Characterization of oceanic Noctiluca blooms not associated with hypoxia in the Northeastern Arabian Sea

Lotliker, Aneesh A.; Baliarsingh, Sanjiba Kumar; Trainer, Vera L.; Wells, Mark L.; Wilson, Cara; Bhaskar, T. V. S. Udaya; Samanta, Alakes; Shahimol, S.R.

doi:10.1016/j.hal.2018.03.008

Cited by 47 publications

(17 citation statements)

References 17 publications

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“…What is different, however, is that this increase in winter monsoon Chl a concentrations is not being fuelled by diatoms; the ubiquitous, trophically important, siliceous photosynthetic organisms, which dominated winter phytoplankton communities in the AS during the 1960s International Indian Ocean Expeditions (IIOE) and the mid-1990's Joint Global Ocean Flux Studies (JGOFS) 4,28 . Rather, this is due to blooms of the mixotrophic green dinoflagellate Noctiluca scintillans Suriray (synonym Noctiluca scintillans Macartney) [29][30][31][32][33][34] . Since they were first detected in the early 2000s 29,31,32,35,36 green Noctiluca blooms have become increasingly more pervasive over diatoms ( Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Since they were first detected in the early 2000s 29,31,32,35,36 green Noctiluca blooms have become increasingly more pervasive over diatoms ( Fig. S5) and more widespread, occurring every winter with predictable regularity 33,[35][36][37][38][39][40] .…”

Section: Resultsmentioning

confidence: 99%

“…In this study 35 , we showed using shipboard experiments in which natural populations were exposed to suboxic seawater 36 that endosymbionts in Noctiluca cells photosynthesized more efficiently under suboxic conditions. More recent studies 33,34,39 , have attributed the advent of Noctiluca blooms to acute "silicate stress", a situation that would prevent diatom populations from attaining bloom proportions, particularly in the northwestern AS where they have been the predominant algal group in the past 28,29,32,46 . Our examination of winter-time nutrient concentrations coincident with Noctiluca blooms provides no evidence of silicate stress 31 , but instead raises the intriguing possibility that autotrophic phytoplankton in the contemporary AS ecosystem may in fact be experiencing acute "nitrate stress".…”

Section: Resultsmentioning

confidence: 99%

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Ecosystem state change in the Arabian Sea fuelled by the recent loss of snow over the Himalayan-Tibetan Plateau region

Goés

Tian

Gomes

et al. 2020

Sci Rep

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The recent trend of global warming has exerted a disproportionately strong influence on the Eurasian land surface, causing a steady decline in snow cover extent over the Himalayan-tibetan plateau region. Here we show that this loss of snow is undermining winter convective mixing and causing stratification of the upper layer of the Arabian Sea at a much faster rate than predicted by global climate models. over the past four decades, the Arabian Sea has also experienced a profound loss of inorganic nitrate. in all probability, this is due to increased denitrification caused by the expansion of the permanent oxygen minimum zone and consequent changes in nutrient stoichiometries. these exceptional changes appear to be creating a niche particularly favorable to the mixotroph, Noctiluca scintillans which has recently replaced diatoms as the dominant winter, bloom forming organism. Although Noctiluca blooms are non-toxic, they can cause fish mortality by exacerbating oxygen deficiency and ammonification of seawater. As a consequence, their continued range expansion represents a significant and growing threat for regional fisheries and the welfare of coastal populations dependent on the Arabian Sea for sustenance. The Arabian Sea (AS) is a unique, low-latitude oceanic ecosystem because it is influenced by monsoonal winds that reverse their direction seasonally 1. These reversing winds cause dynamic shifts in surface currents and alterations in the pycnocline, which help fertilize its normally nutrient-depleted surface layers. However, the mechanisms that drive water-column mixing, the upward transport of nutrients and the consequent upsurge of phytoplankton biomass during the summer (Jun.-Sep.) and the winter (Nov.-Feb.) monsoons are different 2-6. During the summer monsoon, nutrient enrichment is via coastal upwelling, which begins when the adjacent land mass becomes warmer relative to the AS, and low pressure develops over the Arabian Peninsula 3,7,8. During this time of the year, strong topographically-steered southwesterly winds blowing over the AS form a low-level atmospheric jet called the Findlater Jet 9. This jet induces a northeastwardly flow of the surface currents, leading to strong upwelling of deep, nutrient-rich waters, causing large phytoplankton blooms along the coasts of Somalia, Yemen, and Oman 3,5,6,10,11. In contrast, during winter, when the Eurasian continent cools, nutrient enrichment is via deep penetrative convective mixing as a result of excessive heat loss from the AS surface layer caused by cold and dry northeasterly winds blowing from the snow-covered Himalayan-Tibetan Plateau (HTP) 4,5. The erosion of the thermocline, and entrainment of deep (100-150 m) nutrient-rich waters into the surface layer of the AS, begins as early as Dec., and has a major influence on winter phytoplankton blooms observable as far south as 14°N 4,11,12 .

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Ecosystem state change in the Arabian Sea fuelled by the recent loss of snow over the Himalayan-Tibetan Plateau region

Goés

Tian

Gomes

et al. 2020

Sci Rep

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“…By mid-February the activity of both cyclonic and anticyclonic eddies are responsible for the dispersal of this seed population of Noctiluca eastwards into the central and eastern Arabian Sea, ultimately engulfing the entire northern Arabian Sea (Gomes et al, 2009;Yan et al, 2019). First discovered in the early 2000's (Prakash et al, 2008;Prakash et al, 2017), these Noctiluca blooms have since become increasingly pervasive and widespread in the Arabian Sea, occurring with predictable regularity every year from December to mid of March (do Rosário Gomes et al, 2014;Goes et al, 2016;Lotliker et al, 2018;Prakash et al, 2017;Werdell et al, 2014). At the time the main sediment trap work and the JGOFS-India field studies were carried out (1989 -1997), cyanobacteria dominated the phytoplakton community in the Arabian Sea except during the peak of the upwelling seasons in the western Arabian Sea and during the winter bloom in the northern Arabain Sea (Garrison et al, 1998;Garrison et al, 2000).…”

Section: Noctiluca Bloomsmentioning

confidence: 99%

“…In their study, Piontkovski et al (2017) were able to show a gradual descent of Noctiluca cells into the water column towards the oxycline following peak blooms at the surface. More recently based on observations that showed that Noctiluca blooms of the eastern Arabian Sea were not associated with hypoxic waters Lotliker et al (2018) argued that low oxygen waters were not the cause of Noctiluca blooms. Their conclusions were not backed by any https://doi.org/10.5194/bg-2020-82 Preprint.…”

Section: Noctiluca Bloomsmentioning

confidence: 99%

Present past and future of the OMZ in the northern Indian Ocean

Rixen¹,

Cowie²,

Gaye³

et al. 2020

Preprint

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Abstract. Decreasing concentrations of dissolved oxygen and the resulting expansion of anaerobic ecosystems is a major threat to marine ecosystem services because it favors the formation of greenhouse gases such as methane, endangers the growth of economically important species, and increases the loss nitrate. Nitrate is one of the potential primary nutrients, which availability controls the marine productivity. The Arabian Sea and the Bay of Bengal are home to ~ 59 % of the Earth's marine sediments exposed to severe oxygen depletion and approximately 21 % of the total volume of oxygen-depleted waters (oxygen minimum zones, OMZs). The balance between physical oxygen supply and the biological oxygen consumption controlled the oxygen concentrations. In the Arabian Sea and most likely also in the Bay of Bengal the supply of oxygen sustained by mixing and advection associated with mesoscale eddies compensated the biological oxygen consumption. These steady states maintain low (hypoxic) oxygen concentrations allowing the competition between anaerobic and aerobic processes. However, due to slightly higher oxygen concentrations, the aerobic nitrite oxidization inhibits the anaerobic nitrite reduction and thus denitrification (the reduction of nitrate to N2) to become significant in the Bay of Bengal. A feedback mechanism caused by the negative influence of decreasing oxygen concentrations on the biological oxygen demand helped to maintain these steady states. Furthermore, it might have also counteracted a reduced physical oxygen supply into the Arabian Sea caused by climate-driven changes in the ocean's circulation during the last 6000 years. However, due to human-induced global changes, the OMZs in Arabian Sea and the Bay of Bengal intensified and expanded, which included also the occurrence of anoxic events on the Indian shelf. This affects benthic ecosystems, and in the Arabian Sea it seems to have initiated a regime shift within the pelagic ecosystem structure. Consequences for biogeochemical cycles are unknown, which, in addition to the poor representation of mesoscale features reduces the reliability of predictions of the future OMZ development in the northern Indian Ocean.

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Biophysical Control on the Variability in the Upper Layer Production Pattern of the North-Eastern Arabian Sea

Smitha,

Hussain

2023

Dynamics of Planktonic Primary Productivity in the Indian Ocean

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Characterization of oceanic Noctiluca blooms not associated with hypoxia in the Northeastern Arabian Sea

Cited by 47 publications

References 17 publications

Ecosystem state change in the Arabian Sea fuelled by the recent loss of snow over the Himalayan-Tibetan Plateau region

Ecosystem state change in the Arabian Sea fuelled by the recent loss of snow over the Himalayan-Tibetan Plateau region

Present past and future of the OMZ in the northern Indian Ocean

Biophysical Control on the Variability in the Upper Layer Production Pattern of the North-Eastern Arabian Sea

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