Numerical study on the impact of the 18.6‐year period nodal tidal cycle on water masses in the subarctic North Pacific

Osafune, Satoshi; Yasuda, Ichiro

doi:10.1029/2011jc007734

Cited by 19 publications

(11 citation statements)

References 41 publications

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“…9b). This linkage of the generation of the higher baroclinic modes with the damping of SST anomalies is consistent with the earlier studies using ocean models where surface buoyancy flux forcing was prescribed (Liu and Shin 1999;Nonaka and Xie 2000;Osafune and Yasuda 2012;Thompson and Ladd 2004). In particular, Thompson and Ladd (2004) identified the forcing of the first and the second baroclinic mode variability separately in their OGCM simulation through a modal decomposition analysis, where the second mode variability is linked to surface buoyancy forcing.…”

Section: B Generation Of Higher Baroclinic Modessupporting

confidence: 70%

“…The dominance of the spiciness component of OHC anomalies highlights an important role of the KOE region as an origin of the eastward-propagating OHC signals. In earlier forced OGCM experiments, such eastward-propagating, higher mode Rossby waves or spiciness anomalies are initiated by the surface buoyancy forcing (e.g., Liu and Shin 1999;Nonaka and Xie 2000;Osafune and Yasuda 2012;Thompson and Ladd 2004). Our CGCM simulation points to a new mechanism for the initiation of the eastwardpropagating signals, namely the anomalous spiciness generation associated with the decadal-scale latitudinal excursion of the SAFZ in KOE region and the subsequent transformation of the spiciness signals into higher baroclinic modes Rossby waves.…”

Section: Summary and Discussionmentioning

confidence: 89%

“…The equivalent barotropic structure to the west is expected to be unaffected by the mean current, because of the cancellation of the wave propagation tendencies due to advection and change of background meridional vorticity gradient (Pedlosky 1996;Liu 1999). Similar eastwardpropagating higher baroclinic mode signals have been discussed with ocean models forced with prescribed surface buoyancy forcing (Liu 1999;Nonaka and Xie 2000;Thompson and Ladd 2004;Osafune and Yasuda 2012).…”

Section: Vertical Structuresmentioning

confidence: 93%

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Origin of Decadal-Scale, Eastward-Propagating Heat Content Anomalies in the North Pacific*

Taguchi

Schneider

2014

Journal of Climate

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Upper ocean heat content (OHC) is at the heart of natural climate variability on interannual-to-decadal time scales, providing climate memory and the source of decadal prediction skill. In the midlatitude North Pacific Ocean, OHC signals are often found to propagate eastward as opposed to the frequently observed westward propagation of sea surface height, another variable that represents the ocean subsurface state. This dichotomy is investigated using a 150-yr coupled GCM integration. Simulated OHC signals are distinguished in terms of two processes that can support eastward propagation: higher baroclinic Rossby wave (RW) modes that are associated with density perturbation, and spiciness anomalies due to density-compensated temperature and salinity anomalies. The analysis herein suggests a unique role of the Kuroshio-Oyashio Extension (KOE) region as an origin of the spiciness and higher mode RW signals. Wind-forced, westward-propagating equivalent barotropic RWs cause meridional shifts of the subarctic front in the KOE region. The associated anomalous circulation crosses mean temperature and salinity gradients and thereby generates spiciness anomalies. These anomalies are advected eastward by the mean currents, while the associated surface temperature anomalies are damped by airsea heat exchange. The accompanying surface buoyancy flux generates higher baroclinic, eastward-propagating RWs. The results suggest that the large OHC variability in the western boundary currents and their extensions is associated with the spiciness gradients and axial variability of oceanic fronts.

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Section: B Generation Of Higher Baroclinic Modessupporting

confidence: 70%

Section: Summary and Discussionmentioning

confidence: 89%

Section: Vertical Structuresmentioning

confidence: 93%

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Origin of Decadal-Scale, Eastward-Propagating Heat Content Anomalies in the North Pacific*

Taguchi

Schneider

2014

Journal of Climate

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“…On the basis of a modeling study, Deutsch et al (2006) have suggested that variations in ventilation are important for decadal O 2 variations. Osafune and Yasuda (2012) also drew from a modeling study to argue that tidal mixing could induce O 2 variations through the development of a winter mixed layer due to upward salt flux over broad areas. Here we roughly estimate O 2 oscillations through air-sea gas exchange associated with differences in mixed layer depths (Broecker & Peng, 1974) using climatological winds in the region (Kalnay et al, 1996) and a broadly used formulation of the gas transfer velocity (Wanninkhof, 1992).…”

Section: (E) Winter Ventilation Associated With Variations In Mixed Lmentioning

confidence: 99%

Decline and Bidecadal Oscillations of Dissolved Oxygen in the Oyashio Region and Their Propagation to the Western North Pacific

Sasano

Takatani

Kosugi

et al. 2018

Global Biogeochemical Cycles

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During the period 1954–2014, concentrations of dissolved oxygen (O2) in the Oyashio region of the western subarctic North Pacific has been oscillating over bidecadal timescales and significantly decreasing over the isopycnal layer spanning σθ = 26.6–27.5 kg/m3. The cycles of oscillation (16.4–19.6 years) are almost consistent and synchronized within 1 year over this density layer and are probably controlled by the nodal tidal cycle of 18.6 years and/or atmospheric forcing. The mean rate of the long‐term decrease is the highest (−0.70 ± 0.06 μmol · kg−1 · year−1) in the temperature minimum layer. The O2 decline there is predominantly attributed to a reduction of ventilation in winter due to warming and freshening. On the other hand, the O2 decline in deeper layers down to the oxygen minimum layer is attributable to a reduction in ventilation in the Sea of Okhotsk associated with a reduction in sea ice formation and propagation of its impact through diapycnal mixing adjacent to the Bussol' Strait. These trends of bidecadal oscillations and decline of O2 were also found in the downstream to the east in the 165°E section at latitudes 30°N–42.5°N on σθ = 26.8 kg/m3 and with attenuated amplitudes at latitudes of 40°N–45°N in the oxygen minimum layer on σθ = 27.4 kg/m3. These results indicate that the signal of secular declines of O2, together with bidecadal oscillations, is being propagated broadly from the Oyashio source region into the interior of the Pacific Ocean.

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“…This positive autocorrelation could be the result of a set of harmonic and sub-harmonic temperature cycles introduced by the Earth's nutation of 18.6 yr. For example, a similar temperature cycle of 18.6/3 = 6.2 yr has been demonstrated in the Barents Sea (Yndestad 1999), and this effect has an impact on water-mass variations (e.g. Osafune & Yasuda 2012).…”

Section: Comparison Of Time-series At Ows Mikementioning

confidence: 99%

Comparison of gridded sea surface temperature datasets for marine ecosystem studies

Boehme¹,

Lonergan²,

Todd³

2014

Mar. Ecol. Prog. Ser.

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In assessing impacts of a changing environment on the structure and functioning of marine ecosystems, the challenge remains to distinguish the effects of noise and of temporal and spatial autocorrelation from environmental drivers of biotic change. One analytical approach is to de-trend the data and use the resulting residuals; an alternative method involves use of the raw anomalies and a reduction of the degrees of freedom (df ) to make the hypothesis testing more conservative. Here, we assess the comparability of 3 gridded sea surface temperature (SST) datasets -ERSST V3b, HadISST, and OISST V2 -to in situ measurements. The 1° gridded HadISST and OISST V2 showed the highest similarity, while the weaker correlations with ERSST V3b probably are attributable to its coarser 2°grid. We investigated the performance of 2 commonly applied statistical methods to resolving autocorrelation, and proceeded to correlation analyses between the SST datasets and 2 contemporaneous 15 yr time-series of the somatic growth condition of annual cohorts of Atlantic salmon Salmo salar, which migrate to the Norwegian Sea. For these latter analyses, reducing df could not fully resolve the problem of high positive autocorrelation. The 3 oceanographic datasets do not provide the same correlative outcomes and levels of significance with the salmon time-series. When analysing time-series that pre-date the availability of satellite data, the choice of dataset is restricted to either ERSST V3b or HadISST; but for recent studies (1982 onwards) OISST V2 also is available, and it will be important to assess the relative merits of the 3 SST data sources when interpreting contrasting correlative outcomes.

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Numerical study on the impact of the 18.6‐year period nodal tidal cycle on water masses in the subarctic North Pacific

Cited by 19 publications

References 41 publications

Origin of Decadal-Scale, Eastward-Propagating Heat Content Anomalies in the North Pacific*

Origin of Decadal-Scale, Eastward-Propagating Heat Content Anomalies in the North Pacific*

Decline and Bidecadal Oscillations of Dissolved Oxygen in the Oyashio Region and Their Propagation to the Western North Pacific

Comparison of gridded sea surface temperature datasets for marine ecosystem studies

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