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2006 Atmosphere

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Information about 2006 Atmosphere
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Published on October 12, 2007

Author: AscotEdu

Source: authorstream.com

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Atmospheric D14C:  Atmospheric D14C Radiocarbon short course Jim Randerson Department of Earth System Science University of California, Irvine Outline:  Outline Atmospheric circulation Atmospheric distribution of CO2, d13C, D14C Suess Effect Atmospheric isotopic disequilibria Pre-Industrial Atmospheric Radiocarbon Tracing the fate of bomb radiocarbon Early 1960s Contemporary components Future Biosphere-atmosphere exchange Ocean-atmosphere exchange Time Constants for Atmospheric Mixing:  Time Constants for Atmospheric Mixing East-west mixing at mid latitudes takes ~ 3 - 4 weeks North-south mixing across the equator is ~ 1 year Australian Government, Bureau of Meteorology East-west mixing in the tropics is slow compared with vertical convection – surface air from Equatorial Asia does not reach the Amazon – first it is lofted off the surface Meridional Atmospheric Circulation:  Meridional Atmospheric Circulation Plumb and McConalogue [1988] ‘Using surface flask measurements to study tropical biology is like searching for your keys underneath the street lamp, even though you dropped them by your car.’ --Joe Berry Implications of Meridional Atmospheric Circulation for Trace Gas Observations :  Implications of Meridional Atmospheric Circulation for Trace Gas Observations Strong vertical convection in the tropics carries signals (imparted to trace gases) away from the surface and into the mid and upper troposphere Surface observations (e.g., the flask networks) are great for studying boreal and polar regions, but inadequate for studying tropical biosphere-atmosphere exchange or tropical ocean exchange Any inert source released into the atmosphere is well mixed through-out the northern and southern hemispheres after 3 years, since the interhemispheric mixing time is ~ 1 year th = 1 year, so the difference from background after 3 years is (1 - e-3) Stratospheric Circulation :  Stratospheric Circulation Air enters the stratosphere in the tropics Return flux from stratosphere to the troposphere occurs in the extratropics (poleward of 30°) Residence time of air the lower stratosphere is ~ 1.5 years Strat-trop exchange (STE) is greatest during spring ESPERE Stratospheric Residence Times:  Stratospheric Residence Times Troposphere air mixes relatively quickly – air at point r was in contact with the surface, on average, 0.74 years ago. Air entering the stratosphere takes on average 2.7 years to return to the surface Holzer and Hall, 2000 GISS chemical transport model Diurnal Rectifier Forcing:  Diurnal Rectifier Forcing Daily mean: Accumulation of CO2 near the ground, depletion aloft Denning, 1996 Seasonal Rectifier Forcing:  Seasonal Rectifier Forcing Annual mean: Accumulation of CO2 near the ground, depletion aloft Dilution of photosynthesis signal through deep mixing Transport of low-CO2 air into upper troposphere Accumulation of respiration signal near the surface Elevated CO2 in lower troposphere Denning, 1996 CO2 Concentrations Build Up in the Nocturnal Boundary Layer- Amazon Basin:  CO2 Concentrations Build Up in the Nocturnal Boundary Layer- Amazon Basin ABLE Aircraft Observations April – May 1987 Harriss et al. Chou et al. Implications of the Rectifier Effect for Trace Gas Observations :  Implications of the Rectifier Effect for Trace Gas Observations A diurnally varying CO2 source that is in net balance over 24 hours will cause a positive concentration anomaly at the surface when averaged over 24 hrs. A seasonally varying source that is annually balanced will cause a positive concentration anomaly at the surface when averaged over a year If these effects are not considered carefully in models, it could lead to biases in model estimates of carbon sources and sinks Slide13:  CO2 (ppm) Year Latitude NOAA/CMDL Latitudinal Distribution of Carbon Dioxide Conway, et al. [1994] Tans et al. [2001] The Flying Carpet of Contemporary Atmospheric Carbon Dioxide has Three Key Features :  The Flying Carpet of Contemporary Atmospheric Carbon Dioxide has Three Key Features A long-term growth rate that is set by fossil fuel emissions and ocean and land carbon sinks A latitudinal (north-south) gradient that is caused by fossil fuel emissions in the northern hemisphere and an interhemispheric exchange time of ~1 year A large seasonal cycle in the northern hemisphere caused by asynchronous terrestrial net primary production and heterotrophic respiration. Heterotrophic respiration consists of decomposition by bacteria and fungi plus respiration from herbivores (minor component). Slide15:  Where are Fossil Fuel Emissions into the Atmosphere? Global Trend Change in latitudinal distribution with decade Latitude distribution Randerson et al. [1997] Surface Fluxes – Northern Hemisphere Temperate and Boreal Terrestrial Ecosystems :  Surface Fluxes – Northern Hemisphere Temperate and Boreal Terrestrial Ecosystems g C / m2 / month J F M A M J J A S O N D Rh NPP NEP The Terrestrial Sink from the N-S CO2 gradient:  The Terrestrial Sink from the N-S CO2 gradient The observed gradient is shallower than expected from the distribution of fossil fuel and land use in atmospheric models. Tans et al. 1990 W-E mixing is so rapid that trace gas gradients are very difficult to detect. Need a gradient to infer regional sources/sinks NOAA/CMDL Latitudinal Distribution of Carbon Dioxide Conway, et al. [1994] Land/Ocean sinks from 13C:  Land/Ocean sinks from 13C The basic equation C3 ~ 20‰ C4 ~ 4.4‰ O ~ 2‰ A terrestrial sink makes the atmosphere heavier ( more enriched in d13C) An ocean sink has little effect on atmospheric 13C A C4 sink looks like ocean to the atmosphere As with CO2, the atmosphere shows signs of terrestrial uptake, mainly at high latitudes. But the “disequilibrium” problem makes the interpretation of 13C very challenging. Slide19:  Suess Effect: Fossil fuel-driven depletion of atmospheric D14C Jacobson [2000] SUESS HE RADIOCARBON CONCENTRATION IN MODERN WOOD,  SCIENCE, 122 (3166): 415-417 1955 Slide20:  Suess Effect: The Pre-Bomb Depletion of Atmospheric D14C by Fossil Fuels Also Applied to the Depletion of Atmospheric d13C by Fossil Fuels Francey et al. [1999] d13C (per mil) CO2 (ppm) SUESS HE RADIOCARBON CONCENTRATION IN MODERN WOOD  SCIENCE 122 (3166): 415-417 1955 The d13C Isotopic Disequilibrium:  The d13C Isotopic Disequilibrium Atm. d13C (‰) time Gba Gab Isotopic Disequilibrium tb tb = Mean Residence Time -6.5 -8.0 Atmospheric Isotopic Disequilibrium :  Atmospheric Isotopic Disequilibrium Isotopic reservoirs in ocean or land reservoirs that are not in steady state with the contemporary atmosphere Increases with the mean residence time of carbon in the terrestrial or oceanic reservoir exchanging with the atmosphere The impact of disequilibrium on atmospheric D14C levels also depends on the size of the gross flux. The product of the disequilibrium and the gross flux is known as the ‘disequilibrium forcing’ and has units of: Gt C ‰/yr Radiocarbon disequilibria can be either positive or negative Tropical forests are currently enriching the atmosphere in 14C (a positive disequilibrium) Southern ocean continues to expose pre-bomb DIC to the atmosphere, depleting the atmosphere in 14C (a negative disequilibrium) Age of respiration from the CASA model:  Age of respiration from the CASA model Randerson et al. [2006] A cohort of NPP will return to the atmosphere with the following age distribution. The Product of Net Primary Production and Mean Residence Times of Carbon in Terrestrial Ecosystems Determines Isotopic Disequilibrium Forcing:  The Product of Net Primary Production and Mean Residence Times of Carbon in Terrestrial Ecosystems Determines Isotopic Disequilibrium Forcing Years g C / m2 NPP MRT Boreal forests and tropical forests have large disequilibrium forcing terms Contemporary Atmospheric Radiocarbon:  Contemporary Atmospheric Radiocarbon Joos et al., data from Levin, Manning Why is there a seasonal cycle in the northern hemisphere in the early 1960s? Why is New Zealand becoming more enriched than Europe in 1990s? Why should we care about atmospheric D14C variability? Controls on Pre-Industrial Atmospheric D14C:  Controls on Pre-Industrial Atmospheric D14C Tropospheric levels represents the balance between cosmogenic production (in the stratosphere and upper troposphere) and the flux into the deep ocean Atmospheric D14C can increase either from an increase in cosmogenic production or from a shutdown in deepwater formation Flux into the ocean and land carbon reservoirs is proportional to the 14C/12C ratio of the troposphere The D14C of the carbon flux into the terrestrial biosphere or ocean surface is exactly the same as the D14C of atmospheric CO2 at the time of the flux Cosmogenic Production of 14C:  Cosmogenic Production of 14C Cosmogenic production is 2.3-2.5 RCUs per year 1 RCU = 1 x 1026 atoms of 14C = 2.3 Kg 14C/yr Depends on sunspot activity, magnetic field of the earth Braziunas, Fung, and Stuiver, GBC 1996 Pre-Industrial D14C Distribution:  Pre-Industrial D14C Distribution Braziunas, Fung, and Stuiver, GBC 1996 Interhemispheric pre-industrial gradient depends on the strength of deep water ventilation in Southern Ocean and North Atlantic/North Pacific Most Aboveground Nuclear Tests were Conducted in the Northern Hemisphere:  Most Aboveground Nuclear Tests were Conducted in the Northern Hemisphere Randerson et al. [2002] Slide30:  RCUs per month RCUs (x 1026 14C atoms) Year b) a) c) 1 box stratosphere mass 2 box stratosphere mass stratosphere inputs and losses t = 2.5 year tlower = 1.9 years tupper = 5.0 years Sratosphere D14C Data from Telegadas, 1971 summarized by Tans, 1981 Stratospheric Inputs and Losses from Weapons Tests ~ 625 RCUs from bombs Test Ban Treaty of 1963 Randerson et al. [2002] Linus Pauling, 1901-1994:  Linus Pauling, 1901-1994 1954: Receives the Nobel Prize in Chemistry for "his research into the nature of the chemical bond and its applications to the elucidation of the structure of complex substances.“ 1963: Awarded the Nobel Peace Prize for 1962. Watson and Crick published their double helix paper in Nature in 1953 – receiving the Nobel Prize in 1962 The scientific basis for understanding radiation effect on DNA were nascent/non-existent (i.e., The Firecracker Boys by Dan O’Neill) Linus Pauling Institute Observed Bomb 14C in the Atmosphere: Northern Hemisphere:  Observed Bomb 14C in the Atmosphere: Northern Hemisphere Year 14C (‰) Nydal and Lovseth [1996] Fruholmen, Norway 71°N Average of 5 Stations North of 37°N 14C (‰) Because STE is greatest during spring, radiocarbon levels were at a maximum during summer (a phase delay of ¼ cycle) Composition of the stratospheric radiocarbon flux has changed over time:  Composition of the stratospheric radiocarbon flux has changed over time Randerson et al. [2002] Snapshot: Atmosphere Anomalies 1965:  Snapshot: Atmosphere Anomalies 1965 Ocean component: Land component: Without land exchange, the bomb spike would have been ~50‰ higher Slide35:  Ocean component: Land component: Snapshot: Atmosphere Anomalies 1990 By 1990, the land enriches the northern atmosphere because respiration has a higher D14C than the atmosphere Slide36:  Total Atmospheric D14C Anomaly in 1990 Includes fossil fuels, terrestrial biosphere, ocean, and stratosphere (including cosmogenic production and tropospheric recycling) contributions Randerson et al. [2002] Contributions to Contemporary Interhemispheric Variations in D14CO2:  Contributions to Contemporary Interhemispheric Variations in D14CO2 Krakauer et al., Tellus [In Press] Atmospheric Variability has the Potential to Affect the Dating of Rapid Turnover Carbon Pools:  Atmospheric Variability has the Potential to Affect the Dating of Rapid Turnover Carbon Pools Krakauer Slide39:  Fruholmen, Norway 71°N Levin and Hesshaimer 2001 Slide40:  Δ14C measurements of corn from the continental U.S. during the summer of 2004 Continental Variations in Atmospheric D14C Slide41:  Hsueh et al. [Submitted] Slide42:  Hsueh What is the Future of Atmospheric Radiocarbon?:  What is the Future of Atmospheric Radiocarbon? Will atmospheric D14C drop below 0 per mil? The Future of Atmospheric Radiocarbon:  The Future of Atmospheric Radiocarbon Cadeira et al. GRL 1998 With a IPCC ‘Business as Usual’ fossil fuel trajectory, Atmospheric D14C will drop below 0‰ in another two decades. Atmospheric levels will be below -150‰ by the end of the 21st century Slide45:  Year D14C a) b) c) d) Atmosphere or NPP MRT = 13 years MRT = 24 years MRT = 48 years Heterotrophic Respiration Contributions of the Terrestrial Biosphere to the Seasonal Cycle of Atmospheric D14C Reverses Phase Atmospheric Radiocarbon Summary:  Atmospheric Radiocarbon Summary Northern Hemisphere (extra tropical) stratosphere-troposphere mixing is greatest during April and May CO2 from the land biosphere is currently more enriched in D14C than the contemporary atmosphere, reverse in 1960s The Southern Ocean is the biggest sink for atmospheric radiocarbon atoms Tropical D14C values can be 5‰ to 15‰ more enriched than NH ‘background’ observation stations Both tropical forests and the ventilated thermocline have decadal turnover times FF in NH and outcropping of intermediate waters in SH drive down D14C near poles What is the effect of the rectifier effect on sampling atm. D14C near ecosystems?:  What is the effect of the rectifier effect on sampling atm. D14C near ecosystems? Assume that you are sampling the atmosphere near the surface with a constant speed pump NaOH samplers Slow fill canisters, with a pinhole valve Assume that ecosystem respiration is more enriched in D14C than the background atm. Answer: Sampling the atmosphere at a constant speed will lead to a greater amount of CO2 in your sample from respiration during nighttime periods, because the concentration of CO2 is higher during periods when respiration is trapped near the surface This will enrich the sample in D14C relative to the background atmosphere. What is the effect of the rectifier effect on sampling atm. D14C near ecosystems?:  What is the effect of the rectifier effect on sampling atm. D14C near ecosystems? Assume that you are sampling the atmosphere near the surface with a constant speed pump NaOH samplers Slow fill canisters, with a pinhole valve Assume that ecosystem respiration is more enriched in D14C than the background atm. Slide49:  Broecker and Peng [1998] Two key ocean parameters (unknowns) Two constraints: Ocean inventory of bomb radiocarbon Penetration depth of bomb radiocarbon Slide50:  Broecker and Peng [1998] Slide51:  Broecker and Peng [1998] Broecker proved that that biomass burning was not 10-15 Pg C/yr, as claimed by Woodwell, using radiocarbon, in part, as a constraint on rates of ocean uptake of CO2 Slide52:  Broecker and Peng [1998] Approach:  Approach GISS atmospheric transport model Interactive biosphere-atmosphere exchange in 8 continental scale regions Satellite NDVI used to estimate seasonal cycle of APAR in each region Northern Hemisphere light use efficiency, Q10, and 13C discrimination values optimized using the seasonal cycle from flask data Ocean surface D14C and surface fluxes prescribed from LLNL ocean model (Caldeira and Duffy) Stratospheric 14C inputs injected into the atmospheric model at 200mb in regions north of 30°N. Russians: Nova Zemlya Americans: Pacific Ocean – Northern Tropics

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