Nutrients; Aerobic Carbon Production and Consumption · 2. Nutrients - chemical info 3. Nutrient...
Transcript of Nutrients; Aerobic Carbon Production and Consumption · 2. Nutrients - chemical info 3. Nutrient...
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Nutrients; Aerobic Carbon
Production and Consumption
OCN 623 – Chemical Oceanography
5 February 2013
Reading: Libes, Chapters 8 - 10
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1. Overview - photosynthesis & respiration
2. Nutrients - chemical info
3. Nutrient regeneration - effect on vertical nutrient profiles
4. Nutrient trends across the oceans
5. Apparent oxygen utilization (AOU) in the ocean
6. Composition of particles driving AOU
Outline
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The next few lectures can be summarized by the
Redfield-Richards Equation:
CO2 + N + P + H20 Organic matter + O2
Redfield-Richards Equation
R
P
We will look first at the so-called “inorganic nutrients”:
N, P and Si
They are also called “biolimiting elements” -- Why?
1. Small reservoir size in oceans
2. Fast turnover time
3. Required for many kinds of biological activity
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Inorganic Nutrients
1. Physical Speciation (operational definitions!)
A. Dissolved -- pass thru a specified filter (e.g.,
0.45 µm pore size)
B. Particulate -- retained by a specified filter
C. Colloidal -- pass thru conventional filters, but are
not dissolved
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2. Chemical Speciation
A. Phosphorus
i. Dissolved Inorganic Phosphorus (DIP)
a. pH-dependent speciation of Orthophosphate:
H3PO4
H2PO4-
HPO42- (most important at sw pH)
PO43-
b. Polyphosphate – linked phosphatepolymers
ii. Dissolved Organic Phosphorus (DOP) – e.g., Phospholipids, ATP, ADP
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B. Nitrogen
Redox-dependent speciation of dissolved forms:
Species Oxid State
NO3- (nitrate) +V
NO2- (nitrite) +III
N2O (nitrous oxide) +I
N2 (dinitrogen) 0
NH4+ or NH3 -III
Organic-N -III (e.g., Urea H2N-CO-NH2)
NH4+ (ammonium ion)
NH3 (ammonia )
Dissolved Inorganic
Nitrogen (DIN)
Dissolved Organic
Nitrogen (DON)
Nitrate + nitrite
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C. Silica
Soluble forms:
H2SiO3 (95% of total dissolved silica – over a broad pH range)
HSiO3- (5% of total dissolved silica)
SiO32- (<<1% of total dissolved sillica)
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Nutrient Regeneration and AOU
(dissolved species)
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Modified from Sarmiento & Gruber 2006
RESPIRATION
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Nutrient Vertical Profiles
( µµµµM ) ( µµµµM ) ( µµµµM )
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Open-Ocean Nutrient Profiles Phosphorus
[P]
Depth
2000 m
several
µmol L-1
DIPDOP
High consumption of inorganic nutrients;
high production of organic nutrients
Slow release of inorganic nutrients
due to decomposition of falling
particles; slow utilization of organic
nutrients
Main processes controlling vertical distribution of nutrients:
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Open-Ocean Nutrient Profiles - Nitrogen
[N]
Depth
2000 m
tens of
µmol L-1
DON NO3-O2
NO2-
NH4+
Low-[O2] loss of NO3-
(denitrification)
Denitrification (nitrate reduction):
2NO3- + CH2O + 8H+ + 6e- → N2 + CO2 + 5H2O
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Nitrite - An Indicator of “Suboxia”
Typically, nitrate and nitrite are measured together (reported as
their sum). However, nitrite maxima can be observed:
Subsurface
maximum
(presumably due
to suboxic zone
in/on particles
O2-minimum zone
maximum
NH4+ profiles look similar (two maxima)
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Oxygen – Nutrient DiagramsRedfield-Richards Equation in Action – NW Pacific
Actually, NO3- + NO2
-.
For simplicity, ignore
NH4+
Redfield: AOU/∆P = 138/1 = 138
AOU/∆N = 138/16 = 9
Slope ≅ -12 µM O2
µM NO3Slope ≅ -120 µM O2
µM PO4
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Why Are Nutrient Concs Different in Each Ocean?
Look at Ocean Net Flow at 4000 m
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Dissolved Oxygen at 4000 m
Figure 10.3a
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Dissolved Nitrate at 4000 m
Figure 10.3d
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Measurement & Use of AOU
[Measured]
[Preformed]
NEquator
For biogeochemically regenerated elements in seawater, the Redfield-
Richards Equation indicates:
[Measured] = [Preformed] + [Oxidative]
[Oxidative] ≡ Change in conc due to organic matter oxidation
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[Measured] = [Preformed] + [Oxidative]
PmeasuredPpreformed Poxid
[P]
Depth
O2, measured O2,preformed
AOU
[O2]
Depth
AOU ≡ - [O2, oxidative]
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Apparent Oxygen Utilization at 4000 m
From Libes (2009) website
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(mol/L)
(Solve for ∆C)
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Use appropriate local
Redfield (C:P) ratio
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Denitrification (nitrate reduction):
2NO3- + CH2O + 8H+ + 6e- → N2 + CO2 + 5H2O
AOU and Denitrification
Figure 10.6
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Particle Composition
C : N
8.4
14
7.8
11.8
5.2
Spatial
differences
Temporal
differences
(highest C:N due to lack of nutrients)
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Homework Due: Tues, 12 Feb 2013
1. Using online HOT data (http://hahana.soest.hawaii.edu/hot/hot-
dogs/bextraction.html) for Station ALOHA, calculate the C:N:P ratio of
sinking particulate organic matter in the top 800 m of the North Pacific
Gyre in March 2006. Are the ratios you calculate reasonable?
2. Compute the AOU of the 4000-m deep water at Station ALOHA. How
do your results compare with the results shown in class?
For both questions: Be sure to show all of your calculations, and explain
exactly what data you used.