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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

Ocean Acidification

Stable Isotopes

Radioactive Isotopes

Nutrients and Production

POC Export and Respiration

O2: Ventilation versus Respiration



Ocean Distributions – versus depth, versus ocean

Atlantic

Pacific

Points:

1. Uniform surface

concentrations

2. Surface depletion -

Deep enrichment

3. DIC < Alk

4. DDIC > DAlk

See Key et al (2004)

GBC

Q?


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)

mirrors O2.


Paleo Nutrient Distributions

Boyle and Keigwin (1982) Science

Data in benthic forams – North Atlantic


Controls on Ocean Distributions

A) Photosynthesis/Respiration

Organic matter (approximated as CH2O for this example) is produced and consumed as follows:

CH2O + O2 CO2 + H2O

Then:

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

Work Backwards

DAlk / DDIC ≈ 0.66

= 2/3

= 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

last

interglacial

Holocene

last glacial

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.

Assumptions:

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


δ environments13C in different reservoirs

E & H Fig. 5.6


Distillation of meteoric water environments – 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

to cloud.

Cloud gets lighter


Secular equilibrium environments

t1/2 daughter = 0.8 hr

t1/2 parent = 

parent

daughter

Activity

(log scale)

! Daughter grows

in with half life of

the daughter!

t1/2

time (hr)


222 environmentsRn Example Profile from

North Atlantic

Does Secular Equilibrium Apply?

t1/2222Rn << t1/2 226Ra

(3.8 d) (1600 yrs)

YES!

A226Ra = A222Rn

222Rn

226Ra

Why is 222Rn activity

less than 226Ra?


Particle and environments234Th Export

Coale & Bruland 1987

Vertical zonation of 234Th removal



The Redfield or "RKR" Equation environments (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

or

(CH2O)106(NH3)16(H3PO4)

Algal Protoplasm

The actual chemical species assimilated during this reaction are:

HCO3- NO3- PO43-

NO2-

NH4+


Food Web Cartoon environments

Follow the N!

Follow the C!

Follow the O2!

Fe plays a role!

DON

Euphotic Zone (~100m)

At steady state:

New NO3 =

O2 flux to atm =

PON (and DON) export

PON


Surface fingerprints ventilation

Atm. environments

Mixed layer

thermocline

ventilation

outcrop

Air-sea O2 flux

subtropics

ΔAOU

time

Surface fingerprints: ventilation

Atm.

Mixed layer

Decrease

ventilation

thermocline

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…


Surface fingerprints export

outcrop environments

Surface fingerprints: export

Atm.

Atm.

Mixed layer

Mixed layer

Increase

export flux

thermocline

thermocline

Export flux

Similar AOU anomalies may be caused by increased export flux, with very different signatures of O2/CO2 gas exchange.

subtropics

Air-sea O2 flux

ΔAOU

time


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