What caused Glacial-Interglacial CO 2 Change? Douglas L. Love Meto 658A Spring 2006
Suggested papers: Reviews: Archer et al., 2000 Newer ideas:Zeng 2003 Toggweiler et al. 2005 Paillard and Perenin 2005 Broecker and Henderson 1998Broecker and Peng 1998
Archer et al, 2000 David ArcherArne WinguthDavid LeaNatalie Mahowald U ChicagoU WisconsinUCSBNCAR
Archer et al, 2005 Glacial pCO 2 was 80-90 μatm lower than interglacial Radiative forcing from CO 2 accounts for half of climate change Tight repeatable corellation between pCO 2 Ice volume Temperature records
Glacial pCO 2 was 80-90 μatm lower than in the interglacial Radiative forcing from CO 2 accounts for half of climate change “The terrestrial biosphere and soil carbon reservoirs would have to be approximately double in size to deplete pCO 2 by 80 μatm.” “δ 13 C from deep-sea CaCO 3, more 12 C 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, 2000 Glacial cycles: Advances and retreats of ice sheets Documented by isotopic composition of seawater Oxygen in CaCO3: 16 O is selectively sequestered in glacial ice. Oceans become enriched in 18 O
Archer et al, 2005 Clear physical link between Northern Hemisphere summer heating and ice sheets No easy link from orbital variations to pCO 2. pCO 2 rise clearly precedes the 18 O of the atmosphere by several thousand years (an indicator of melted ice sheets) Implies that pCO2 is a primary driver of melting. Alternatively, pCO 2 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, 2005 “Because CO 2 is more soluble in colder water, colder sea surface temperatures could lower pCO 2. However, the magnitude of the glacial cooling can account for only a small fraction of the observed pCO 2 drawdown.”
Archer et al, 2005 A New model of Ocean and Sediment Geochemistry - Mechanisms to lower glacial pCO 2 : 1.Increase biological activity at surface so that Carbon sinks to deep sea sediments as particles Increase Ocean Inventory of PO 4 3- and NO 3 - 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 NO 3 -
2. Change the pH of the whole ocean Convert seawater CO 2 into HCO 3 - and CO 3 =, which can’t evaporate in the atmosphere. pH is regulated by balance between influx of dissolved CaCO 3 and removal by burial of CaCO 3 sediments. Timescale of 5-10 kyears is within observed timescales. Archer et al, 2005 A New model of Ocean and Sediment Geochemistry - Mechanisms to lower glacial pCO 2 :
Archer et al, 2005 2. Change the pH of the whole ocean Conditions under which it could occur: 1)Glacial rate of weathering is higher 2)CaCO 3 deposition shifts to deep sea 3)Rate of CaCO 3 production decreased 4)CaCO 3 compensation may also affect pCO 3 response to the biological pump in #1. Results: burial efficiency would increase the Ocean would become more basic degradation of biological C in sediments would promote Calcite dissolution, further increasing Ocean pH.
Two Caveats: Archer et al, 2005 A New model of Ocean and Sediment Geochemistry - Mechanisms to lower glacial pCO 2 : “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 predict…conditions which we are unable to observe except indirectly via clues preserved in the sedimentary record.”
Archer et al, 2005 A New model of Ocean and Sediment Geochemistry - Mechanisms to lower glacial pCO 2 - CO 2 pump scenarios: 1.Fe fertilization of existing NO 3 or PO 4 pools attains glacial pCO 2 values in box models But not in circulation models 2. Increase NO 3 - by 50% Attains glacial pCO 2 for a few thousand years until CaCO 3 compensation lowers Ocean pH. Requires a change in the Redfield Ratio.
Archer et al, 2005 A New model of Ocean and Sediment Geochemistry - Mechanisms to lower glacial pCO 2 - CO 3 = pump scenarios: Coral reef hypothesis: lowered sea level causes a decrease in shallow CaCO 3 deposition, which drives increased deposition in the deep sea Increased pH would lower pCO 2 Not backed up by deep-sea cores Rain ratio hypothesis: decrease in CaCO 3 production or in- crease in organic carbon production could shift Ocean pH. A doubling of H 4 SiO 4 could explain it, but can’t be rationalized. Predicted distribution of CaCO 3 on seafloor is a poor fit.
Archer et al, 2005 A New model of Ocean and Sediment Geochemistry – Procedures and summaries: Present Day Ocean simulation pCO 2 within 2 μatm of observed values Distribution of CaCO 3 a poor fit: Present-day CaCO3 distribution on seafloor Modeled Present-day CaCO3 distribution on seafloor
A New model of Ocean and Sediment Geochemistry: Archer et al, 2005 The Glacial Ocean model description: High Lat. Air temperatures 10°-15° C colder than now Tropical cooling 1°-2° C cooler from plankton and O isotope ratios Glacial flow field estimated from best “second guess” velocities Atlantic overturning shallower and 30% slower than now δ 13 C tracer says Southern Ocean was high-nutrient, low Oxygen, contradicting Cd data.
Archer et al, 2005 A 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. NO 3 - decreases from 110 x 10 12 mol to 80 x 10 12 mol. pCO 2 lowered by 8 μatm. CO 3 = and H 4 SiO 4 tweaked until burial rates of CaCO 3 and SiO 2 are those of present day. 17% H 4 SiO 4 decrease yields a 70% SiO 2 burial increase. Organic C production increased from 0.198 to 0.210 Acidification of ocean overwhelms iron fertilization, increasing pCO 2 to 280 μatm.
Archer et al, 2005 A New model of Ocean and Sediment Geochemistry: Collapse of the terrestrial biosphere: 13 C/ 12 C ratio in deep sea CaCO 3 was.4% o lower, indicating that an isotopically-depleted carbon reservoir released 40 x 10 15 mol C, raising the Ocean-Atmosphere inventory by 1% Possible sources: Terrestrial biomass: 40 x 10 15 mol C Soil organic carbon: 120 x 10 15 mol C Sedimentary C on continental shelves
A New model of Ocean and Sediment Geochemistry: Archer et al, 2005 Collapse of the terrestrial biosphere: Reconstructions call for 2-3 x this δ 13 C value. Initially raises pC0 2 to 305 μatm. Reaction with CaCO 3 will neutralize the added CO 2 Lowering to 297 μatm predicts a lowering of 17 μatm in the future. After compensation, pCO 2 is 295 μatm.
Archer et al, 2005 A New model of Ocean and Sediment Geochemistry: Tropical Temperatures Lowering Tropical Sea Surface Temperature by 4°C decreases pCO 2 by 5 μatm. Biological production is altered Stratification decreases, organic Carbon increases. SiO 2 decreases as H 4 SiO 4 recycling decreases. Small increase in pCO 2.
Archer et al, 2005 Constraints on the cause of glacial/ interglacial atmospheric pCO 2 Deglacial increase leads ice volume, eliminating sea-level- driven explanations such as submersion of continental shelves Deglacial transition was slow: 6-14 kyears. The pCO 2 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 CaCO 3 and SiO 2 on sea floor
1.Ocean circulation models are more diffusive than the modern ocean, underestimating the pCO2 sensitivity to the biological pump 2. Increase the glacial NO 3 - inventory beyond the PO 4 3- limitation, assuming the Redfield N/P number was different in glacial time. 3.Double the inventory of H 4 SiO 4 in the ocean, raising the pH of the deep ocean. Archer et al, 2005 Solution: challenge one or more of the basic assumptions of chemical oceanography!
Prince George’s 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 2 Secondary 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 “Archer’s 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 CO 2 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 CO 2 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 δ13C,.35% o, land-carbon difference (Holocene - LGM) 460
The sequence of events surrounding Termination II and their implication for the cause of glacial-interglacial CO 2 changes Substitute or correct paper? Wallace S. Broecker and Gideon M. Henderson, Paleoceanography, V 13, No 4, PP. 352-364, August 1998 Wallace Broecker, Lamont-DohertyGideon Henderson, now at Oxford
Broecker and Henderson, 1998 Clues from the Vostok ice core: Antarctic Temperature and atmospheric CO 2 increased together for 8000 years, bounded by A drop in dust flux at the onset A drop in δ 18 O at the finish A similar lag between dust flux and foraminiferal δ 18 O in the Southern Ocean indicates that the δ 18 O in Vostok ice is a valid proxy for ice volume. Synchronous changes in CO 2 and Southern Hemisphere temperatures preceded melting of Northern Hemisphere ice Nutrient reorganization in North Atlantic occurs with or after the sea level rise
Broecker and Henderson, 1998 Clues from the Vostok ice core: The previous observations eliminate many scenarios proposed to explain the CO 2 rise Those which rely on sea level change Conveyor-related nutrient redistribution North Atlantic cooling Southern Ocean scenarios become the front runners. The most popular, Iron fertilization, has 2 problems: Much of the dust demise occurs prior to the change in CO 2, so there must be a threshold value above which it does not increase. The CO 2 rise continues for 4-5 kyr after the dust flux has fallen to zero.
Broecker and Henderson, 1998 Clues from the Vostok ice core: Problems with iron fertilization causing the rise in CO 2 may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during Glacial periods. In this case, residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon This would explain the slow rampup of atmospheric CO 2.
Broecker and Henderson, 1998 Timing is everything for Broecker and Henderson. More comfortable than their predecessors with relating time markers, their whole theoretical setup is based on these time relationships. O2 created by photosynthesis has the Isotopic composition of surface seawater, which is controlled by global ice volume. Turnover time is 1-2 kyears. Therefore, δ 18 O atm should have risen 1.4 % o with δ 18 O ocean.
Broecker and Henderson, 1998 They then claim that the Dole Effect, where the atmosphere is enriched in 18 O by 23.5% o over the ocean, keeps it steady. The first assumption is that variation in ocean surface δ 18 O is the only contributor to changes in δ 18 O atm. They then present similar offsets between events as indicating a good correlation.
Broecker and Henderson, 1998 Broecker’s Bipolar Seesaw concept is also an important consideration, where deepwater formation alternates between the North and South Atlantic. This eliminates mechanisms that occur only in the North Atlantic. Cooling in the Southern Ocean at the same time as CO 2 is falling is considered as a cause, but is nowhere strong enough to cause the observed drop. Changing the productivity or alkalinity is also suggested as a control of Oceanic CO 2. Observations indicate that these changes moved in the opposite direction. Nitrogen fixation by iron fertilization is considered, but the residence time for NO 3 is too long to keep it locally confined.
Broecker and Henderson, 1998 Tentative conclusions: δ 18 O constrains the rise in atmospheric CO 2 to have preceded the melting of the North American ice sheets. This eliminates seal level change, North Atlantic Nutrient redistribution, and North Atlantic cooling as causes. Iron fertilization can’t explain Southern Ocean paleoproductivity the long duration of the CO 2 rise Increased dust flux in the glacials caused more nitrogen fixation, which allowed a greater CO 2 drawdown in surface waters. Long residence time of NO 3 in ocean explains how CO 2 can continue to increase after the dust flux ix zero, and means productivity changes can be global.
Newer ideas 1: Zeng, Ning, Glacial-Interglacial Atmospheric CO2 Change - the Glacial Burial Hypothesis Readily available from http://www.atmos.umd.edu/~zeng
Newer ideas 1: Zeng, N Advancing ice sheets buried vegetation and soil carbon accumulated during warm periods. Simulation over 2 cycles found a 547 Gt carbon release, resulting in a 30 ppmv increase in atmospheric CO 2, the remainder absorbed by the Ocean. Atmospheric δ 13 C drops by.3% o at deglaciation, followed by a rapid rise to a high interglacial value, in response to oceanic warming and regrowth on land. With other ocean-based mechanisms, offers a full explanation of the observed atmospheric CO 2 change.
Newer ideas 1: Zeng, N Fig. 8. Modeled atmospheric CO 2 (a) and land carbon storage (b) from the control run and 5 sensitivity experiments described in the text: control is in black line, SST in green, CO 2 v120 in yellow, SoilD5h in red, Soil D20k in blue, and WarmGlac in purple. The largest change of a 55 ppmv deglacial CO 2 increase is due to a cooler glacial ocean in addition to the land carbon release (green) and a 40 ppmv increase due to a long delayed regrowth (blue).
Newer ideas 1: Zeng, N Data from Table 1: Land carbon difference, Holocene - LGM
Newer ideas 1: Zeng, N Look for it: On the ground Back in time In the models In comparisons
Glacial bottom waters were possibly much more saline May have an unsuspected large density Glacial deep stratification could account for the difference. Ice formation around Antarctica involves Brine rejection over the Continental Shelves Is directly linked to changes in Sea Ice Formation Antarctic ice-sheet extent
Kitchen Experiment: mixing saline water Cold 30% salt water Warm 10% salt water They mixed immediately.
Newer ideas 3: Toggweiler, Climate Change from below Adkins et al, 2002, showed bottom waters around Antarcti- ca are significantly saltier than the rest of the ocean, appar- ently from accumulation of brine during sea ice production. This shows that the glacial deep ocean was more stably stratified than it is today. Geothermal heat would have slowly warmed it from below, destabilizing it, like a discharging capacitor. Just 2°C is enough to destabilize it. This would take 10,000 years. This matches: Heinrich Events in the North Atlantic. Bond cycles in Greenland Ice Cores Bi-polar seesaw between Greenland and Antarctica He gives several examples separated by 7000 years.
Newer ideas 3: Toggweiler, Climate Change from below This injects salt into the upper North Atlantic, kick- starting thermohaline circulation. Reinvigorated circulation warms up Greenland and the North Atlantic. This confirms the finding that the warmest intervals in Greenland occur during the interstadials that follow Heinrich and Antarctic Intervals. This contradicts the prevailing view –these events are caused by fresh water input –Explains why interstadials after Heinrich events are longer and warmer than others.
Short paper. Is it the right one? So I wrote and asked! Newer ideas 3: Toggweiler, Climate Change from below Woah! Preprint!
Newest ideas yet: Toggweiler et al Another new idealized general circulation model explains: tight correlation between atmospheric CO 2 and Antarctic temp lead of Antarctic temp over CO 2 at terminations Shift of ocean’s δ 13 C minimum from N. Pacific to Atlantic sector of the southern Ocean Changes occur at transitions between on and off states of the southern overturning circulation.
Proposal: overturnings occur in nature through a positive feedback that involves mid-latitude westerly winds. Glacial climates seem to have equatorward-shifted westerlies which allow more respired CO2 to accumulate in the deep ocean. Warm climates like the present have poleward shifted westerlies that flush respired CO2 out of the deep ocean.
Newest ideas yet: Toggweiler et al Contains 6 pages of good references at the end.
But wait – there’s MORE! A silicon-induced “alkalinity pump” hypothesis The Ocean Research Institute, University of Tokyo In order to maintain atmospheric CO 2 at 190-200 ppm, alkalinity and pH in the surface ocean must be higher by ~85 μeq/L and ~.14 units, respectively. Proposal: species change in phytoplankton produced only 20-25% Carbonate plus Opal during ice ages vs 90% now. Quotes Broecker and Peng
and more! Carbon Storage on exposed continental shelves during the glacial-interglacial transition Montenegro et al Up to ~10,000 years before present, time-dependent estimate of inundated carbon is in good agreement with the increase in the atmospheric reservoir. Carbon stock of the LGM exposed shelves cannot be ignored and merits more detailed attention from modelling and reconstructions. Quotes Zeng (2003)
and Still more! A movable trigger: Fossil fuel CO 2 and the onset of the next glaciation Archer and Ganopolski Uses models of how much CO 2 and cooling is required to start an ice age to predict how soon the next ice age will come, considering how much CO 2 we have/will put in the atmosphere. “A carbon release from fossil fuels… of 500 Gton C could prevent glaciation for the next 500,000 years….The duration and intensity of the projected interglacial period are longer than have been seen in the last 2.6 million years.” Quotes Archer et al, Broecker and Henderson, and Paillard’s PhD thesis
one more… The climate instability of glacial times probably resulted frm abrupt switches in ocean circulation. Figure shows Climate (temperature) stability as a function of freshwater input at high latitudes in the North Atlantic. a.unperturbed present-day state b.Last Glacial Maximum c.An intermediate situation 50,000 years ago. Dansgaard-Oeschger events d.Figure shows Climate Quotes himself. Glacial Hiccups Didier Paillard
And finally, Aric Global Climate Change Student Guide Palaeoclimatic Change: CO2 Feedbacks Reviews the many hypotheses of the causes of CO2 changes, and the phase relationships of CO2, ice volume and termperature, that have passed through many stages over the last decade or so. Gives a review of all factors involved, with equations. Ocean ΣCO 2 profileOcean δ 13 C profile
Conclusions: There are many partial solutions This problem is a hard nut to crack. Truth, however, is elusive prey - Sandra Collins, Pittsburgh Post-Gazette, March 26 2005