Presentation on theme: "Orbital-Scale Changes in Carbon Dioxide and Methane Ice Cores Orbital-Scale Changes in CO2 Carbon in the Deep Ocean Orbital-Scale Changes in CH4 Orbital-Scale."— Presentation transcript:
Orbital-Scale Changes in Carbon Dioxide and Methane Ice Cores Orbital-Scale Changes in CO2 Carbon in the Deep Ocean Orbital-Scale Changes in CH4 Orbital-Scale Climatic Roles: CO2 and CH4 Adrienne, Ally, Chase, Mohamed, Patrick, Travious
Ice Cores Break Down http://www.nsf.gov/news/special_rep orts/science_nation/icecorelab.jsp
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.
Drilling Scientists 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.
Dating Ice Cores This ice core shows 12 Years of layering
Climate Readings Over Time
Trapping Air Bubbles in Ice Snow Accumulation Rate Greenland =.5 m/yr Antarctica =.05 m/yr
Verifying Ice Core Measurements of Ancient Air Before interpreting records of greenhouses gases trapped in ice cores Measuring air bubbles deposited in the upper layers of ice in cores taken from recent years
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 forms Organic carbon, which includes both living and dead organic matter. Inorganic carbon, which consists mainly of ions dissolved in water.
How Ice Cores Are Dated – Ice 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.
Orbital-Scale Changes in CO2
Orbital-scale Changes in CO 2 CO 2 concentrations and Ice volume correlations date back more than 650,000 years Where could the 90- ppm decline of CO 2 in the atmosphere during glacial intervals have gone?
Vegetation-soil Reservoirs Extensive information on vegetation and soil carbon stores e.g. lake cores containing pollen Shows that continents had less vegetation during glaciations than during interglaciations not like today Totals ~25% less vegetation (2160-1630 tons) 1.Expansive ice sheets displaced or covered forests 2.Forests then replaced by grassland This means there is additional carbon missing from land vegetation and soil on top of that missing from the atmosphere!
Ocean Reservoirs 30ppm CO 2 values in surface ocean waters Surface waters exchange CO 2 too rapidly (within a few years) with the atmosphere Question: If glacial atmosphere CO 2 values were to decrease by 30%, what would happen soon after to surface ocean values? Answer: Surface ocean CO 2 values would also decrease by ~30%. Deep-ocean waters are only remaining available carbon reservoir
Total CO 2 Transferred <1000 billion tons of carbon removed from the atmosphere, vegetation, soil and surface oceans and added to the deep ocean. Keep these numbers in mind…
Carbon Transfer from Land to Ocean Organic carbon in vegetation has negative δ 13 C values of -25% Inorganic carbon has values near 0% Most organic carbon transferred converts to inorganic This causes inorganic carbon δ 13 C values to become even more negative 12 C-enriched carbon was added to deep ocean waters during glaciations
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 δ 13 C from land δ 13 C carbon total δ 13 C x=-0.34 If x=δ 13 C value of glacial inorganic carbon in the ocean, then δ 13 C values shifted to - 0.34% Shows correlation between carbon transfer and ice volume δ 13 C value variations greater than -.4% suggest that other factors may be in effect Do these intervals look familiar to anyone?
To Re-Cap Ice core samples show a decrease in atmospheric CO 2 of 90 ppm (~30%) Terrestrial vegetation was ~25% less, as well Surface oceans (in equilibrium with the atmosphere) also had less CO 2 (~30) CO 2 must have gone into deep-ocean waters Determined using evidence obtained from ice cores, continental lake floor cores, Pacific ocean seafloor cores, δ 13 C measurements in foraminifera and δ 13 C/δ 18 O correlations
Carbon in the Deep Ocean
CO 2 Solubility in Seawater Changes in ocean temperature affect solubility of CO 2 CO 2 dissolves faster in cold water ~10 ppm per 1ºC drop Surface water has cooled from 2º C to -4ºC in last 20k years Deep sea cooled an avg. 2ºC to -3ºC Should cause a ~20-30 ppm drop in atmospheric CO 2 levels
Effect of Salinity on CO 2 Solubility CO 2 dissolves easier in low salinity water Glacial oceans were saltier because of freshwater locked in ice (avg. increase of 1.1‰) Increase in ocean salinity would raise atmospheric CO 2 by 11 ppm 11 ppm increase offsets 20-30 ppm decrease from temp. change to ~14 ppm CO 2 decrease
An example of modern-day carbon production of the surface ocean. 1.Photosynthesis occurs creating phytoplankton. 2.Phytoplankton incorporate with organic matter and sink to the deep ocean. May have been responsible for reduced atmospheric CO 2 levels during glaciations. Biological Transfer and Carbon Pumping
More on Photosynthesis Photosynthesis: 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2 Calcium Carbonate Pump H 2 O + CO 2 → H 2 CO 3 H 2 CO 3 → H + + HCO 3 - Ca 2+ + 2HCO 3 → CaCO 3 + H 2 O + CO 2
Carbon Pumping Continued Organic material that falls to ocean floor remains unless it is moved to surface by upwelling High productivity occurs in areas where upwelling provides nutrients to surface
The Iron Fertilization Hypothesis as proposed by John Martin An iron “boost” brought on by strong glacial winds Possibly stimulates more productivity and carbon pumping to the deep ocean May deliver other key elements to stimulate carbon productivity and is still being debated
Glacial Carbon Pump CO 2 at surface decreases as photosynthesis increases The carbon that is fixed by photosynthesis is 12 C and therefore 13 C becomes more abundant Differences in δ 13 C levels indicates strength of the carbon pump
Changes in Deep Water Circulation How it's measured Equation used to track carbon transfers on Earth.
Circulation of Ocean
Changes in Deep-water Circulation δ 13 C measurements from foraminifera suggest circulation patterns have changed. Focuses on regional δ 13 C variations δ 13 C aging also affects patterns
Changing sources of Atlantic deep water
Deep-Ocean Carbon Deposit Causes 1. Evidence of carbon transfer from ice to ocean δ 13 C and δ 18 O Benthic forminifera measurements to detect δ 13 C levels during glaciation 2. Increased CO 2 solubility in Seawater Affected by temperature and salinity 3. Biological transfer from surface waters Carbon pumps Iron fertilization hypothesis 4. Changes in deep-water circulation Regional variations Atlantic circulation changes
Carbon In the Deep Ocean Review Cold seawater dissolves CO 2 easier CO 2 levels will drop by 9 ppm for each 1º of ocean cooling CO 2 dissolves better in seawater with a lower salinity An increase in ocean salinity would raise atmospheric CO 2 by 11 ppm Surface water has cooled from 2º C to -4ºC in last 20k years Deep sea temperature averages cooled 2ºC to -3ºC Should cause a ~20-30 ppm drop in atmospheric CO 2 levels
Orbital Scale Changes in CH 4
Most natural Methane production occurs in wetlands Requires oxygen poor environments Microbes in wetlands consume oxygen quicker than it can diffuse from the atmosphere Fermentation occurs -microorganisms (methanogens) ferment acetate and H 2 -CO 2 into methane and carbon dioxide
Methane Formation in Wetlands
Methane Concentrations in Ice Cores Vostock Ice, 23,000 year intervals cycle Maxima 650-700 ppb Minima 350-450 ppb Very similar to northern hemisphere summer insolation
Insolation Effects on Monsoons High insolation heats land faster than ocean Warm land air expands and rises Low pressure brings in water vapor
Monsoons, Insolation and Methane Monsoon intensity related to insolation levels Monsoons increase wetland area size More wetlands-more methane being produced
Summary Methane is naturally produced in wetlands Insolation levels and monsoon intensity are linked Methane variations at the 23,000 year cycle linked to changes in summer monsoons Higher insolation= more monsoons= more methane
Orbital scale climatic roles of co2 and ch4 Forcing Feedback
Milankovitch Milankovitch theory
Milankovitch cycles Three different cycles – 23,000 year (Precession) – 41,000 year (Obliquity) – 100,000 year (Eccentric)
Summary of cycles 23,000 year cycle – Co2 and methane act as a forcing 41,000 year cycle – Co2 and methane act as a feedback 100,000 year cycle – Co2 and methane act as a combination of a large feedback role and a smaller forcing role.
23,000 year cycle highlights Both greenhouse gases – Forcing – Response Co2 – Response Methane – Response
41,000 year cycle highlights Both greenhouse gases – Feedback – Response – Not forcing? Co2 – Signals
100,000 year cycle highlights Both greenhouse gases – Mixed feedback/forcing role – Not clear? Changes in Earth ’ s orbit – Summer insolation forcing
Time lags and phases Co2 Ice sheets Earth ’ s orbit – Summer insolation forcing Leads –“ forcing ” or a “ feedback ” ?
Recap Phasing of gases Changes in ice volume
Recap Ice Cores Orbital-Scale Changes in CO2 Carbon in the Deep Ocean Orbital-Scale Changes in CH4 Orbital-Scale Climatic Roles: CO2 and CH4
http://en.wikipedia.org/wiki/D13C http://bcs.whfreeman.com/ruddiman/con_index.htm?11 http://www.nsf.gov/news/special_reports/science_nation/icecorelab. jsp Ruddiman, W. (2008). Earth's climate past and future. (2 ed.). New York: W.H. Freeman and Company. Works Cited