northward bottom water and southward deep water transports became weaker from 1985 to 2005, consistent with the speculation from the observed temperature increase of the bottom water along its main path in previous studies. Although these water property changes suggest a slowdown of the meridional overturn in the North Pacific and large transport changes in the deep layers (below 4000 m) are estimated from an inverse method, significant heat transport changes were not detected. The estimated temperature transport change of 0.1 PW between the two sections was mainly due to shallow overturn changes, especially changes in the Kuroshio. To describe variability due to the Kuroshio changes, we estimated mass and heat transport changes from long-term observations of the Kuroshio in the Okinawa Trough, and we determined decadal variability of temperature transports, which was consistent with the variability estimated from sea-surface flux data sets.

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Section: Resultsmentioning

confidence: 99%

Changes in water properties and transports along 24°N in the North Pacific between 1985 and 2005

Kouketsu¹,

Fukasawa²,

Kaneko³

et al. 2009

J. Geophys. Res.

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“…JMA utilizes two research vessels, Ryofu Maru and Keifu Maru , for its repeat hydrographic and shipboard ADCP surveys along 137°E (refs 19, 20). Hull-mounted 75 kHz broadband ADCPs from Teledyne RD Instruments were used before spring 2010, and they were switched to 38 kHz Ocean Surveyor ADCPs thereafter.…”

Section: Methodsmentioning

confidence: 99%

“…In the northwest Pacific, repeat shipboard ADCP surveys have been conducted by Japan Meteorological Agency (JMA) along the 137°E meridian on the semi-annual or seasonal basis in the past two decades1920 (see the Methods section for more details of the JMA ADCP data). As shown in Fig.…”

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confidence: 99%

Submesoscale transition from geostrophic flows to internal waves in the northwestern Pacific upper ocean

et al. 2017

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With radar interferometry, the next-generation Surface Water and Ocean Topography satellite mission will improve the measured sea surface height resolution down to 15 km, allowing us to investigate for the first time the global upper ocean variability at the submesoscale range. Here, by analysing shipboard Acoustic Doppler Current Profiler measurements along 137°E in the northwest Pacific of 2004–2016, we show that the observed upper ocean velocities are comprised of balanced geostrophic flows and unbalanced internal waves. The transition length scale, Lt, separating these two motions, is found to depend strongly on the energy level of local mesoscale eddy variability. In the eddy-abundant western boundary current region of Kuroshio, Lt can be shorter than 15 km, whereas Lt exceeds 200 km along the path of relatively stable North Equatorial Current. Judicious separation between the geostrophic and internal wave signals represents both a challenge and an opportunity for the Surface Water and Ocean Topography mission.

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“…Since they focused on trans‐Pacific changes and compared the values averaged all throughout the section, their results indicated overall trends, but details about changes of NPIW and the zonal structure of the changes were not clear. Nakano et al [2005] found variability of the area of NPIW core in a section along 137°E and explained that the variability was caused mainly by the horizontal east‐west shift of the NPIW distribution which extends from east to west like a tongue. They suggested that this shift was due to variability in the strength of the Kuroshio recirculation gyre, which in turn was due to a wind curl anomaly around the Aleutian Low brought by a Rossby wave from the eastern Pacific.…”

Section: Introductionmentioning

confidence: 90%

Changes of North Pacific Intermediate Water properties in the subtropical gyre

Kouketsu

Kaneko

Kawano

et al. 2007

Geophysical Research Letters

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A comparison of trans‐Pacific hydrographic observations revealed changes in properties of North Pacific Intermediate Water (NPIW) in the subtropical gyre of the North Pacific from 1980s and 1990s to 2000s. Salinities decreased on density surfaces above the NPIW salinity minimum and increased below the salinity minimum. The potential temperature of the NPIW core increased by 0.10 – 0.17°C, although the salinity of NPIW core did not change substantially. The pattern of salinity changes on neutral surfaces was consistent with a density decrease of the NPIW core. It is suggested that the property changes of the NPIW core can be explained by NPIW warming.

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Interannual and Decadal Variabilities of NPIW Salinity Minimum Core Observed along JMA’s Hydrographic Repeat Sections

Cited by 25 publications

References 25 publications

Changes in water properties and transports along 24°N in the North Pacific between 1985 and 2005

Changes in water properties and transports along 24°N in the North Pacific between 1985 and 2005

Submesoscale transition from geostrophic flows to internal waves in the northwestern Pacific upper ocean

Changes of North Pacific Intermediate Water properties in the subtropical gyre

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