Biogeochemical tracers of the marine cyanobacterium Trichodesmium

Carpenter, Edward; Harvey, H. Rodger; Fry, Brian; Capone, Douglas G.

doi:10.1016/s0967-0637(96)00091-x

Cited by 311 publications

(242 citation statements)

References 32 publications

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“…This value, however, was lower than that reported by for North Pacific Station ALOHA samples of Trichodesmium thiebautii and T. erythraeum (B250 fg C mm À3 ) and Carpenter et al (1997) for field samples of T. thiebautii from the tropical North Atlantic (424 fg C m À3 ). While these higher values suggest that the chosen carbon content parameter could underestimate modeled Trichodesmium biomass, the chosen value from Tuit et al (2004) was more representative of the species, strain and size of the representative for Trichodesmium considered here and, more importantly, was cultured and measured under controlled conditions.…”

Section: Carbon Content a Volumetric Carbon Content Forcontrasting

confidence: 62%

Modeled contributions of three types of diazotrophs to nitrogen fixation at Station ALOHA

et al. 2007

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A diagnostic model based on biomass and growth was used to assess the relative contributions of filamentous nonheterocystous Trichodesmium and unicellular cyanobacteria, termed Groups A and B, to nitrogen fixation at the North Pacific Station ALOHA over a 2-year period. Average (and 95% confidence interval, CI) annual rates of modeled monthly values for Trichodesmium, Group B and Group A were 92 (52), 14 (4) and 12 (8) mmol N per m 2 per year, respectively. The fractional contribution to modeled instantaneous nitrogen fixation by each diazotroph fluctuated on interannual, seasonal and shorter time scales. Trichodesmium fixed substantially more nitrogen in year 1 (162) than year 2 (12). Group B fixed almost two times more nitrogen in year 1 (17) than year 2 (9). In contrast, Group A fixed two times more nitrogen in year 2 (16) than year 1 (8). When including uncertainties in our estimates using the bootstrap approach, the range of unicellular nitrogen fixation extended from 10% to 68% of the total annual rate of nitrogen fixation for all three diazotrophs. Furthermore, on a seasonal basis, the model demonstrated that unicellular diazotrophs fixed the majority (51%-97%) of nitrogen during winter and spring, whereas Trichodesmium dominated nitrogen fixation during summer and autumn (60%-96%). Sensitivity of the modeled rates to some parameters suggests that this unique attempt to quantify relative rates of nitrogen fixation by different diazotrophs may need to be reevaluated as additional information on cell size, variability in biomass and C:N, and growth characteristics of the different cyanobacterial diazotrophs become available.

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Section: Carbon Content a Volumetric Carbon Content Forcontrasting

confidence: 62%

Modeled contributions of three types of diazotrophs to nitrogen fixation at Station ALOHA

et al. 2007

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“…Presumably because 15 N-depleted N 2 gas is ultimately produced via preferential loss of 14 N, this process is responsible for enriching the oceanic fixed-N inventory in 15 N (δ 15 N ∼ 5 ‰ relative to atmospheric N 2 ; Sigman et al, 2009) as compared to sources (e.g. −1 to −2 ‰ for N 2 fixation; Carpenter et al, 1997).…”

Section: A Altabet Et Al: An Eddy-stimulated Hotspot For Fixed Nmentioning

confidence: 99%

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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“…The magnitude of isotopic fractionation for a process is given by the fractionation factor (ε), though as seen below there can be a substantial difference between an "effective" or observed ε, which can also be referred to as the apparent "isotope effect", and the fractionation factor inherent to the process. N 2 fixation has been widely observed to produce little isotopic fractionation (Minagawa and Wada, 1986;Macko et al, 1987;Carpenter et al, 1997;Delwiche and Steyn, 1970) such that combined N produced by this process has a δ 15 N value close to that of atmospheric N 2 (by definition δ 15 N=0‰). In the marine environment, N 2 fixers such as Trichodesmium typically have δ 15 N values between 0 and −2‰.…”

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

114

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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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Biogeochemical tracers of the marine cyanobacterium Trichodesmium

Cited by 311 publications

References 32 publications

Modeled contributions of three types of diazotrophs to nitrogen fixation at Station ALOHA

Modeled contributions of three types of diazotrophs to nitrogen fixation at Station ALOHA

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

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Biogeochemical tracers of the marine cyanobacterium Trichodesmium

Cited by 311 publications

References 32 publications

Modeled contributions of three types of diazotrophs to nitrogen fixation at Station ALOHA

Modeled contributions of three types of diazotrophs to nitrogen fixation at Station ALOHA

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

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