nutrients; aerobic carbon production and consumption · 2. nutrients - chemical info 3. nutrient...
TRANSCRIPT
Nutrients; Aerobic Carbon
Production and Consumption
OCN 623 – Chemical Oceanography
5 February 2013
Reading: Libes, Chapters 8 - 10
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
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
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
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
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
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)
Nutrient Regeneration and AOU
(dissolved species)
Modified from Sarmiento & Gruber 2006
RESPIRATION
Nutrient Vertical Profiles
( µµµµM ) ( µµµµM ) ( µµµµM )
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:
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
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)
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
Why Are Nutrient Concs Different in Each Ocean?
Look at Ocean Net Flow at 4000 m
Dissolved Oxygen at 4000 m
Figure 10.3a
Dissolved Nitrate at 4000 m
Figure 10.3d
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
[Measured] = [Preformed] + [Oxidative]
PmeasuredPpreformed Poxid
[P]
Depth
O2, measured O2,preformed
AOU
[O2]
Depth
AOU ≡ - [O2, oxidative]
Apparent Oxygen Utilization at 4000 m
From Libes (2009) website
(mol/L)
(Solve for ∆C)
Use appropriate local
Redfield (C:P) ratio
Denitrification (nitrate reduction):
2NO3- + CH2O + 8H+ + 6e- → N2 + CO2 + 5H2O
AOU and Denitrification
Figure 10.6
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)
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.