Marine biology and geochemistry in Earth System Models

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Marine biology and geochemistry in Earth System
Models Andrew Watson School of Environmental
Science University of East Anglia Norwich NR4
7TJ UK
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Major effects of marine biology on the Earth
system.

• Biological pump for atmospheric CO2
• - sets natural atmospheric CO2 on time scales 102
  105 years.
• Sulphur gas impact on cloud albedo via CCN
  production.
• Production of sediments carbonate sink and
  organic carbon sink.
• Major influence on atmospheric CO2 and O2 over
  millions of years.

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Why do you need biology and geochemistry in earth
system models?

• Studies of the long-term habitability of the
  earth
• Faint young sun
• major glaciations
• Sudden warmings
• Response to major impact events

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The Dim young sun evolution of atmosphere and
solar output
time
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Long term (gt105 year) concentrations of
atmospheric CO2, O2, CH4 etc are set by
biota-geochemical interactions.
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Major glaciations

• Some (or all?) may be related to changes in
  greenhouse gases, driven by biological change.

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A Neoproterozoic Snowball Earth?
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Why do you need marine biology and geochemistry
in earth system models?

• Studies of the long-term habitability of the earth

• The Quaternary climate the classic Earth system
  problem.
• CO2 changes are largely ocean-driven.
• Cannot be correctly modelled without
  representation of
• short-term processes (e.g. air-sea exchange
• Long-term processes (sedimentary accumulation and
  dissolution).

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Vostok core proxies
CO2 controlled by ocean chemistry,
biology,circulation?
Deuterium in ice proxy for local temperature
Methanesourced from wetlands?
Atmospheric dust signal leads other indicators
Sea-salt sodium proxy for wind strength?
Atmospheric d18O proxy for biosphere productivity
?
The driver? Summertime insolation, N. hemisphere
Source Petit, J.R. et al., 1999. Nature, 399
429-436.
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Why do you need marine biology and geochemistry
in earth system models?

• Studies of the long-term habitability of the
  earth

• The Quaternary climate the classic Earth system
  problem.

• Short term (100 year) feedbacks on global
  change

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Possible Marine biological effects on carbon
uptake, next 100 years.
Process Effect on CO2 uptake

• Iron fertilisation or change in atmospheric iron
  supply.
• NO3 fertilisation
• pH change mediates against calcite-precipitating
  organisms
• Reduction in overturning circulation interaction
  with nutrient utilisation
• Other unforeseen ecosystem changes

?
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Modelling the marine ecosystem in ESMs

• Complex ecosystem too costly (and not enough
  knowledge) to model at species level.
• Simple models, NPZD single nutrient, primary
  producer, consumer.
• More complex, functional groups of
  phytoplankton, size classes of zooplankton.

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Biogeochemical functional groups

• Nutrients
• NO3, PO4, Si, Fe
• Phytoplankton Fix carbon
• Diatoms large, need Fe, NO3, Si.
• Non-Diatoms small, need Fe, NO3
• Coccolithophores produce CaCO3
• Phaeocystis produce DMS
• Others
• Zooplankton
• Mesozooplankton Eat everything, produce large
  sinking flux
• Microzooplankton Eat small phytoplankton,
  produce small sinking flux
• Bacteria
• Viruses

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Biogeochemical functional groups

• Nutrients
• NO3, PO4, Si, Fe
• Phytoplankton Fix carbon
• Diatoms large, need Fe, NO3, Si.
• Non-Diatoms small, need lower Fe, NO3
• Coccolithophores produce CaCO3
• Phaeocystis produce DMS
• Others
• Zooplankton
• Mesozooplankton Eat everything, produce large
  sinking flux
• Microzooplankton Eat small phytoplankton,
  produce small sinking flux
• Bacteria
• Viruses

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Biogeochemical functional groups

• Nutrients
• NO3, PO4, Si, Fe
• Phytoplankton Fix carbon
• Diatoms large, need Fe, NO3, Si.
• Non-Diatoms small, need Fe, NO3
• Coccolithophores produce CaCO3
• Phaeocystis produce DMS
• Others
• Zooplankton
• Mesozooplankton Eat everything, produce large
  sinking flux
• Microzooplankton Eat small phytoplankton,
  produce small sinking flux
• Bacteria
• Viruses

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Biogeochemical functional groups

• Nutrients
• NO3, PO4, Si, Fe
• Phytoplankton Fix carbon
• Diatoms large, need Fe, NO3, Si.
• Non-Diatoms small, need Fe, NO3
• Coccolithophores produce CaCO3
• Phaeocystis produce DMS
• Others
• Zooplankton
• Mesozooplankton Eat everything, produce large
  sinking flux
• Microzooplankton Eat small phytoplankton,
  produce small sinking flux
• Bacteria
• Viruses

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Biogeochemical functional groups

• Nutrients
• NO3, PO4, Si, Fe
• Phytoplankton Fix carbon
• Diatoms large, need Fe, NO3, Si.
• Non-Diatoms small, need Fe, NO3
• Coccolithophores produce CaCO3
• Phaeocystis produce DMS
• Others
• Zooplankton
• Mesozooplankton Eat everything, produce large
  sinking flux
• Microzooplankton Eat small phytoplankton,
  produce small sinking flux
• Bacteria
• Viruses

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Biogeochemical functional groups

• Nutrients
• NO3, PO4, Si, Fe
• Phytoplankton Fix carbon
• Diatoms large, need Fe, NO3, Si.
• Non-Diatoms small, need Fe, NO3
• Coccolithophores produce CaCO3
• Phaeocystis produce DMS
• Others
• Zooplankton
• Mesozooplankton Eat everything, produce large
  sinking flux
• Microzooplankton Eat small phytoplankton,
  produce small sinking flux
• Bacteria
• Viruses

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Biogeochemical functional groups

• Nutrients
• NO3, PO4, Si, Fe
• Phytoplankton Fix carbon
• Diatoms large, need Fe, NO3, Si.
• Non-Diatoms small, need Fe, NO3
• Coccolithophores produce CaCO3
• Phaeocystis produce DMS
• Others
• Zooplankton
• Mesozooplankton Eat everything, produce large
  sinking flux
• Microzooplankton Eat small phytoplankton,
  produce small sinking flux
• Bacteria
• Viruses

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Nitrate concentrations in surface water the
HNLC regions
Annual mean surface nitrate, ?mol kg-1
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Annual average chlorophyll
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In all the HNLC regions, iron release experiments
have now shown that diatom blooms are stimulated
by addition of iron. These depress surface CO2
and nutrients. Why? Large cells such as diatoms
have small surface-to-volume ratio. Their growth
is limited at low Fe concentrations by rate of
diffusive transport of Fe into the cell.
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Effect of iron on HNLC ecosystems
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Two-component plankton biogeochemistry BIOGEM
(Ridgwell)
aeolian
dust
deposition
e
temperature

insolation
dissolution
atmospher
un-off
non-diatom
diatom
r
productivity
productivity
ocean
surface
continental
scavenging
ior
inter
dissolution
ocean
sedimentation
sedimentary
diagenesis
sediments
burial
KEY
C
dust
Fe
CaCO
Si
PO
3
4
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PISCES model (Bopp et al., 2003).
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Dust/marine biology/CO2 climate feedback in the
earth system.
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f1 temperature ? dust
Data from the Vostok ice core.
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f2 dust ? atmospheric CO2
Bopp et al
Ridgwell

• Marine biological effect results of two
  different models and a hypothetical response

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f3 atmospheric CO2 ? temperature.

• Use climate sensitivities for glacial
  interglacial cycle from models, 2ºC antarctic
  temperature change for 200-280 ppm CO2 change.

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?
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Conclusions

• Simple marine biology sub-models for earth system
  models now exist.
• First order effects on climate dynamics over
  periods gt 102 years.
• Magnitude of effects uncertain.
• To do list

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