Biogeochemistry of the Surficial Sediments of the Western and Eastern Continental Shelves of India

Jacob, J.; Chandramohanakumar, N.; Jayaraj, K. A.; Raveendran, T.V.; Balachandran, K.K.; Joseph, T.; Nair, M.; Achuthankutty, C.T.; Nair, K.K.C.; George, Roy; Ravi, Zeena P.

doi:10.2112/06-0794.1

Cited by 15 publications

(8 citation statements)

References 20 publications

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“…Sediments in the northern part (north of 13 • N) of the inner shelf are composed of 61 % silt, 21 % clay and 18 % sand. The transect at 15 • N (close to the CaTS transect) in particular is dominated by fine-grained particles (∼ 72 % silt and ∼ 27 % clay) and has been found to be organic-rich (3.2 % C org ), with ∼ 22 % labile organic matter (carbohydrates and proteins) (Jacob et al, 2008). The outer shelf (at depth > 60 m) occupies around two-thirds of the total area (Mallik, 2008).…”

Section: Study Sitementioning

confidence: 98%

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Benthic mineralization and nutrient exchange over the inner continental shelf of western India

et al. 2014

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Abstract. The western Indian continental shelf is one of the most productive coastal systems of the world ocean. This system experiences extreme changes in its oxygen regime, being normoxic from November to May and suboxic (denitrifying)/anoxic from June to October, owing to the biogeochemical response to cyclical monsoonal influence. In order to understand the impact of the seasonally varying oxygen regime on benthic mineralization, nutrient exchange and, in turn, on the shelf ecosystem, we carried out the first ever intact-core incubations during two contrasting seasons -spring intermonsoon and fall intermonsoon (late southwest monsoon) at a 28 m-deep fixed site on the inner shelf off Goa, dominated by fine-grained cohesive sediments. The results showed that incomplete sediment oxygen consumption (SOC) occurred during April as opposed to the complete SOC and subsequent sulfide flux observed in the fall intermonsoon incubations. The sediments acted as a perennial net source of DIN (dissolved inorganic nitrogen i.e. NO Slow oxidation of organic carbon (C org ) under anoxia, lower temperature and reduced benthic faunal activity appeared to decrease benthic mineralization by 25 % as suggested by the drop in the C org oxidation rate from 63.8 mmol C m −2 d −1 in April to 47.8 mmol C m −2 d −1 in October. This indicated a higher preservation of C org during the late southwest monsoon. Sediment porosity, C org content and nutrients did not show significant variations from April to October. Porewaters were found to be enriched with NH

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Section: Study Sitementioning

confidence: 98%

“…The outer shelf (at depth > 60 m) occupies around two-thirds of the total area (Mallik, 2008). Organic-poor (C org < 1 %), coarse, sandy sediments dominate the outer shelf region (Rao and Wagle, 1997;Jacob et al, 2008). The sedimentation rate over the inner shelf (at 45 m depth, off Goa) has been found to be 1.5 mm yr −1 ).…”

Section: Study Sitementioning

confidence: 99%

Benthic mineralization and nutrient exchange over the inner continental shelf of western India

et al. 2014

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“…the potential to be transported to the coastal environment during tidal exchange or flood events. The origin of sedimentary OM deposited on the continental shelf of the Arabian Sea has previously been something of a paradox, with one group suggested that the shelf sediments contained high concentrations of labile biological OM during the summer and winter monsoon seasons (Madhupratap et al, 1996) while the other group reported far less labile sedimentary OM (Jacob et al, 2008). The extent of degradation of OM in the estuaries has bearing on the remineralization of OM in the shelf and slope regions of the Arabian Sea.…”

Section: Potential Fate Of Terrigenous Ommentioning

confidence: 99%

Sources and distribution of organic matter in thirty five tropical estuaries along the west coast of India-a preliminary assessment

Pradhan

Shirodkar

et al. 2014

Estuarine, Coastal and Shelf Science

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Section: Study Sitementioning

confidence: 99%

Benthic mineralization and nutrient exchange over the inner continental shelf of western India

Pratihary¹,

Naqvi²,

Narvenkar³

et al. 2013

Preprint

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The western Indian continental shelf is one of most productive coastal systems of the world ocean. This system undergoes extreme change in oxygen regime being normoxic from November to May and suboxic/anoxic from June to October owing to the biogeochemical response to cyclical monsoonal influence. In order to understand its impact on benthic mineralization, nutrient exchange and in turn on the shelf ecosystem, we carried out first ever intact core incubation experiments by covering two contrasting seasons i.e. Spring intermonsoon and fall intermonsoon (late southwest monsoon). The results show that the shelf sediments act as a perennial net source of DIN, PO₄^3– and SiO₄^4– to the overlying water column. DIN efflux increased from 1.4 to 3.21 mmol m^–2 d^–1 from April to October of which NH₄⁺ comprises 59–100%. During oxic regime about 75% of diffusing NH₄⁺ appears to be nitrified (2.55 mmol m^–2 d^–1) of which about 77% remains coupled to benthic denitrification. Consequently 58% of NH₄⁺ flux gets lost in active coupled nitrification-denitrification process causing substantial N loss (1.98 mmol m^–2 d^–1) in the sediment. The continental shelf sediment switches over from being a NO₃^– source during oxic regime to a NO₃^– sink during low oxygen regime. During suboxia benthic denitrification being fed by NO₃^– from overlying water causes N loss at a rate of 1.04 mmol m^–2 d^–1. N loss continues even in sulfidic condition during October possibly through chemolithoautotrophic denitrification at a potential rate of 3.21 mmol m^–2 d^–1. PO₄^3– flux increased more than 4 fold during October as compared to April due to reductive dissolution of Fe and Mn oxides. The SiO₄^4– flux increases during anoxia due to higher availability of siliceous ooze as a result of diatom blooms during the monsoon season.

Porewater was found to be enriched with NH₄⁺, PO₄^3– and SiO₄^4– while depleted in NO₃^– and NO₂^– in these organic rich sediments. Sedimentary oxygen consumption decreased by ~28% under anoxia presumably due to the decrease of temperature as well as lower abundance of benthic fauna. Anoxia also appears to reduce benthic mineralization by 25% as C_org mineralization rate decreased from 63.83 mmol C m^–2 d^–1 in April to 47.83 mmol C m^–2 d^–1 in October. This is explained as due to slow oxidation of refractory C_org under anoxia apart from effect of lower te...

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Biogeochemistry of the Surficial Sediments of the Western and Eastern Continental Shelves of India

Cited by 15 publications

References 20 publications

Benthic mineralization and nutrient exchange over the inner continental shelf of western India

Benthic mineralization and nutrient exchange over the inner continental shelf of western India

Sources and distribution of organic matter in thirty five tropical estuaries along the west coast of India-a preliminary assessment

Benthic mineralization and nutrient exchange over the inner continental shelf of western India

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