OCN520 Fall 2009 Mid-Term #2 Review. Since Mid-Term #1 Ocean Carbonate Distributions Ocean Acidification Stable Isotopes Radioactive Isotopes Nutrients and Production POC Export and Respiration O2: Ventilation versus Respiration.
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OCN520 Fall 2009
Mid-Term #2 Review
Since Mid-Term #1
Ocean Carbonate Distributions
Nutrients and Production
POC Export and Respiration
O2: Ventilation versus Respiration
Sarmiento and Gruber (2002) Sinks for Anthropogenic Carbon
Physics Today August 2002 30-36
Ocean Distributions – versus depth, versus ocean
1. Uniform surface
2. Surface depletion -
3. DIC < Alk
4. DDIC > DAlk
See Key et al (2004)
Ocean Distributions of, DIC, Alk, O2 and PO4 versus Depth and Ocean
The main features are:
1. uniform surface values
2. increase with depth
3. Deep ocean values increase from
the Atlantic to the Pacific
4. DIC < Alk
DDIC > DAlk
5. Profile of pH is similar in
shape to O2.
6. Profile of PCO2 (not shown)
Paleo Nutrient Distributions
Boyle and Keigwin (1982) Science
Data in benthic forams – North Atlantic
Controls on Ocean Distributions
Organic matter (approximated as CH2O for this example) is produced and consumed as follows:
CH2O + O2 CO2 + H2O
CO2 + H2O H2CO3*
H2CO3* H+ + HCO3-
HCO3- H+ + CO32-
As CO2 is produced during respiration we should observe:
pH DIC Alk PCO2
The trends will be the opposite for photosynthesis.
B) CaCO3 dissolution/precipitation
CaCO3(s) Ca2+ + CO3 2-
Also written as:
CaCO3(s) + CO2 + H2O Ca2+ + 2 HCO3-
As CaCO3(s) dissolves, CO32- is added to solution. We should observe:
pH DIC Alk PCO2
DDIC/DAlk ≈ 1.5/1
DAlk / DDIC ≈ 0.66
= 2 mol Org C /
1 mol CaCO3
Emerson and Hedges Color Plate
Example: Estimation of temperature in ancient ocean environments
CaCO3(s) + H218O CaC18OO2 + H2O
The exchange of 18O between CaCO3 and H2O
The distribution is Temperature dependent
d18O of planktonic and benthic foraminifera
from piston core V28-238 (160ºE 1ºN)
Planktonic and Benthic differ due to differences
in water temperature where they grow.
1. Organism ppted CaCO3 in isotopic equilibrium
with dissolved CO32-
2. The δ18O of the original water is known
3. The δ18O of the shell has remained unchanged
Planktonic forams measure sea surface T
Benthic forams measure benthic T
δ13C in different reservoirs
E & H Fig. 5.6
Distillation of meteoric water – large kinetic fractionation occurs between
ocean and vapor. Then rain forming in clouds is in equilibrium with vapor
and is heavier that the vapor. Vapor becomes progressively lighter.
dD and d18O get lower with distance from source.
Water evaporation is a kinetic effect.
Vapor is lighter than liquid. At 20ºC the difference is 9‰ (see Raleigh plot).
The BP of H218O is higher than for H216O
Air masses transported to
higher latitudes where it is cooler.
water lost due to rain
raindrops are rich in 18O relative
Cloud gets lighter
t1/2 daughter = 0.8 hr
t1/2 parent =
! Daughter grows
in with half life of
222Rn Example Profile from
Does Secular Equilibrium Apply?
t1/2222Rn << t1/2 226Ra
(3.8 d) (1600 yrs)
A226Ra = A222Rn
Why is 222Rn activity
less than 226Ra?
Particle and 234Th Export
Coale & Bruland 1987
Vertical zonation of 234Th removal
Annual Mean Surface Nitrate
The Redfield or "RKR" Equation (A Model)
The mean elemental ratio of marine organic particles is given as:
P : N : C = 1 : 16 : 106
The average ocean photosynthesis (forward)
and aerobic ( O2 ) respiration (reverse) is written as:
106 CO2 + 16 HNO3 + H3PO4 + 122 H2O + trace elements (e.g. Fe)
light (h n)
( C106H263O110N16P ) + 138 O2
The actual chemical species assimilated during this reaction are:
Food Web Cartoon
Follow the N!
Follow the C!
Follow the O2!
Fe plays a role!
Euphotic Zone (~100m)
At steady state:
New NO3 =
O2 flux to atm =
PON (and DON) export
Air-sea O2 flux
An increase in AOU due to decreased ventilation will cause changes in air-sea fluxes of both O2 and CO2 coincident with the ventilation change…
Similar AOU anomalies may be caused by increased export flux, with very different signatures of O2/CO2 gas exchange.
Air-sea O2 flux