Oceans
and
anthropogenic CO2
By Monika Kopacz
EPS 131
(Atmospheric) sources of
anthropogenic CO2
Fossil fuels (oil, gas, coal)
Biomass burning (deforestation and others)
Farming
Land-use conversion
Production of cement
Total about 7 Pg (1015 g) per year
Atmospheric concentration
Figure adapted from Whitehouse Initiative on Global Climate Change
What do we want to learn?
Anthropogenic CO2 presence in the oceans:
sources, sinks, fluxes
Changes that have occurred so far, are
occurring right now and are anticipated in the
future
Should we be concerned or will Mother Nature
heal itself?
Box model of CO2 fluxes
* Right now: not in steady state
Figure adapted from Feely et al., 2001
CO2 air-sea fluxes
Trends:
– Equatorial Pacific: strong source of CO2 throughout
the year
– Subtropical oceans: upwelling and uptake depend on
water temperature
– High-latitude oceans: mostly deep water upwelling in
the winter and biological uptake during spring and
summer
 Dependencies: Along with pressure differences, fluxes
depend on gas transfer velocity (derived from other
tracers), solubility (function of temperature and salinity)
Facts about CO2 uptake
CO2 is more than twice soluble in cold water
than in warm water
Marine phytoplankton transforms CO2 to organic
carbon
(Vertical gradient of dissolved inorganic carbon: 20% due to solubility pump, 80%
due to biological pump)
Calculating CO2 uptake
 Using oceanic tracers such as carbon-14,
tritium and chlorofluorocarbons (CFC’s) to:
– directly measure fluxes into ocean and
circulation within
– simulate CO2 uptake and distribution with a
model (based on previously measured
quantities)
Separating anthropogenic CO2 from
natural
From: Gruber, N., 1998: “Anthropogenic CO2 in the Atlantic Ocean.” Global
Biogeochem. Cycles
C *  C  Ceq (S , T , Alk 0 )
fCO2  280  atm
1
 rC:O2 (O2  O )  ( Alk  Alk 0  rN :O2 (O2  O2sat ))
2
sat
2
C*  quasi  conservativetracer
rC:O2 , rN :O2  stochiometric ratios during photosynthesis
respiration, here assumed const.
Separating anthropogenic CO2 from
natural (contd.)
n
i
Cdiseq   f i Cdiseq
i 1
n
i
Cant  C *   f i Cdiseq
( )
i 1
  isopycnal surface (surface of const. density )
Anthropogenic
CO2
distribution
Gruber, N., 1998:
“Anthropogenic CO2 in
the Atlantic Ocean.”
Global Biogeochem.
Cycles
And “Global CO2
survey”
Ocean as a sink for CO2:
Solution to global warming?

Ocean as a sink for CO2:
Solution to global warming?
Limitations to ocean CO2
uptake: limited buffering
capability

Climate implications
Increased level of CO2 in surface water
 30% decrease in carbonate ion by midcentury  reduction of coral reef *
More anthropogenic co2  Global
warming  warming of the oceans 
Slower circulation  another ice age
* "Effect of calcium carbonate saturation state on the calcification rate
of an experimental coral reef“ by Takahashi
Ideas for restoring steady state
Sequestration
Collecting industrial CO2 and depositing it
in deep ocean (>1000m), much like it is
already being deposited in the earth
Conclusions:
Ocean carbon cycle is currently not in
steady state
Future climate change
Most realistic solution: decrease pollution