Presentation on theme: "Triple Oxygen Isotopes 11/1/10"— Presentation transcript:
1Triple Oxygen Isotopes 11/1/10 Lecture outline:atmospheric O2 cyclemass-independentfractionation in thestratosphereΔ17O asproductivity proxy- ocean today- paleo-evidenceA C141 military aircraft is regularly used for atmospheric gas sampling, especially in polar regions
3Mass-independent fractionation of O in stratosphere This anomalousO2 “leaks” intothe troposphere,enters biosphere,and becomesfractionated alongmass-dependentline.Can define anomalous17O signal as:average air usedas standard,reported as parts per meg(1 in 106)empiricallydeterminedThiemens and Heidenreich, 1983; Theimens, 1999 (review)
4Isotopic analysis of CO2 samples collected in S.H. at various altitudesThiemens et al., GRL, 1995Which are the high-altitudesamples? Why?But I thought we said thatthe stratospheric signal wasa depletion of 17O relativeto the mass-dependent line?So Thiemens provedthat the Δ17O anomalyis generated in theupper stratosphereENDMEMBER #1Why the large difference in analytical errorbetween 14CO2 and 17CO2?
5Closed biological system – steady state Δ17O (wrt air)? Luz et al., GRL, 1999“steady state” mass-dependent O2falls on this line (from samples above),defines a mass-dependent end-member,vs. the mass-independent stratsophericendmemberd17Oslope = 0.52intercept0.155ENDMEMBER #2d18O
6Mass-independent oxygen fractionation schematic NOTE: these authors are using troposphericair (HLA) as their standard for δ17O, δ18O, Δ17O- contains signature of stratospheric 17O anomalyAll of these fluxes are in steady state.Idea: A change in any of these fluxes willresult in a new steady state value oftropospheric and surface ocean Δ17O of O2.Luz et al., 1999
7Triple oxygen Isotopes as measure of ocean productivity Idea:1) measure O2 conc in surface water2) measure Δ17O in surface waterThree scenarios:If photosynthesis > respiration,then [O2]> saturation, Δ17O > waterin equilibrium w/air2) If respiration > photosynthesis,then [O2}< saturation, Δ17O > water3) if no biological activity,then [O2] = saturation, Δ17O = waterin equilibrium with airHow is ocean productivitytraditionally measured?satellite photo coccolithophore bloom off Newfoundland
8Ocean Net Productivity – model and results Bender, Perspective, Science 2000Luz and Barkan, 2000Tracers for net and gross production. Δ17O and [O2]/[O2]sat values for seawater at equilibrium with air. Black lines: Coevolution of 17O and [O2]/[O2]sat for photosynthesis and respiration in a closed system. Coevolution lines are plotted for net/gross production > 0 [photosynthesis (P) > respiration (R)] and < 0 (P < R). Data points are for the euphotic zone of the Atlantic Ocean near Bermuda on 7 July The ratio of net/gross O2 production, which can be read from this diagram, is ~0.05 in the mixed layer (top 10 m) and 0.1 in the upper part of the euphotic zone (depth of 20 to 60 m).
9Using Δ17O to calculate past biosphere production in ice cores Luz et al., 1999RESULTSHmmmm… productivity didn’t change by much during glacialbut terrestrial biosphere was significantly reduced …. ocean productivitymust have increased during the glacial to compensate the loss of terr. productivity
10Using Δ17O to calculate past biosphere production in ice cores: a continuous Δ17O recordObservations:GISP and Antarctic valuessimilar within error- glacial values are higherFacts:CO2 lower duringglacial(should increase Δ17O)land productivitydiminished (fewertrees; should decreaseΔ17O)So what about glacialocean productivity??Crosses = GISP2Triangles = Siple DomeBlunier et al., 2002
11Causes of glacial Δ17O enrichment CO2 is the stepping stone foranomalous O2 formation;less CO2 = less anomalous O2;values trend towards biologic (+155 per meg)this effect clearly dominated glacial Δ17O valuesmodel suggests that CO2 should have caused a much largerincrease in Δ17O (+70 per meg vs. observed +38 per meg)-so imply an 80% reduction in productivity during the glacial-if land reduced, then ocean productivity may not have changed(-88 to +140% poorly constrained)