SOES6002 - Toby Tyrrell
The Ocean Carbon Cycle
Average composition of phytoplankton.
•Quantitative description of natural cycle.
•Behaviour over the next 100 years.
OA402 - Modelling in Environmental and Earth System Science (Toby Tyrrell)
Approx. 50% of dry weight of marine organic matter is carbon
Two Pumps
Schematic of Global Natural C Cycle
(Land & Ocean)
Reservoirs: Gt C,
Fluxes Gt C yr-1
From: Climate Change 1994, (IPCC Report), 1995, U. Cambridge Press.
Oceanic Carbon Cycle and the future
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SOES6002 - Toby Tyrrell
Quantitative Ocean C Cycle
Important Ocean Calcifiers
coral reefs
coralline algae
coccolithophores
foraminifera
pteropods
In:Climate Change 2001, IPCC Report, U. Cambridge Press, 2001.
Dissolution of calcium carbonate in
deep waters.
PIC more durable
than POC…
until the lysocline.
Stores of carbon on Earth surface
(ignoring rocks).
35
Deep Ocean
2.3
Surface Ocean
1.9
Land biota and soils
0.6
Atmosphere
000’s Gtonnes C
Large majority of Earth surface carbon is in the deep ocean.
From: M.E.Q. Pilson “An Introduction to the Chemistry of the Sea”, Prentice Hall, 1998
Oceanic Carbon Cycle and the future
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SOES6002 - Toby Tyrrell
Stores of carbon in the Ocean.
from “An Introduction to Marine Biogeochemistry” S.M. Libes, Wiley Press, 1992.
(POC total is different from Biota total because most POC is detritus;
PIC reservoir is small).
Large majority of deep ocean carbon is in DIC.
Distribution of DIC among Different
Carbon Species.
For instance, 1800 µMol HCO3 kg-1, 200 µMol CO3 kg-1 and
20 µMol CO2(aq) kg-1, depending on pH.
Large majority of deep ocean DIC is bicarbonate!
Distribution depends on pH.
Typical DIC Profiles by Ocean.
From: T Takahashi (1989) The carbon dioxide puzzle, Oceanus, 32: 22-29.
Oceanic Carbon Cycle and the future
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SOES6002 - Toby Tyrrell
TCO2 Sections
in Different
Oceans.
From: RA Feely, CL Sabine, T
Takahashi, R Wanninkhof (2001)
Uptake and storage of CO2 in the
ocean, Oceanography, 14: 18-32.
Always
Plenty of
Dissolved
Inorganic
Carbon
(TCO2) in
the Sea...
(GEOSECS/TTO datasets)
DOC Section, S. Pacific.
Negligible direct effect of CO2
levels on organic pump...
From: DA Hansell, CA Carlson (2001) Marine dissolved organic matter
and the carbon cycle, Oceanography, 14: 18-32.
Average deep ocean DOC concentration is about 40 µMol kg-1.
Oceanic Carbon Cycle and the future
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SOES6002 - Toby Tyrrell
Magnitude of pre-anthropogenic
carbon fluxes to/from the ocean.
Magnitude
of internal
carbon
fluxes
within the
ocean.
Pattern of ingassing/outgassing of CO2.
Net ingassing
because for
year 1995.
The Ocean Carbon Cycle
•Quantitative description of natural cycle.
•Behaviour over the next 100 years.
From: RA Feely, CL Sabine, T Takahashi, R Wanninkhof (2001) Uptake and
storage of CO2 in the ocean, Oceanography, 14: 18-32.
Oceanic Carbon Cycle and the future
OA402 - Modelling in Environmental and Earth System Science (Toby Tyrrell)
5
SOES6002 - Toby Tyrrell
Atmospheric CO2 over the last 2000 years
Industrial Revolution
from “An Introduction to Marine Biogeochemistry” S.M. Libes, Wiley Press, 1992.
Atmospheric CO2 over the last 160,000 years
Increasing DIC in the Ocean
BATS = Bermuda Atlantic Time Series
HOT = Hawaii Ocean Time-Series
From: M.E.Q. Pilson “An Introduction to the Chemistry of the Sea”, Prentice Hall, 1998
Oceanic Carbon Cycle and the future
from: DM Karl et al (2001) Building the Longterm Picture: the US JGOFS Time-Series
Programs, Oceanography, 14: 18-32.
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SOES6002 - Toby Tyrrell
Invasion of
Anthropogenic CO2
Future of the Ocean
Carbon Cycle as
Atmospheric CO2
continues to rise?
From: RA Feely, CL Sabine, T
Takahashi, R Wanninkhof (2001)
Uptake and storage of CO2 in the
ocean, Oceanography, 14: 18-32.
Ocean Will Continue to be an
Increasing Sink for CO2...
However, Uptake Potential will Decline
Uptake potential = ∆(TCO2)E
At present,
one third of all
emissions end
up in the
ocean. In the
future, this will
decrease to
less than one
quarter.
∆(pCO2)
Ecosystem Model (Palmer & Totterdell, 2001, Deep-Sea Research I, 48: 1169)
in an ocean-atmosphere GCM (Cox et al, 2000, Nature, 408: 184)
Oceanic Carbon Cycle and the future
Ecosystem Model (Palmer & Totterdell, 2001, Deep-Sea Research I, 48: 1169)
in an ocean-atmosphere GCM (Cox et al, 2000, Nature, 408: 184)
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SOES6002 - Toby Tyrrell
2
Decrease in
Uptake Potential
Important Ocean Calcifiers
coral reefs
coralline algae
coccolithophores
Uptake potential = ∆(TCO2)E
∆(pCO2)
HadOCC model:
Ecosystem model (Palmer & Totterdell,
2001, Deep-Sea Research I, 48: 1169)
in an ocean-atmosphere GCM (Cox et
al, 2000, Nature, 408: 184)
CO3-dependent calcification in
foraminifera and coccolithophores
foraminifera
pteropods
Malformed coccoliths at low [CO3]
High [CO3]
Low [CO3]
(Riebesell et al, 2000, Nature, 407: 364)
(Zeebe & Westbroek, submitted)
Oceanic Carbon Cycle and the future
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SOES6002 - Toby Tyrrell
Invading CO2 will Acidify the Ocean and
Reduce Carbonate Ion Concentration
Net community calcification rate (mMol CaCO3 m-2 d-1)
Coral Reef in Biosphere 2
(Langdon et al, 2000, Glob.
Biogeochem. Cycles, 14: 639)
(from RE Zeebe & D Wolf-Gladrow (2001) CO2 in Seawater, Elsevier)
Trouble Ahead for Ocean Calcifiers?
•Calcification by coral reefs is sensitive to
carbonate ion concentration
Large Uncertainty in
Vegetation & Soil Feedbacks
(JA Kleypas et al, Science, 284 (5411), 118-120, 1999)
(C Langdon et al, Global Biogeochemical Cycles, 14 (2), 639654, 2000.)
•Calcification by coccolithophores is sensitive to
carbonate ion concentration
(U Riebesell et al, Nature, 407 (6802), 364-367, 2000)
•Thickness of foraminifera shells is sensitive to
carbonate ion concentration
(S Barker & H Elderfield, Science, 297 (5582), 833-836, 2002)
Oceanic Carbon Cycle and the future
Cox et al (2000) Nature, 408:184.
** What about the Ocean? **
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SOES6002 - Toby Tyrrell
What about Feedbacks?
(Effect of Human-Induced Changes
to Ocean Functioning)
1. Investigate whether similar uncertainties
(for atm. pCO2) reside in the ocean
2. Only consider up to year 2100
3. Compare results of three models (HadOCC,
HILDA, 3-Box)
Chuck, Tyrrell, Totterdell, Holligan (submitted)
3-Box model of C cycling.
Equilibrium Without Emissions
Carbon Dioxide
Emissions
Absorption by
Terr. Biosphere
Oceanic Carbon Cycle and the future
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SOES6002 - Toby Tyrrell
Regreening
of the
Terrestrial
Biosphere
CO2 Emissions
Response to Emissions
Generally Small Effects of Ocean Changes
Change to Ocean
Increased River Phosphate (RP)
Temperature Effect (+4°C) on C
Chemistry
Increase Phytoplankton Growth Rate
Decrease Mixing (Increase
Stratification)
Decrease Calcification (-50%)
Increase Calcification (+50%)
Increase Particle Export Efficiency
Decrease Particle Export Efficiency
Model
3-Box HILDA HadOCC
-3
+19
-2
+33
-8
+25
-35
+35
-4
-10
+10
+1
+1
-6
+6
-4
+12
-4
+4
-8
+16
+22
Largest effect on year 2100 pCO2 = 35 ppm, small
compared to possible 250 ppm due to terrestrial changes
Oceanic Carbon Cycle and the future
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SOES6002 - Toby Tyrrell
Conclusions
Caveats
1. The future behaviour of the ocean appears to be more
predictable than of the terrestrial biosphere.
1. Do we know the ocean well enough to be sure that
there will be no surprises? (probably not)
2. While the ocean will continue to be an important CO2
sink, greater fractions of emissions will remain in the
atmosphere in the future.
2. Only considered up to year 2100 in this study; will be
larger uncertainties in the ocean after that.
3. The ocean will mitigate but not prevent global warming.
3. Only considered carbon here - ignored methane
clathrates, DMS, N2O, etc.
CAUTION
We Don’t Yet
Fully
Understand
The Ocean...
Chance
measurements
have revealed
increasing DOC...
MW Lomas et al, EOS,
83(48): 559-567, 26
November 2002.
Oceanic Carbon Cycle and the future
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