Presentation on theme: "Orbital-Scale Changes in Carbon Dioxide and Methane"— Presentation transcript:
1 Orbital-Scale Changes in Carbon Dioxide and Methane Adrienne, Ally, Chase, Mohamed, Patrick, TraviousIce CoresOrbital-Scale Changes in CO2Carbon in the Deep OceanOrbital-Scale Changes in CH4Orbital-Scale Climatic Roles: CO2 and CH4
4 Ice Cores Drilling into glacial ice allows us to see back in time. Each winter new snow fall packs on top of previous snow. This creates a new band each year.
5 DrillingScientists searching for the oldest ice in an ice sheet, drill from the top of the highest ice domes.Drilling is done over the summer in which it takes a few summers to drill completely through an ice sheet.Some ice cores can be dated by counting annually deposited layers.
6 Dating Ice CoresThis ice core shows 12 Years of layering
8 Trapping Air Bubbles in Ice Snow Accumulation RateGreenland = .5 m/yrAntarctica = .05 m/yr
9 Verifying Ice Core Measurements of Ancient Air Before interpreting records of greenhouses gases trapped in ice coresMeasuring air bubbles deposited in the upper layers of ice in cores taken from recent years
10 Orbital Scale Carbon Transfer: Carbon Isotopes Most carbon occurs in oxygen-rich environments in the atmosphere, oceans, and vegetation.Carbon moves among these reservoirs in one of two formsOrganic carbon, which includes both living and dead organic matter.Inorganic carbon, which consists mainly of ions dissolved in water.
11 How Ice Cores Are DatedIce layers are counted from the top layer down starting from the year ice coring began.Ice flow models are based on the physical properties of the ice sheet.Why are air bubbles in ice cores younger than the ice in which they are sealed?Because the surrounding ice was deposited many years earlier. If deposition of ice is fast the age difference between the bubbles and the ice enclosing them will only be a few hundred years. If the deposition is slow the age offset can be as large as 2000 years or more.
13 Orbital-scale Changes in CO2 CO2 concentrations and Ice volume correlations date back more than 650,000 yearsWhere could the 90-ppm decline of CO2 in the atmosphere during glacial intervals have gone?
14 Vegetation-soil Reservoirs Extensive information on vegetation and soil carbon stores e.g. lake cores containing pollenShows that continents had less vegetation during glaciations than during interglaciations not like todayTotals ~25% less vegetation ( tons)Expansive ice sheets displaced or covered forestsForests then replaced by grasslandThis means there is additional carbonmissing from land vegetation and soilon top of that missing from the atmosphere!
15 Deep-ocean waters are only remaining available carbon reservoir Ocean Reservoirs30ppm CO2 values in surface ocean watersSurface waters exchange CO2 too rapidly (within a few years) with the atmosphereQuestion: If glacial atmosphere CO2 values wereto decrease by 30%, what would happensoon after to surface ocean values?Answer: Surface ocean CO2 values wouldalso decrease by ~30%.Deep-ocean waters are only remaining available carbon reservoir
16 Total CO2 Transferred <1000 billion tons of carbon removed from the atmosphere, vegetation, soiland surface oceans and addedto the deep ocean.Keep these numbers in mind…
17 Carbon Transfer from Land to Ocean Organic carbon in vegetation has negative δ13C values of -25%Inorganic carbon has values near 0%Most organic carbon transferred converts to inorganicThis causes inorganic carbon δ13C values to become even more negative12C-enriched carbonwas added to deepocean waters during glaciations
18 Do these intervals look familiar to anyone? Carbon Transfer from Land to Ocean (38,000) (0%) (530) (-25%) = (38,530) (x%) Inorganic C Mean C added Mean Glacial ocean Mean in ocean δ13C from land δ13C carbon total δ13C x=-0.34If x=δ13C value of glacial inorganic carbon in the ocean, then δ13C values shifted to -0.34%Shows correlation between carbon transfer and ice volumeδ13C value variations greater than -.4% suggest that other factors may be in effectDo these intervals look familiar to anyone?
19 To Re-CapIce core samples show a decrease in atmospheric CO2 of 90 ppm (~30%)Terrestrial vegetation was ~25% less, as wellSurface oceans (in equilibrium with the atmosphere) also had less CO2 (~30)CO2 must have gone into deep-ocean watersDetermined using evidence obtained from ice cores, continental lake floor cores, Pacific ocean seafloor cores, δ13C measurements in foraminifera and δ13C/δ18O correlations
21 CO2 Solubility in Seawater Changes in ocean temperature affect solubility of CO2CO2 dissolves faster in cold water ~10 ppm per 1ºC dropSurface water has cooled from 2º C to -4ºC in last 20k yearsDeep sea cooled an avg. 2ºC to -3ºCShould cause a ~20-30 ppm drop in atmospheric CO2 levels
22 Effect of Salinity on CO2 Solubility CO2 dissolves easier in low salinity waterGlacial oceans were saltier because of freshwater locked in ice (avg. increase of 1.1‰)Increase in ocean salinity would raise atmospheric CO2 by 11 ppm11 ppm increase offsets ppm decrease from temp. change to ~14 ppm CO2 decrease
23 Biological Transfer and Carbon Pumping Photosynthesis occurs creating phytoplankton.Phytoplankton incorporate with organic matter and sink to the deep ocean.May have been responsible for reduced atmospheric CO2 levels during glaciations.An example of modern-day carbon production of the surface ocean.
24 More on Photosynthesis 6CO2 + 6H2O → C6H12O6 + 6O2Calcium Carbonate PumpH2O + CO2 → H2CO3H2CO3 → H+ + HCO3-Ca2++ 2HCO3 → CaCO3 + H2O + CO2
25 Carbon Pumping Continued Organic material that falls to ocean floor remains unless it is moved to surface by upwellingHigh productivity occurs in areas where upwelling provides nutrients to surface
26 The Iron Fertilization Hypothesis as proposed by John Martin An iron “boost” brought on by strong glacial windsPossibly stimulates more productivity and carbon pumping to the deep oceanMay deliver other key elements to stimulate carbon productivity and is still being debated
27 Glacial Carbon PumpCO2 at surface decreases as photosynthesis increasesThe carbon that is fixed by photosynthesis is 12C and therefore 13C becomes more abundantDifferences in δ 13C levels indicates strength of the carbon pump
28 Changes in Deep Water Circulation How it's measured Equation used to track carbon transfers on Earth.The standard established for carbon-13 work was the Pee Dee Belemnite or (PDB) and was based on a Cretaceous marine fossil, Belemnitella americana, which was from the Pee Dee Formation in South Carolina.
30 Changes in Deep-water Circulation δ13C measurements from foraminifera suggest circulation patterns have changed.Focuses on regional δ13C variationsδ13C aging also affects patterns
31 Changing sources of Atlantic deep water The percentage of deep water originating in the North Atlantic and flowing of the equator during the last 1.25 Myr has been consistently lower during glaciations than during interglaciations.
32 Deep-Ocean Carbon Deposit Causes 1. Evidence of carbon transfer from ice to oceanδ13C and δ18OBenthic forminifera measurements to detect δ13C levels during glaciation2. Increased CO2 solubility in SeawaterAffected by temperature and salinity3. Biological transfer from surface watersCarbon pumpsIron fertilization hypothesis4. Changes in deep-water circulationRegional variationsAtlantic circulation changes
33 Carbon In the Deep Ocean Review Cold seawater dissolves CO2 easierCO2 levels will drop by 9 ppm for each 1º of ocean coolingCO2 dissolves better in seawater with a lowersalinityAn increase in ocean salinity would raise atmospheric CO2 by 11 ppmSurface water has cooled from 2º C to -4ºC in last 20k yearsDeep sea temperature averages cooled 2ºC to -3ºCShould cause a ~20-30 ppm drop in atmospheric CO2 levels
35 Orbital Scale Changes in CH4 Most natural Methane production occurs in wetlandsRequires oxygen poor environmentsMicrobes in wetlands consume oxygen quicker than it can diffuse from the atmosphereFermentation occurs -microorganisms (methanogens) ferment acetate and H2-CO2 into methane and carbon dioxide
41 Summary Methane is naturally produced in wetlands Insolation levels and monsoon intensity are linkedMethane variations at the 23,000 year cycle linked to changes in summer monsoonsHigher insolation= more monsoons= more methane
42 Orbital scale climatic roles of co2 and ch4 ForcingFeedback
44 Milankovitch cycles Three different cycles 23,000 year (Precession) 41,000 year (Obliquity)100,000 year (Eccentric)
45 Summary of cycles 23,000 year cycle 41,000 year cycle Co2 and methane act as a forcing41,000 year cycleCo2 and methane act as a feedback100,000 year cycleCo2 and methane act as a combination of a large feedback role and a smaller forcing role.
46 23,000 year cycle highlights Both greenhouse gases Co2 Methane Forcing ResponseCo2Methane
47 41,000 year cycle highlights Both greenhouse gases Co2 Feedback ResponseNot forcing?Co2Signals
48 100,000 year cycle highlights Both greenhouse gases Mixed feedback/forcing roleNot clear?Changes in Earth’s orbitSummer insolation forcing
49 Time lags and phases Co2 Ice sheets Earth’s orbit Leads Summer insolation forcingLeads“forcing” or a “feedback” ?