Stable Isotope Tracers

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1 OCN 623 Chemical Oceanography Stable Isotope Tracers Reading: Emerson and Hedges, Chapter 5, p

2 Stable Isotope Tracers Trace source/sink and pathways of nutrients and chemicals in the ocean. Tracers of biological, physical, geological ocean processes Record past changes in physical, chemical, and biological processes in the ocean.

3 Outline Stable Isotopes - Introduction & Notation Isotope Fractionation Some Oceanographic Applications

4 Isotopes of Elements The chemical characteristic of an element is determined by the number of protons in its nucleus. Atomic Number (Z) = number of protons = defines the chemistry Atomic Mass = protons + neutrons (N) Isotopes = Atoms with same Z but different N

5 The chart of the nuclides (protons versus neutrons) for elements 1 (Hydrogen) through 12 (Magnesium) Valley of Stability Most elements have more than one stable isotope. 1:1 line

6 Full Chart of the Nuclides 1:1 line With Z>20, number of neutrons becomes greater than the number of protons because Coulomb energy (i.e., electrostatic repulsion) has Z 2 dependence

7 Examples: H, He, C, N and O Element Symbol Protons Neutrons % Abundance Half-life Hydrogen H D ( 2 H) T ( 3 H) to τ 1/2 = y Helium 3 He He Carbon 12 C C C τ 1/2 = 5730 y Nitrogen 14 N N Oxygen 16 O O O All Isotopes of a given element have the same chemical properties, yet there are small differences due to the fact that heavier isotopes typically form stronger bonds and diffuse slightly slower % abundance is for the average Earth s crust, ocean and atmosphere

8 Measurement reporting convention (δ or delta units): Delta Notation for 18 O: ( ) 18 O 16 O Sample ( ) Standard ( ) Standard 18 O 16 O δ 18 O = 18 O 16 O ( 18 O 16 O) 1000 = Sample 18 O 16 O Example: If ( 18 O/ 16 O) sample = ( 18 O/ 16 O) Standard ( ) Standard 1 ( ) Standard δ 18 O = O 16 O 18 O 16 O δ 18 O = x 1000 = -5 ( ) Standard Generally reported as ratio of a heavy (i.e., rare) isotope to a light (i.e., abundant) isotope Using a mass spectrometer, isotope ratios can be measured much more precisely than absolute abundances of isotopes If δ > 0, the sample is enriched in the heavy isotope relative to a standard; If δ < 0, the sample is depleted in the heavy isotope relative to a standard.

Each isotopic measurement is reported relative to a standard Element

Atmospheric He Boron δ11b 11B/10B NIST SRM 951 Carbon δ13c 13C/12C

Mean Ocean Water (SMOW) Standard Light Antarctic Precipitation (SLAP)

org/wikipedia/commons/ e/e4/canyon-diablo-meteorite.

Standard Light Antarctic Precipitation (SLAP) Pee Dee Belemnite (PDB)

9 Each isotopic measurement is reported relative to a standard Element δ value Ratio Standard Hydrogen δd 2H/1H Helium δ3he 3He/4He Atmospheric He Boron δ11b 11B/10B NIST SRM 951 Carbon δ13c 13C/12C Pee Dee Belemnite (PDB) Nitrogen δ15n 15N/14N Atmospheric N2 Standard Mean Ocean Water (SMOW) Standard Light Antarctic Precipitation (SLAP) e/e4/canyon-diablo-meteorite.jpg Standard Mean Ocean Water (SMOW) Oxygen Sulfur δ18o 18O/16O Standard Light Antarctic Precipitation (SLAP) Pee Dee Belemnite (PDB) δ17o 17O/16O Standard Mean Ocean Water (SMOW) δ34s 34S/32S Canyon Diablo Troilite (CDT) c/cf/meteor.jpg

10 Isotope Fractionation Change in an isotopic ratio that arises as a result of a chemical or physical process Types of isotopic fractionation that cause changes in isotopic compositions: Equilibrium fractionation Kinetic fractionation Mass-independent fractionation Fractionation Factor (α): α A-B = R A / R B, where R A and R B are isotope ratios in materials A and B

11 Isotope Fractionation Example: equilibrium fractionation of oxygen isotopes in liquid water (l) relative to water vapor (g). H 2 16 O(l) + H 2 18 O(g) H 2 18 O(l) + H 2 16 O(g) At 20ºC, the equilibrium fractionation factor is: α = ( 18 O/ 16 O) l / ( 18 O/ 16 O) g =

12 Equilibrium fractionation Exchange reactions in which isotopes are exchanged between two or more species (with isotopic preference). Bidirectional (reversible) chemical reactions Usually applies to inorganic species Temperature dependent Generally, the heavy isotope will be concentrated in the phase in which it is most strongly bound (i.e., its lowest energy state). Solid > liquid > vapor Covalent > ionic, etc.

13 Equilibrium fractionation - Example The carbonate system involving gaseous CO 2 (g), aqueous CO 2 (aq), aqueous bicarbonate HCO 3 - and carbonate CO It is an important system that exhibits equilibrium isotope effects for both carbon and oxygen isotopes. For example: 13 CO 2 (g) + H 12 CO 3-12 CO 2 (g) + H 13 CO 3 - The heavier isotope ( 13 C) is preferentially concentrated in the chemical compound in which it is most strongly bound. In this case 13 C will be concentrated in HCO as opposed to CO 2 (g). 0 HCO 3! For this reaction: α = (H 13 CO 3 - / H 12 CO 3- ) / ( 13 CO 2 / 12 CO 2 ) α = at 0ºC and at 30ºC ε ( o /oo)!2!4!6!8!10!12 CO 3 2! (Mook, 1986) CO 3 2! (Zhang et al., 1995) CO 2 (g) CO 2 (aq) ε = (α 1) 10 3! T ( C) Zeebe and Wolf-Gladrow, 2001

14 Kinetic fractionation One isotope reacts, diffuses, or evaporates faster than the other. Can be due to chemical, physical, or biological processes. Occurs during irreversible reactions like photosynthesis, when the rate of chemical reaction is sensitive to atomic mass. Essentially all isotopic effects involved with formation / destruction of organic matter are kinetic. Usually, the lighter isotope reacts or diffuses faster. Reaction products are enriched in the lighter isotopes; reservoir of reactants is depleted in the lighter isotopes. Magnitude of isotope effect is temperature and pressure dependent.

15 Kinetic fractionation - An Ideal Example 12 C 16 O 2 (mass = x 16 = 44) These must have the same kinetic energy 13 C 16 O 2 (mass = x 16 = 45) E k = 1 2 mv2 E k = 1 2 m v 2 1 A A = 2 m v B B 2 v A = v B m B m A 1 2 = = so 12 CO 2 travels 1.1% faster than 13 CO 2. All isotope effects involving organic matter are kinetic. Example: 12 CO 2 + H 2 O 12 CH 2 O + O 2 faster 13 CO 2 + H 2 O 13 CH 2 O + O 2 slower Thus organic matter gets depleted in 13 C during photosynthesis (i.e., δ 13 C becomes more negative). Terrestrial plants: ca. -19 (range -26 to -7 ) Marine plants: ca. -14 (range -22 to -8 )

16 Rayleigh Distillation Fractionation occurs when water molecules evaporate from sea surface. Equilibrium effect when water molecules condense from vapor to liquid form (rain is heavier than vapor). Vapor becomes progressively lighter (i.e., δd and δ 18 O get lower) with distance from source. Evaporation from ocean creates depleted clouds. 10 C 17 Air masses transported to higher latitude/altitude where it is cooler. Water lost due to rain; raindrops are enriched in 18 O relative to cloud. 20 C 9 Vapor 9 Rain 0 Rain 8 Continent Cloud gets lighter 0 Ocean All values are δ 18 O Emerson & Hedges, 2008

17 Rayleigh Distillation Example: Evaporation Condensation Processes δ 18 O in cloud vapor and condensate (rain) plotted versus the fraction of remaining vapor for a Raleigh process. The isotopic composition of the residual vapor is a function of the fractionation factor between vapor and water droplets. The drops are enriched in 18 O. The vapor is progressively depleted. δ 18 O ( ) Fraction of remaining water Vapor (cloud) Condensate (rain/snow) 11 R V R V0 =ƒ (α-1) 25 R V is the isotopic ratio of the vapor R V0 is the initial isotopic ratio of the vapor ƒ is the fraction of vapor remaining α is the fractionation factor Cloud temperature ( C) Fractionation increases with decreasing temperature Emerson & Hedges, 2008

18 δ 18 O in Average Rain vs. Temperature

20 Examples: Stable Isotope Applications in Oceanography 3 He to study deep ocean circulation in the Pacific 18 O to determine freshwater balance in the Arctic Ocean 18 O as an indicator of the ice ages

21 Examples: Stable Isotope Applications in Oceanography 3 He to study deep ocean circulation in the Pacific 18 O to determine freshwater balance in the Arctic Ocean 18 O as an indicator of the ice ages

22 3 He Plume from East Pacific Rise Broecker and Peng, 1982

23 3 He at 2500 m depth

Downlo The fact that the helium signal from *St. 22 to 30, 800 1to 1400 m 0St. 22 to 30, 1 70C) m to bottom 3 1 to 23, all deepths +St. He Plume from Loihi Seamount (Hawaii) 4.3 4.2 4.

25 ± RIRA = 23.4 + 1.9 (1 a errors). oefficient for this fit was r2 = ison, a short-dashed line indi3he/4he = 1.

Shallow samples to 1400 m) are shown as solid mples (from 1700 m to the bote stations are shown as open nce, all the remaining samples edition in the northeast Pacific osses.

120 E 120 W 60 W 80 N 60 N 60 N P17NE P17 P17CA P17CCA 40 N P8 P9 P10 P13 P13J P14 20 N P1 P15 0! P17 P31 P8 P9 P10 P13 P13J P14 20 N P4 P18 P15 0! 0! P16 P17 P31 P21 20 S P15 P15SA P11 40 S P17E S3 P14 60 S P17 A21 S4 80 S 80 S 120 E 1000 2000 180!

24 Downlo The fact that the helium signal from *St. 22 to 30, 800 1to 1400 m 0St. 22 to 30, 1 70C) m to bottom 3 1 to 23, all deepths +St. He Plume from Loihi Seamount (Hawaii) ~8CM3/g) 4He (1 centration versus 4He concensamples ame suite of TT-01 4 EPR oncentration units are in cubic gram at standard temperature linear least-squares fit (longa slope of 3He/4He = (3.25 ± RIRA = (1 a errors). oefficient for this fit was r2 = ison, a short-dashed line indi3he/4he = 1.0 x 10-5 expecttroduced along the mid-ocean 3He concentration versus 4He ar-field samples collected along 2 through 30. Shallow samples to 1400 m) are shown as solid mples (from 1700 m to the bote stations are shown as open nce, all the remaining samples edition in the northeast Pacific osses. Linear regression fits to s show that the shallow Loihi long to a distinct population. JdFR Oceanographic Sections and Stations used in the Pacific WOCE Atlas o 180! 120 E 120 W 60 W 80 N 60 N 60 N P17NE P17 P17CA P17CCA 40 N P8 P9 P10 P13 P13J P14 20 N P1 P15 0! P17 P31 P8 P9 P10 P13 P13J P14 20 N P4 P18 P15 0! 0! P16 P17 P31 P21 20 S P15 P15SA P11 40 S P17E S3 P14 60 S P17 A21 S4 80 S 80 S 120 E ! W W S P19 P21 20 S 20 S P6 P6 40 S 40 N P3 20 N P19 20 S P17CA P17CCA P2 P24 P18 P16 P17 40 N P4 0! 60 N P17NE P1W 40 N P3 20 N 60 W 80 N 60 N P2, P2T P W 80 N P1W P1 180! 120 E 80 N 40 S P15 P15SA 40 S Fig. 5. 8(3He)% contoured in section view for WOCE line P17 along 1 35 W. In this section, the Loihi plume appears as an upturning of the 8(3He) contours in the depth range from 900 to 1400 m, between latitudes 150 and 25 N as indicated by the dashed ellipse. The plume core centered at 8 N and a depth of 2500 m is helium from the EPR, whereas the weaker signal north of 32 N and at a depth of 2000 m is from the JdFR. P11 P17E S3 P14 60 S P17 A21 60 S S4 80 S 80 S 120 E 180! 120 W 60 W Lupton, 1996

3 He at 1100 m depth Fig. 6. 8(3He)% contoured on a surface at a depth of 1 100 m, showing the broad lateral extent of the Loihi plume.

25% (1 cr). This figure includes data from eight different expeditions spanning the time interval from 1985 to 1994.

25 3 He at 1100 m depth Fig. 6. 8(3He)% contoured on a surface at a depth of m, showing the broad lateral extent of the Loihi plume. In some cases, bottle data were interpolated to m deep surface. The contour interval is 1 % in 8(3He); the accuracy of the measurements is 0.25% (1 cr). This figure includes data from eight different expeditions spanning the time interval from 1985 to Although these data are not synoptic, the sampling period is relatively short compared with the time scale for circulation at this depth. Helium data along WOCE lines P4 and P16 were provided by W. Jenkins (4, 23). Lupton, 1996

26 Examples: Stable Isotope Applications in Oceanography 3 He to study deep ocean circulation in the Pacific 18 O to determine freshwater balance in the Arctic Ocean 18 O as an indicator of the ice ages

sources 18 Fig. 7. Distribution of O in the surface waters Ž depth 15 m.

27 Freshwater balance in the Arctic Ocean Balances of mass, salt, δ 18 O, and nutrients allow us to separate the contributions of the individual freshwater sources 18 Fig. 7. Distribution of O in the surface waters Ž depth 15 m. of the Arctic Ocean and the adjacent seas. Schlosser et al., 1999 Ekwurzel et al., 2001

28 Freshwater balance in the Arctic Ocean δ 18 O Pacific Water River Runoff Sea-ice Meltwater from P. Schlosser

29 Examples: Stable Isotope Applications in Oceanography 3 He to study deep ocean circulation in the Pacific 18 O to determine freshwater balance in the Arctic Ocean 18 O as an indicator of the ice ages

Warmer water lighter δ 18 O in CaCO 3 2) δ 18 O of seawater

30 δ 18 O in Marine CaCO 3 The δ 18 O of the CaCO 3 is a function of: 1) Temp of seawater that foraminifera are growing in: Warmer water lighter δ 18 O in CaCO 3 2) δ 18 O of seawater that foraminifera are growing in: Depends on latitude Depends on sea level

31 δ 18 O Paleothermometer 28 G. menardii less 18 O Temperature ( o C) N. pachyderma (d.) G. sacculifer O. universa G. ruber (pink) 12 more 18 O 8 1 G. bulloides e.g. Bemis et al., Paleoceanography, 1998 δ 18 O shell- water ( ) Temperature dependence of equilibrium fractionation between 16 O and 18 O during precipitation of CaCO 3

Gridded Surface Seawater δ 18 O Note the higher δ 18 O sw in the evaporation belts and the lower δ 18 O sw in the high latitudes, which are dominated by excess

32 Gridded Surface Seawater δ 18 O Note the higher δ 18 O sw in the evaporation belts and the lower δ 18 O sw in the high latitudes, which are dominated by excess precipitation. Any δ 18 O-temperature relationship depends primarily on the δ 18 O of the water from which the carbonate is precipitated.

33 high δ 18 O low δ 18 O Changes in ice volume also influence δ 18 O of the ocean

34 δ 18 O in marine carbonates and paleotemperature records Vostok ice core Warmer/ less ice Colder/ more ice Figure The lower curve shows smoothed! 18 O for marine carbonates (SPECMAP), the middle curve shows!d of ice in the Vostok ice core, and the upper curve the temperature calculated from!d at Vostok at the time of deposition of the ice relative to the present mean annual temperature. Vostok data is from Jouzel, et al., (1987, 1993, 1996).

35 Figure 6.3. Variations of deuterium (!D; black), a proxy for local temperature, and the atmospheric concentrations of the greenhouse gases CO 2 (red), CH 4 (blue), and nitrous oxide (N 2 O; green) derived from air trapped within ice cores from Antarctica and from recent atmospheric measurements (Petit et al., 1999; Indermühle et al., 2000; EPICA community members, 2004; Spahni et al., 2005; Siegenthaler et al., 2005a,b). The shading indicates the last interglacial warm periods. Interglacial periods also existed prior to 450 ka, but these were apparently colder than the typical interglacials of the latest Quaternary. The length of the current interglacial is not unusual in the context of the last 650 kyr. The stack of 57 globally distributed benthic! 18 O marine records (dark grey), a proxy for global ice volume fl uctuations (Lisiecki and Raymo, 2005), is displayed for comparison with the ice core data. Downward trends in the benthic! 18 O curve refl ect increasing ice volumes on land. Note that the shaded vertical bars are based on the ice core age model (EPICA community members, 2004), and that the marine record is plotted on its original time scale based on tuning to the orbital parameters (Lisiecki and Raymo, 2005). The stars and labels indicate atmospheric concentrations at year IPCC Fourth Assessment Report, Working Group I Report "The Physical Science Basis", Chapter 6 Palaeoclimate

δ 18 O as Indicator of Climate for the Past 65 Million Years 0 δ 18 O ( ) 1 0 1 2 3 Partial or ephemeral Full scale and permanent Northern Hemisphere ice sheets Antarctic ice sheets?

36 δ 18 O as Indicator of Climate for the Past 65 Million Years 0 δ 18 O ( ) Partial or ephemeral Full scale and permanent Northern Hemisphere ice sheets Antarctic ice sheets? Mid-Eocene Climatic Optimum Early Eocene Climatic Optimum ETM2 PETM (ETM1) Ice-free temperature ( C) 4 Mid-Miocene Climatic Optimum 5 Pleistocene Pliocene Miocene Oligocene Eocene Palaeocene Age (millions of years ago) Stacked deep-sea benthic foraminiferal oxygen-isotope curve. The δ18o temperature scale, on the right axis, was computed on the assumption of an ice-free ocean; it therefore applies only to the time preceding the onset of large-scale glaciation on Antarctica (about 35 million years ago). Zachos et al., 2008

Stable Isotope Tracers

Stable Isotope Tracers OCN 623 Chemical Oceanography 5 March 2015 Reading: Emerson and Hedges, Chapter 5, p.134-153 (c) 2015 David Ho and Frank Sansone Outline Stable Isotopes - Introduction & Notation