Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

Toyoda, Takahiro; Fujii, Yosuke; Kuragano, Tsurane; Kosugi, Naohiro; Sasano, Daisuke; Kamachi, Masafumi; Ishikawa, Yoichi; Masuda, Shuhei; Sato, Kanako; Awaji, Toshiyuki; Hernández, Fabrice; Ferry, Nicolas; Guinehut, S.; Martin, Matthew J.; Peterson, K. Andrew; Good, Simon; Valdivieso, Maria; Haines, Keith; Storto, Andrea; Masina, Simona; Köhl, Armin; Yin, Yan; Shi, Li; Alves, Oscar; Smith, G. C. Moore; Chang, Yehui; Vernières, Guillaume; Wang, Xiaochun; Forget, Gaël; Heimbach, Patrick; Wang, Ou; Fukumori, Ichiro; Lee, Tong; Zuo, Hao; Balmaseda, Magdalena

doi:10.1007/s00382-015-2762-3

Cited by 18 publications

(14 citation statements)

References 51 publications

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“…The subsurface NPESTMW originates from a deep mixed layer in its formation region over the late winter, and this region can therefore be inferred from surface conditions. February and March are selected as the late winter since the MLDs in these months are both quite deep (Toyoda et al, , ). In addition, the distribution of a deep mixed layer varies from year to year, and the late winter climatology may fail to catch.…”

Section: Methodsmentioning

confidence: 99%

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Decadal Variability of North Pacific Eastern Subtropical Mode Water

et al. 2018

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A significant decadal variability of the North Pacific Eastern Subtropical Mode Water (NPESTMW), related to the Pacific Decadal Oscillation, is identified from the gridded Argo and EN4 observational data sets. To investigate the decadal variability of the NPESTMW volume, the high-resolution Estimating the Circulation and Climate of the Ocean, Phase II simulation is used to diagnose the volume budget of the NPESTMW density layer in the NPESTMW formation region (20°-36°N, 160°-120°W) between 1992 and 2016. Results show that NPESTMW is formed through subduction of low potential vorticity (PV) water. This low-PV water subduction is mainly determined by mixed layer depth change and lateral induction, which account for approximately 58% and 32%, respectively. The decadal NPESTMW volume anomaly is originated from the Pacific Decadal Oscillation-induced decadal anomaly of air-sea buoyancy flux. This decadal buoyancy flux anomaly drives the decadal anomaly of mixed layer depth change, then causes anomalous subduction, and leads to anomalous low-PV water subduction. The decadal NPESTMW volume anomaly is finally generated by this anomalous low-PV water subduction.

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Section: Methodsmentioning

confidence: 99%

“…The PDO index is defined as time series of the first empirical orthogonal function of SST north of 20°N in the Pacific. A recent study by Toyoda et al () suggested that the wintertime mixed layer depth (MLD) anomalies in the NPESTMW formation region also negatively correlate with the PDO index on both interannual and decadal time scales.…”

Section: Introductionmentioning

confidence: 99%

Decadal Variability of North Pacific Eastern Subtropical Mode Water

et al. 2018

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“…The ORA (Ocean Reanalysis) Intercomparison Project was initiated under CLIVAR GSOP and GODAE‐Oceanview and has produced a series of papers examining global ocean reanalyses and focusing on different aspects of the ocean state (e.g., steric sea level, air‐sea fluxes, ocean heat, and salt content among others). These were then brought together in a special issue of Climate Dynamics (Balmaseda et al, ; Chevallier et al, ; Karspeck et al, ; Palmer et al, ; Shi et al, ; Storto et al, ; Masina et al, ; Toyoda, Fujii, Kuragano, Kamachi, et al, ; Toyoda, Fujii, Kuragano, Kosugi, et al, ; Tietsche et al, ; Valdivieso et al, ). A further paper on the polar oceans was later added (Uotila et al, ).…”

Section: Introductionmentioning

confidence: 99%

The Mean State and Variability of the North Atlantic Circulation: A Perspective From Ocean Reanalyses

et al. 2019

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The observational network around the North Atlantic has improved significantly over the last few decades with subsurface profiling floats and satellite observations and the recent efforts to monitor the Atlantic Meridional Overturning Circulation (AMOC). These have shown decadal time scale changes across the North Atlantic including in heat content, heat transport, and the circulation. However, there are still significant gaps in the observational coverage. Ocean reanalyses integrate the observations with a dynamically consistent ocean model and can be used to understand the observed changes. However, the ability of the reanalyses to represent the dynamics must also be assessed. We use an ensemble of global ocean reanalyses to examine the time mean state and interannual-decadal variability of the North Atlantic ocean since 1993. We assess how well the reanalyses are able to capture processes and whether any understanding can be gained. In particular, we examine aspects of the circulation including convection, AMOC and gyre strengths, and transports. We find that reanalyses show some consistency, in particular showing a weakening of the subpolar gyre and AMOC at 50 • N from the mid-1990s until at least 2009 (related to decadal variability in previous studies), a strengthening and then weakening of the AMOC at 26.5 • N since 2000, and impacts of circulation changes on transports. These results agree with model studies and the AMOC observations at 26.5 • N since 2005. We also see less spread across the ensemble in AMOC strength and mixed layer depth, suggesting improvements as the observational coverage has improved.

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“…We calculated the monthly MLD anomalies in the bloom and prebloom months. Note that the reanalysis ensemble used to determine the mean MLD field well reproduced both the seasonal MLD cycle and interannual variability by effectively synthesizing oceanic and atmospheric (via surface forcing from atmospheric reanalyses) observations and dynamical models, with the model errors canceling out through ensemble averaging [ Toyoda et al ., a, b]. Positive MLD anomalies were seen in the last two months before the blooms (Figure ).…”

Section: Physical Conditions Associated With Bloomsmentioning

confidence: 96%

Physical forcing of late summer chlorophyll a blooms in the oligotrophic eastern North Pacific

Toyoda

Okamoto

2017

JGR Oceans

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We investigated physical forcing of late summer chlorophyll a (chl a) blooms in the oligotrophic eastern North Pacific Ocean by using ocean reanalysis and satellite data. Relatively large chl a blooms as defined in this study occurred in August–October following sea surface temperature (SST) anomaly (SSTA) decreases, mixed layer deepening, and temperature and salinity increases at the bottom of the mixed layer. These physical conditions were apparently induced by the entrainment of subsurface water resulting from the destabilization of the surface layer caused by anomalous northward Ekman transport of subtropical waters of higher salinity. Salinity‐normalized total alkalinity data provide supporting evidence for nutrient supply by the entrainment process. We next investigated the impact of including information about the entrainment on bloom identification. The results of analyses using reanalysis data and of those using only satellite data showed large SSTA decreases when the northward Ekman salinity transports were large, implying that the entrainment of subsurface water is well represented in both types of data. After surface‐destabilizing conditions were established, relatively high surface chl a concentrations were observed. The use of SST information can further improve the detection of high chl a concentrations. Although the detection of high chl a concentrations would be enhanced by finer data resolution and the inclusion of biogeochemical parameters in the ocean reanalysis, our results obtained by using existing reanalysis data as well as recent satellite data are valuable for better understanding and prediction of lower trophic ecosystem variability.

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Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses

Cited by 18 publications

References 51 publications

Decadal Variability of North Pacific Eastern Subtropical Mode Water

Decadal Variability of North Pacific Eastern Subtropical Mode Water

The Mean State and Variability of the North Atlantic Circulation: A Perspective From Ocean Reanalyses

Physical forcing of late summer chlorophyll a blooms in the oligotrophic eastern North Pacific

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