ENSO Modulations due to Interannual Variability of Freshwater Forcing and Ocean Biology-induced Heating in the Tropical Pacific

Gao, Chuan; Kang, Xiaojiao; Zhi, Hai; Wang, Zhanggui; Feng, Li‐Cheng

doi:10.1038/srep18506

Cited by 36 publications

(28 citation statements)

References 39 publications

(63 reference statements)

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“…The barrier layer thickness (BLT) was reduced primarily in the northern IAB and the Gulf of Papua and Coral Sea by ∼5 to 15 m (Figures b, d, and f). In the Coral Sea west of 160°E, the MLD can deepen by ∼3–6 m based on a coupled ocean‐atmosphere model, owing to enhanced evaporation over precipitation, and the MLD anomaly depends on the net buoyancy flux (Zhang et al, ). In the southeast tropical Indian Ocean (SETIO), the MLD, and BLT have been shown to shoal by ∼4–12 m in summer months during El Niño events (Zhang et al, ) consistent with these results.…”

Section: Upper Ocean Circulation and Structurementioning

confidence: 99%

“…The reduced BLT may be due to increased salinity associated with El Niño events (Zhang et al, ). A reduced MLD is likely associated with weakened wind speeds (Figures c–f), increased solar radiation (Drushka et al, ) or increased precipitation over evaporation (Zhang et al, ). For February 2016, in the different regions, the negative MLD anomalies correlated well with linear relationships for the positive total heat flux anomalies, and positive latent heat flux anomalies caused by weakened winds (Figures b–d).…”

Section: Upper Ocean Circulation and Structurementioning

confidence: 99%

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Extreme Marine Warming Across Tropical Australia During Austral Summer 2015–2016

et al. 2018

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During austral summer 2015–2016, prolonged extreme ocean warming events, known as marine heatwaves (MHWs), occurred in the waters around tropical Australia. MHWs arose first in the southeast tropical Indian Ocean in November 2015, emerging progressively east until March 2016, when all waters from the North West Shelf to the Coral Sea were affected. The MHW maximum intensity tended to occur in March, coinciding with the timing of the maximum sea surface temperature (SST). Large areas were in a MHW state for 3–4 months continuously with maximum intensities over 2°C. In 2016, the Indonesian‐Australian Basin and areas including the Timor Sea and Kimberley shelf experienced the longest and most intense MHW from remotely sensed SST dating back to 1982. In situ temperature data from temperature loggers at coastal sites revealed a consistent picture, with MHWs appearing from west to east and peaking in March 2016. Temperature data from moorings, an Argo float, and Slocum gliders showed the extent of warming with depth. The events occurred during a strong El Niño and weakened monsoon activity, enhanced by the extended suppressed phase of the Madden‐Julian Oscillation. Reduced cloud cover in January and February 2016 led to positive air‐sea heat flux anomalies into the ocean, predominantly due to the shortwave radiation contribution with a smaller additional contribution from the latent heat flux anomalies. A data‐assimilating ocean model showed regional changes in the upper ocean circulation and a change in summer surface mixed layer depths and barrier layer thicknesses consistent with past El Niño events.

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Section: Upper Ocean Circulation and Structurementioning

confidence: 99%

Section: Upper Ocean Circulation and Structurementioning

confidence: 99%

Extreme Marine Warming Across Tropical Australia During Austral Summer 2015–2016

et al. 2018

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“…As previously shown, FWF‐induced positive feedback tends to amplify ENSO amplitude, while chlorophyll‐induced negative feedback tends to reduce the ENSO amplitude. These two effects may be compensated for by each other (Zhang et al, , ). Thus, the feedback effects with opposite sign can also be produced in some situation, in which the intensified FWF forcing does not produce the increased amplitude of ENSO when the interannual effect of chlorophyll is at certain intensities (ZH19).…”

Section: Conclusion and Discussionmentioning

confidence: 99%

“…On the FWF side, a large positive FWF anomaly is observed in the western‐central equatorial Pacific during El Niño (Figure a), which not only represents a response to El Niño event but also exerts a positive feedback onto the tropical climate. For example, a large net influx of freshwater into ocean leads to a decrease in sea surface salinity (SSS) and an increase in buoyancy flux, accompanied with a shoaling of the mixed layer (ML) and an enhancement of density stratification in the upper ocean (Kang et al, ; Kang, Zhang, & Wang, ; Zhang et al, ; Zhang et al, ; Zhang et al, ; Zhang & Busalacchi, ; Zheng et al, ; Zheng & Zhang, ). Consequently, vertical entrainment of subsurface cold water into the ML is reduced, and warm SST anomaly tends to be amplified during El Niño evolution.…”

Section: Introductionmentioning

confidence: 99%

Effects on Ocean Biology Induced by El Niño‐Accompanied Positive Freshwater Flux Anomalies in the Tropical Pacific

Tian

Wang

2020

JGR Oceans

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The El Niño and Southern Oscillation (ENSO) can induce large perturbations in freshwater flux (FWF, defined as precipitation minus evaporation) and ocean ecosystem in the tropical Pacific. However, how El Niño-induced FWF can affect the tropical Pacific ecosystem (e.g., chlorophyll) is still unknown. Here, a series of ocean-only experiments are performed using a coupled ocean-physical biogeochemistry model forced by prescribed climatological wind stress. Interannual FWF anomalies observed during the 1997-1998 El Niño event are imposed onto the ocean model in the tropical Pacific, and the related positive FWF anomalies are specified to be varying in its intensity, and the corresponding sensitivity experiments are performed to examine the ocean ecosystem response. In general, chlorophyll increases with the intensities of the El Niño-induced positive FWF anomalies at a certain strength but decreases when the positive FWF forcing is underrepresented (e.g., specified to be its half intensity). Additionally, chlorophyll in the eastern tropical Pacific keeps almost steady during the increasing stage of the El Niño-induced interannual FWF forcing and then rapidly increases after the peak stage of the FWF forcing. The phytoplankton budget and diagnostic analyses are conducted to understand the behavior of chlorophyll in response to varying intensities of FWF forcing. Chlorophyll response to varying intensities of FWF forcing depends on the iron concentration in the mixed layer, suggesting that the ocean ecosystem response may be shifted from one regime to another when FWF forcing reaches a certain intensity. These results offer insights into biophysical interactions and chlorophyll-induced feedback effects on ENSO.Plain Language Summary Chlorophyll is used to represent changes in phytoplankton biomass, and its variability is significantly modulated by multiscale physical processes. In the tropical Pacific, ENSO can induce large perturbations in freshwater flux (FWF) and ocean ecosystem. Given that FWF forcing affects sea surface salinity and buoyancy flux, it is reasonable to ask the following question: Can El Niño-induced FWF forcing affect the tropical Pacific ecosystem (e.g., phytoplankton and chlorophyll)? Here we examine the effect of FWF forcing on ocean biology using a coupled physics-biogeochemistry model, in which FWF forcing is explicitly represented with varying intensity. Results suggest that chlorophyll concentration in the eastern equatorial Pacific tends to increase in response to El Niño-accompanied positive FWF anomalies. However, a regime shift can occur when the FWF forcing intensity is underrepresented (e.g., specified to be its half intensity), with chlorophyll concentration tending to decrease instead. The behavior of chlorophyll in response to varying FWF forcing intensities is regulated by the iron concentration in the mixed layer, suggesting that the ocean ecosystem response may be shifted from one regime to another when FWF forcing reaches a certain intensity. These results offer insights into bi...

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“…Near the southern and northern boundaries, sponge layers are introduced for relaxing the model temperature and salinity fields to the observational data from World Ocean Atlas 2001 (WOA01). More model details can be found in Zhang et al (2006Zhang et al ( , 2015. The OGCM is initiated from the WOA01 salinity and temperature fields and is integrated for 50 years using atmospheric climatological forcing fields, including the solar radiation, precipitation and wind stress from the NCEP/NCAR reanalysis product.…”

Section: The Ogcm and Experimentsmentioning

confidence: 99%

Scaling wind stirring effects in an oceanic bulk mixed layer model with application to an OGCM of the tropical Pacific

Zhu

2017

Clim Dyn

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ENSO Modulations due to Interannual Variability of Freshwater Forcing and Ocean Biology-induced Heating in the Tropical Pacific

Cited by 36 publications

References 39 publications

Extreme Marine Warming Across Tropical Australia During Austral Summer 2015–2016

Extreme Marine Warming Across Tropical Australia During Austral Summer 2015–2016

Effects on Ocean Biology Induced by El Niño‐Accompanied Positive Freshwater Flux Anomalies in the Tropical Pacific

Scaling wind stirring effects in an oceanic bulk mixed layer model with application to an OGCM of the tropical Pacific

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