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Transcript of Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern...
![Page 1: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/1.jpg)
Nitrate isotopes as a constraint on the ocean's fixed N budget
Angela Knapp, University of Southern California
Peter DiFiore, Princeton University
Curtis Deutsch, UCLA
Fred Lipschultz, BIOS
Sargasso Sea nitrate N isotopes, GCM experiments,and Atlantic N2 fixation
Daniel Sigman, Princeton University
![Page 2: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/2.jpg)
Talk outline
• Nitrate N isotopes from a Sargasso Sea transect: estimate of “recently” fixed nitrate in Sargasso Sea water column
• MOM3 simulations forced with various Atlantic N2 fixation fields predict recently fixed nitrate in the Sargasso Sea
• Uncertainties: impact of other processes on the N isotopes of nitrate
• Nitrate O isotopes: correct nitrate N isotopes for nitrate assimilation?
![Page 3: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/3.jpg)
N and O isotopes
N : 14N 99.6337% 15N 0.3663%
O : 16O 99.7630% 17O 0.0375% 18O 0.1995%
15N (vs. atm. N2) = (((15N/14N)sample/(15N/14N)air) - 1)*1000‰
18O (vs. VSMOW) = (((18O/16O)sample/(18O/16O)VSMOW) - 1)*1000‰
![Page 4: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/4.jpg)
Nitrate reduction:14NO3
- ⇒ 14NO2-
15NO3- → 15NO2
-
15ε = ((14k/15k) - 1)*1000‰
N16O3- ⇒ N16O2
-
N18O16O2- → N18O16O-
18ε = ((16k/18k) - 1)*1000‰
15ε ~ 15N 3NO - - 15N 3NO - consumed (inst.)18ε ~ 18O 3NO - - 18O 3NO - consumed (inst.)
Kinetic isotope effect
14k
15k
16k
18k
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MS 172 Figure 5
0
5
10
15
20
0 0.5 1 1.5 2
[NO3-] (factor of initial value)
newly fixed Nadded
15N~ -2-0‰
water columndenitrification
ε ∼ 20-30‰
sedimentarydenitrification
ε ∼ 0‰
nitrateuptake
ε ∼ 5‰
NO3- 15N
(‰ . )vs air
Complementary constraints from[NO3
-], N* and 15N
N*
![Page 6: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/6.jpg)
Dep
thBATS Validation Cruise 32 (October, 2002):Stations sampled for nitrate and DON isotopes
IncreasingN2 fixation?~2 yr vent. age increase
![Page 7: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/7.jpg)
Nitrate data
1000
800
600
400
200
0
depth (m)
2520151050
[NO3-] (µM)
1086420
15N (‰ vs. air)
108642
δ18
O (‰ vs. VSMOW)
28.0
27.5
27.0
26.5
26.0
25.5
25.0
sigma theta
BATS, 32º N
32º N, 76º W
30º N 29º N 28º N 27º N 26º N 25º N 24º N 23º N 22º N 20º N 19º N cruise
avg
a b c
d e fN2 fix.?
NO3-
assim.?
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Nitrate 15N in the Sargasso Sea water column
15N of nitrate (‰ vs. air)
[NO3-] (µM)
•No evidence of southward N2 fixation increase or a southward accumulation of newly fixed nitrate in the thermocline•Basis for average Sargasso Sea profile
![Page 9: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/9.jpg)
1200
1000
800
600
400
200
0
depth (m)
543210-1-2[NO3
-] from N2 fix (µM)
654321NO
3
- 15 (‰ . )N vs air
1.00.80.60.40.20.0-0.2 fraction of NO3
- from N2 fix
a b c
Estimating ‘recently’ fixed nitrate
(15N - 15Nimported)
(15Nnew - 15Nimported)f =
(5.3‰ - 15N)
6.3‰=
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From a recently fixed nitrate pool to aN2 fixation rate
Atlantic
Atlantic
S N
S N
“Plan A”
“Plan B”
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Deutsch et al. 2007 Atlantic field; 45°N-S; 27.85 Tg N yr-1
Gruber and Sarmiento 1997; 45°N-0°; 28.1 Tg N yr-1
GS ‘97 N. Atl. rate extended to 45°N-45°S; 56.1 Tg N yr-1
MOM4 simulations of the recently fixed nitrate field
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Recently fixed NO3-
(mol N m-2)
Total NO3-
(mol N m-2)
Recent/
Total
data
This study 0.81 3.03 0.27
models
Deutsch 0.77 3.48 0.22
GS I 1.24 3.99 0.31
GS II 1.97 4.80 0.41
data
This study 1.02 16.78 0.06
models
Deutsch 2.30 18.19 0.13
GS I 3.26 19.20 0.17
GS II 5.63 21.71 0.26
0-60
0 m
0-12
00 m
Column inventories
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N2 fixation
distribution
Recently fixed NO3- in
North AtlanticRecently fixed NO3
- in South Atlantic
GS I
(North Atlantic only) 63.1% 36.9%
GS II’
(North + South Atlantic) 54.0% 46.0%
GS III’
(South Atlantic only) 44.1% 55.9%
Interhemispheric exchange of recently fixed nitrate
Hemispheric asymmetry:North Atlantic tends to collect recently fixed nitrate
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15N enrichment in the nitrate entering the Atlantic?Southern Ocean data
Sigman et al. 1999
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Uniform nitrate 18O below 300 min this region
15N of nitrate (‰ vs. air)
“18O-corrected” 15N of nitrate
18O of nitrate (‰ vs. SMOW)
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Low latitude N cycling and the loss of nitrate O isotope signals
The O isotopes may not record the N and O isotope enrichmentof imported nitrate.
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High nitrate 18Oin the
shallow Sargasso Sea
15N of nitrate (‰ vs. air)
“18O-corrected” 15N of nitrate
18O of nitrate (‰ vs. SMOW) 18ε/15ε = 1.0
![Page 18: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/18.jpg)
Decoupling of nitrate N and O isotopes by
simultaneous nitrate assimilation and nitrification
Monterey Bay: Wankel et al., 2007
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Conclusions• Nitrate N isotopes indicate 2 µM or more of recently fixed nitrate
in the Sargasso Sea thermocline.
• Coherent spatial trends are not apparent in the region studied. This suggests that gradients in N2 fixation are too weak to imprint nitrate N isotope gradients on the circulating thermocline. We did not sample an adequately wide range in ventilation age to follow the ‘isopycnal’ approach used by Gruber and Sarmiento (1997) for N*.
• We essentially follow a diapycnal approach by our use of MOM3 with high latitude sponge walls. In this context, the isotope data suggest a relatively low rate for N2 fixation in the Atlantic (30 Tg N yr-1 or less, a la Deutsch et al. 1997).
• Uncertainties include the possible impacts of nitrate assimilation inside and outside the Atlantic on the 15N of nitrate in the interior. The nitrate O isotopes were discussed in this context.
• GEOTRACES should provide the opportunity to do this for real.
![Page 20: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/20.jpg)
The End
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What if N2 fixation aboundswhere denitrification is prevalent?
Deutsch et al. 2004
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Low nitrate 15N in the Sargasso Sea thermocline:Consistent with N2 fixation input
Knapp et al. 2005
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Conclusions
• Nitrate N and O isotopes have fundamentally different behavior, making them powerful complements.
• Coupled N and O isotope systematics:– Newly produced nitrate: 18O ~ 0‰ vs. SMOW– Nitrate assimilation: 18ε = 15ε (~ 5-10‰)– Denitrification: 18ε = 15ε (20-30‰)
• Application to the eastern North Pacific margin:– 18O:15N anomaly ((15,18) min.) in the thermocline– Interpretations:
• addition of low-15N N from N2 fixation• an active NO3
-/NO2- redox cycle in or near the suboxic
zone
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15N enrichment in the nitrate entering the Atlantic?Southern Ocean data
DiFiore et al. 2006
SAMW ~ 7.2‰
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Algal nitrate assimilation: 18ε~15ε
Granger et al., 2004
Progressive nitrate consumption 18ε/15ε = 1.0
![Page 26: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/26.jpg)
The cycle and budget of N in the ocean
NO3- N2
N2Norg (NO3-)
![Page 27: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/27.jpg)
MS 172 Figure 5
0
5
10
15
20
0 0.5 1 1.5 2
[NO3-] (factor of initial value)
newly fixed Nadded
15N~ -2-0‰
water columndenitrification
ε ∼ 20-30‰
sedimentarydenitrification
ε ∼ 0‰
nitrateuptake
ε ∼ 5‰
NO3- 15N
(‰ . )vs air
Complementary constraints from[NO3
-], N* and 15N
![Page 28: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/28.jpg)
N isotopes in the whole ocean N budget
Brandes and Devol 2002
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80
60
40
20
0∆
18
O of NO
3
-
(
‰
vs. starting value)
806040200
∆ δ
15
N of NO
3
-
( ‰ vs. starting value)
δ
18
O: δ
15
N = 1.0
δ
18
O: δ
15
N = 0.8
Ochrobacter sp. (n = 6)
P. denitrificans sw (n = 4)
P. denitrificans fw (n = 2)
P. aureofaciens sw (n = 4)
P. aureofaciens fw (n = 1)
P. stutzeri (n = 4)
25
20
15
10
5
0∆
18
O of NO
3
-
(
‰
vs. starting value)
2520151050
∆ δ
15
N of NO
3
-
( ‰ vs. starting value)
1:1
δ
18
O: δ
15
N = 0.6
freshwater
seawater
R. sphaeroides
Denitritification: 18ε~15ε
Granger et al., in review 18ε/15ε = 0.95
![Page 30: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/30.jpg)
Decoupling of nitrate N and O isotopes by
simultaneous nitrate assimilation and nitrification
f = 0.5 ; e = 5‰NO3
- NO3- NO3
-
5‰ 0‰ e = 5‰ 8.5‰ 3.5‰ 5‰ 1.75‰ N H2O 1.5‰ 0‰
NH4+ NO3
-
1.5‰ 1.5‰ 0‰Nitracline
Monterey Bay: Wankel et al., 2007
![Page 31: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/31.jpg)
The nitrate O isotopes are usefulbecause of
what they don’t record
Nitrogen atoms in marine nitrate:
nitrification nitrate assimilation
Norg
NO3-
N2 fixation
denitrification
nitrification nitrate assimilation
NO3- denitrification
Oxygen atoms in marine nitrate:
a. b.
![Page 32: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/32.jpg)
The nitrate O isotopes are usefulbecause of
what they don’t record
Nitrogen atoms in marine nitrate:
nitrification nitrate assimilation
Norg
NO3-
N2 fixation
denitrification
nitrification nitrate assimilation
NO3- denitrification
Oxygen atoms in marine nitrate:
15e = 25‰
15e = 5‰
d15 = -1N ‰
15e = 17‰
d18 = 0O ‰ 18e = 15e
18e = 15e
a. b.
![Page 33: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/33.jpg)
Summary of systematics
Nitrogen atoms in marine nitrate:
nitrification nitrate assimilation
Norg
NO3-
N2 fixation
denitrification
nitrification nitrate assimilation
NO3- denitrification
Oxygen atoms in marine nitrate:
15e = 25‰
15e = 5‰
d15 = -1N ‰
15e = 17‰
d18 = 0O ‰ 18e = 15e
18e = 15e
a. b.
![Page 34: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/34.jpg)
N2 fixation
distribution
Recently fixed NO3- in
North AtlanticRecently fixed NO3
- in South Atlantic
GS I
(North Atlantic only) 65.7% 34.3%
GS II
(North + South Atlantic) 55.0% 45.0%
GS III
(South Atlantic only) 47.1% 52.9%
Hemispheric asymmetry
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Stations on the Baja
California margin
Contour every 750 m[O2]<5 µM
van Geen cruise, Nov. 1999
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All stations
Red = N (~Point Conception)Blue = S (~S tip of Baja)
12840
18
O of NO3- (‰ . )vs VSMOW
1400
1200
1000
800
600
400
200
0
16128415
N of NO3- (‰ . )vs air
30020010000 2 ( )µM
-30 -20 -10 0*N ( )µM
50403020100
[NO3-] ( )µM
[NO3-]
18O
15
N
a
b
c
d
e
*N [O2 ]
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12
10
8
6
4
2
0
16141210864
15 N of NO3- (‰ . )vs air
1:1
12
10
8
6
4
2
0
1614121086415 N of NO3
- (‰ . )vs air
SBB
12
10
8
6
4
2
0
1614121086415 N of NO3
- (‰ . )vs air
a cb
12
10
8
6
4
2
0
161412108615 N of NO3
- (‰ . )vs air deep ENP
1:1
Deviations from 1:1 variation in
nitrate 18O and 15N
Southern Baja stations All stations
(15,18) = 15N - 18O - 5.5‰
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Figure 3
a.
c.
b.
d.
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Nitrate isotopes near southern tip of Baja
-3 -2 -1 0 1(15,18) (=
15 - ( N
18 + 5.5‰))O
1600
1400
1200
1000
800
600
400
200
0-10 0*N ( )µM
50403020100[NO3
-] ( )µM
161284015
N or18
O of NO3- (‰ . )vs air or SMOW
[NO3-]
18
O 15
N
ab
c
d
e
*N
(15,18)
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Cause of the (15,18) minimum?
Nitrogen atoms in marine nitrate:
nitrification nitrate assimilation
Norg
NO3-
N2 fixation
denitrification
nitrification nitrate assimilation
NO3- denitrification
Oxygen atoms in marine nitrate:
15e = 25‰
15e = 5‰
d15 = -1N ‰
15e = 17‰
d18 = 0O ‰ 18e = 15e
18e = 15e
a. b.
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Cause of the (15,18) minimum?
Nitrogen atoms in marine nitrate:
nitrification nitrate assimilation
Norg
NO3-
N2 fixation
denitrification
nitrification nitrate assimilation
NO3- denitrification
Oxygen atoms in marine nitrate:
15e = 25‰
15e = 5‰
d15 = -1N ‰
15e = 17‰
d18 = 0O ‰ 18e = 15e
18e = 15e
a. b.
NO3- NO2
- …
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Quantifying putative processes from the (15,18) anomaly
For 200-800 m:N2 fix. ~ 0.65*denit.N* minimum:-12 µM -24 µM
At 200 m:NO2
- ox. > 0.7*NO2- red.
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Bering Sea shelf:O/N isotope decoupling by in situ nitrification18
16
14
12
10
8
6
4
18
O of NO
3-
(‰ . )vs VSMOW
1412108
15 N of NO3- (‰ . )vs air
25
20
15
10
5
0
NO3 - (μ)M
B. BrunelleM.B.: Wankel et al.
![Page 44: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/44.jpg)
Polar Antarcticnitrate isotope fractionation
P. Difiore
![Page 45: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/45.jpg)
Southern Baja station results compared to stations further North
-20 -15 -10 -5 0N* (µM)
1400
1200
1000
800
600
400
200
0
50403020100
[NO3
-] (µM)
-3 -2 -1 0 1(15,18) (=
15 - ( N
18 + 5.5‰))O
1284018
O of NO3- (‰ . )vs VSMOW
16128415
N of NO3- (‰ . )vs air
[NO3-]
18
O
15
N
a
b
c
d
e
*N(15,18)
![Page 46: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/46.jpg)
HOT Station ALOHA
Is the open tropical Pacificthe source of the (15,18) minimum ?
5000
4000
3000
2000
1000
0
depth (m)
642015 N or18 O of NO3
- (‰ . )vs air or SMOW
40200[NO3
-] ( )µM
-3 -2 -1 0 1*N ( )µM
-3 -2 -1 0(15,18) (= 15 - ( N 18 + 5.5‰))O
a b c d e
15 N18 O
![Page 47: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/47.jpg)
ENP vs. HOT
-10 0N* (µM)
28.0
27.5
27.0
26.5
26.0
25.5
25.0
24.5
σθ
( kg m
-3)
16128415
N of NO3- (‰ . )vs air
108642018
O of NO3- (‰ . )vs VSMOW
-3 -2 -1 0 1(15,18) (=
15 - ( N
18 + 5.5‰))O
50403020100[NO3
-] ( )µM
[NO3-]
18
O
15
N
a
b
c
d
e
*N Baja S tip
HOT
(15,18)
![Page 48: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/48.jpg)
N2 fixation = 0.65*denitrification
[NO3-]B - [NO3
-]M
Nitrate 15N
Nitrate (15,18)
observations(200-800 m)
![Page 49: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/49.jpg)
NO2- oxidation > 0.7*NO2
- reduction at 200 m
Assumptions: (1) 15εNiO = 15εNiR, (2) 18ε/15εNiO = 18ε/15εNiR
![Page 50: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/50.jpg)
12
10
8
6
4
2
0
16141210864
15 N of NO3- (‰ vσ. air)
1:1
12
10
8
6
4
2
0
1614121086415 N of NO3
- (‰ vσ. air)
SBB
a cb
12
10
8
6
4
2
0
161412108615 N of NO3
- (‰ . )vs air deep ENP
1:1
Why no anomaly in the
Santa Barbara Basin?
![Page 51: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/51.jpg)
Where there is very little dissolved [O2], …
Deutsch et al. 2004
![Page 52: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/52.jpg)
J. Granger, unpub.
Marine denitrification: 18ε~15ε
50
40
30
20
10
0
-5.5 -4 -3 -2 -1 0([ln NO3
-]/[NO3-initial])
a15ε = 5‰
15ε = 30‰
5040302010018 O of NO3
- (‰ . )vs initial
50
40
30
20
10
0 b
15ε:18ε = 1 0.9 , 1.1
.Ps aureofaciens ( =3)n . P denitrificans ( =1)n . Ps stutzeri ( =2)n .Ochrobacter sp ( =1)n
Progressive nitrate consumption
![Page 53: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/53.jpg)
Model quantification of putative N2 fixation
-1.5
-1.0
-0.5
0.0
0.5
(15,18)
1.00.80.60.40.20.0N2 / ( / )fixation denitrification F D
=0S =S M
15
10
5
0
18
OB
(‰ . )vs SMOW
20151050 15N
B (‰ . )vs air
(15,18)= -1.3‰= 0‰
Increasing D
Increasing F
, =0S, =S M
![Page 54: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/54.jpg)
NO2- oxidation ~ 0.85*NO2
- reduction at 200 m
Assumptions: (1) complete NO2-/H2O O exchange; (2) 15εNiO = 15εNiR
-3
-2
-1
0
(15,18) (‰)
1.51.00.50.0NO2
- / oxidation NO2
- reduction
(200-800 )observed m
(200 )observed m
![Page 55: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/55.jpg)
Oceanic N Budget
N2 Fixation
Rivers
Atmosphere
Inputs Total
Benthic Denit.
W.C. Denit.
Sedimentation
Outputs Total
Imbalance
Residence time
Flux (TgN/yr)Codispoti and
Christensen 1985
Gruber and
Sarmiento 1997
Brandes and
Devol 2002
25
25
25
75
60
60
21
141
125
42
15
182
85
80
15
180
-66 +2
110-330
25
25
160-380
200-280
75
25
300-380
0 or -200
> 5000 yr ~ 3500 yr < 2000 yr
inpu
tsou
tput
s
N2Norg (NO3-)
NO3- N2
![Page 56: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/56.jpg)
NO3- NO3
-
NO2-
NO3-
NO3-
NO2- NH4
+
Organic nitrogen
VACUOLE
CHLOROPLAST
a
b
c d
Figure 4 -- Granger et al.
![Page 57: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/57.jpg)
80
60
40
20
0
-6-5-4-3-2-10
ln ([NO3
-
]/[NO3
-
initial])
15
ε = 25 ‰
15
ε = 5 ‰
b
80
60
40
20
0
Δδ
15
N of NO
3-
(
‰
vs. starting value)
1101001000
8 6 4 2 0
ln ([NO3
-
])
a
Ochrobacter sp. (n = 6)
P. denitrificans sw (n = 4)
P. denitrificans fw (n = 2)
P. aureofaciens sw (n = 4)
P. aureofaciens fw (n = 1)
P. stutzeri (n = 4)
![Page 58: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/58.jpg)
Open tropical Pacific:source of the minimum ??
12
10
8
6
4
2
0
18
O of NO
3-
(‰ . )vs VSMOW
1614121086415 N of NO3
- (‰ . )vs air
ENP HOT
![Page 59: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/59.jpg)
Quantifying putative NO3-/NO2
- cycling fromthe (15,18) anomaly
![Page 60: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/60.jpg)
Figure 9
![Page 61: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/61.jpg)
Internal ocean cycle(algal assimilation/remineralization)
dominates variations in nitrate concentration
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
WOCE data; ODV: R. Schlitzer
![Page 62: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/62.jpg)
Mechanism for isotope fractionationduring algal nitrate assimilation
Needoba et al., 2004
Granger et al., 2004
![Page 63: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/63.jpg)
Isotope fractionation during denitrification:two nitrate reduction enzymes
NO3- NO3
-
NO2-
NO3-
a bc
d
NAR
NAPNO2-
e
periplasm
cytosol
bacterial wall
bacterial membrane18ε~15ε
18ε ~ 0.6*15ε
![Page 64: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/64.jpg)
Variation in the isotope fractionation of nitrate assimilation: balanced vs. unbalanced growth
NO3- NO3
- NO2- e~ 0-5‰
e~ 20‰( )NaR
ambient internal
NADH NAD+
![Page 65: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/65.jpg)
The imprint of the N budget is overwhelmed by the N cycle
Trick: Remove the ‘cycle’ component using PO43-
![Page 66: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/66.jpg)
-40
-40
-30
-30
-20
-20
-10
-10
0
0
N*
1400
1200
1000
800
600
400
200
0
d
16
16
14
14
12
12
10
10
8
8
6
6
15 (‰ . )N of nitrate vs air
1400
1200
1000
800
600
400
200
0
e
SBB versus open ETNP
![Page 67: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/67.jpg)
Low NO3- 15N in the Sargasso Sea thermocline:
Consistent with N2 fixation source for excess NO3-
Knapp et al., 2005
![Page 68: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/68.jpg)
Granger et al., 2004
![Page 69: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/69.jpg)
Needoba et al. in press
light-limited
Comparing the 15N/14N of internal pool nitrate and medium nitratein a cultured diatom (T. weiss.)
Iso
top
e e
ffect
of n
itra
te a
ssim
ilatio
n
light/dark
limited byiron or T
![Page 70: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/70.jpg)
Biogeochemical conditionsalong the ENP margin
40
40
30
30
20
20
10
10
0
0
[NO3-] (µM)
SBB Spring '99 SBB Fall '95 SBB Fall '99 SBB Aug. '77 Liu [1979] SBB Aug. '78 Liu [1979] near SBB 30-33 °N 28-30 °N 25-27 °N 22-25 °N
b
5.0
5.0
4.0
4.0
3.0
3.0
2.0
2.0
1.0
1.0
0.0
0.0
[PO43-
] (µM)c
3002001000
[O2] (µM)
1400
1200
1000
800
600
400
200
0
3002001000
a
![Page 71: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/71.jpg)
![Page 72: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/72.jpg)
4000
3000
2000
1000
0
depth (m)
1.00.0
[O2]/[O 2]sat
43210-1
18 (‰ . )O of nitrate vs VSMOW
0.80.40.0[PO4
3-] regenerated/[PO 4
3-] total
8642015 (‰ . )N of nitrate vs air
M. Lehmann and A. Knapp, unpublished
![Page 73: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/73.jpg)
1200
1000
800
600
400
200
0
depth (m)
2520151050
[NO3-] (µM)
8642015 (‰ . )N vs air
8642018 (‰ . )O vs VSMOW
-6 -4 -2 0 215 - (N 18 + 5.5‰)O
30°N 29°N 28°N 27°N 26°N 25°N 24°N 23°N 22°N 20°N 19°N
A. Knapp, unpublished
Sargasso Sea
![Page 74: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/74.jpg)
Stabilizing feedbacks in the ocean N budget
![Page 75: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/75.jpg)
Quantifying putative N2 fixation fromthe (15,18) anomaly
![Page 76: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/76.jpg)
Model quantification of putative N2 fixation
-2.5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.00.80.60.40.20.0 / ( / )fixation input denitrification output F D
=0:S 200 fit m 200-800 fit m
= :S M 200 fit m 200-800 fit m
15
10
5
0
20151050 15NB (‰ . )vs air
15 - (N 18 + 5.5‰)O= -1.3‰, -2.5‰
Increasing D
Increasing F
![Page 77: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/77.jpg)
J. Granger, unpublished
Marine denitrification: 18ε~15ε
![Page 78: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/78.jpg)
J. Granger, unpublished
Marine denitrification: 18ε~15ε
![Page 79: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/79.jpg)
Nitrification produces NO3- with 18O ~ 0‰
1200
1000
800
600
400
200
0
depth (m)
2520151050
[NO3-] (µM)
8642015 (‰ . )N vs air
8642018 (‰ . )O vs VSMOW
-6 -4 -2 0 215 - (N 18 + 5.5‰)O
30°N 29°N 28°N 27°N 26°N 25°N 24°N 23°N 22°N 20°N 19°N
Subtropical North Atlantic, Bermuda -- Puerto Rico; A. Knapp, unpub.
All nitrateremineralized
![Page 80: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/80.jpg)
1200
1000
800
600
400
200
0
depth (m)
543210-1-2[NO3
-] from N2 fix (µM)
654321NO
3
- 15 (‰ . )N vs air
1.00.80.60.40.20.0-0.2 fraction of NO3
- from N2 fix
a b c
Figure 5
a. b. c.
![Page 81: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/81.jpg)
Nitrate 15N and 18O in the Sargasso Sea
water column
18O of nitrate (‰ vs. SMOW)
![Page 82: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/82.jpg)
Nitrate 15N and 18O in the Sargasso Sea
water column
18Osal of nitrate (‰ vs. SMOW)
![Page 83: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/83.jpg)
Nitrate 15N and 18O in the Sargasso Sea
water column
15N of nitrate (‰ vs. air) corrected for assimilation with 18O
![Page 84: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/84.jpg)
Nitrate 15N and 18O in the Sargasso Sea
water column
∆(15,18)sal of nitrate
![Page 85: Nitrate isotopes as a constraint on the ocean's fixed N budget Angela Knapp, University of Southern California Peter DiFiore, Princeton University Curtis.](https://reader038.fdocuments.in/reader038/viewer/2022110320/56649cc15503460f94988f8a/html5/thumbnails/85.jpg)
1200
1000
800
600
400
200
0
depth (m)
543210-1-2[NO3
-] from N2 fix (µM)
654321NO
3
- 15 (‰ . )N vs air
1.00.80.60.40.20.0-0.2 fraction of NO3
- from N2 fix
a b c