Oceanic Tracers. 3 March Reading: Libes, Chapters 10 and 24. OCN 623 Chemical Oceanography. (c) 2015 Frank Sansone and David Ho

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1 Oceanic Tracers OCN 623 Chemical Oceanography 3 March 2015 Reading: Libes, Chapters 10 and 24 (c) 2015 Frank Sansone and David Ho

2 Outline Global ocean surveys Classes of oceanic tracers 3. Water-mass mixing calculations 4. Quasi-conservative geochemical tracers NO and PO 4 * 5. Anthropogenic transient and deliberate tracers CFCs, SF 6, CF 3 SF 5

3 GEochemical Ocean SECtions Study (GEOSECS) Atlantic from Jul 1972 to May 1973; Pacific from Aug 1973 to Jun 1974; Indian from Dec 1977 to Mar 1978 Latitude 90 S 60 S 30 S 0 30 N 60 N 90 N 180 W 150 W 120 W 90 W 60 W 30 W 0 30 E 60 E 90 E 120 E 150 E 180 Longitude

4 LARGE VOLUME STATION Transient Tracers in the Oceans (TTO) 1981 & 1983 SMALL VOLUME STATION CONTOUR INTERVAL -- 4KM Fig. 1. Cruise track and station locations for the Transient Tracers in the Ocean program. Brewer et al., 1985

5 Classes of Oceanic Tracers 1. Stable Conservative (SC) Potential temperature J = consumption prod rate = 0 Salinity λ = radioactive decay rate const. = 0 Freons SF 6 3 He NO 2. Stable, Non-conservative (SNC) 0 2 J 0 NO - 3 λ= 0 PO 4 - ΣCO 2 CH 4

6 3. Radioactive, Conservative (RC) 222 Rn λ 0 3 H (or T) J = 0 λt { X} = e { X t } 0 λ= t Radioactive, Non-conservative (RNC) 226 Ra J Th λ U Σ 14 CO 2

7 Mixing of Two Water Masses 1. Plot two stable conservative tracers for each water mass on an X-Y plot (e.g., T, S) 2. Link points with a linear mixing line 3. Water samples with compositions falling along the mixing line are composed of mixtures of the two water masses T #1 Mixtures of #1 and #2 fall along this line #2 S

8 Water Mass Mixing Definitions Assume: conservation of mass, heat, salt Definitions: C i = concentration of some stable conservative property in water mass i (end-member concentration) C mix = concentration of some stable conservative property in a water mixture f i = fraction of the water mixture that is from water mass i f mix = 1.0 = f 1 + f f i (mass balance equation)

9 Mixing of Two Water Masses For two water masses, we need two equations with two variables: 1 = f 1 + f 2 C mix = f 1 C 1 + f 2 C 2 When combined: f 1 = C mix C 2 C 1 C 2

10 Mixing of Four Water Masses We need four equations with four variables. For example: 1 = f 1 + f 2 + f 3 +f 4 T mix = f 1 T 1 + f 2 T 2 + f 3 T 3 + f 4 T 4 S mix = f 1 S 1 + f 2 S 2 + f 3 S 3 + f 4 S 4 NO mix = f 1 NO 1 + f 2 NO 2 + f 3 NO 3 + f 4 NO 4 Thus, we need three stable, conservative tracers: T i = temperature of water mass i T mix = temperature of a water mixture S i = salinity of water mass i S mix = salinity of a water mixture NO i = NO of water mass i NO mix = NO of a water mixture

11 NO A Quasi-Conservative Water Mass Tracer ΔO 2 / ΔN = -138 / 16 = -8.6 Thus, during the oxidation of organic matter: For each mole of NO 3 - released to a water mass, ~9 moles of O 2 is removed Broecker (1974): NO 9[NO 3- ] + [O 2 ] "PO" 135[PO 4- ] + [O 2 ]

12 From a Previous Class Slope -12 µm O 2 µm NO 3

13 Conservative Behavior of NO AAIW 1150 m NADW 2270 m Broecker, 1974

14 Table 1.6. fstoichiometnc "Redfield" ratios for consumption ofp, N, C and production ofo 2 during photosynthesis and the. opposite r:eaction during respiration in the ocean All values are relative to a phosphorus value of 1.0. Organic matter Source O 2 p N C Redfield et 01., 1963 a Anderson and Sarmiento, 1994 b ± I 117± ± 10 Anderson, 1995 c /-16/ Kortzinger et 01., 200 Id ± ± ± 15 Hedges et 01., 2002 e a The first and original stoichiometry was determined from observations of the NO;- ratios in ocean deep waters and then assuming a stoichiometry for organic matter. bthis value used the same approach as a and included DIC and Oz on dineutral surfaces below 400 m. cthese values were determined by using C, Hand content of organic compounds that make up plankton, with the assumption that there are 106 moles ofc per mole of P. d These values are based on measurements ofdip, DIN, DIC (corrected for anthropogenic COz) and O 2 on constant density surfaces. ethese values were determined by chemical and NMR analysis of marine planktonic organic matter. A C:P ratio of 106 is assumed. Emerson and Hedges, 2008

15 PO 4 * Another Quasi-Conservative Water Mass Tracer GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 5, NO. 1, PAGES 8'7-117, MARCH 1991 RADIOCARBON DECAY AND OXYGEN UTILIZATION IN THE DEEP ATLANTIC OCEAN Wallace S. Broecker, Sean Blanton, and William M. Smethie, Jr. Lamont-Doherty Geological Observatory of Columbia University, Palisades, New York Gote Ostlund Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, Miami, Florida Abstract. A parameter based on the sum of the concentrations of PO4 and 02 (divided by the Redfield coefficient -ao2/apo4) is used to separate the contributions of the northern and southern components to deep waters in the Atlantic. This separation allows the amount of radiocarbon lost by radiodecay and the amount of oxygen lost to respiration during residence in the deep Atlantic to be calculated. Maps of these quantities reveal strong west to east gradients and weak north to south gradients consistent with ventilation along the western boundary from both ends of the ocean coupled with mixing outward from the boundary. The 02 and InC deficiences are highly correlated, suggesting an 02 utilization rate of 12!.trng per century. The apparent mean isolation time of water in the deep Atlantic is about 200 years. INTRODUCTION Both the distribution of dissolved oxygen and that of radiocarbon in the deep Atlantic are strongly influenced by the mixing between the northern and southern components of deep water. Hence if the extent of changes in 02 content caused by respiration and of changes in the radiocarbon to carbon ratio caused by radioactive decay are to be isolated, then a means must be found to accurately def'me the relative contribution of these two sources to any given water sample. As was shown by Broecker [ 1979] and by Copyright 1991 by the American Geophysical Union. Paper number 90GB /91/90GB Broecker et al. [ 1985], a promising means to do this is through the use of a PO4-O2 based quasi-conservative parameter. Broecker [1974] initially suggested a parameter called "PO" based on the sum of the 02 concentration and a Redfield ratio multiple (i.e., 132) of the PO4 concentration. In this paper we employ a modification of "PO" which we believe yields a more accurate separation of the contributors. We apply this new separation procedure to the expansion of the Geochemical Ocean Sections (GEOSECS) data set for the deep Atlantic made available by the Transient Tracers in the Ocean (TFO), Tropical Atlantic Survey (TAS) and South Atlantic Ventilation Experiment (SAVE). COMPONENT CHARACFERIZATION We base our separation of the northern and southern component contributions to deep waters (i.e., >2000 m) in the Atlantic on a parameter we designate as PO4*. It is related to the measured PO4 and 02 concentrations as follows: eo = eo _ 1.95grn&g The constanterm (1.95) is introduced in order to bring the PO4* values into the range of measured PO4 contents in the deep sea. The revised Redfield ratio (175) relating 02 consumption to PO4 production during respiration is the global average proposed by Broecker et al. [1985]. It is based on the analysis of water column chemical data from six different regions in the ocean deemed suitable for this type of analysis. As is summarized in Table 1, despite the Broecker (1985): ΔO 2 / ΔPO 4 = -175 / 1 = -175 Thus, during the oxidation of organic matter: For each mole of PO 4 - released to a water mass, ~175 moles of O 2 is removed Broecker et al. (1991): [PO * 4 ] [PO 4 ]+ [O 2] 1.95 µmol/kg 175

16 PO 4 * distribution at 3000 m in the world ocean. Sarmiento and Gruber, 2006

17 Separating NADW from AABW Salinity (S) is conservative, but 4 water masses that combine to form NADW have different S. PO 4 * is nearly uniform within AABW and within the four components of NADW (Broecker et al., 1998): AABW: 1.95 ± 0.07 µmol kg -1 NADW: 0.73 ± 0.07 µmol kg -1 Fraction of NADW is: f NADW = 1.95 [PO 4 * ] 'o N O ) o o o O O % Broecker et al., 1991

18 Transient Tracers Usually anthropogenic compounds with time-varying sources (or sinks) CFCs, SF 6, 14 C, 3 H They enter the surface waters of the ocean either via gas exchange (e.g., CFCs, SF 6, 14 C) or water vapor exchange ( 3 H) Transient tracers allow: Penetration of surface perturbations into the interior of the oceans to be visualized. Delineation of pathways that newly formed subsurface water follows after leaving the surface. Investigation of ocean circulation and mixing, and validation/ calibration of GCMs. Determination of water mass formation rates Estimation of anthropogenic CO 2 inventory in the ocean

19 800 N.H. CFC & SF 6 atm. mixing ratios 140 CFC-11, CFC-12, SF 6 x 100 (ppt) CFC-11 (ppt) CFC-12 (ppt) SF 6 x 100 (ppt) CFC-113 (ppt) CFC-113 (ppt) Year 0

20 Solubilities of CFCs & SF 6 Strong function of temperature Increases as temperature decreases Ranges by a factor of about 3.5 between 0 and 25 C Weaker function of salinity Decreases as salinity increases Varies by 50% between salinity of 0 and 35 Solubilities are well known (± 1% or better) CFC-11 & CFC-12: Warner and Weiss, Deep Sea Res. I, 32: , 1985 CFC-113: Bu and Warner, Deep Sea Res. I, 42: , 1995 SF 6 : Bullister, Wisegarver and Menzia, Deep Sea Res. I, 49: , 2002

21 Pathway of Labrador Sea Water Rhein et al. (2002)

22 Jenkins and Smethie, Oceanus, 1996

23 Estimate Ocean Uptake of Anthropogenic CO 2 pcfc-11 pcfc-12 Anthropogenic CO 2 0 m 500 m 1000 m Key et al. (2004)

24 Most commonly used: Deliberate Tracers SF 6, (Sulfur Hexafluoride) 3 He CF 3 SF 5 (Trifluoromethylsulfur Pentafluoride) Deliberate tracers used to study: Vertical mixing in the ocean Pathways of newly formed deep water Air-sea gas exchange

25 In situmeasurement of Vertical Eddy Diffusion Example -use injected SC tracer to measure rate of vertical eddy diffusion (diapychnal mixing): Sulfurhexafluoride(SF 6 ), very soluble gas Santa Monica Basin Perflurodecalin(PFD), emulsified insoluble liquid Trifluoromethyl sulfur pentaflouride(sf 5 CF 3 ), soluble gas (Ho et al., 2008) Add tracer at point in water col Height above injection depth, m 51days 8 days Measure tracer diffusion over time Use gas chromatograph with electron-capture detector Conc, fmoll -1 Detection limit = 10 8 molecules!

26 Measurement of Vertical Eddy Diffusivity North Atlantic Ocean SF 6 injected at 310 m Measured tracer diffusion over time K z = 1.1 x 10-5 m 2 s 1 Ledwell et al., 1993

27 Diapycnal diffusivity at the upper boundary of the tropical North Atlantic oxygen minimum zone Donata Banyte, 1 Toste Tanhua, 1 Martin Visbeck, 1 Douglas W. R. Wallace, 2 Johannes Karstensen, 1 Gerd Krahmann, 1 Anke Schneider, 1 Lothar Stramma, 1 and Marcus Dengler m depth K z = (1.19 ± 0.18) x 10-5 m 2 s -1 Banyte et al., 2012

28 Diapycnal Mixing in the Antarctic Circumpolar Current J. R. LEDWELL AND L. C. ST. LAURENT Woods Hole Oceanographic Institution, Woods Hole, Massachusetts J. B. GIRTON Applied Physics Laboratory, University of Washington, Seattle, Washington J. M. TOOLE Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 1500 m depth K z = (1.3 ± 0.2) x 10-5 m 2 s -1 Ledwell et al., 2011

29 Figure 1. Locations of in situ mesoscale iron enrichment studies (white symbols), iron and/or phosphorous enrichments (green symbols), bloom studies in naturally high iron waters (red symbols), and oceanic geoengineering trials or pilot studies (yellow diamonds), including iron fertilization (Markels and Barber, 2001) and nutrient upwelling using ocean pipes (Lovelock and Rapley, 2007; White et al., 2010). All are overlaid on a map of surface nitrate concentrations for the world ocean. Nitrate concentrations courtesy of the National Oceanographic Data Centre Boyd et al., 2012

30 T SF 6 Fe Chl NO 3 CO 2 Coale et al., 1996

31 Homework - Due Tues, March 10, 2015 The following concentrations were measured in a seawater sample collected from a station in the southern Pacific Ocean (so-called "Pacific and Indian Ocean Common Water"; depth = 3250 m; temperature = 1.6 C). The table also lists data for the concentrations found in pure "end-member" water masses that make up the Common Water. What are the relative proportions of these three water masses inthe Common Water? What assumptions do you need to make? Salinity NO 3, μm O 2,μM Pacific and Indian Ocean Common Water North Atlantic Deep Water Antarctic Intermediate Water Antarctic Bottom Water