Influence of upwelling induced near shore hypoxia on the Alappuzha mud banks, South West Coast of India

Gireeshkumar, T.R.; Mathew, Dayana; Pratihary, Anil; Naik, Hema; Narvekar, K.U.; Araujo, Jesly; Balachandran, K.K.; Muraleedharan, K. R.; Thorat, B. R.; Nair, M.; Naqvi, S.W.A.

doi:10.1016/j.csr.2017.03.009

Cited by 29 publications

(7 citation statements)

References 28 publications

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“…Seasonally, the risk of hypoxia is highest in the entire AS and western BoB (i.e., Oman, Iran, Pakistan, India, Sri Lanka) in summer/fall due to a combination of wind‐ and wave‐driven upwelling, as well as potentially an increase in biological oxygen demand. This is consistent with prior reports of hypoxia linked to seasonal upwelling within the the western AS (Piontkovski & Al‐Oufi, 2015), the eastern AS (Banse, 1959; Carruthers et al., 1959; Gireeshkumar et al., 2017; Gupta et al., 2016, 2021; Jaleel et al., 2014, 2015, 2021; Martin et al., 2010; S. Naqvi et al., 2000, 2006; Padmakumar et al., 2016; Parameswaran et al., 2018; Shirodkar et al., 2018), and the western BoB (S. Naqvi et al., 1979; Satpathy et al., 2013). We note that there are more historically reported cases of seasonal hypoxia in the eastern AS and western BoB than the other two regions analyzed in our study (Figure 7).…”

Section: Summary and Discussionsupporting

confidence: 92%

Coastlines at Risk of Hypoxia From Natural Variability in the Northern Indian Ocean

Pearson

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2022

Global Biogeochemical Cycles

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Coastal hypoxia—harmfully low levels of oxygen—is a mounting problem that jeopardizes coastal ecosystems and economies. The northern Indian Ocean is particularly susceptible due to human‐induced impacts, vast naturally occurring oxygen minimum zones, and strong variability associated with the seasonal monsoons and interannual Indian Ocean Dipole (IOD). We assess how natural factors influence the risk of coastal hypoxia by combining a large set of oxygen measurements with satellite observations to examine how the IOD amplifies or suppresses seasonal hypoxia tied to the Asian Monsoon. We show that on both seasonal and interannual timescales hypoxia is controlled by wind‐ and coastal Kelvin wave‐driven upwelling of oxygen‐poor waters onto the continental shelf and reinforcing biological feedbacks (increased subsurface oxygen demand). Seasonally, the risk of hypoxia is highest in the western Arabian Sea in summer/fall (71% probability of hypoxia). Major year‐to‐year impacts attributed to the IOD occur during positive phases along the eastern Bay of Bengal (EBoB), where the risk of coastal hypoxia increases from moderate to high in summer/fall (21%–46%) and winter/spring (31%–42%), and along the eastern Arabian Sea (i.e., India, Pakistan) where the risk drops from high to moderate in summer/fall (53%–34%). Strong effects are also seen in the EBoB during negative IOD phases, when the risk reduces from moderate to low year‐round (∼25% to ∼5%). This basin‐scale mapping of hypoxic risk is key to aid national and international efforts that monitor, forecast, and mitigate the impacts of hypoxia on coastal ecosystems and ecosystem services.

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Section: Summary and Discussionsupporting

confidence: 92%

Coastlines at Risk of Hypoxia From Natural Variability in the Northern Indian Ocean

Pearson

Resplandy

Poupon

2022

Global Biogeochemical Cycles

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“…As global warming and eutrophication have perturbed the O 2 budget of the ocean, degradation of habitat fitness for aerobic marine organisms has occurred both regionally and globally 3 , 4 , 8 . Importantly, recently reported time-series data suggest the occurrence of upwelling-induced continuous hypoxia events (~1–2 weeks) in shallower layers 37 . In our study, however, natural phytoplankton assemblages and the diatom T. weissflogii benefited from reduced O 2 concentrations that were low enough to be detrimental for most marine animals 15 , 38 .…”

Section: Discussionmentioning

confidence: 93%

Enhancement of diatom growth and phytoplankton productivity with reduced O2 availability is moderated by rising CO2

et al. 2022

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Many marine organisms are exposed to decreasing O2 levels due to warming-induced expansion of hypoxic zones and ocean deoxygenation (DeO2). Nevertheless, effects of DeO2 on phytoplankton have been neglected due to technical bottlenecks on examining O2 effects on O2-producing organisms. Here we show that lowered O2 levels increased primary productivity of a coastal phytoplankton assemblage, and enhanced photosynthesis and growth in the coastal diatom Thalassiosira weissflogii. Mechanistically, reduced O2 suppressed mitochondrial respiration and photorespiration of T. weissflogii, but increased the efficiency of their CO2 concentrating mechanisms (CCMs), effective quantum yield and improved light use efficiency, which was apparent under both ambient and elevated CO2 concentrations leading to ocean acidification (OA). While the elevated CO2 treatment partially counteracted the effect of low O2 in terms of CCMs activity, reduced levels of O2 still strongly enhanced phytoplankton primary productivity. This implies that decreased availability of O2 with progressive DeO2 could boost re-oxygenation by diatom-dominated phytoplankton communities, especially in hypoxic areas, with potentially profound consequences for marine ecosystem services in coastal and pelagic oceans.

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“…The global oxygen loss has been suggested to be about 2% of the total ocean inventory per decade since 1960 ( Schmidtko et al, 2017 ) and the O 2 concentration of ocean has been predicted to decline to about 200 μmol L −1 by the end of the century (−5 μmol kg −1 per decade) ( Breitburg et al, 2018 ). In addition, upwelling-induced hypoxia events have been shown in sunlit layers in time-series observations ( Gireeshkumar et al, 2017 ), and typhon-driven mixing would churn deep seawater of low O 2 and high CO 2 to surface layer. Therefore, diazotrophs and other phytoplankton are inevitably exposed to extreme low O 2 and high CO 2 conditions.…”

Section: Discussionmentioning

confidence: 99%

Deoxygenation enhances photosynthetic performance and increases N2 fixation in the marine cyanobacterium Trichodesmium under elevated pCO2

Gao²

2023

Front. Microbiol.

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Effects of changed levels of dissolved O2 and CO2 on marine primary producers are of general concern with respect to ecological effects of ongoing ocean deoxygenation and acidification as well as upwelled seawaters. We investigated the response of the diazotroph Trichodesmium erythraeum IMS 101 after it had acclimated to lowered pO2 (~60 μM O2) and/or elevated pCO2 levels (HC, ~32 μM CO2) for about 20 generations. Our results showed that reduced O2 levels decreased dark respiration significantly, and increased the net photosynthetic rate by 66 and 89% under the ambient (AC, ~13 μM CO2) and the HC, respectively. The reduced pO2 enhanced the N2 fixation rate by ~139% under AC and only by 44% under HC, respectively. The N2 fixation quotient, the ratio of N2 fixed per O2 evolved, increased by 143% when pO2 decreased by 75% under the elevated pCO2. Meanwhile, particulate organic carbon and nitrogen quota increased simultaneously under reduced O2 levels, regardless of the pCO2 treatments. Nevertheless, changed levels of O2 and CO2 did not bring about significant changes in the specific growth rate of the diazotroph. Such inconsistency was attributed to the daytime positive and nighttime negative effects of both lowered pO2 and elevated pCO2 on the energy supply for growth. Our results suggest that Trichodesmium decrease its dark respiration by 5% and increase its N2-fixation by 49% and N2-fixation quotient by 30% under future ocean deoxygenation and acidification with 16% decline of pO2 and 138% rise of pCO2 by the end of this century.

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Influence of upwelling induced near shore hypoxia on the Alappuzha mud banks, South West Coast of India

Cited by 29 publications

References 28 publications

Coastlines at Risk of Hypoxia From Natural Variability in the Northern Indian Ocean

Coastlines at Risk of Hypoxia From Natural Variability in the Northern Indian Ocean

Enhancement of diatom growth and phytoplankton productivity with reduced O2 availability is moderated by rising CO2

Deoxygenation enhances photosynthetic performance and increases N2 fixation in the marine cyanobacterium Trichodesmium under elevated pCO2

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