Climatically linked oscillations in Arabian Sea denitrification over the past 1 m.y.: Implications for the marine N cycle

Altabet, Mark A.; Murray, David; Prell, Warren L

doi:10.1029/1999pa900035

Cited by 144 publications

(189 citation statements)

References 50 publications

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“…In contrast, ocean-wide δ 15 NO − 3 averages are near 5 and 2 ‰, respectively (Sigman et al, 2009). At our other Peru OMZ stations, maximal δ 15 NO − 3 is typically ∼ 15 ‰ and values as high as 24 ‰ have been reported from other OMZ's (Altabet et al, 1999). Although the extrema are relatively shallow (100 m), these N-loss indicators at Station 7 extend broadly over the water column down to 400 m depth, corresponding to the layer of lowest O 2 concentration (Figs.…”

Section: An N-loss Hotspotsupporting

confidence: 54%

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

et al. 2012

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Abstract. Fixed nitrogen (N) loss to biogenic N 2 in intense oceanic O 2 minimum zones (OMZ) accounts for a large fraction of the global N sink and is an essential control on the ocean's N-budget. However, major uncertainties exist regarding microbial pathways as well as net impact on the magnitude of N-loss and the ocean's overall N-budget. Here we report the discovery of a N-loss hotspot in the Peru OMZ associated with a coastally trapped mesoscale eddy that is marked by an extreme N-deficit matched by biogenic N 2 production, high NO − 2 levels, and the highest isotope enrichments observed so far in OMZ's for the residual NO − 3 . High sea surface chlorophyll in seaward flowing streamers provides evidence for offshore eddy transport of highly productive, inshore water. Resulting pulses in the downward flux of particles likely stimulated heterotrophic dissimilatory NO − 3 reduction and subsequent production of biogenic N 2 within the OMZ. A shallower biogenic N 2 maximum within the oxycline is likely a feature advected by the eddy streamer from the shelf. Eddy-associated temporal-spatial heterogeneity of N-loss, mediated by a local succession of microbial processes, may explain inconsistencies observed among prior studies. Similar transient enhancements of N-loss likely occur within all other major OMZ's exerting a major influence on global ocean N and N isotope budgets.

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Section: An N-loss Hotspotsupporting

confidence: 54%

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

et al. 2012

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“…Average oceanic δ 15 N (∼average oceanic δ 15 NO − 3 ), though, is well below the one estimated from the known range in the ε den. inherent to the microbial process as estimated from bacterial cultures and/or from the relationship between NO − 3 removal and δ 15 NO − 3 (20 to 30‰; Wellman et al, 1968;Miyake and Wada, 1971;Cline and Kaplan, 1975;Brandes et al, 1998;Altabet et al, 1999;Voss et al, 2001) …”

Section: Controls On Average Oceanic δ 15 Nmentioning

confidence: 99%

Constraints on oceanic N balance/imbalance from sedimentary <sup>15</sup>N records

Altabet

2007

Biogeosciences

109

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Abstract. According to current best estimates, the modern ocean's N cycle is in severe deficit. N isotope budgeting provides an independent geochemical constraint in this regard as well as the only means for past reconstruction. Overall, it is the relative proportion of N 2 fixation consumed by water column denitrification that sets average oceanic δ 15 N under steady-state conditions. Several factors (conversion of organic N to N 2 , Rayleigh closed and open system effects) likely reduce the effective fractionation factor (ε) for water column denitrification to about half the inherent microbial value for ε den . If so, the average oceanic δ 15 N of ∼5‰ is consistent with a canonical contribution from water column denitrification of 50% of the source flux from N 2 fixation. If an imbalance in oceanic N sources and sinks changes this proportion then a transient in average oceanic δ 15 N would occur. Using a simple model, changing water column denitrification by ±30% or N 2 fixation by ±15% produces detectable (>1‰) changes in average oceanic δ 15 N over one residence time period or more with corresponding changes in oceanic N inventory. Changing sedimentary denitrification produces no change in δ 15 N but does change N inventory. Sediment δ 15 N records from sites thought to be sensitive to oceanic average δ 15 N all show no detectible change over the last 3 kyr or so implying a balanced marine N budget over the latest Holocene. A mismatch in time scales is the most likely meaningful interpretation of the apparent conflict with modern flux estimates. Decadal to centennial scale oscillations between net N deficit and net surplus may occur but on the N residence timescale of several thousand years, net balance is achieved in sum. However, sediment δ 15 N records from the literature covering the period since the last glacial maximum show excursions of up to several ‰ that are consistent with sustained N deficit during the deglaciation followed by readjustment and establishment of balance in the early Holocene.Correspondence to: M. A. Altabet (maltabet@umassd.edu) Since imbalance was sustained for one N residence time period or longer, excursions in ocean N inventory of 10 to 30% likely occurred. The climatic and oceanographic changes that occurred over this period evidently overcame, for a time, the capacity of ocean biogeochemistry to maintain N balance.

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“…Water column distributions of δ 15 N in NO − 3 and N 2 in the open Arabian Sea exhibit large changes brought about by the microbial consumption/production of these species (Brandes et al, 1998;Naqvi et al, 1998a, b;Altabet et al, 1999). Denitrification has been known to involve pronounced massdependent fractionation (preferential reduction of 14 NO − 3 over 15 NO − 3 ) in seawater (Cline and Kaplan, 1975), leading to an enrichment of 15 N in the NO − 3 pool and its depletion in the N 2 pool.…”

Section: Nitrogen Isotopic Fractionation During Denitrificationmentioning

confidence: 99%

Coastal versus open-ocean denitrification in the Arabian Sea

Naqvi

Naik²,

Pratihary³

et al. 2006

Biogeosciences

157

132

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Abstract. The Arabian Sea contains one of the three major open-ocean denitrification zones in the world. In addition, pelagic denitrification also occurs over the inner and midshelf off the west coast of India. The major differences between the two environments are highlighted using the available data. The perennial open-ocean system occupies two orders of magnitude larger volume than the seasonal coastal system, however, the latter offers more extreme conditions (greater nitrate consumption leading to complete anoxia). Unlike the open-ocean system, the coastal system seems to have undergone a change (i.e., it has intensified) over the past few decades presumably due to enhanced nutrient loading from land. The two systems also differ from each other with regard to the modes of nitrous oxide (N 2 O) production: In the open-ocean suboxic zone, an accumulation of secondary nitrite (NO

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Climatically linked oscillations in Arabian Sea denitrification over the past 1 m.y.: Implications for the marine N cycle

Cited by 144 publications

References 50 publications

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

Constraints on oceanic N balance/imbalance from sedimentary <sup>15</sup>N records

Coastal versus open-ocean denitrification in the Arabian Sea

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Climatically linked oscillations in Arabian Sea denitrification over the past 1 m.y.: Implications for the marine N cycle

Cited by 144 publications

References 50 publications

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

An eddy-stimulated hotspot for fixed nitrogen-loss from the Peru oxygen minimum zone

Constraints on oceanic N balance/imbalance from sedimentary &lt;sup&gt;15&lt;/sup&gt;N records

Coastal versus open-ocean denitrification in the Arabian Sea

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Constraints on oceanic N balance/imbalance from sedimentary <sup>15</sup>N records