What caused Glacial-Interglacial CO2 Change?Douglas L. LoveMeto 658ASpring 2006
Suggested papers:Reviews:Archer et al., 2000Newer ideas:Zeng 2003Toggweiler et al. 2005Paillard and Perenin 2005Broecker and Henderson 1998Broecker and Peng 1998
Archer et al, 2000David ArcherArne WinguthDavid LeaNatalie MahowaldU ChicagoU WisconsinUCSBNCAR
Archer et al, 2005 Glacial pCO2 was 80-90 atm lower than interglacial Radiative forcing from CO2 accounts for half of climate change Tight repeatablecorellation between
Glacial pCO2 was 80-90 atm lower than in the interglacial Radiative forcing from CO2 accounts for half of climate change
The terrestrial biosphere and soil carbon reservoirs would have to be approximately double in size to deplete pCO2 by 80 atm.
13C from deep-sea CaCO3, more 12C rich during glacial time, tells us that if anything, the terrestrial biosphere released carbon during glacial time [Shackleton, 1977]Archer et al, 2005
Archer et al, 2000Glacial cycles: Advances and retreats of ice sheets Documented by isotopic composition of seawater Oxygen in CaCO3: 16O is selectively sequestered in glacial ice. Oceans become enriched in 18O
Archer et al, 2005 Clear physical link between Northern Hemisphere summer heating and ice sheets
No easy link from orbital variations to pCO2.
pCO2 rise clearly precedes the 18O of the atmosphere by several thousand years (an indicator of melted ice sheets) Implies that pCO2 is a primary driver of melting.
Alternatively, pCO2 could be driven by changes in meteorological forcing: dust delivery of trace metals to the ocean surface an acausal correlation between Northern Hemisphere summer insolation and ice volume
Archer et al, 2005Because CO2 is more soluble in colder water, colder sea surface temperatures could lower pCO2.
However, the magnitude of the glacial cooling can account for only a small fraction of the observed pCO2 drawdown.
Archer et al, 2005A New model of Ocean and Sediment Geochemistry -Mechanisms to lower glacial pCO2:Increase biological activity at surface so that Carbon sinks to deep sea sediments as particles
Increase Ocean Inventory of PO43- and NO3-Change the ratio of nutrient to C in phytoplankton Iron limitation of biological production at surface indicates a Southern Ocean Biological Pump could have intensified in a dustier, more iron-rich environment.Glacial dust could stimulate the rate of Nitrogen fixation, increasing the ocean pool of NO3-
2. Change the pH of the whole ocean
Convert seawater CO2 into HCO3- and CO3=, which cant evaporate in the atmosphere.
pH is regulated by balance between influx of dissolved CaCO3 and removal by burial of CaCO3 sediments.
Timescale of 5-10 kyears is within observed timescales.
Archer et al, 2005A New model of Ocean and Sediment Geochemistry -Mechanisms to lower glacial pCO2:
Archer et al, 20052. Change the pH of the whole ocean Conditions under which it could occur:Glacial rate of weathering is higherCaCO3 deposition shifts to deep seaRate of CaCO3 production decreasedCaCO3 compensation may also affect pCO3 response to the biological pump in #1.Results: burial efficiency would increasethe Ocean would become more basicdegradation of biological C in sediments would promote Calcite dissolution, further increasing Ocean pH.
Two Caveats:Archer et al, 2005A New model of Ocean and Sediment Geochemistry -Mechanisms to lower glacial pCO2:The ocean carbon cycle is a complicated system, controlled by biological processes we are only beginning to understand. Thus the formulation of the model is not completely con-strained by our understanding of the underlying processes. Furthermore, we use the model to predictconditions which we are unable to observe except indirectly via clues preserved in the sedimentary record.
Archer et al, 2005A New model of Ocean and Sediment Geochemistry -Mechanisms to lower glacial pCO2 - CO2 pump scenarios:Fe fertilization of existing NO3 or PO4 pools attains glacial pCO2 values in box modelsBut not in circulation models
2. Increase NO3- by 50%Attains glacial pCO2 for a few thousand years until CaCO3 compensation lowers Ocean pH. Requires a change in the Redfield Ratio.
Archer et al, 2005A New model of Ocean and Sediment Geochemistry -Mechanisms to lower glacial pCO2 - CO3= pump scenarios:Coral reef hypothesis: lowered sea level causes a decrease in shallow CaCO3 deposition, which drives increased deposition in the deep seaIncreased pH would lower pCO2Not backed up by deep-sea coresRain ratio hypothesis: decrease in CaCO3 production or in-crease in organic carbon production could shift Ocean pH.A doubling of H4SiO4 could explain it, but cant be rationalized.Predicted distribution of CaCO3 on seafloor is a poor fit.
Archer et al, 2005A New model of Ocean and Sediment Geochemistry Procedures and summaries:Present Day Ocean simulationpCO2 within 2 atm of observed valuesDistribution of CaCO3 a poor fit:Present-day CaCO3 distribution on seafloorModeled Present-day CaCO3 distribution on seafloor
A New model of Ocean and Sediment Geochemistry:Archer et al, 2005The Glacial Ocean model description:High Lat. Air temperatures 10-15 C colder than nowTropical cooling 1-2 C cooler from plankton and O isotope ratiosGlacial flow field estimated from best second guess velocitiesAtlantic overturning shallower and 30% slower than now13C tracer says Southern Ocean was high-nutrient, low Oxygen, contradicting Cd data.
Archer et al, 2005A New model of Ocean and Sediment Geochemistry:The Glacial Ocean model results: Iron flux to sea surface increases by 2.5 goes to regions that already receive sufficient iron. NO3- decreases from 110 x 1012 mol to 80 x 1012 mol. pCO2 lowered by 8 atm. CO3= and H4SiO4 tweaked until burial rates of CaCO3 and SiO2 are those of present day.17% H4SiO4 decrease yields a 70% SiO2 burial increase.Organic C production increased from 0.198 to 0.210Acidification of ocean overwhelms iron fertilization, increasing pCO2 to 280 atm.
Archer et al, 2005A New model of Ocean and Sediment Geochemistry:Collapse of the terrestrial biosphere:13C/12C ratio in deep sea CaCO3 was .4%o lower, indicating that an isotopically-depleted carbon reservoir released 40 x 1015 mol C, raising the Ocean-Atmosphere inventory by 1%Possible sources:Terrestrial biomass: 40 x 1015 mol C Soil organic carbon: 120 x 1015 mol C Sedimentary C on continental shelves
A New model of Ocean and Sediment Geochemistry:Archer et al, 2005Collapse of the terrestrial biosphere:Reconstructions call for 2-3 x this 13C value.Initially raises pC02 to 305 atm. Reaction with CaCO3 will neutralize the added CO2 Lowering to 297 atm predicts a lowering of 17 atm in the future. After compensation, pCO2 is 295 atm.
Archer et al, 2005A New model of Ocean and Sediment Geochemistry:Tropical Temperatures Lowering Tropical Sea Surface Temperature by 4C decreases pCO2 by 5 atm. Biological production is altered Stratification decreases, organic Carbon increases. SiO2 decreases as H4SiO4 recycling decreases. Small increase in pCO2.
Archer et al, 2005Constraints on the cause of glacial/ interglacial atmospheric pCO2 Deglacial increase leads ice volume, eliminating sea-level-driven explanations such as submersion of continental shelves Deglacial transition was slow: 6-14 kyears. The pCO2 response is much faster. Glacial rates of weathering and burial were not much different than today. Isotopic signatures of C, N, B, Cd, Ba Distribution of CaCO3 and SiO2 on sea floor
Ocean circulation models are more diffusive than the modern ocean, underestimating the pCO2 sensitivity to the biological pump Increase the glacial NO3- inventory beyond the PO43- limitation, assuming the Redfield N/P number was different in glacial time.Double the inventory of H4SiO4 in the ocean, raising the pH of the deep ocean.Archer et al, 2005Solution: challenge one or more of the basic assumptions of chemical oceanography!
Prince Georges Memorial Library System:Keyword Search: ti:(Greenhouse Puzzles, Part II) 0 record(s) found. USMAI (all campuses) Number of hitsRequest permutation (No Adjacency)0 Words= Greenhouse Puzzles Part II
Greenhouse puzzles Part 2Secondary sources: A silicon-induced alkalinity pump hypothesis, Marine Inorganic Chemistry/ Department of Chemical Oceanography, The Ocean Research Institute ORI, University of Tokyo, Japan http://www.ori.u-tokyo.ac.jp/en/special/topics_4/topics-e.htm(refers to Broecker and Peng, Part 2 1994 version as Archers World. Also references Martin, J.H., The Iron Hypothesis)
Field-based Atmospheric Oxygen Measurements and the Ocean Carbon Cycle, PHD Thesis by Britton Bruce Stephens, Chapter 6, The Influence of Antarctic Sea Ice on Glacial-Interglacial CO2 Variations
Modeling of marine biogeochemical cycles with an emphasis on vertical particle fluxes, PhD Theis by Regina Usbeck, http://www.awi-bremerhaven.de/GEO/Publ/PhDs/RUsbeck/RUsbeck.html
Zeng, Ning, Glacial-Interglacial Atmospheric CO2 Change - the Glacial Burial Hypothesis. http://www.atmos.umd.edu/~zeng
Greenhouse puzzles Part 2 Secondary sources:ORI: biological pump model of atmospheric CO2 variability
Stephens: Harvardton-Bear index: Actual atmospheric CO2 change /potential change due to cooling of low-latitude surface box
Usbeck: compares others works with recent estimates of total Corg accumulation
Zeng: Ocean 13C, .35%o, land-carbon difference (Holocene