Poleward Shift in Ventilation of the North Atlantic Subtropical Underwater

Yu, Lisan; Jin, Xiangze; Hao, Ling

doi:10.1002/2017gl075772

Cited by 16 publications

(26 citation statements)

References 47 publications

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“…The meridional mean position of the climatological SSS‐max is located at approximately 25°N. Consistent with the annual‐mean pattern reported in Yu et al (), the sea surface isohalines on the poleward side (between 25°N and 45°N) of the SSS‐max show a larger poleward movement than those on the equatorward side (between 15°N and 25°N) of the SSS‐max. On seasonal timescales, the poleward expansion of the SSS‐max occurs in all seasons, with a maximum in spring.…”

Section: Discussionsupporting

confidence: 88%

“…These authors found that the annual subduction rate had an upward trend from 1979 to 2012, which is consistent with thicker and saltier STUW. In this study, we find that the annual‐mean subduction rate increases by 0.29 ± 0.07 Sv per decade, which agrees with results from Yu et al (). In this section, the decadal patterns of the subduction area/rate are analyzed, and how subduction connects the decadal changes in the SSS‐max to the decadal changes in the STUW properties is explored.…”

Section: Mechanismsupporting

confidence: 93%

“…The water mass in the North Atlantic is defined by a salinity range of 36.7–37.1, a temperature range of 20.4–22.4 °C, and a potential density range of 25.6–26.3 kg/m 3 . The annual mean subduction rate is calculated following the approach used in Yu et al ():

S = - \frac{1}{T} \int_{T_{1}}^{T_{2}} ((), \frac{\partial h}{\partial t} + u_{b} \cdot \nabla h + w_{b}) italicdt

where h denotes the mixed layer depth, which is determined by the depth at which the potential density is 0.125 kg/m 3 larger than that at the sea surface (Monterey & Levitus, ). T represents 1 year, and T 1 and T 2 represent the times when effective detrainment starts and ends, respectively.…”

Section: Methodsmentioning

confidence: 99%

“…During the analysis period of 1979–2012, the northern side of the SSS‐max displaced northward by 1.2 ± 0.36°, whereas the equatorward side of the SSS‐max showed little change. Yu et al () found that the expansion shifted and expanded the ventilation zone of the STUW northward and northwestward, leading to a 35% increase in the annual‐mean production of the STUW. Their analysis was focused on the annual‐mean perspectives of the SSS‐max shift and its effects on the STUW.…”

Section: Introductionmentioning

confidence: 99%

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Recent Decadal Change in the North Atlantic Subtropical Underwater Associated With the Poleward Expansion of the Surface Salinity Maximum

Líu

Lin

2019

JGR Oceans

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Yu et al. (2017, https://doi.org/10.1002/2017GL075772) reported that the annual mean sea surface salinity maximum (SSS‐max) in the North Atlantic expanded northward by 0.35 ± 0.11° per decade over the 34‐year data record (1979–2012). The expansion shifted and expanded the ventilation zone northward and increased the production of the Subtropical Underwater (STUW). As a result, the STUW became deeper, thicker, and saltier. In this study, the seasonal characteristics of the poleward expansion of the North Atlantic SSS‐max and their effects on the STUW are examined. The results show that the SSS‐max expansion occurred primarily during boreal spring (April, May, and June) and expanded northward by 0.43 ± 0.21° per decade over the 34‐year period. The annual volume of the STUW increased by 0.21 ± 0.09 1014 m3 per decade over the same period, and the spring (April, May, and June) volume increased by 0.31 ± 0.02 1014 m3 per decade (a relative increase of 48 ± 1%). The characteristics of the decadal changes in STUW were attributable to the increased subduction rate associated with the northward expansion of the SSS‐max. The annual subduction rate increased by 0.29 ± 0.07 Sv per decade over the 34 years, and the greatest increase of 1.73 ± 0.61 Sv per decade occurred in April. The change in subduction associated with the expansion of the SSS‐max appeared to be consistent with the Atlantic Multidecadal Oscillation.

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Section: Discussionsupporting

confidence: 88%

Section: Mechanismsupporting

confidence: 93%

S = - \frac{1}{T} \int_{T_{1}}^{T_{2}} ((), \frac{\partial h}{\partial t} + u_{b} \cdot \nabla h + w_{b}) italicdt

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Recent Decadal Change in the North Atlantic Subtropical Underwater Associated With the Poleward Expansion of the Surface Salinity Maximum

Líu

Lin

2019

JGR Oceans

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“…SPTW is primarily produced by subduction, which is a process that transfers the properties at the sea surface to the permanent thermocline (Qiu & Huang, ). Subduction occurs within the SPTW formation area (Figure d), which is bounded by isohalines of 35.6–36.4 psu and isotherms of 19–25 °C at 10 m. The annual subduction rate of SPTW is calculated following Yu et al ():

italicSub = - \frac{1}{t} \int_{t_{1}}^{t_{2}} ((), \frac{\partial h}{\partial t} + u_{b} \nabla h + w_{b}) italicdt,

where w b and u b are the vertical and horizontal velocities at the bottom of the mixed layer, respectively; t is 1 year; t 1 and t 2 are the months in which the effective detrainment starts and ends, respectively; h denotes the mixed layer depth (MLD), which is calculated using a density threshold of 0.125 kg/m 3 (Monterey & Levitus, ); and w b is calculated as

w_{EK} - \frac{β}{f} \int_{h}^{0} italicvdz

, where the first right‐hand term is Ekman pumping and the second right‐hand term is the β term, which denotes a reduction in vertical velocity induced by horizontal advection. The geostrophic velocity is derived from EN4.2.1 (Good et al, ) assuming zero velocity at 2,000 m. The Ekman pumping is derived from the ERA‐Interim data set produced by the European Centre for Medium Range Weather Forecasts (Dee et al, ).…”

Section: Methodsmentioning

confidence: 99%

Salt Sinking in the Upper South Pacific Subtropical Gyre From 2004 to 2016

2019

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The salinity in the 50–300‐m water column of the South Pacific subtropical gyre (10°S–30°S) increased from 2004 to 2016. The observed changes are primarily associated with changes in the South Pacific Tropical Water (SPTW) volume, which increased at a rate of (3.17 ± 0.25) 1014 m3 per decade in the region of 10–30°S and 150°E–90°W. The increases in the SPTW volume are caused by increased SPTW production, which increased at a rate of 3.45 ± 2.65 Sv per decade. The temporal variability in the mixed layer accounts for 75 ± 32% of the observed increase in SPTW production. The increases in temporal changes in the mixed layer are due to a deeper mixed layer depth (MLD) in austral winter and a shallower MLD in austral spring. The possible drivers of MLD changes at the air‐sea surface are examined. Among the wind stress curl, buoyancy fluxes, and the turbulence induced by wind stress, changes in the surface buoyancy fluxes play the most important role in the deepening of the MLD during austral winter, and changes in the wind stress play a leading role in the shoaling of the MLD during austral spring. Changes in the buoyancy fluxes during winter and changes in the wind stress in spring can be attributed to increases in the Southern Annular Mode from 2004 to 2016. This study highlights the strong modulation of SPTW formation by decadal climate variability over the subtropical South Pacific.

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Interannual variability in the subduction of the South Atlantic subtropical underwater

Liu

Wei

2021

Clim Dyn

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The South Atlantic subtropical underwater (STUW) is a high-salinity water mass formed by subduction within the subtropical gyre. It is a major component of the subtropical cell and affects stratification in the downstream direction due to its high salinity characteristics. Understanding the interannual variability in STUW subduction is essential for quantifying the impact of subtropical variability on the tropical Atlantic. Using the output from the ocean state estimate of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO), this study investigates the interannual variability in STUW subduction from 1992 to 2016. We find that heat fluxes, wind stress, and wind stress curl cause interannual variability in the subduction rate. Heat fluxes over the subduction area modulate the sea surface buoyancy and regulate the mixed layer depth (MLD) during its deepening and shoaling phases. Additionally, the wind stress curl and zonal wind stress can modulate the size of the subduction area by regulating the probability of particles entrained into the mixed layer within 1 year of tracing. This analysis evaluates the influence of subtropical wind patterns on the South Atlantic subsurface high-salinity water mass, highlighting the impact of heat and wind on the interannual changes in the oceanic component of the hydrological cycle.

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Poleward Shift in Ventilation of the North Atlantic Subtropical Underwater

Cited by 16 publications

References 47 publications

Recent Decadal Change in the North Atlantic Subtropical Underwater Associated With the Poleward Expansion of the Surface Salinity Maximum

Recent Decadal Change in the North Atlantic Subtropical Underwater Associated With the Poleward Expansion of the Surface Salinity Maximum

Salt Sinking in the Upper South Pacific Subtropical Gyre From 2004 to 2016

Interannual variability in the subduction of the South Atlantic subtropical underwater

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