Impacts of the IOD-associated temperature and salinity anomalies on the intermittent equatorial undercurrent anomalies

Li, Junde; Liang, Chao; Tang, Youmin; Liu, Xiaohui; Lian, Tao; Shen, Zheqi; Li, Xiaojing

doi:10.1007/s00382-017-3961-x

Cited by 20 publications

(14 citation statements)

References 49 publications

(82 reference statements)

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“…Another interesting but challenging question that should be addressed in the future is how salinity anomalies affect the upper ocean structure and SST. Recent studies have demonstrated that changes in stratification and density fields associated with salinity anomalies significantly affect upper ocean temperature and circulation (Kido & Tozuka, 2017;J. Li et al, 2018;Masson et al, 2004;Zhang et al, 2016).…”

Section: Journal Of Geophysical Research: Oceansmentioning

confidence: 99%

“…Subsurface salinity also undergoes large variation associated with the IOD, with a different spatial pattern from that of SSS (Kido & Tozuka, ). These salinity variations lead to variations in the mixed layer depth, barrier layer thickness, and upper ocean stratification, which may potentially affect the evolution of SST anomalies (Kido & Tozuka, ; J. Li et al, ; Masson et al, ; Qiu et al, ). Therefore, an accurate description of salinity variations, and understanding of their generation mechanisms are important for the IOD itself.…”

Section: Introductionmentioning

confidence: 99%

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Anatomy of Salinity Anomalies Associated With the Positive Indian Ocean Dipole

2019

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Mechanisms of salinity anomalies associated with the positive Indian Ocean Dipole (pIOD) are investigated through a series of sensitivity experiments and an online budget analysis using a regional ocean model. Special emphasis is placed on the contribution from the rectified effects due to high-frequency variability, which was not quantitatively discussed in previous studies. The results from sensitivity experiments show that positive sea surface salinity (SSS) anomalies in the southeastern tropical Indian Ocean are primarily caused by reduction in precipitation and partly by enhanced evaporation due to increased wind speed, while negative SSS anomalies in the central-eastern equatorial Indian Ocean are generated by zonal advection anomalies induced by anomalous wind stress, consistent with previous studies. Completely new results are that the modulation of nonlinear salinity advection associated with mesoscale eddies also plays an important role in determining the spatial pattern of SSS anomalies, especially in the southeastern tropical Indian Ocean. On the other hand, subsurface salinity anomalies are almost entirely caused by wind stress effects mediated by ocean dynamical processes. Further decomposition of advective anomalies suggests that they are mainly explained by the pIOD-related current anomalies governed by equatorial wave dynamics. However, a vertical shift of nonlinear freshening due to high-frequency variability also substantially contributes to the generation of positive subsurface salinity anomalies in the eastern equatorial Indian Ocean. Our results show that large-scale oceanic changes in response to the pIOD-related atmospheric anomalies are the key drivers of the observed salinity anomalies, while some nonlinear effects also seem to be at work. Plain Language SummaryThe positive Indian Ocean Dipole (pIOD) is characterized by anomalous cooling in the eastern tropical Indian Ocean and warming in the western tropical Indian Ocean and exerts significant impacts on the local and global climate. The signatures of the pIOD have been detected not only in the upper ocean temperature but also in salinity, which is a fundamental parameter along with temperature. Accompanied by the anomalous atmospheric circulation and precipitation pattern, surface and subsurface salinity in the tropical Indian Ocean is known to undergo significant variations associated with the pIOD. In this study, the relative importance of various factors in the generation of these salinity variation and physical processes behind them are quantitatively assessed using a regional ocean model. The results demonstrate that the anomalous large-scale ocean circulation induced by wind anomalies is the dominant factor that causes significant salinity variation, while anomalous precipitation and evaporation also play a secondary role. More comprehensive analyses reveal that contributions from mesoscale eddies and short timescale variations, which have been overlooked in past studies, are also important for the generation of salinity anomalie...

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Section: Journal Of Geophysical Research: Oceansmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Anatomy of Salinity Anomalies Associated With the Positive Indian Ocean Dipole

2019

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“…IOD is an oscillation of the sea-surface temperature between the eastern and western side of the tropical Indian Ocean. Similarly to the El Nino Phenomenon in the Pacific Ocean, IOD has a strong influence on the climate-ocean system of the Indian Ocean and affects surface and subsurface currents 101 .…”

Section: Morphometric Analysismentioning

confidence: 99%

Connectivity and population structure of albacore tuna across southeast Atlantic and southwest Indian Oceans inferred from multidisciplinary methodology

Nikolic

Montes

Lalire³

et al. 2020

Sci Rep

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Albacore tuna (Thunnus alalunga) is an important target of tuna fisheries in the Atlantic and Indian Oceans. The commercial catch of albacore is the highest globally among all temperate tuna species, contributing around 6% in weight to global tuna catches over the last decade. The accurate assessment and management of this heavily exploited resource requires a robust understanding of the species’ biology and of the pattern of connectivity among oceanic regions, yet Indian Ocean albacore population dynamics remain poorly understood and its level of connectivity with the Atlantic Ocean population is uncertain. We analysed morphometrics and genetics of albacore (n = 1,874) in the southwest Indian (SWIO) and southeast Atlantic (SEAO) Oceans to investigate the connectivity and population structure. Furthermore, we examined the species’ dispersal potential by modelling particle drift through major oceanographic features. Males appear larger than females, except in South African waters, yet the length–weight relationship only showed significant male–female difference in one region (east of Madagascar and Reunion waters). The present study produced a genetic differentiation between the southeast Atlantic and southwest Indian Oceans, supporting their demographic independence. The particle drift models suggested dispersal potential of early life stages from SWIO to SEAO and adult or sub-adult migration from SEAO to SWIO.

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“…They are mainly caused by eastward pressure gradient force anomalies due to higher (lower) sea level in the western (eastern) equatorial IO (Figures a and b). At the same time, nonlinear advection of zonal momentum also plays a role (Chen et al, ; Li et al, ).…”

Section: Dynamical Diagnosis On the Impacts Of Salinity Anomaliesmentioning

confidence: 99%

“…Given that three‐dimensional processes, such as horizontal and vertical advection of temperature, play a crucial role in the evolution of SST anomalies associated with the pIOD (Halkides & Lee, ; Li et al, ; Murtugudde et al, ), it is important to consider the impacts of salinity anomalies on these processes. In this regard, Li et al () have shown that the pIOD‐related salinity anomalies and associated zonal density gradient accelerate the Equatorial Undercurrent (EUC) through sensitivity experiments using a regional ocean model. However, as both temperature and salinity are nudged to prescribed values in their experiments, it was difficult to discuss their impacts on SST.…”

Section: Introductionmentioning

confidence: 99%

Experimental Assessments on Impacts of Salinity Anomalies on the Positive Indian Ocean Dipole

2019

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Impacts of salinity anomalies associated with the positive Indian Ocean Dipole (pIOD) are assessed through novel sensitivity experiments using a regional ocean model (Regional Ocean Model System) and detailed diagnostics of heat and momentum budget. During the pIOD, density stratification in the eastern equatorial Indian Ocean is enhanced due to anomalous surface freshening and subsurface saltening. This causes momentum inputs from the wind forcing to be more strongly trapped in the surface layer, and zonal and vertical current anomalies to be more confined to the upper layer. As a result, upward transports of cold water from below the thermocline to the surface layer are significantly suppressed, and the cooling in the eastern equatorial Indian Ocean is suppressed by as much as 1.0°C. The above arguments are further corroborated by a set of sensitivity experiments using a linear continuously stratified ocean model, which can isolate the effect of stratification change caused by salinity anomalies associated with the pIOD in the Regional Ocean Model System simulation. Our results suggest that salinity does play an active role in the evolution of the pIOD, rather than being passively affected by large-scale anomalous atmospheric and oceanic conditions. Plain Language Summary Salinity modulates the upper ocean circulation and temperature by changing the density of seawater and dynamical/themodynamical processes that control them. Recent studies have demonstrated that the tropical Indian Ocean experiences significant salinity variation associated with the Indian Ocean Dipole (IOD), which is a dominant climate mode in the tropical Indian Ocean and exerts widespread impacts on the global climate. However, how these salinity anomalies affect the upper ocean properties and feedback onto the IOD are not quantitatively understood. Here, we investigate the roles played by salinity variation associated with the positive IOD (pIOD) by conducting a series of sensitivity experiments using a regional ocean model. The results from our experiments show that these pIOD-related salinity anomalies act to shift the current anomalies upward and weaken the surface cooling by about 1.0°C in the eastern equatorial Indian Ocean. This is because enhanced salinity stratification traps momentum imparted by wind to the upper layer and alters the structure of the equatorial circulation. The validity of this mechanism is supported by detailed heat and momentum budget analyses, as well as sensitivity experiments using a simplified ocean model. These results provide clear evidences that salinity plays an active role in the evolution of the pIOD.

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Impacts of the IOD-associated temperature and salinity anomalies on the intermittent equatorial undercurrent anomalies

Cited by 20 publications

References 49 publications

Anatomy of Salinity Anomalies Associated With the Positive Indian Ocean Dipole

Anatomy of Salinity Anomalies Associated With the Positive Indian Ocean Dipole

Connectivity and population structure of albacore tuna across southeast Atlantic and southwest Indian Oceans inferred from multidisciplinary methodology

Experimental Assessments on Impacts of Salinity Anomalies on the Positive Indian Ocean Dipole

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