Coastal versus open-ocean denitrification in the Arabian Sea

Naqvi, S.W.A.; Naik, Hema; Pratihary, Anil; D’Souza, W.; Narvekar, P.V.; Jayakumar, D. A.; Devol, Allan H.; Yoshinari, Tadashi; Saino, Toshiro

doi:10.5194/bg-3-621-2006

Cited by 159 publications

(150 citation statements)

References 59 publications

(68 reference statements)

Supporting

Mentioning

132

Contrasting

Order By: Relevance

“…Lower bottom-water oxygen levels result in less oxidation of particulate and dissolved reduced sulphur compounds with the result that more reduced sulphur is buried (high sulphide retention efficiency; Canfield, 1994;Passier et al, 1997) and that sulphide may escape from the sediments to the water column (Brüchert et al, 2003;Lavik et al, 2009). Hydrogen sulphide release from anoxic sediments has been reported for permanently anoxic systems such as the Black Sea and Cariaco basin as well as for more dynamic settings experiencing hydrogen-sulphide release events (Namibian coastal upwelling, Brüchert et al, 2003, Lavik et al, 2009; the Indian shelf, Naqvi et al, 2006). Recently, Lavik et al (2009) reported detoxification of sulphidic waters from the Namibian shelf by chemolithotrophs (of the γ -and β-proteobacteria) in the water column that completely consumed the sulphide and created a buffer zone between toxic, sulphidic subsurface waters and oxic surface waters.…”

Section: The Effect Of Oxygen On Diagenetic Pathways and Sediment-watmentioning

confidence: 99%

Coastal hypoxia and sediment biogeochemistry

2009

View full text Add to dashboard Cite

Abstract. The intensity, duration and frequency of coastal hypoxia (oxygen concentration <63 µM) are increasing due to human alteration of coastal ecosystems and changes in oceanographic conditions due to global warming. Here we provide a concise review of the consequences of coastal hypoxia for sediment biogeochemistry. Changes in bottomwater oxygen levels have consequences for early diagenetic pathways (more anaerobic at expense of aerobic pathways), the efficiency of re-oxidation of reduced metabolites and the nature, direction and magnitude of sediment-water exchange fluxes. Hypoxia may also lead to more organic matter accumulation and burial and the organic matter eventually buried is also of higher quality, i.e. less degraded. Bottom-water oxygen levels also affect the organisms involved in organic matter processing with the contribution of metazoans decreasing as oxygen levels drop. Hypoxia has a significant effect on benthic animals with the consequences that ecosystem functions related to macrofauna such as bio-irrigation and bioturbation are significantly affected by hypoxia as well. Since many microbes and microbial-mediated biogeochemical processes depend on animal-induced transport processes (e.g. re-oxidation of particulate reduced sulphur and denitrification), there are indirect hypoxia effects on biogeochemistry via the benthos. Severe long-lasting hypoxia and anoxia may result in the accumulation of reduced compounds in sediments and elimination of macrobenthic communities with the consequences that biogeochemical properties during trajectories of decreasing and increasing oxygen may be different (hysteresis) with consequences for coastal ecosystem dynamics.

show abstract

Section: The Effect Of Oxygen On Diagenetic Pathways and Sediment-watmentioning

confidence: 99%

Coastal hypoxia and sediment biogeochemistry

2009

View full text Add to dashboard Cite

show abstract

“…It is important to note the distinct decline of nitrates in the central Arabian Sea, which is within core of the perennial denitrification zone, indicative of enhanced utilization of nitrates due to intensification of denitrification. The nutrient and DO depth profiles of the central Arabian Sea are known to be governed by the availability of nutrients from subsurface waters of adjacent productive zones of the eastern and western Arabian Sea, even though the open-ocean and coastal suboxic zones are not contiguous (Naqvi et al 2006). Hence, enhanced productivity, and thereby intensification of denitrification, in adjacent productive zones can be expected to leave their imprint in intermediate to deeper water nitrate contents of the central Arabian Sea as well.…”

Section: Changes In Nutrients (Nitrates Phosphates and Silicates)mentioning

confidence: 99%

“…The seasonal monsoon winds lead to coastal upwelling along the western margins of the Arabian Sea and the Bay of Bengal (Currie et al 1973;Shankar et al 2002). The intense upwelling in the Arabian Sea feeds nutrients to its surface waters, making it one of the most productive oceanic regions (Prasanna Naqvi et al 2006 and references therein). The deep waters of the Arabian Sea are composed of waters from south of the Equator and marginal seas like the Red Sea and the Persian Gulf (Shetye et al 1994).…”

Section: Introductionmentioning

confidence: 99%

Decadal Variations in Oceanic Properties of the Arabian Sea Water Column since Geosecs

Bhushan

Dutta²,

Agnihotri³

et al. 2014

Radiocarbon

View full text Add to dashboard Cite

ABSTRACT. This article reports temporal changes in the measured oceanic geochemical properties of the Arabian Sea and the equatorial Indian Ocean by reoccupying six stations investigated during the GEOSECS expedition in 1977 and 1978. Observed differences are interpreted in terms of plausible changes in the environment and climate that have occurred in response to natural or anthropogenic processes. The depth profiles of major parameters such as dissolved oxygen, ΣCO 2 , major nutrients (silicates, nitrates, and phosphates), and radiocarbon in dissolved inorganic carbon were measured during the cruises between 1994 and 1998 along with temperature and salinity. Most stations in the Arabian Sea show an increase in salinity by ~0.2 to 0.3 salinity units in the top 400 m, whereas one station in the equatorial Indian Ocean showed a decrease in salinity by ~0.1 units, indicating a likely change in the evaporation-precipitation (E-P) balance. The ΣCO 2 increased by an average of 8 µM within the top 1200 m of the Arabian Sea. The depth profiles of nitrates and dissolved oxygen for the central Arabian Sea stations show significant variations, while only marginal changes are seen for silicates and phosphates relative to the GEOSECS data. The decrease in Δ 14 C of surface waters is due to the steady decrease in atmospheric 14 C concentration since GEOSECS, and the Δ 14 C increase in subsurface waters is attributed to the downward vertical diffusion of bomb 14 C interpreted in terms of atmosphere to ocean transfer and lateral advection of water masses.

show abstract

“…On the other hand, denitrification in anoxic water bodies has a large isotope effect of ∼ −25 ‰ (e.g., Brandes et al, 1998; Voss et al 2001). To date, little is known about the isotope fractionation of anammox in the water column, but it is generally assumed that anammox, just like denitrification, coincides with considerable, possibly similar, isotope fractionation (Naqvi et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

Nitrogen isotope dynamics and fractionation during sedimentary denitrification in Boknis Eck, Baltic Sea

Dähnke

Thamdrup

2013

Biogeosciences

View full text Add to dashboard Cite

The global marine nitrogen cycle is constrained by nitrogen fixation as a source of reactive nitrogen, and denitrification or anammox on the sink side. These processes with their respective isotope effects set the marine nitrate N-15-isotope value (delta N-15) to a relatively constant average of 5 parts per thousand. This value can be used to better assess the magnitude of these sources and sink terms, but the underlying assumption is that sedimentary denitrification and anammox, processes responsible for approximately one-third of global nitrogen removal, have little to no isotope effect on nitrate in the water column. We investigated the isotope fractionation in sediment incubations, measuring net denitrification and nitrogen and oxygen stable isotope fractionation in surface sediments from the coastal Baltic Sea (Boknis Eck, northern Germany), a site with seasonal hypoxia and dynamic nitrogen turnover. Sediment denitrification was fast, and regardless of current paradigms assuming little fractionation during sediment denitrification, we measured fractionation factors of 18.9 parts per thousand for nitrogen and 15.8 parts per thousand for oxygen in nitrate. While the input of nitrate to the water column remains speculative, these results challenge the current view of fractionation during sedimentary denitrification and imply that nitrogen budget calculations may need to consider this variability, as both preferential uptake of light nitrate and release of the remaining heavy fraction can significantly alter water column nitrate isotope values at the sediment-water interface

show abstract

Coastal versus open-ocean denitrification in the Arabian Sea

Cited by 159 publications

References 59 publications

Coastal hypoxia and sediment biogeochemistry

Coastal hypoxia and sediment biogeochemistry

Decadal Variations in Oceanic Properties of the Arabian Sea Water Column since Geosecs

Nitrogen isotope dynamics and fractionation during sedimentary denitrification in Boknis Eck, Baltic Sea

Contact Info

Product

Resources

About