On the Variability of Arabian Sea Mixing and its Energetics

Singh, S. V.; Valsala, Vinu; Prajeesh, A. G.; Balasubramanian, Sridhar

doi:10.1029/2019jc015334

Cited by 15 publications

(11 citation statements)

References 35 publications

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“…The correlation between Niño 3.4 index and average SST anomaly in the study region is the highest at the lag of one month ( R 2 = 0.56, p < 0.001; Figure 6b), and the process of increasing temperature lasted for three months via lag analysis ( R 2 ≥ 0.5, p < 0.001; Figure 6b). The occurrence of strong 2015/2016 El Niño event caused significantly increasing SST in the study area (60°–72°E, 10°–20°N; the green rectangle in Figure 6c; Singh et al., 2019). As shown in Figure 7, the temperature at 0–50 m was much higher than normal since the beginning of El Niño; and it lasted for more than 1 year, coinciding with the period of 2015–2016 El Niño event.…”

Section: Resultsmentioning

confidence: 87%

Effect of El Niño‐Related Warming on Phytoplankton's Vertical Distribution in the Arabian Sea

Chen

et al. 2021

JGR Oceans

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In this study, we analyzed the effect of warming in ecological responses due to seasonal cycle and 2015/2016 El Niño event on the vertical distribution of phytoplankton within the entire euphotic zone (0–100 m) in the eastern Arabian Sea using BGC‐Argo data during 2015–2019. We found that phytoplankton in different layers had different responses to warming. Phytoplankton biomass (defined as the integrated chlorophyll a concentration in this paper) decreased in 0–50 m layer while it increased in 50–100 m layer during spring (March‐June) and 2015/2016 El Niño event. At the same time, the vertical expansion of warming (temperature >28 °C), together with nitrate and silicate co‐limitation, triggered the formation of subsurface chlorophyll maximum layer, which became thinner and deeper during these warming periods. Results from the generalized additive models showed that the monthly 28 °C isotherm can be used as a first approximation to separate vertical water column where warming had opposite signed effects. For a 0–50 m layer of poor nutrients due to the mixed layer shoaling and reduced atmospheric deposition, a negative effect of warming on phytoplankton was seen if the temperature was higher than 28 °C. But, for a 50–100 m layer of rich nutrients, a positive effect of warming on phytoplankton was seen if the temperature was within the range of 25.5–28.0 °C and the light was enhanced. These results shed light on the effect of global warming on subsurface phytoplankton and may help research of the same topic regarding future warming.

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Section: Resultsmentioning

confidence: 87%

Effect of El Niño‐Related Warming on Phytoplankton's Vertical Distribution in the Arabian Sea

Chen

et al. 2021

JGR Oceans

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“…For the physical parameterization of vertical mixing, NEMURO is coupled with a vertical 1‐D mixed layer model which has a second‐order turbulence closure scheme as in Ikeda (1986), Mellor and Yamada (1982), Valsala et al (2018), and Singh et al (2019). The model has 51 vertical layers spanning a domain from the surface to 250 m by a constant resolution of 5 m.…”

Section: Model Data and Methodologymentioning

confidence: 99%

“…For the physical parameterization of vertical mixing, NEMURO is coupled with a vertical 1-D mixed layer model which has a second-order turbulence closure scheme as in Ikeda (1986), Mellor and Yamada (1982), Valsala et al (2018), andSingh et al (2019). The model has 51 vertical layers spanning a domain from the surface to 250 m by a constant resolution of 5 m. Mellor and Yamada (1982), is a Level 2 second-order closure model based upon the assumption that the local viscous dissipation balances the shear and buoyancy production.…”

Section: Physical Modelmentioning

confidence: 99%

Understanding the Role of Nutrient Limitation on Plankton Biomass Over Arabian Sea Via 1‐D Coupled Biogeochemical Model and Bio‐Argo Observations

et al. 2020

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Arabian Sea (AS) is known to have seasonal phytoplankton blooms during winter and summer driven by dynamically distinct physical forcing mechanisms and associated nutrient dynamics. A 1‐D coupled physical‐biogeochemical model based on North Pacific Ecosystem Model for Understanding Regional Oceanography (NEMURO) with nitrogen and silicon cycles is adapted for the AS environment. The model is implemented to investigate the role of nitrogen (nitrate + ammonium) versus silicate limitation on plankton biomass. The seasonal cycle of plankton biomass is well simulated by the model along bio‐Argo (during a period from 2013 to 2016) and ship cruise tracks (for the single year 2009). Further, three sensitivity simulations are conducted by suppressing (1) nitrate availability (representing new production), (2) ammonium availability (representing regenerated production), and (3) silicate availability (for diatom production). The new production represents 80% of the total primary production in the AS and implicitly controls 70% of total zooplankton production annually. The regenerated production augments small phytoplankton (by ~50%; e.g., flagellates) and small zooplankton (by ~20%; e.g., ciliates) growth with negligible effects on large phytoplankton (e.g., diatom) and predatory zooplankton (e.g., copepods). The diatom production remains within the observed range due to silicate limitation which is fundamental in the model for realistic simulation of chlorophyll. Silicate is the primary limiting nutrient in diatom bloom in the subsurface chlorophyll maxima with maximum limitation occurring during the winter season, due to the deeper silicicline as compared to shallower nitricline. At the surface, both nitrogen and silicate co‐limit the total production; however, nitrogen is a stronger limiter than silicate from March to June. The study highlights the relative role of silicate versus total nitrogen (nitrate + ammonium) in limiting primary production in the AS.

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“…A number of observational and numerical modeling studies have been conducted to investigate the processes at work during the formation and spreading of ASHSW Prasad 1996, 1999;Rochford 1964;Prasad and Ikeda 2002a,b;Joseph and Freeland 2005;Chowdary and Gnanaseelan 2005;Wang et al 2013;Singh et al 2019;Zhang et al 2020). These studies demonstrated that both ocean dynamics and the atmospheric forcing can modulate the salinity variation in the Arabian Sea with short-term variability resulting from tropical cyclones (Wang et al 2013) and mesoscale eddies (Zhang et al 2020).…”

Section: Introductionmentioning

confidence: 99%

“…Unlike the northwestern Arabian Sea where ocean dynamics are dominant, the northeastern Arabian Sea is less prone to mesoscale eddies and strong currents. Singh et al (2019) indicated buoyancy production of turbulent kinetic energy as the mechanism governing convective mixing and associated mixed layer variability in the northeastern Arabian Sea during the winter monsoon.…”

Section: Introductionmentioning

confidence: 99%

Winter Convective Mixing in the Northern Arabian Sea during Contrasting Monsoons

Thoppil

Wallcraft

Jensen

2022

Journal of Physical Oceanography

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Along-track Argo observations in the northern Arabian Sea during 2017 – 19 showed by far the most contrasting winter convective mixing; 2017 – 18 was characterized by less intense convective mixing resulting in a mixed layer depth of 110 m, while 2018 – 19 experienced strong and prolonged convective mixing with the mixed layer deepening to 150 m. The response of the mixed layer to contrasting atmospheric forcing and the associated formation of Arabian Sea High Salinity Water (ASHSW) in the northeastern Arabian Sea are studied using a combination of Argo float observations, gridded observations, a data assimilative general circulation model and a series of 1-D model simulations. The 1-D model experiments show that the response of winter mixed layer to atmospheric forcing is not only influenced by winter surface buoyancy loss, but also by a preconditioned response to freshwater fluxes and associated buoyancy gain by the ocean during the summer that is preceding the following winter. A shallower and short-lived winter mixed layer occurred during 2017 – 18 following the exceptionally high precipitation over evaporation during the summer monsoon in 2017. The precipitation induced salinity stratification (a salinity anomaly of -0.7 psu) during summer inhibited convective mixing in the following winter resulting in a shallow winter mixed layer (103 m). Combined with weak buoyancy loss due to weaker surface heat loss in the northeastern Arabian Sea, this caused an early termination of the convective mixing (February 26, 2018). In contrast, the winter convective mixing during 2018 – 19 was deeper (143 m) and long-lived. The 2018 summer, by comparison, was characterized by normal or below normal precipitation which generated a weakly stratified ocean pre-conditioned to winter mixing. This combined with colder and drier air from the land mass to the north with low specific humidity lead to strong buoyancy loss, and resulted in prolonged winter convective mixing through March 25, 2019.

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On the Variability of Arabian Sea Mixing and its Energetics

Cited by 15 publications

References 35 publications

Effect of El Niño‐Related Warming on Phytoplankton's Vertical Distribution in the Arabian Sea

Effect of El Niño‐Related Warming on Phytoplankton's Vertical Distribution in the Arabian Sea

Understanding the Role of Nutrient Limitation on Plankton Biomass Over Arabian Sea Via 1‐D Coupled Biogeochemical Model and Bio‐Argo Observations

Winter Convective Mixing in the Northern Arabian Sea during Contrasting Monsoons

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