Glacialinterglacial variations in atmospheric CO2

1
warmer less ice

• Specific questions
• What caused glacial/interglacial CO2 changes?
• What impact did they have on climate and its
  variation?
• Broader questions
• How important is CO2 to climate? (Is CO2 change
  needed to generate glacial cycles?)
• How can climate change alter the physical and
  biological processes that mediate CO2 fluxes?
  (Iron fertilization, Antarctic overturning)

higher CO2

warmer
Siegenthaler et al., 2005 Jouzel et al., 2007
Lisiecki and Raymo, 2005
2
Preindustrial carbon cycle
2.5C ocean cooling ?30 ppm
95Pg/45ppm
33Pg/15ppm
500

3 salinity increase ?6.5 ppm
3
(No Transcript)
4
C cycle controls on pCO2 of surface waters
?
?
5
Hypothesized drivers of glacial/interglacial CO2
change
6
C cycle response to a decrease in CaCO3 production
CO32-gtCO32-sat.
lysocline
CO32-ltCO32-sat.
50 decrease ? 55 ppm

lysocline deepens 1 km
7
Low latitude biological pump
8
CO2 response to the major nutrient reservoir size
Deep North Pacific O2 depletion
Sigman et al. 1998
9
The oceans major nutrient reservoirs

• P reservoir is an unlikely driver of G/I CO2
  change
• By modern fluxes, P residence time gt16 kyr
• Rapid change in the P reservoir requires a
  special process
• Broeckers shelf P uptake must wait for sea level
  rise
• What about fixed nitrogen?
• Residence time 3 kyrs (N2 fixation/denitrificatio
  n)
• Evidence for reduced denitrification during cold
  periods suggestion of enhanced pressure for N2
  fixation
• The controls on the NP of primary production are
  poorly understood, so NP changes may be possible
• Problem N budget feedbacks may stabilize the
  ocean N reservoir

10
Candidate negative feedbacks in the ocean N
budget
-

Cooling
Deutsch et al. 2004
11
Incomplete nutrient consumption in the polar ocean
Surface nitrate
Surface chlorophyll
12
Efficiency of the biological pump
Efficiency of the biological pump?Fraction of
major nutrient in ocean interior that is
regenerated
Caveat Sea ice limitation of air-sea exchange
13
CO2 effects of Southern Ocean changes
14
dissolution event
15
MD84-552 Indian Antarctic
Low ?14C
Effect on CO2 Mechanisms? Stratification
Biotic response

Francois et al., 1997
16
Sea ice impact onAntarctic CO2 release
17
North Atlantic trigger for Antarctic CO2 release?

18
Carbon theme speakers

• COLIN PRENTICE Terrestrial C cycle
• ANDY WATSON Ocean circulation impacts
• STEVE EMERSON Calcium carbonate dynamics
• ED BROOK Constraints from timing
• INEZ FUNG Anthropogenic C cycle

19
Extra slides
20
Preindustrial carbon cycle
21
Response to a halving of the CaCO3Corg rain ratio
Sigman and Boyle, 2000
22
Modern Southern OceanSubantarctic vs. Antarctic
south
equatorward
23
C cycle controls on pCO2 of surface waters
Corg DIC only
HCO3- 2CO32- OH- - H
CaCO3 ALK/DIC2
CO2(aq) H2CO3 HCO3- CO32-