OS13B - 0536
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OS13B - 0536 Modeling the Distribution and 15 N of Nitrogen Gas and Nitrogen Species in the Black Sea S. K. Konovalov 1 , C. A. Fuchsman 2 and J.W. Murray 2 1. Marine Hydrophysical Institute, Kapitanskaya St. 2a, Sevastopol 99000 Ukraine; and 2. School of Oceanography, University of Washington, Box 355351 Seattle WA 98195-5351 Abstract Distributions of NO 3 - , NO 2 - , NH 4 + , N 2 and PON and their 15 N values in the Black Sea were measured in order to unravel the cycling of nitrogen, especially the role of anammox (NO 2 - + NH 4 + = N 2 ). We have constructed a steady state coupled physical-biogeochemical model of the water column. The physical model is a vertical transport model that includes simulation of entrainment and intrusions from the Bosporus Plume. The biogeochemical model includes mass balance equations for 14 N and 15 N. Comparison of observations and model results show: 1. The chemical distributions can be fit by adjusting the respective reaction rate constants 2. This steady state model can not simultaneously fit the concentrations and stable isotope data without including some process that removes heavy nitrogen 1. Cruises and Samples Data for this study was collected during recent cruises in the Black Sea: •R/V Bilim September 2000 •R/V Knorr May 2001 •R/V Knorr April 2003 (Track and Station Locations shown in Fig. 1) The cruise web sites with data are located at: http://oceanweb.ocean.washington.edu/cruises/Knorr2001 http://oceanweb.ocean.washington.edu/cruises/Knorr2003 Fig. 1 10. Model #2 – Vertical Zonation of Processes: Reactions with S , HS - We allowed the reaction between NO 3 - and NH 4 + to occur in the region of the NO 3 - gradient (Fig. 11). The origin of the NH 4 + is from regenerated PON and its concentration remains low because it is rapidly utilized. Light 14 N-NO 3 - would be preferentially used to make light N 2 . The heavy 15 N-NO 3 - that remains diffuses downward to be reduced by S to NH 4 + in the lower layer (thus making heavy NH 4 + ). Fig. 11 Fig. 12 Conclusions: •This model correctly simulates 15 N-N 2 and 15 N-NO 3 - but not 15 N-NH 4 + and 15 N-PON which are too heavy (Fig. 12). • The 15 N-NH 4 + maximum is too shallow. 11. Model #3 – Vertical Zonation of Processes: Scavenging by MnO 2 Heavy NH 4 + is removed, possibly by preferential adsorption of NH 4 + by MnO 2 . Light NH 4 + is left to react with NO 2 - to make light N 2 . The adsorbed (and heavy NH 4 + ) is released back to the water when the MnO 2 is reduced in the anoxic layer (Fig. 13). 15% of the upward flux of NH 4 + is removed to the anoxic zone and the isotopic fractionation () required is -20‰. Fig. 13 Fig. 14 Conclusion: •The simulation results in distributions close to those observed (Fig. 14). • Light N 2 is made. • 15 N-NH 4 + reaches a maximum at the right depth, then decreases to minimum values that help to produce light N 2 •The 15N-PON is similar to those observed. S tatio n s o f th e 2 0 0 3 K N O R R V o y ag e #1 7 2 , L eg# 7 , 8 , 9 (C ) 2000. R em ote Sensing D ep artm ent, M HI S tation s: 2 0 o n L eg # 7 ( ) 4 8 o n L eg # 8 ( ) 1 4 o n L eg # 9 ( ) R ed Y ellow B lack 2. Nitrogen Species Fig. 2 shows an example of distributions of NO 3 - , NO 2 - and NH 4 + •NO 3 - increases to a maximum at t = 15.6 then decreases to 0 at t = 15.95 •NO 2 - has a small maximum centered at t = 15.8 •NH 4 + starts to increase at t = 15.95 The N 2 /Ar data from 2000, 2001 and 2003 are plotted as the ratio of sample/saturation versus density in Fig. 3. •The water column is usually supersaturated with N2 with a maximum centered at t ≈ 16.0. •Supersaturation in the shallow layers results from upward flux of N 2 from the suboxic zone. •There is significant interannual variability. •The concentrations can be reset to atmospheric saturation after intense storms. Exam ple ofN O 3 - , N O 2 - and N H 4 + forR /V Knorr 2003 C enter ofw estern G yre Suboxic Zone 0 10 20 30 40 NH 4 + 1 6 .8 1 6 .4 16 1 5 .6 1 5 .2 1 4 .8 1 4 .4 14 1 3 .6 S igm a T h eta 0 1 2 3 4 NO 3 - M 0 0.1 0.2 0.3 0.4 NO 2 - B la ck S ea C en tra l G yre N H 4+ N O 3- N O 2- Leg 8 Station 30 Fig. 2 0.98 1 .00 1.02 1 .04 S am p le/S atu ra tion N 2 /Ar 17 16 15 14 13 12 Sigm a-T heta 2 0 0 0 M 10L41 K n o rr 2 0 0 1 S tatio n 2 K n o rr 2 0 0 1 S tatio n 14 K n o rr 2 0 0 3 C en tral G yre K n o rr 2 0 0 3 S tatio n 20 10 0 % satu ratio n T h e co re o f th e C IL F reshly in ten siv ely v en tilated N 2 /A r solubility ratio vsdensity D atefrom Bilim 2000, K norr2001 and Knorr2003 CIL Bilim Atm Eq Fig. 3 4. Nitrogen Isotope Distributions (Fig. 5) 15 N-NO 3 - increases to a maximum of ≈ 18‰ in the suboxic zone then decreases with depth. Above the suboxic zone values are about 8‰ which is higher than average NO 3 - in seawater ( 15 N-NO 3 - ≈ 4.5 to 6‰) (Fig. 6) 15 N-NH 4 + is very low in the deepwater (≈ 2‰) and increase to a maximum of 7‰ at the base of the suboxic zone, then decrease slightly. (Fig. 7) 15 N-N 2 in the suboxic zone maximum is extremely light ( 15 N-N 2 ≈0.0‰) compared to SW in equilibrium with the atmosphere ( 15 N-N 2 ≈ 0.7‰) and to the other forms of N that are sources for N 2 ( 15 N-NO 3 - ≥ 8‰; 15 N-NH 4 + ≥ 8‰; 1 5N -PON = 2.7 to 9.0‰). 4 8 12 16 20 1 6 .5 16 1 5 .5 15 1 4 .5 14 S igm a T h eta 15 N-NO 3 - N ear B o sp oru s K n orr 2003 C en tra l G yre K n orr 2003 C en tra l G yre K n orr 2001 N ear B o sp oru s K n orr 2001 Fig. 5 SW avg 15 N-NO 3 - versusdensity suboxic zone Fig. 6 15 N -NH 4 + versusdepth 15 N -PO N versusdensity 0 .0 0 .4 0 .8 1 .2 15 N-N 2 17 16 15 14 13 12 Sigm a-T heta B ilim 20 00 M 10L41 K n o rr 2 001 S tatio n 2 K n o rr 2 001 S tatio n 14 K n o rr 2 003 C en tral G yre K n o rr 2 003 S tatio n 20 A n equ libriu m v alu e T h e co re o f th e C IL 15 N-N 2 versusdensity Atm ospheric equilibrium D uring denitrification N 2 becom eslightand NO 3 becom esheavy Suboxic Zone: D epleted values Strong Tem peralVariability CIL Enriched surface values Fig. 7 suboxic 5. Physical Biogeochemical Model We utilized a 1.5-D physical transport model (Fig. 8) that includes simulation of the Bosporus Plume and assumes isopycnal distribution of all properties (Samodurov and Ivanov, 1998; Ivanov and Samodurov, 2001). The resulting 1-D vertical balance equations can be written as: k = vertical diffusion coefficient; = diffusive flux, w = vertical velocity and wC = the advective flux occurring due to displacement of the Black Sea deep waters with the waters from the Bosporus plume, R = rate of biogeochemical production-consumption, Cb = concentration in the “Bosporus plume” C = concentration in the ambient water. The model has been verified using 137 Cs data from 1986 to 2003. 6. Biogeochemical Transformations Transformations of O 2 , PON, DON, NO 3 - , NO 2 - , N 2 , NH 4 + , H 2 S, S 0 and dissolved and particulate Mn(II) and Mn(IV) and Fe(II) and Fe(III) are included in the model. Dissolved organic N is split into labile (DON(L)) and refractory (DON(R) fractions. Particulate organic nitrogen is split into the fraction sinking from the euphotic zone (PON) and the fraction that is bacterially produced (PON(B)). Equations that parameterize biogeochemical transformations are written to follow either “chemical” or Michaelis-Menten kinetics. Thus, oxidation of sulfide by oxygen is parameterized as a chemical process. Microbiologically mediated processes, like oxidation of PON by oxygen are parameterized by Michaelis-Menten kinetics. The specific (k) and maximum () rates were taken from publications, when available, and adjusted to fit the data. All values of k and were assumed constant. 8. Simulation of 15 N distributions To simulate 14 N/ 15 N fractionation, all reactions were written in terms of both 14 N and 15 N. The rate of 15 N transformations is proportional to the rate of 14 N transformations, to the ratio of [ 15 N]/[ 14 N], and fractionation factors 1000 + 1, where is the isotopic enrichment factor. Thus, the rate of oxidation of 15 N-PON is Published data on fractionation () or isotopic enrichment () factors are limited. It is often difficult to identify, if the published values are specific for individual reactions or processes that may involve a number of reactions. Still, the published values for the isotopic enrichment factors () generally vary from 0 to 40‰. The enrichment factors () required to fit the data are given below: •nitrate (NO 3 - ) reduction, for all reductants (e.g. CH 2 O, S) = 25 - 30‰ •nitrite (NO 2 - ) reduction and oxidation = 10 - 15‰ •reactions of particulate organic nitrogen to NH 4 + = 2 -5‰ •ammonium (NH 4 + ) consumption or oxidation (e.g. Anammox) = 0 to a few ‰ C F lux k wC z b C C w k w R C C z z z z C k z 2 2 R k HS O 2 2 2 1/2 PON O PON t O O -0.02 -0.01 0 .00 V ertical v elo city (w ), m /d ay 17.0 16.5 16.0 15.5 15.0 14.5 S igm a-t 0 .0 0 .4 0 .8 1 .2 1 .6 V e rtic a l d iffu s io n (k b ), m 2 /d ay Fig. 8 PhysicalM odel 9. Model #1 Simulation The model was tuned to simulate 15 N profiles in the oxic and anoxic layers (Fig. 10). The initial conditions derived from the real observations are shown as dashed lines. Simulations are shown for 90 days, 1 year and 13 years. Variations in () for denitrification and anammox did not change the final result. Complete consumption of NO 3 - (NO 2 - ) and NH 4 + does not result in any fractionation. Steady State profiles are easily obtained for 15 N-NO 3 - and 15 N-NH 4 + but 15 N-N 2 decreases initially then increases rapidly. At steady state (after several decades?) the 15 N-N 2 must equal 8‰, much higher than the observed values of 0.0‰. Conclusions (Doesn’t explain all data): •Can’t simultaneously model 15 N of N 2 , NO 3 - and NH 4 + . •Can’t make light 15 N-N 2 by total consumption of NO 3 - and NH 4 + . 15 14 15 2 15 14 2 2 1/2 1 N PON N PON N PON O N PON t t O O N PON 0 1 2 3 N v alu e 1 7.0 1 6.5 1 6.0 1 5.5 1 5.0 1 4.5 Sigm a-t 0 20 40 60 N v alu e 0 20 40 60 80 N v alu e 1 7.0 1 6.5 1 6.0 1 5.5 1 5.0 1 4.5 1 7.0 1 6.5 1 6.0 1 5.5 1 5.0 1 4.5 15 N -N 2 -gas In 0 d ays. In 90 days. In 1 y ear. In 13 years. 15 N-NH 4 + In 0 d a y s. In 9 0 days. In 1 year. In 1 3 years. N-NO 3 - In 0 days. In 9 0 d ays. In 1 year. In 1 3 y ears. V ersio n 2.4.14.2. Fig. 10 Conclusion Steady State model runs are not successful at simulating the observed 15 N distributions in the suboxic zone of the Black Sea unless we assume a process to remove heavy 15 N-NH 4 + . Comparison of model and data suggest three possibilities: 1. The 15 N data we are using are not representative. 2. There is a process to transport heavy NH 4 + from the suboxic zone to the anoxic zone. 3. The 15 N profiles are not at steady state. 0 .2 0 .4 0 .6 0 .8 1 1 .2 15 N -N 2 , ‰ 1 7 1 6 1 5 Sigm a-t M o d el # 2 D ata M odel 0 4 8 12 16 15 N -P O N , ‰ 1 7 1 6 1 5 0 2 4 6 8 1 0 15 N-NH 4 , ‰ 1 7 1 6 1 5 Sigm a-t 0 20 40 60 80 15 N-NO 3 , ‰ 1 7 1 6 1 5 0 100 200 300 O xy gen (O 2 ) & S u lfid e (H 2 S) , M 17.0 16.0 15.0 Sigm a-t 0 .0 4 .0 8 .0 1 2 .0 N itrate (N O 3 - ) & N 2 e x . g as , M 0 .0 0 .1 0 .2 0 .3 0 .4 N itrite (N O 2 - ) & S u lfu r (S 0 ) , M 0 10 20 30 40 50 A m m onium , M O 2 NO 3 - NH 4 + H 2 S NO 2 S 0 N 2 NO 2 - + N H 4 + NH 4 + M n (II) + O 2 (N H 4 ) x M n(IV ) (N H 4 ) x M n (IV ) + H 2 S N H 4 + M n (II) 0 .2 0 .4 0 .6 0 .8 1 1 .2 15 N -N 2 , ‰ 17 16 15 S igm a-t M od el # 3 D ata M odel -4 0 4 8 1 2 15 N -P O N , ‰ 1 7 1 6 1 5 0 2 4 6 8 15 N-NH 4 , ‰ 17 16 15 S igm a-t 0 20 40 60 80 15 N-NO 3 , ‰ 1 7 1 6 1 5 Acknowledgement This work is a part of the next projects: NSF MCB 0132101; NSF OCE #0081118; NATO CLG #9791211 0 1 2 3 4 NO 3 - 120 80 40 0 A verage D ep th (m ) 0 5 10 15 20 25 NH 4 + 0 2 4 6 8 10 N 2 E xcess C en tra l S tatio n s N O 3 - u M N H 4+ uM N 2 E xcess u M N 2 E xcess u M A verage V erticalN itrogen Balance in/outofsuboxic zone in C entralG yre G radient(m olN m -4 ) NO 3 - 0.13 NH 4 + 0.17 TotalN in = 0.30 N 2up 0.21 N 2dow n 0.08 TotalN out= 0.59 There istw ice asm uch flux ofN outasN 2 than flux ofN in asN O 3 - and N H 4 + . The difference probably com esfrom rem ineralization of PO N Fig. 4 3. N itrogen Balance 7. D ata and M odelSimulations W e have found thatPO N (~50% ) and D O N (~40% )are the m ain sourcesofN to the box included in thism odel( = 14.5 to 17.2) Them ain N sinksare the upw ard fluxesofN 2 (~70% )and NO 3 (~30% ) 0 100 200 300 O x y g en (O 2 ) & S u lfid e (H 2 S) , M 17.0 16.0 15.0 Sigm a-t 0 .0 4 .0 8 .0 1 2 .0 N itrate (N O 3 - ) & N 2 ex . g as, M 0 .0 0 .1 0 .2 0 .3 0 .4 N itrite (N O 2 - ) & S u lfu r (S 0 ) , M 0 10 20 30 40 50 A m m onium , M O 2 NO 3 - NH 4 + H 2 S NO 2 Suboxic zone S 0 N 2 Fig. 9 Them odelcan describe allthe data. 0 100 200 300 O x y gen (O 2 ) & S ulfid e (H 2 S) , M 1 7.0 1 6.0 1 5.0 Sigm a-t 0 .0 4 .0 8 .0 1 2 .0 N itrate (N O 3 - ) & N 2 ex . g as, M 0 .0 0 .1 0 .2 0 .3 0 .4 N itrite (N O 2 - ) & S u lfur (S 0 ) , M 0 10 20 30 40 50 A m m onium , M O 2 NO 3 - NH 4 + H 2 S NO 2 S 0 N 2 NO 3 - (NO 2 - ) + NH 4 + NO 3 - (NO 2 - ) + S 0 (H 2 S)
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OS13B - 0536 Modeling the Distribution and 15 N of Nitrogen Gas and Nitrogen Species in the Black Sea S. K. Konovalov 1 , C. A. Fuchsman 2 and J.W. Murray 2 - PowerPoint PPT Presentation
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OS13B - 0536 Modeling the Distribution and 15N of Nitrogen Gas and Nitrogen Species in the Black Sea
S. K. Konovalov1, C. A. Fuchsman2 and J.W. Murray2
1. Marine Hydrophysical Institute, Kapitanskaya St. 2a, Sevastopol 99000 Ukraine; and 2. School of Oceanography, University of Washington, Box 355351 Seattle WA 98195-5351
OS13B - 0536 Modeling the Distribution and 15N of Nitrogen Gas and Nitrogen Species in the Black Sea
S. K. Konovalov1, C. A. Fuchsman2 and J.W. Murray2
1. Marine Hydrophysical Institute, Kapitanskaya St. 2a, Sevastopol 99000 Ukraine; and 2. School of Oceanography, University of Washington, Box 355351 Seattle WA 98195-5351
AbstractDistributions of NO3
-, NO2-, NH4
+, N2 and PON and their 15N values in the Black Sea were measured in order to unravel the cycling of nitrogen, especially the role of anammox (NO2
- + NH4+ = N2). We have constructed a steady state
coupled physical-biogeochemical model of the water column. The physical model is a vertical transport model that includes simulation of entrainment and intrusions from the Bosporus Plume. The biogeochemical model includes mass balance equations for 14N and 15N. Comparison of observations and model results show:1. The chemical distributions can be fit by adjusting the respective reaction rate constants2. This steady state model can not simultaneously fit the concentrations and stable isotope data without including some process that removes heavy nitrogen
1. Cruises and SamplesData for this study was collected during recent cruises in the Black Sea:•R/V Bilim September 2000•R/V Knorr May 2001•R/V Knorr April 2003 (Track and Station Locations shown in Fig. 1)
The cruise web sites with data are located at:http://oceanweb.ocean.washington.edu/cruises/Knorr2001http://oceanweb.ocean.washington.edu/cruises/Knorr2003
Fig. 1
10. Model #2 – Vertical Zonation of Processes:Reactions with S, HS-
We allowed the reaction between NO3- and NH4
+ to occur in the region of the NO3-
gradient (Fig. 11). The origin of the NH4
+ is from regenerated PON and its concentration remains low because it is rapidly utilized. Light 14N-NO3
- would be preferentially used to make light N2. The heavy 15N-NO3
- that remains diffuses downward to be reduced by S to NH4+ in
the lower layer (thus making heavy NH4+).
Fig. 11
Fig. 12
Conclusions:•This model correctly simulates 15N-N2 and 15N-NO3
- but not 15N-NH4
+ and 15N-PON which are too heavy (Fig. 12). •The 15N-NH4
+ maximum is too shallow.
11. Model #3 – Vertical Zonation of Processes:Scavenging by MnO2
Heavy NH4+ is removed, possibly by preferential adsorption of NH4
+ by MnO2. Light NH4
+ is left to react with NO2- to make light N2. The adsorbed (and heavy
NH4+) is released back to the water when the MnO2 is reduced in the anoxic
layer (Fig. 13). 15% of the upward flux of NH4+ is removed to the anoxic zone
and the isotopic fractionation () required is -20‰.
Fig. 13
Fig. 14
Conclusion:•The simulation results in distributions close to those observed (Fig. 14). •Light N2 is made.• 15N-NH4
+ reaches a maximum at the right depth, then decreases to minimum values that help to produce light N2
•The 15N-PON is similar to those observed.
S ta tio n s o f th e 2 0 0 3 K N O R R V o y ag e # 1 7 2 , L eg # 7 , 8 , 9
(C ) 2 0 0 0 . R em o te S en s in g D ep artm en t, M H I
S ta tio n s:2 0 o n L eg # 7 ( )4 8 o n L eg # 8 ( )1 4 o n L eg # 9 ( )
R edY e llo w
B lack
2. Nitrogen SpeciesFig. 2 shows an example of distributions of NO3
-, NO2- and NH4
+
•NO3- increases to a maximum at t = 15.6 then decreases to 0 at t = 15.95
•NO2- has a small maximum centered at t = 15.8
•NH4+ starts to increase at t = 15.95
The N2/Ar data from 2000, 2001 and 2003 are plotted as the ratio of sample/saturation versus density in Fig. 3. •The water column is usually supersaturated with N2 with a maximum centered at t ≈ 16.0. •Supersaturation in the shallow layers results from upward flux of N2 from the suboxic zone.•There is significant interannual variability. •The concentrations can be reset to atmospheric saturation after intense storms.
Example of NO3-, NO2
- and NH4+ for R/V Knorr 2003
Center of western Gyre
Suboxic Zone
0 10 20 30 40
N H 4 +
16 .8
16 .4
16
15 .6
15 .2
14 .8
14 .4
14
13 .6
Sig
ma
Th
eta
0 1 2 3 4
N O 3 - M
0 0 .1 0 .2 0 .3 0 .4
N O 2 - B la ck S ea C en tra l G y re
N H 4 +N O 3 -N O 2 -
Leg 8 Station 30
Fig. 2
0 .9 8 1 .0 0 1 .0 2 1 .0 4S a m p le /S a tu ra tio n N 2/A r
1 7
1 6
1 5
1 4
1 3
1 2
Sig
ma-
Th
eta
B ilu m 2 0 0 0 M 1 0 L 4 1K n o rr 2 0 0 1 S ta tio n 2K n o rr 2 0 0 1 S ta tio n 1 4K n o rr 2 0 0 3 C en tra l G y reK n o rr 2 0 0 3 S ta tio n 2 01 0 0 % sa tu ra tio nT h e co re o f th e C IL
F re sh lyin ten s iv e lyv en tila ted
N2/Ar solubility ratio vs densityDate from Bilim 2000, Knorr 2001 and Knorr 2003
CIL
Bilim
Atm Eq
Fig. 3
4. Nitrogen Isotope Distributions(Fig. 5) 15N-NO3
- increases to a maximum of ≈ 18‰ in the suboxic zone then decreases with depth. Above the suboxic zone values are about 8‰ which is higher than average NO3
- in seawater (15N-NO3- ≈ 4.5 to 6‰)
(Fig. 6) 15N-NH4+ is very low in the deepwater (≈ 2‰) and increase to a
maximum of 7‰ at the base of the suboxic zone, then decrease slightly.(Fig. 7) 15N-N2 in the suboxic zone maximum is extremely light (15N-N2≈0.0‰) compared to SW in equilibrium with the atmosphere (15N-N2 ≈ 0.7‰) and to the other forms of N that are sources for N2 (15N-NO3
- ≥ 8‰; 15N-NH4
+ ≥ 8‰; 15N-PON = 2.7 to 9.0‰).
4 8 12 16 2 0
16 .5
16
15 .5
15
14 .5
14
Sig
ma
Th
eta
1 5 N -N O 3 -
N ea r B o sp oru s K n o rr 2 0 0 3C en tra l G y re K n o rr 2 0 03C en tra l G y re K n o rr 2 0 01N ea r B o sp oru s K n o rr 2 0 0 1
Fig. 5
SWavg
15N-NO3- versus density
suboxic zone
Fig. 6
15N-NH4+ versus depth15N-PON versus density
0 .0 0 .4 0 .8 1 .21 5N -N 2
1 7
1 6
1 5
1 4
1 3
1 2
Sigm
a-T
heta
B ilim 2 0 0 0 M 1 0 L 4 1K n o rr 2 0 0 1 S ta tio n 2K n o rr 2 0 0 1 S ta tio n 1 4K n o rr 2 0 0 3 C e n tra l G y reK n o rr 2 0 0 3 S ta tio n 2 0A n eq u lib riu m v a lu eT h e co re o f th e C IL
15N-N2 versus density
Atmosphericequilibrium
During denitrification N2 becomes light and NO3 becomes heavySuboxic
Zone: Depleted values
Strong Temperal Variability
CIL
Enriched surfacevalues
Fig. 7
suboxic
5. Physical Biogeochemical ModelWe utilized a 1.5-D physical transport model (Fig. 8) that includes simulation of the Bosporus Plume and assumes isopycnal distribution of all properties (Samodurov and Ivanov, 1998; Ivanov and Samodurov, 2001). The resulting 1-D vertical balance equations can be written as:
k = vertical diffusion coefficient; = diffusive flux, w = vertical velocity and wC = the advective flux occurring due to displacement of the Black Sea deep waters with the waters from the Bosporus plume, R = rate of biogeochemical production-consumption, Cb = concentration in the “Bosporus plume” C = concentration in the ambient water.
The model has been verified using 137Cs data from 1986 to 2003.
6. Biogeochemical TransformationsTransformations of O2, PON, DON, NO3
-, NO2-, N2, NH4
+, H2S, S0 and dissolved and particulate Mn(II) and Mn(IV) and Fe(II) and Fe(III) are included in the model. Dissolved organic N is split into labile (DON(L)) and refractory (DON(R) fractions. Particulate organic nitrogen is split into the fraction sinking from the euphotic zone (PON) and the fraction that is bacterially produced (PON(B)). Equations that parameterize biogeochemical transformations are written to follow either “chemical” or Michaelis-Menten kinetics.
Thus, oxidation of sulfide by oxygen is parameterized as a chemical process.
Microbiologically mediated processes, like oxidation of PON by oxygen are parameterized by Michaelis-Menten kinetics.
The specific (k) and maximum () rates were taken from publications, when available, and adjusted to fit the data. All values of k and were assumed constant.
8. Simulation of 15N distributionsTo simulate 14N/15N fractionation, all reactions were written in terms of both 14N and 15N. The rate of 15N transformations is proportional to the rate of 14N transformations, to the ratio of [15N]/[14N], and fractionation factors 1000 + 1,where is the isotopic enrichment factor.
Thus, the rate of oxidation of 15N-PON is
Published data on fractionation () or isotopic enrichment () factors are limited.
It is often difficult to identify, if the published values are specific for individual reactions or processes that may involve a number of reactions. Still, the published values for the isotopic enrichment factors () generally vary from 0 to 40‰.
The enrichment factors () required to fit the data are given below:
•nitrate (NO3-) reduction, for all reductants (e.g. CH2O, S) = 25 - 30‰
•nitrite (NO2-) reduction and oxidation = 10 - 15‰
•reactions of particulate organic nitrogen to NH4+ = 2 -5‰
•ammonium (NH4+) consumption or oxidation (e.g. Anammox) = 0 to a few ‰
CFlux k wC
z
b
C C wk w R C C
z z z z
C
kz
2 2R k H S O
2
2 21/ 2
PON OPON
t O O
-0 .0 2 -0 .0 1 0 .0 0V e rtic a l v e lo c ity (w ), m /d a y
1 7 .0
1 6 .5
1 6 .0
1 5 .5
1 5 .0
1 4 .5
Sigm
a-t
0 .0 0 .4 0 .8 1 .2 1 .6V e rtic a l d iffu s io n (k b), m 2/d a y
Fig. 8 Physical Model
9. Model #1 SimulationThe model was tuned to simulate 15N profiles in the oxic and anoxic layers (Fig. 10). The initial conditions derived from the real observations are shown as dashed lines. Simulations are shown for 90 days, 1 year and 13 years. Variations in () for denitrification and anammox did not change the final result. Complete consumption of NO3
- (NO2-) and NH4
+ does not result in any fractionation.
Steady State profiles are easily obtained for 15N-NO3- and 15N-NH4
+
but 15N-N2 decreases initially then increases rapidly. At steady state (after several decades?) the 15N-N2 must equal 8‰, much higher than the observed values of 0.0‰.
Conclusions (Doesn’t explain all data): •Can’t simultaneously model 15N of N2, NO3
- and NH4+.
•Can’t make light 15N-N2 by total consumption of NO3-
and NH4+.
15 14 15
215
142 21/ 2
1N PON N PON N PON ON PON
t t O ON PON
0 1 2 3N v a lu e
1 7 .0
1 6 .5
1 6 .0
1 5 .5
1 5 .0
1 4 .5
Sig
ma-
t
0 2 0 4 0 6 0N v a lu e
0 2 0 4 0 6 0 8 0N v a lu e
1 7 .0
1 6 .5
1 6 .0
1 5 .5
1 5 .0
1 4 .5
1 7 .0
1 6 .5
1 6 .0
1 5 .5
1 5 .0
1 4 .5
1 5N -N 2-g a sIn 0 d ay s .In 9 0 d a y s .In 1 y ea r .In 1 3 y e a rs .
1 5N -N H 4+
In 0 d a y s .In 9 0 d a y s .In 1 y e a r .In 1 3 y e a rs .
N -N O 3-
In 0 d ay s .In 9 0 d a y s .In 1 y ea r .In 1 3 y e a rs .
V ers io n 2 .4 .1 4 .2 .Fig. 10
Conclusion
Steady State model runs are not successful at simulating the observed 15N distributions in the suboxic zone of the Black Sea unless we assume a process to remove heavy 15N-NH4
+.
Comparison of model and data suggest three possibilities:1. The 15N data we are using are not representative.2. There is a process to transport heavy NH4
+ from the suboxic zone to the anoxic zone. 3. The 15N profiles are not at steady state.
0 .2 0 .4 0 .6 0 .8 1 1 .2
1 5N -N 2 , ‰
1 7
1 6
1 5
Sig
ma-
t M o d e l # 2D ataM o d e l
0 4 8 1 2 1 6
1 5N -P O N , ‰
1 7
1 6
1 5
0 2 4 6 8 1 0
1 5N -N H 4 , ‰
1 7
1 6
1 5
Sigm
a-t
0 2 0 4 0 6 0 8 0
1 5N -N O 3 , ‰
1 7
1 6
1 5
0 1 0 0 2 0 0 3 0 0O x y g en (O 2) & S u lfid e (H 2S ), M
1 7 .0
1 6 .0
1 5 .0
Sig
ma-
t
0 .0 4 .0 8 .0 1 2 .0N itra te (N O 3
-) & N 2 ex . g a s , M
0 .0 0 .1 0 .2 0 .3 0 .4
N itrite (N O 2-) & S u lfu r (S 0) , M
0 1 0 2 0 3 0 4 0 5 0
A m m o n iu m , M
O 2
N O 3-
N H 4+
H 2S
N O 2
S 0
N 2
N O 2- + N H 4
+
N H 4 + M n (II) + O 2 (N H 4) xM n (IV )
(N H 4) xM n (IV ) + H 2S N H 4 + M n (I I)
0 .2 0 .4 0 .6 0 .8 1 1 .2
1 5N -N 2 , ‰
1 7
1 6
1 5
Sigm
a-t M o d e l # 3
D ataM o d e l
- 4 0 4 8 1 2
1 5N -P O N , ‰
1 7
1 6
1 5
0 2 4 6 8
1 5N -N H 4 , ‰
1 7
1 6
1 5
Sigm
a-t
0 2 0 4 0 6 0 8 0
1 5N -N O 3 , ‰
1 7
1 6
1 5
AcknowledgementThis work is a part of the next projects: NSF MCB 0132101; NSF OCE #0081118; NATO CLG #9791211
0 1 2 3 4
N O 3-
12 0
80
40
0
Ave
rage
Dep
th (
m)
0 5 10 15 20 25N H 4
+
0 2 4 6 8 10
N 2 E x cess
C en tra l S ta tio n sN O 3 - u MN H 4 + u MN 2 E xcess u MN 2 E xcess u M
Average Vertical Nitrogen Balance in/out of suboxic zone in Central Gyre
Gradient (mol N m-4)NO3
- 0.13NH4
+ 0.17Total N in = 0.30
N2up 0.21N2down 0.08Total N out = 0.59
There is twice as much flux of N out as N2 than flux of N in as NO3
- and NH4+. The difference probably
comes from remineralization of PONFig. 4
3. Nitrogen Balance
7. Data and Model Simulations
We have found that PON (~50%) and DON (~40%) are the main sources of N to the box included in this model ( = 14.5 to 17.2)
The main N sinks are the upward fluxes of N2 (~70%) and NO3 (~30%)
0 1 0 0 2 0 0 3 0 0O x y g en (O 2) & S u lfid e (H 2S ), M
1 7 .0
1 6 .0
1 5 .0
Sig
ma-
t
0 .0 4 .0 8 .0 1 2 .0N itra te (N O 3
-) & N 2 ex . g a s , M
0 .0 0 .1 0 .2 0 .3 0 .4
N itrite (N O 2-) & S u lfu r (S 0) , M
0 1 0 2 0 3 0 4 0 5 0
A m m o n iu m , M
O 2
N O 3-
N H 4+
H 2S
N O 2S u b o x icz o n e
S 0
N 2
Fig. 9
The model can describe all the data.
0 1 0 0 2 0 0 3 0 0O x y g en (O 2) & S u lfid e (H 2S ), M
1 7 .0
1 6 .0
1 5 .0
Sig
ma-
t
0 .0 4 .0 8 .0 1 2 .0N itra te (N O 3
-) & N 2 ex . g a s , M
0 .0 0 .1 0 .2 0 .3 0 .4
N itrite (N O 2-) & S u lfu r (S 0) , M
0 1 0 2 0 3 0 4 0 5 0
A m m o n iu m , M
O 2
N O 3-
N H 4+
H 2S
N O 2
S 0
N 2
N O 3-(N O 2
-) + N H 4+
N O 3-(N O 2
-) + S 0(H 2S )
