Unresolved Issues Cuffy and Vimeux (2001) show that Cuffy and Vimeux (2001) show that  90% of  T can be explained by variations in CO 2 and CH 4 Reasonably firm grasp on causes of CH 4 variations (Monsoon forcing) Reasonably firm grasp on causes of CH 4 variations (Monsoon forcing)  What produced CO 2 variations?  Variations are large – 30%  Show rapid changes – drop of 90 ppm from interglacial to glacial

Physical Oceanographic Changes in CO 2 During glaciations physical properties change During glaciations physical properties change  Temperature and salinity  Affect solubility of CO 2 (aq) and thus pCO 2 90% of the CO 2 decrease unexplained by physical processes

Exchange of Carbon Carbon in rock reservoir exchanges slowly Carbon in rock reservoir exchanges slowly  Cannot account for 90 ppm change in 10 3 y Rapid exchange of carbon must involve near- surface reservoirs Rapid exchange of carbon must involve near- surface reservoirs

Changes in Soil Carbon Expansion of ice sheets Expansion of ice sheets  Covered or displaced forests  Coniferous and deciduous trees Displaced forests replaced by steppes and grasslandsDisplaced forests replaced by steppes and grasslands –Have lower carbon biomass Pollen records in lakes Pollen records in lakes  Indicate glacial times were dryer and less vegetated than interglacial  Estimates of total vegetation reduced by 25% (15-30%) during glacial maxima CO 2 removed from atmosphere did not go into vegetation on land!CO 2 removed from atmosphere did not go into vegetation on land!

Where is the Missing Carbon? Carbon from reduced CO 2 during glacial times Carbon from reduced CO 2 during glacial times  Not explained by physical properties of surface ocean  Did not go into biomass on land  Must have gone into oceans  Surface ocean not likely Exchanges carbon with atmosphere too rapidlyExchanges carbon with atmosphere too rapidly Most areas of ocean within 30 ppm of atmosphereMost areas of ocean within 30 ppm of atmosphere –Glacial surface ocean must also have been lower, like atmosphere  Deep ocean only likely remaining reservoir

Interglacial-Glacial Change in Carbon At LGM, reduction of carbon occurred in atmosphere, vegetation and soils on land and in surface ocean At LGM, reduction of carbon occurred in atmosphere, vegetation and soils on land and in surface ocean This carbon (1010 gigatons) must have been moved to deep ocean This carbon (1010 gigatons) must have been moved to deep ocean Ice core data indicate atmospheric CO 2 30% lower Ocean mixed layer in equilibrium with atmosphere so it too was lower by 30% Terrestrial vegetation 25% lower Mass balance indicates 2.7% increase in deep ocean

Tracking Carbon  13 C values can be used to determine how carbon moved from surface reservoirs to deep ocean  13 C values can be used to determine how carbon moved from surface reservoirs to deep ocean Major carbon reservoirs have different amounts of organic and inorganic carbon Major carbon reservoirs have different amounts of organic and inorganic carbon  Each with characteristic  13 C values

 13 C Changes During Photosynthesis Large KIE during carbon fixation by plants Large KIE during carbon fixation by plants  Magnitude depends on C-fixation pathway

 13 C Tracks Carbon Transfer Isotope mass balance quantifies transfer of terrestrial C org to deep ocean Isotope mass balance quantifies transfer of terrestrial C org to deep ocean  C inorg *  13 C inorg + C org *  13 C org = C tot *  13 C  (38,000*0‰) + (530*-25‰) = (38530*x)  Solving for x = -0.34‰  Just this transfer predicts a shift in deep ocean DIC of –0.34‰  Isotopic change recorded in benthic foraminifera

Change in Benthic  13 C Oscillations in benthic  13 C correspond to benthic  18 O Oscillations in benthic  13 C correspond to benthic  18 O  100,000 and 41,000 year cycles  Confirm transfer of organic carbon to deep ocean during ice sheet expansion  13 C shifts greater than ~0.4‰  13 C shifts greater than ~0.4‰  Suggesting additional factors have affected oceanic  13 C values

Increase the Ocean Carbon Pump If biological productivity and C org export were higher in surface waters during glacial intervals If biological productivity and C org export were higher in surface waters during glacial intervals  Atmospheric CO 2 could be fixed in shallow ocean by phytoplankton  Sinking dead organic matter transfers that carbon to the deep ocean Biological productivity and export can only increase if essential nutrients increase in surface ocean Biological productivity and export can only increase if essential nutrients increase in surface ocean  Increases in wind-driven upwelling of deep, nutrient-rich water  Increases in the nutrient concentration of deep water that is already upwelling

The Iron Hypothesis In the 1980s, the late John Martin suggested that In the 1980s, the late John Martin suggested that  Carbon uptake during plankton growth in many regions of the world's surface ocean  Was limited not by light or the nutrients N and P But by the lack of the trace metal ironBut by the lack of the trace metal iron Iron is typically added to the open ocean as a component of dust particles Iron is typically added to the open ocean as a component of dust particles

The Iron Hypothesis Correlations between dust and atmospheric carbon dioxide levels in ancient ice core records Correlations between dust and atmospheric carbon dioxide levels in ancient ice core records  Suggest that the ocean would respond to natural changes in iron inputs  Higher glacial winds would increase the amount of windblown dust containing Fe to oceans  Stimulate phytoplankton growth Increasing carbon uptake and decrease atmospheric CO 2Increasing carbon uptake and decrease atmospheric CO 2 Alter the greenhouse gas balance and climate of the earthAlter the greenhouse gas balance and climate of the earth

Evidence for Iron hypothesis Some areas of the ocean contain high amounts of essential nutrients (N, P) Some areas of the ocean contain high amounts of essential nutrients (N, P)  Yet low amounts of chlorophyll (HNLC) Phytoplankton require Fe in small amounts for growth Phytoplankton require Fe in small amounts for growth  “Bottle experiments” demonstrate conclusively that addition of Fe stimulates phytoplankton growth  CO 2 uptake If Iron Hypothesis increased biological pump, iron addition must increase production and export

Open-Ocean Iron Enrichment "Give me half a tanker full of iron and I'll give you an ice age“ (John Martin) "Give me half a tanker full of iron and I'll give you an ice age“ (John Martin) Results of “fertilizing” large patches of the ocean with iron Results of “fertilizing” large patches of the ocean with iron  Showed strong biological response and chemical draw-down of CO 2 in the water column  But what was the fate of this carbon?  Plant uptake of carbon in the ocean is generally followed by zooplankton bloom Grazers respond to the increased food supplyGrazers respond to the increased food supply –Producing a blizzard of fecal pellets that descend through the water column –Exporting the carbon to the deep sea

Quantifying Carbon Export Thorium is a naturally occurring element that by its chemical nature is "sticky" Thorium is a naturally occurring element that by its chemical nature is "sticky"  Due to its natural radioactive properties, relatively easy to measure. Analysis of a series of samples collected during the 1995 FeEx II Analysis of a series of samples collected during the 1995 FeEx II  Indicated that as iron was added  Plant biomass increased  Total thorium levels decreased indicating carbon export

Quantifying Carbon Export After some delay After some delay  Particulate organic carbon export increased in the equatorial Pacific Relationship between uptake and export not 1:1 Relationship between uptake and export not 1:1  The iron-stimulated biological community showed  Very high ratios of export relative to carbon uptake  Thus the efficiency of the biological pump had increased dramatically

Quantifying Carbon Export Results of similar iron fertilization of Southern Ocean Results of similar iron fertilization of Southern Ocean  Slower biological response  Total thorium levels never responded  The biological pump was not activated Speculate that difference Speculate that difference  Slowness of the biological community's response to stimulation in colder waters  Biological pump may have turned on later

Persistence of Patch Sea surface color satellite image taken 32 days after the addition of Fe Sea surface color satellite image taken 32 days after the addition of Fe  Colored ring indicates area of high chlorophyll  Believed to be a result of the increased Fe

Iron Fertilization is Hot Topic Iron fertilization of the ocean captured attention of entrepreneurs and venture capitalists Iron fertilization of the ocean captured attention of entrepreneurs and venture capitalists  See potential for enhancing fisheries and gaining “C credits” through large-scale ocean manipulations

Marshall Islands Territorial waters of the Marshall Islands Territorial waters of the Marshall Islands  Leased to conduct an iron fertilization experiment The new businesses involved suggest that The new businesses involved suggest that  Iron fertilization process will reduce atmospheric CO 2 levels  Allowing Marshall Islands to profit by trading carbon credits with more industrialized nations  Increased fisheries as a consequence of enhanced phytoplankton production Iron additions could alter the ocean in unforeseen ways Iron additions could alter the ocean in unforeseen ways  Creating a polluted ocean with new opportunistic species that do not support enhanced fisheries

 13 C DIC Tracks Productivity Photosynthesis removes 12 C from surface ocean and exports it to deep ocean Photosynthesis removes 12 C from surface ocean and exports it to deep ocean  Close correlations between  13 C DIC and nutrients

Measuring Changes in the Carbon Pump Greater productivity during glaciations pumps more C org to deep sea, reduces atmospheric CO 2 Greater productivity during glaciations pumps more C org to deep sea, reduces atmospheric CO 2 Past changes in strength of carbon pump Past changes in strength of carbon pump  Recorded in planktic and benthic foraminifer

Past Changes in the Ocean Carbon Pump  13 C planktic-benthic are tantalizingly large when CO 2 is low and small when CO 2 is high  13 C planktic-benthic are tantalizingly large when CO 2 is low and small when CO 2 is high  Correlation not perfect  May explain as much as 25 ppm CO 2 lowering Best documented in equatorial regions Best documented in equatorial regions  Worse in Southern Ocean  Even HNLC regions  Detailed records lacking

Changes in Deep Water Circulation  13 C can be used to trace carbon transfer  13 C can be used to trace carbon transfer  Photosynthetic rate  Sets  13 C and nutrient levels in surface waters Water gets down-welled and carry the signalsWater gets down-welled and carry the signals  These factors can produce regional differences in the  13 C DIC Deep waters in different ocean basinsDeep waters in different ocean basins Monitors changes in deep water circulation with timeMonitors changes in deep water circulation with time

Modern Deep Ocean Circulation High  13 C values in N. Atlantic results from High  13 C values in N. Atlantic results from  High production in surface waters in subtropical latitudes  Transported north and sinks In contrast, intermediate waters originate in Antarctica In contrast, intermediate waters originate in Antarctica  Seasonal production produces lower 13 C enrichment These contrasts allows water masses to be tracked These contrasts allows water masses to be tracked

Atlantic Deep Water  13 C Deep water formed in N. Atlantic have high  13 C values and low nutrient concentrations Deep water formed in N. Atlantic have high  13 C values and low nutrient concentrations Intermediate waters formed in the Southern Ocean have low  13 C values and high nutrient concentrations Intermediate waters formed in the Southern Ocean have low  13 C values and high nutrient concentrations

 13 C Aging As the C org in deep water is gradually oxidized As the C org in deep water is gradually oxidized  12 C-rich CO 2 released lowering  13 C DIC  Particularly evident in deep Pacific waters

Past Changes in  13 C DIC  13 C of benthic foraminifera indicate changes in Atlantic deep water flow at the LGM  13 C of benthic foraminifera indicate changes in Atlantic deep water flow at the LGM  Northern water did not sink as deeply, not as dense  Relative increase in water flowing from Antarctica Knowing the  13 C of the source region (planktic foraminifera) Knowing the  13 C of the source region (planktic foraminifera)  Percent contribution from each region can be determined

Changing Sources of Atlantic Deep Water Long records of  13 C indicate cyclic changes in deep water sources Long records of  13 C indicate cyclic changes in deep water sources  North sources dominate during interglacial  Southern sources dominate during glacial  100,000 year cycle During glacial During glacial  Low  13 C water from Antarctica  Increase flux of 12 C carbon from continents  Additive effects explains large shifts noted earlier

Summary  13 C results indicate an important link  13 C results indicate an important link  Size of N. Hemisphere ice sheets  Formation of deep water in N. Atlantic Less deep water formed in the N. Atlantic Less deep water formed in the N. Atlantic  Every time ice sheets grew at a 100,000 year cycle  Must have affected atmospheric CO 2 concentrations But how?But how?

Changes in Ocean Chemistry CO 2 levels in surface waters sensitive to carbonate ion concentration CO 2 levels in surface waters sensitive to carbonate ion concentration  CO 3 2- produced when corrosive bottom waters dissolve CaCO 3  When CO 3 2- returned to surface waters Combine with CO 2 to form HCO 3 -Combine with CO 2 to form HCO 3 - Thus reducing CO 2 content of surface oceanThus reducing CO 2 content of surface ocean The corrosiveness of deep water determined by the weight of foraminifer shells The corrosiveness of deep water determined by the weight of foraminifer shells  Depth of the CCD Southern Ocean particularly vulnerable to changes in carbon ion concentration Southern Ocean particularly vulnerable to changes in carbon ion concentration

Carbon System Controls on CO 2 Increase biologic carbon pump in coastal and tropical ocean Increase carbon pump in Antarctic Change chemistry of Antarctic surface water Change chemistry of shallow Southern Ocean subsurface water