New evidence for enhanced preservation of organic carbon in contact with oxygen minimum zone on the western continental slope of India

Paropkari, A.L.; Babu, C. Prakash; Mascarenhas, A.

doi:10.1016/0025-3227(93)90185-x

Cited by 58 publications

(30 citation statements)

References 14 publications

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“…The phylogenetic analysis of the clones derived from OMZ sediments of AS showed a wide representation of various taxonomic groups as the eastern Arabian Sea sediments underlying the OMZ consist of laminated mud, rich in organic matter (Paropkari et al 1993), which forms an excellent habitat for the microorganisms to flourish. Gupta (2000) in his review on the phylogeny of prokaryotes states that phylum Proteobacteria is of biological significance as it is the most dominant and diverse group of the microbial assemblage.…”

Section: Phylogenetic Analysismentioning

confidence: 99%

16S rRNA-based bacterial diversity in the organic-rich sediments underlying oxygen-deficient waters of the eastern Arabian Sea

Divya

Parvathi

Bharathi

et al. 2011

World J Microbiol Biotechnol

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The eastern Arabian Sea has a unique and permanent oxygen minimum zone (OMZ) that extends along the western continental margin of India. The sediment below this region is rich in organic matter. This study describes the bacterial community structure and diversity in OMZ sediments of the eastern Arabian Sea (AS) through 16S rRNA clone library analysis. Phylogenetic analysis of the sequences demonstrated that phylum Proteobacteria (52%), followed by Planctomycetes (12.7%), Chloroflexi and an unidentified bacterial group (8.8% each) were represented in the library. Deltaproteobacteria was the dominant class (62.5%) in phylum Proteobacteria with clones falling in orders Syntrophobacterales and Desulfovibrionales. Few minor phylogenetic groups, corresponding to Spirochetes, Firmicutes, Acidobacteria and Verrucomicrobia were found. Unidentified candidate groups falling in OP11, OP8 and OP3 were represented by 0.9, 2.9 and 3.9%, respectively and two clusters of the cloned sequences in this study showed very low identity to known sequences. This is the first report that discusses the phylogenetic groups in the OMZ sediments of eastern Arabian Sea individually and compares it with available data from marine hypoxic locales and water mass. LIBSHUFF statistics revealed high richness of the bacterial community of the Arabian Sea OMZ (AS-OMZ) compared to the other regions.

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Section: Phylogenetic Analysismentioning

confidence: 99%

16S rRNA-based bacterial diversity in the organic-rich sediments underlying oxygen-deficient waters of the eastern Arabian Sea

Divya

Parvathi

Bharathi

et al. 2011

World J Microbiol Biotechnol

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“…Paropkari et al, 1992Paropkari et al, , 1993van der Weijden et al, 1998), based on correspondence between mid-slope C org enrichment and the OMZ. Also, in studies of size-fractionated sediments from sites across the Pakistan margin OMZ, Keil and Cowie (1999) showed evidence of enhanced C org loadings (relative to available surface area) at sites within the OMZ and close to its lower boundary.…”

Section: Controls On Om Distributionmentioning

confidence: 99%

“…Paropkari et al, 1992Paropkari et al, , 1993van der Weijden et al, 1998;Keil and Cowie, 1999), and the Arabian Sea OMZ to be suggested as the modern equivalent of settings with OM-rich deposits found in the geological record (Demaison and Moore, 1980). However, margins of the Arabian Sea differ markedly in productivity, and OMZ sediments experience differing degrees of O 2 depletion and thus have different benthic communities and degrees of bioturbation (Cowie, 2005).…”

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confidence: 99%

Comparative organic geochemistry of Indian margin (Arabian Sea) sediments: estuary to continental slope

et al. 2014

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Abstract. Surface sediments from sites across the Indian margin of the Arabian Sea were analysed for their elemental and stable isotopic organic carbon (C org ) and total nitrogen compositions, grain size distributions and biochemical indices of organic matter (OM) source and/or degradation state. Site locations ranged from the estuaries of the Mandovi and Zuari rivers to depths of ∼ 2000 m on the continental slope, thus spanning nearshore muds and sands on the shelf and both the oxygen minimum zone (OMZ) on the upper slope (∼ 200-1300 m) and the seasonal hypoxic zone that appears on the shelf. Source indices showed mixed marine and terrigenous OM within the estuaries, but consistent predominance (80-100 %) of marine OM on the shelf and slope. Thus, riverine terrigenous OM is diluted or replaced by autochthonous marine OM and/or is efficiently re-mineralised, within or immediately offshore of the estuaries. Organic C contents of surface shelf sediments varied from < 0.5 wt % in relict shelf sands to up to ∼ 4 wt % for nearshore muds, while upper slope sites within the OMZ showed a wide range (∼ 2 to 7 + wt %), progressively decreasing below the OMZ to ≤ 1 wt % at 2000 m. Thus, major variability (∼ 5 wt %) was found at slope sites within the OMZ of similar depth and near-identical bottom-water O 2 concentrations. A strong relationship between %C org and sediment grain size was seen for sediments within the OMZ, but lower relative C org contents were found for sites on the shelf and below the OMZ. Further, C org loadings, when related to estimated sediment surface area, indicated distinct enrichment of C org in the OMZ sediments relative to sites above and below the OMZ and to sediments from normoxic margins. Diagenetic indices confirmed that lower C org content below the OMZ is associated with more extensive OM degradation, but that shelf sediment OM is not consistently more degraded than that found within the OMZ. Together, the results indicate that OM distribution across the margin is controlled by interplay between hydrodynamic processes and varying preservation associated with O 2 availability. This inference is supported by multiple regression analysis. Hydrodynamic processes (expressed as %Silt) followed by O 2 availability, can explain the large majority of %C org variability when the shelf and slope are considered as a whole. However, while O 2 becomes the primary influence on %C org for sediments below the OMZ, %Silt is the primary influence across the OMZ and, apparently, the shelf. Thus, reduced O 2 exposure is responsible for OM enrichment within the OMZ, but hydrodynamic processes are the overriding control on sediment OM distributions across both the shelf and the OMZ.

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“…Higher levels of organic carbon (1-4 wt % and up to 16 wt%) occur in the continental slope sediments of the eastern Arabian Sea, Indian Ocean (Paropkari et al 1987), and the explanation for these levels is still a matter of debate. Some workers consider that anoxia is the most M. Thamban · V. Purnachandra Rao ( ) National Institute of Oceanography, Dona Paula 403 004, Goa, India S. V. Raju Oil India Limited, Duliajan 786 602, Assam, India important deciding factor (Demaison and Moore 1980;Paropkari et al 1992Paropkari et al , 1993, while others (Pedersen and Calvert 1990;Pedersen et al 1992;Calvert et al 1995) suggest that productivity in conjuction with factors like sediment characteristics and texture, rather than anoxia, are important for the high organic content. Here, we examine the distribution of organic carbon in the sediment cores retrieved from three physiographic settings on the upper continental slope and discuss the factors responsible for its preservation.…”

Section: Introductionmentioning

confidence: 96%

Controls on organic carbon distribution in sediments from the eastern Arabian Sea Margin

1997

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Sediment cores from the upper continental slope of the eastern Arabian Sea have high organic carbon (OC), CaCO , and sand content at the top. The values decrease with increasing depth in the Holocene and Upper Pleistocene. Topographic highs show highest OC and lower CaCOin the Holocene clayey sediments and vice versa in the Pleistocene sandy sediments. The OC is immature and marine or a mixture of both marine and terrestrial in the Holocene sediments and is mostly terrestrial and/or reworked marine in the Pleistocene sediments. Productivity is the main controlling factor for the organic carbon enrichment. Texture and reworking also influence the organic carbon variations.

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New evidence for enhanced preservation of organic carbon in contact with oxygen minimum zone on the western continental slope of India

Cited by 58 publications

References 14 publications

16S rRNA-based bacterial diversity in the organic-rich sediments underlying oxygen-deficient waters of the eastern Arabian Sea

16S rRNA-based bacterial diversity in the organic-rich sediments underlying oxygen-deficient waters of the eastern Arabian Sea

Comparative organic geochemistry of Indian margin (Arabian Sea) sediments: estuary to continental slope

Controls on organic carbon distribution in sediments from the eastern Arabian Sea Margin

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