Spec TopicsMarine Chemistry
Spec TopicsMarine Chemistry SIO 269
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SIO 269 Special Topics in Marine Chemistry An Isotope Perspective of the Carbon Cycle Lecture 1 Photosynthesis and Respiration Readings O Leary 1981 Laws et al 2001 Discussion papers for next week Holsten et al 2004 Mar Micropaleontology 53117132 Wakeham et al 2004 Chenlilcglmgeolo 205427442 LEHNG L l i i 39i I I 2 MAY 13431955 1 BIG SUR ST PK Dis 0 39 11 i39 1 39quot EV r quotquot39L f l 1 2 a Cu m 39 P a 5 i SIZE 7 z isquot 3 7 F DAG iw use u k39 g 39 Hm 390 in a Mn 13 034 L o I39 032 i a u i 7 i J J i 1 i 12 16 a0 24 4 a 12 COASTAL REDWOOD FOREST L2301FT Fig L Diurnal variation in the mutantration and i ol pe ratios pf atmospheric Hal39me dioxide in a coastal redwood forest of Califumm A Little SlOCentric Historical Perspective C D Keeling 1958 and 1961 Keeling Curves In 1954 57 Harmon Craig measured the isotopic composition of a variety of natural materials and observed that plants had a 613C signature near 27o In 1958 an1961 Charles D Keeling used the seasonal variation in the 613C of atmospheric CO2 to determine the carbon isotopic composition of CO2 respired by terrestrial plants The basis of the determination is a plot of 613Catm vs 1CO2 atm 5130atm m1COZatm 613CR Where 513CR is the carbon isotopic composition of the respired CO2 and m CO 613C 613CR 2background background Use night time data where the assumption is that only respiration is altering atmospheric CO2 cocentrations Variations in the concentration of atmospheric CO2 and its isotopic composition Borrego Valley Peru Current swarm 3934 f I I 1 T I I I I I I I 1 I l I I I BORREGD WLLEV amour 39mc h NOV IB39Z D I955 PREA URE no EL IIDOFT 395 PRES URE PERU CUH EMT 4 napnoxmnTE I 15 39quotquot WIND vzcma w 539 39 M2 rs3 wwn vccvon r3 y 5g39 i I 39 and I immlhukmsl s IE 10 5395 39 Immrhq39km 755 55 I i D AIR I F R u 4 2 ID EVEdw TEMPERATURE I mnrngr n U m 39 39 1392 39 39Na 39 E 42 E tquot N u WATER VOn Illa a JL i I 05 me O 4 39 MN m m 5 ff 1 39 39 99 I Hg G8 c rW39 I H UU J 7 quotI a 39 i SC I quot I I 39a Lula u 70 I u I 1 39 4 I H V Hail I 770 I I 6 e l I j 63 us dry aw I 3 I H as L Fcoe quotV quotl39 quotH 39 o I H c I I 32 3 l I I Ivol I I c l H o I I us mummxr I Imam I c a I 031 Ikmz uI I quotI39I1quotL T IfTE7T391I39 quot 39q 39 t r39 12quotquot 24 2 2a 12 1 39 39 Jan 31 F631 FEB 12 16 20 2 a a 12 EAST PACIFIC OCEAN 239583 w To 3 38439w When CO2 T From Keeling 1961 Relationship between 5130a and 002a Measured Quantities 7 V n I I 1 e a CC ISITAL HEDWW WEE j 1 EFFElm NEVADA FCREST V r 39 39 g a INJYD H39HS AVG quotAIMUSES V 7 7 l 7 9 Jar1g 39 i 7 7 51513 fir E i 13 if a 3 r r A i 1 P 5 7 pp 39 39 chainsaw alga i I EMBE 1 g 395 quot v V r V l 39 39 52 1334 335 413 O4 Peg ifDI Fig 3 Raletian bchwmz catberm ismope retina and emmmtratiun ut39 angpha n nutban dmmrie rm Cutiiomia stations Keeling 1958 Graphical Representation of the Keeling Plot Application 5 I Sampled cog 51303 10 523 N Q 15 Q 8 20 Background 002 613Cb 0393 3950 25 39 source C02 51335 30 I l 0 0001 0002 0003 1c rnolumol391 Figure l Graphical illustration ofthe Keeling plot method given as equation 3 in the text The carbon isotope composition of two endpoints of source C02 EI3CSJ and wellmixed background atmospheric CO 393Ch are shown in solid circles The carbon isotope composition of sampled air f uCgl is shown by open circles Isotope ratios are plotted against the inverse of CO concentration c Note the distance ofthe samples from the intercept 813CS is the same as my 813CR And 513GB is my 1quotCBamkgmund 1c is the same as my 1COZaltm Important that sampling is done over a con range in excess of 75 ppm Pataki et al 2003 Original Keeling Plot Solutions These calculations are made over short time periods lt12 hrs Miliiimmn ilzmir num I IF JM h rlm39 V I 1 aymi inn high231quot I blisammn I39M 1139 1 g rlr E 39 llllll39llllli39ll TI l in rillquot quot fi39iml prpii 39V iquot39nl 3quotquot quotm 1955 1 Bi 5m 3mm BurkquotI l L39alifzirni Til IE IS Jlujr illl lHE r TJI u ll H 33 VIPmm l Tuecmi39lu Entinnnl Pinkquot i39nlifhrnin Hlfrll39 1 3 Iun 3 3 Hiil 74quot I 11 ESEI ll DTli T HMt Cr Ty gtEl l13 l39 lin ui i EIJIF 5 LLIg 39 21m fulfil jv37 H 39Ilum E39r 39139p l rinmii I ndinnn Ellll i39l i Aug H 2 Hart s PREG quotm39llim mv lElllll 31 AWLt 3quot Hgl h El 397 2 1139 llLEEJ quotI l 1 Hum 39 Cliymriir T Zafitiuul T nrk Iug xin lmi 1 l T prl 3W4 0 Ilfi ii 39i39 mil2 ll EH I limk Lti39kril39 I Wmlaizuyi n lii39ll lll F39 it 3 i HSIE 39 Ell III 2334 Hull 7 3 igmri Awlmlclni h glimml Virginia r 2 mm 32 2 im A 139 7 M Maquot nnMi 7 J Apr swiftang la 39l39l39iiflmi Virginia 2 ill ilnr 3 III 7 mi 25 I39iIZIMI I 1 1 Apr Hcm39n39rli Pimlw Adannu L JIIIIP it 13 lIll 39 3N1 32H 397 ll 3939I Ill 3I39Il Email 5 l39i l4 rIuvur 39lIill Ariarant 2mm Is an Mu 3H1 39 HRH 7 is llig ELIE Pilate I ul39k Valuingmil gt T 71 S Jim ll 371 iUl l T I M 233 I39lI39II39H 7 Early urn l39u39lll39 Wig Hut I39L Fulifnrnin 114 T Jun 335 3M 55 ii EH 3211 I lI JH F Yummill Milliml PI II LZ Palil39nruiu l1l vIF 1391 Jilin 3 l 1L3 F l l TL l quotI Ill 39l I31il S 11 m39 in dnlu 211 1inl lh IDES 39 lming minim ma due 1 insqu39iinz39m dam 513C background 613C R Keeling 1961 Caveat Spread in 813CR observed for various biomes 20 l l o 22 g 24 n a 26 Co 28 30 o 32 I I I y ea a 6 o o o 6 04 00 7 63 5 s 9 71 5 07 9 IS 9 ages 9 Figure 8 A box plot of data distribution of the carbon isotope composition of ecosystem respiration BUCK for four forest hiorne types in North and South America The boxes enclose 50 of the data population with the centerline showing the median value The error bars Show the upperlower quartile 15 X interquartile distance Points that lie outside of this range are shown by open circles Sample sizes ranged from 6 to I for the boreal Forests and temperate broadleaf forests respectively Pataki et al 2003 Similar results were obtained by Keeling Pt Barrow 71 0N 248i 06o Mauna Loa 19 N 203i 090 Cape Grim 41 S 175i 06 Also short term experiments appear to capture primarily the respiration of carbohydrates for example Park and Epstein 1961 observed that in the dark the CO2 respired was up to 8 heavier than the total plant carbon Bottom Line 8130 composition of atmospheric CO2 at any one location must be affected by several processes dCOzldt photosynthesis respiration plantbiochemical respiration soil airsea gas exchange volcanic CO2 Ca003 weathering Time scales of volcanic CO2 and Ca003 weathering What about airsea gas exchange 100 Gt Cyr how does this relate to global photosynthesisrespiration rates Latitudinal distribution of air sea gas exchange Is there variability in the isotopic composition of biomass resulting from photosynthesis and respiration pathways Summarized by O Leary major conclusion holds for most plants Park and Epstein 1960 that ribulose bisphosphate carboxylase RuBisCO is the enzyme responsible for the most widely expressed discrimination against 13002 not diffusion into the cell or the subsequent respiration Range of isotope signatures expected for C3 versus C Plants Modern grasses C4 grasses 5130 7126 1 11 21 03 grasses 5 30 267 23 95 E The Major Carbon Fixation Pathways Emergent 03 Plants Erm39 iOrganism ronmenq 12 Calvin in Higher Plants Assimilation amp Fixalion Biosynlhesis I 002002 1 I C Cs ycle CC KK Rubcsoo E 20 aquot la12 0 5 sugars 3 Essay quotr a I intermediate 1 a b 95 of plants P C4 and CAM Planls phosphoglyceric acid PGA Cycle Cn H20 9 To blosynthesis as above reazuin I A blSCO J u u 15 oxaloacetlc acud Subaqueous Plants and Chemoauirotrophs I H0031 l 39IB HCO3 03mg CnHZOn ll 1 ll J 2 Rubiscu coz cog x 05 To biosynihesis as above Carbon Isotopes and Biosynthesis Isotopic composition of AA relative to mass weighted average 2AA 13 o Algal Component 5 C U 310 39215 0 1393 39 Macko Fogel Hire 8 Hearing 198 743 V Total organic 3 5 matter m e t 13 Proteins g 5 Anabaena SD gt N source a 2 quotit u 40 no w m H Hemicellulose F 4 39i39 g Biosynthettc P recurwrs 1311 hp no A alkg E4 PGA Py Py PGA A 6K9 A 54 Py A 1U 3 51 9 phe sler his Vlal 33 glly 1hr erg ii 1339 IEILI lys Carbohydrates Amino Acid Flgll39a 14 Carbonisotopic compositions or individual amino acids syn Ceuose thesized by the cyanobacten a Anabaena 5p Strain IF Hz xing and Mia39 utilizing cultures and Strain BA iNHf utilizing culture Abundances of 13C are expressed in terms of e the fractionation relative to the mass L d weighted isotopic composition of all of the amino acids analyzed from each lpl 3 culture Macho et at 1987 The abbreviations speci ed in Table i are used to designate the amino acids Abbreviations above the horizontal axis specify biosynthetic families A aspartic acid qu aketoglutarate PEPE4P phosphoenolpyruvate erymrosevlphosphate PGA phospho glycerir acid and Py pyruvate Histidine his is synthesized by a unique pathway lysine lys is a member oi me aspartic acid tamin except in Eugiena and Fungi where it is a member of the ctketoglutarate family Isotopic Composition of Biochemicals Cont d 39 39 l I I I I I hntarctic 2 I Phytoplankton BE 3211 Jag335m quot E 4D Haiural Papuiat cns Temperate Waters 9 3 J E a 9 2 ED CI 9 0 Arctic I Ice Aigae EL 4 0quot r Redfie d Subtropical Eyres Andarson I I I I I I I I I I 01 113 05 XISPmt Hull T We depieiidn 0i 13iliii lipids reiaiiire id biomass as a iuniiien oi eeiiu lei composiddm wheie me limp and Jigsaw we die maie iractiiens oi tamed iii pidieiiis iipids and eerimiiydiaies iESpECIWEW see equaiien 5 and ieiaied discussidn iiie indicated reliedenemies aieiliased on ismo pic massheience quiiiiiemems and mi ivdncepis ouiiined by Laws iEiEii Hayes 2001 We cross maiiied quot iied elld Andersen indicates the maiden of teiis wiiii CAMP ind i E 1 edit wiiih Iidiilei and much indie ieaiistici abundanc es M H and 1 than iiiose specified by me Idiweiiiieiiai iied eid mimdia Andersen 1995 Before we get to Photosynthesis itself AirWater Gas Exchange for terrestrial and aquatic plants CO2 dissolution is important x I 0 RCOZaqRCOZg Where R 1312 0L 09989 hJWh saqg a 11000 11o El 5 10 1395 Ell 2 5 an mmmml39c Fin 3 The quotC cqullmnum manilamum beiwetn dissolved and gasmus I 1 manned using acidi ed distilled water equili hramd with pure CO mm 5quot m 25 C The open imles am the average values of ve bottles at cash temperature The solid line is the linear regression nl the average values rquot I f K149 t39lIll llel39if Cl 31 U x The dashed Jim and the upcn m39anglcs an the results reported by Vugel fl 3 11971 In this case the lighter isotope is found preferentially in the gaseous aqueous phase not typical for gasses H003 and 0032 aka4 I H at I H Ex 2 9 a w v V n or 3939 u l 39 39 lama 3991 Fla 4 The C fractionarimt betwccn HUD and Easmus C0 cm PEI rmasured using a MaHCG mluliun cqui ibrmud with pun 01 gas Torn 5 C In EST quot11 npcn cmle arc Eh avcl agc h39alauc of funny battles equilibriumd at inch lumpemiuru The arm bunt nu may 11H39Eun ELT E willhin 1J1 aim m the symbuls The littar n maxim uf lhc avcragv valucs gives solid line mm il l I t RWEIJHTJ l IDES t 0mm whim39ll 3915 an twang 0F 005 luwzr man Muuk cl 3E3 1974 upcn 39lnanglts and dashed line values Thu tilled mangits an Emm lmniak and Sakai 1939 0 RCOZgRHCO3 0L 100789 SHCO3g 790 I g ll r 39 g 7 Pan T V T quot n I I Eff4 w 4 5r 7 i u 1o 2 an quot 4n WWIIC Flu 5 The quotC mhmullun bemoan CU mid Eastman ICU mm A measured using a NaHIC39El Ma a solution cquih39brmcd with pun CD gas from 5 C no 251 Thcnpcn ciTElc an u avcragu MallIts DI TIW mules nquilihmmi a Each kmpcmtum Thu citum range from H3 765 hand In we mcusummcms at each bem pcratum A rcgmssmn yiclda solid line mm IEIIIEE IV ZIjnTJ 722 t il m which is sham If m 1W lrvwcr than Ihu Thule v2 ul 9653 lhmtisml mulls EdaIliad lint Thl lll iltl iajlgkta am from Latmink and 53km t 1989 and ir solid squan Emm Thyme i933 On the way to photosynthesis what do we have to consider Diffusion from air into the intercellular space Dissolution and equilibration with H003 for C4 Fixation ie carboxylation to synthesize sugars First let s distinguish thermodynamic and kinetic isotope effects thermodynamic isotope fractionation occurring for processes that are at equilibrium kinetic isotope fractionation occurs because different isotopic species are transformed at different rates Some important fractionation factors The fraction between each pathway ie diffusion fixation can be expressed by the fractionation factor a This is typically calculated as the difference in 8 between the reactants and the products areadantsproduds This is based on O Leary 1981 where 12k13k 8 8reactantsproducts reactants 8product Process 8reactantsproducts Equilibria Solubility of 002 in water 11 equilibriumthermodynamic effect Hydration of 002 to HCO339 90 Transport Processes 002 diffusion in air 44 002 diffusion in water 11 empirical O Leary assumes 0 Chemical Processes Carbonic anhydrase catalyzed hydration of 002 11 Phosphoenolpyruvate carboxylase catalyzed reaction of H003 with phosphoenolpyruvate 20 Ribulose bisphosphate carboxylase catalyzed reaction of 002 with ribulose bisphosphate 29 Diffusion is often rapid compared to other processes in the C fixation the fractionation is not derived from the square root of the ratio of mass 44 and 45 diffusion rate is proportional to the square root of the mass Instead you have to take into account that 002 is diffusion through air mass 288 80 according to Newton the relative acceleration of 002 in air and its isotopic fractionation have to be considered in terms of reduced masses m1m2m1m2 120130 sqrt 44288442884528845288 This gives 44 0 instead of something closer to 11o C3 Steady state where the concentration and isotopic composition of internal CO2 pool is unchanged over time CO gt 2 quott C02in Cfix dCOZindt k1COZout k2 k3CO2in at steady state assume that 0 Then co k1k2 k3 co 2in Zout For Cfix dC dt fix k3 2in Together dC xdt k1k3k2 k3 COZout If k 1 is the rate constant for 13C x vs 12C x Then d13C dt k 1k 3k 2 k 313COZout fix Let s take a look at how we deal with the changing concentration and isotopic composition of Cfix d13C dt dc xRc xdt fix d13Cfixdt RCfix dcfix ldt Cfix dRC xdt Assuming steady state then assume that dRC xdt 0 Le isotopic ratio is not changing over time Remember d13C dt k 1k 3k 2 k 31 COZout fix So at steady state from above d13C xdt Rc x dC dt fix Combining Rc dC xdt k 1k 3k 2 k 313COZout Using dC dt k1k3k2 k3 coZout fix We get RCfix k1k3k2 k3 C020ut k 1k 3k 2 k s 1300Zout For the overall reaction anet knetk net 1213C x121 39Cout 12k13k RCOZout lRCfix anet k1k3k2 k3 k 1k 3k 2 k 3 a1 0L3 k 2 k 3k2 k3 This means that the net fractionation effect depends not just on the fractionation effects of diffusion into the cell or the fixation but also on kzlk3 So this example serves to demonstrate that overall kinetic fractionation cannot simply be expressed as the sum of fractionation effects The net fractionation effect also depends on the relative rates of diffusion and carboxylation C fixation lf CO2 diffusive exchange is rapid compared to fixation k3k2 tends to 0 and fractionation during diffusion in or out is the same ie a1 a2 Then anet a3 But we have to consider the fractionation associated with dissolution as well 11 In this case the 5130 of the plant would be 29 11 o depleted relative to the 8130 of atmospheric CO2 gas open system snet 5130out 23130fix 301 0 However if diffusion is very slow relative to carboxylation k3k2gtgtgt1 Then anet a1 Here the total fractionation observed would equal that for diffusion in air 44 o everything that comes in gets fixed and is not lost closed system here you don t worry about the fractionation associate with solubility because all of the CO2 that dissolves is being fixed no chance for dissolved CO2 to equilibrate with the gaseous phase Generally speaking the observed value is somewhere between 44 and 30 as k2 k3 As diffusion rates get slower compared to fixation rate ie in aquatic environments high photosynthesis rates small stomata etc the 813C of the plant will be less depleted than the case where diffusion is not limiting The concentrations of CO2quot and COZout of the cell also effects the isotopic composition of the plant see O Leary Farquhar 1982 and the Laws Paper COZin k1k3k2 COZout Final expression 8130fix 81300020ut edm s x ediffpCOZinp0020ut Sfix When fixation is limiting pCO2in When diffusion is limiting pCO pCO 0 Zout 2in C4 Carbon Fixation Pathway Diffusion same as C3 Dissolution same as C4 and equilibration with H003 PEP fixation into malate Transport Release of CO2 from malate RuBisCo fixation I EC 39p i 739 s is negative so in perfect world quot 39 EN DE C T C U product could be enriched relative 39 quot339 to atmospheric 002 69o if 39 C02aq was in equilibrium with HCO339 and PEP was the rate CUEjaqzl limitin ste u g p Hum 9 Diagram summarizing the lenie pin relatieneliiipe between dissolved my lini camemsate and the carbon added to plies phoenmlmnrwale in veri er m modulie M m maleaeetate lf diffusion is limiting then neither the hydration to H003 nor the fractionation associated with fixation shows up What do we expect for the 8130 of C4 plants lf fixation rate is liming then the fractionation effect must include the fractionation effect of CO2 dissolution 110 the fractionation effect of CO23ml HCO3 what is this and the fraction effect of PEP fixation 20 What does this give us These scenarios assume that the fractionation associated with RuBisCO is not expressed why In reality you see values around 13o any ideas Also empirical data suggests that C4 plants are less sensitive to the atmospheric CO2 concentration 13 13 5 Cfix 39 5 CCOZout 39 8am 39 sdissHCO3equilPEP 8fix L39 8dif pCOZinpC020ut leaking out The sensitivity to external CO2 really depends on L For C4 L seems to hover around 03 or so 7 735 C3 versus C4 plants 20 Isotopic composition when 35 xation is mgl mi 1 entirely by L 033 7 iffu si on 0 4 D 5 i D Dina Flume In Overaii isnmmn rummnon essentlaiiy the amemme he nveenCOzana biumass asanmumn u Np the ram orpamaipvessures 12 pamai r 39 r inverted and shows 6mm my piants using co2 mm 5 73 The Sui 1mg mpmxem c3 prams and menu a mpresemaxwe c mam mm ma m inOiLaEmgiKslyprnaivaiue nipm nnoandM 1 Til imnznntai dashed line shows that ED is inaepanaem ni pp when L the L fracnun leaks DUt of cell lemmas wemuem in nunmersneam Lei m a C plain is 0 t 71 n g i 1 me 12pm cams mat the biomass ur such a giant mum n2 Enriched m a mauve m 02 m WI gt a 45 Summary of controls on the 8130 of C3 and C4 plants 1 The relative rates of CO2 diffusion into the cell and Cfixation 1 High fixation rates or lower diffusion rates lead to less isotope fractionation being expressed 2 For C4 the fraction of CO2 leaking out between PEP and RuBisCO steps 3 The carbon isotopic composition of source CO2 4 Whether CO2 or HCOsis used for example marine plants although they are Cs can actively transport and use HCO3 when CO2 is limiting how does this affect the 8130 of phytoplankton 5 Terrestrial C3 33 to 22o Variation due to varying importance of CO2 diffusion versus CO2 fixation 6 Terrestrial C4 9 to 16o Variations due to CO2 leakage 7 It is the isotopic composition of internal CO2 that ultimately controls the isotopic composition of the plant since the fractionation factor associated with the carboxylating enzymes is constant 5m my WW V I y 3 V r Y V y The Evolution of Horses An Examp e of the Ctrevolution of Climate and the Biosphere mu quotmay MacFadden 2005 CO2 content of the atmosphere is a strong determinant of the photosynthetic pathway of plants C4 plants because of their carbon acquisition pathway is much less sensitive to changes in CO2 Atmospheric 002 ppmv 700 BOO 500 400 800 200 C3 grasses favoured C4 grasses favoured Lower pCO2 a 10 39 20 Daytime growing season temperature 00 30 40 nd higher T from Cerling et a1 1997 Nature Straight From the Horse s Mouth The carbon isotopic composition of bioapatite enamel from horse teeth Age iMyr Age Mfr A93 iMyr a 15 10 5 U 20 15 1 3 5 C39 20 15 1393 5 I 39Iquotquotlquotquotlquotquotlquotquotl 39Iquotquotlquotquotlquotquotlquotquotl 39lquotquotlquotquotlquotquotlquotquotl 5 Pakistan EastMrica a 12qu 30 1539 o rm lame Amen3 3 quot 3 Wm 3quot I C h 2cm 55 DEEFhanljd a 3 Tim i I c 39 raw 2 q a a j if you E 395 n h n i a a 5 Ll n E ea El D f f 39 Mquot 2 a n 5 r a aluau 2 139 a 39 Eta n nus f 139 is l a m 3quot 10 at Z I n f I 2 a i 15 L L M 115 1illl lluluxll quot1llllxl 5 North 3939 North 3939 39 Ester 39 5 America America Eum p e 3 39 39339 3 39139 i E quot 33 Ni quot Bailram 39 3 o 0 Eielnn n i39 l oEquiti a 6333 2 Wmquot 2 05mm 2 U5 128 a 3 u 5 quot7 203 M3 03 39439 qu 04 3quot a g a a E 1 oo 5 10 301536 i t 39 5 e3 39139 E 53 0 w 5 we a 4 n n 09 9 Eh I Z a 34 aug a n w 15 15 IIIIIIIIIIIIIIIIIIIIII IIIIIIIIlIIIIlIlIIlIII Illlllllllllllllllllll 21 1E 10 E I 15 1 20 15 1393 5 Age Myra Age iM39yri Age ih Iyri from Corling st 211 1997 53936 Tn Modern grasses Massive Changes in swgcuiggsfism Vegetation Coincided With 7 aquot Changes in CO2 and T Widespread expansion of C4 plants after 8 MYA 39 I 20 710 0 Senamel deex 8 14 959 enamel sdwex 14 as Modern mammahan ngominat C47dominated tooth ename met dxel n 309 from Cerling et a1 1997 81307105 15 amosphencsh39ll gt8 Myr mammalian 710 O 5 x9 Fractionation associated with other Cfixation pathways w A From 002 El From 0H 40 acetate 35 methane gt a 30 d 5 g 25 2 3E 20 w 1 5 1 0 5 I 0 TCA 3HP PP APMP AP HUMP S AOM Pathway Reductive TCA 3hydroxypriopionate Pentose phosphate Rubis Reductive Acetyl Co A Zerkle et al 2005 Ml m vuLle v B Possible Cfixation Pathways of the Archaea C1 trgnH c o LHOH HOH 3309 nunw E rhrwmmt 6m cc2 4 CH3 2 l mm mayqu 2 up 2 H co2 A co 1 H O CH3 COSCDA scaly Curl cm 2 Pd CH 0 OOH 9 Reductive AcetylCoA Cycle COASH CHIC Mm v E ms HUH LHOH wo 5 mwl uzuldlu H gt3 M Mn coz Jutlincs of the four known pathways for mutatmphin 39 c reactions catalyzed 39 39cy cnzymcs of thcsc pnth called by bold arrows A Calvin Basshum Ecnson cycle citric acid Eyck C rcductiw ntctyl CCIA pathway pmpicnmc cycln C Assimilmcd 11 urban H n mlcnt de reduced fcrncdcxin CHjj cnzynmbnund 1 CGj enzymebound carbon monoxidc group 4 l slwwnuummn CalvinBasshamBenson Cycle D Reductlve CItrIc ACId Cycle c0241 mu 235 CO coorr 00 fosm A l 343 zo Amula 13Hz M n en 41A I H Ho c ccxsrw com 0 3hydroxyproplonate Cycle 39 I mnlrvnyl Cur JZGDlL IL391 2 mnw Muhdwiulu CODH w W L155 ODH HCH H1l cccH cl coscm u 39 H cosch rim OOH E m I gt1L II Iruh CH coz coorl H H FHJ 90 Mnn39m39r A H m CH HOOC L mmle H co2 I COBCCJK mmmvmunyl DJ All mucumy Su December 2 1998 510 269 Aqueous Chemistry Introduction The goal of this course is to provide a basic understanding of the chemistry of the elements in sea water It will stress basic chemical principles and their application to rationalizing the chemistry of the elements in sea water The course will discuss the following areas Average concentrations of the elements in sea water Speciation of the elements in sea water Reactions occurring at surfaces in sea water Biological chemistry of the elements in sea water Distribution of the elements in sea water All these properties can be viewed as a consequence of the basic chemical properties of the elements electron structure electronegativity ionic size reduction potentials etc and of the role of water as a unique solvent Introduction SALINITY AND THE COMPOSITION OF SEA WATER THE MAJOR ION COMPOSITION OF SEA WATER Traditionally the parameter salinity S has been used to give a measure of the total dissolved solids in sea water Originally this was intended to be an analytical parameter with the units gkg l but this direct approach was quickly superseded by the practice of estimating salinity from alternative simpler procedures e g the measurement of chlorinity or conductivity ratio The concept of a constant composition of sea water is then invoked to relate these parameters to salinity UNESCO 1966 Although the idea of constant composition of sea water is recognized as being not strictly accurate it is a useful device in simplifying the study of the various physicochemical properties of sea water One example of this is the treatment of sea water as a two component systemiwater and seasaltito represent its thermodynamic properties e g osmotic coe lcient or density Another is the treatment of sea water as a constant ionic medium in which the thermodynamics of various chemical process involving minor constituents can be studied e g gas solubility or acidebase equilibria Analytical results for the other major components of sea water are usually expressed relative to chlorinity Table 1 and a standard mean chemical composition of sea water A detailed ionic composition of sea water can then be calculated from these data using the appropriate equilibrium constants for the dissociation of water carbonic and boric acids Table 2 TABLE 1 Standard mean analytical composition of sea water with S 35 chlorinity 19374 Relative 71 Component Concentrations m01kgsoln Reference Chloride 099889 054586 calculated from chlorinity Sulfate 01400 002824 Mom39s amp Riley 1966 Bromide 0003473 000084 Morris amp Riley 1966 Fluoride 0000067 000007 Riley 1965 Sodium 055661 046906 from charge balance Magnesium 006626 005282 Carpenter amp Manella 1973 Calcium 002127 001028 Ri1ey amp Tongudai 1967 Potassium 00206 001021 Riley amp Tongudai 1967 Strontium 000041 000009 Riley amp Tongudai 1967 Boron 0000232 0000416 Uppstrom 1974 Total alkalinity 0002400 average surface water pH 81 101 average surface water a Expressed relative to the chlorinity S180655 Thus the total sulfate molar mass 96062 g at a salinity S is given by 01400 s i ST 96062X180655 mol39kg39soln where 96062 is the molar mass of sulfate ion Introduction TABLE 2 Standard mean chemical composition of sea water S 35 SPeCieS molkgsoln 1 g39kgsoln 1 molkgH2071 g39kgHZO 1 C17 054586 193524 056576 200579 SO 002824 27123 002927 28117 Br 000084 00673 000087 00695 F7 000007 00013 000007 00013 Nalr 046906 107837 048616 111768 Mg2 005282 12837 005475 13307 Ca2 001028 04121 001065 04268 Klr 001021 03991 001058 04137 Sr2 000009 00079 000009 00079 BOH3 000032 00198 000033 00204 BOH 000010 00079 000010 00079 CO 000001 00004 000001 00004 HCO 000177 01080 000183 01117 C032 000026 00156 000027 00162 OH 000001 00002 000001 00002 sum ofcolumn 111994 351717 116075 364531 ionic strength 069734 072275 CONCENTRATIONS OF OTHER It is probably fair to say that all of the elements that are found in nature are to be found ELEMENTS IN SEA WATER in sea water Their concentrations re ect their reactivity or rate of removal from sea water Thus a broad correlation can be found between the concentration of the element in sea water and its mean residence time Amount in reservoir T 7 Rate ofremoval 39 1391 see Figure 1 Note The age of a particle at its nal departure from the system is called the residence time I Inlet System Outlet gt Introduction RELATIONSHIP BETWEEN THE RESIDENCE TIME AND THE DISTRIBUTION OF ELEMENTS N SEA WATER ACCUMULATED ELEMENTS i Q I I E o o I 1 lt7 g Q N I Q c I b Cs Mean Oceamc Concentra on umOIL E E E E E o o o o o o oI J c g I I I I I I 0 lt1 3 u 31 lt7 cm H lt 3 U 9 I I I I Q 1 I I IgtltI m 08 I I I I I I I Ion mo Ion3 IXIOA IgtltIU5 IxIO6 IgtltIO7 Ion8 IXIOQ Mean ResIdence TIme yr FIGURE 1Plot of the concentration of the elements in sea water as a function of their residence time Whit eld 1979 The distribution of elements with depth in sea water is related to their residence time X gt I g 1 gt 100000 yr 3 I 9 1 1000 7100000 yr 3 I X 39gt g Q l lt 1000 yr Elements that have a very long residence time in sea water i e are not subject to effective removal processes are evenly mixed around the ocean and are accumulated in the ocean These are predominantly those elements that make up the major ion composition in sea water Introduction Group Transition Elements Feria d Nd Pm 94 95 96 97 98 99 100101 102103 Np Pu Am Cm Bk Cf Es Fm Md No Lr FIGURE 2 Accumulated elements in sea water RECYCLED ELEMENTS Elements with intermediate residence times in sea water are often involved in recycling due to biological processes The characteristic depth pro le of such an element indicates removal in surface waters and regeneration at depth Transition Elements Period 92 93 94 Np Pu Cm Bk Cf Es 95 96 97 98 99 Fm 100 101 102 lOS FIGURE 3 Recycled elements Introduction SCAVENGED ELEMENTS BIOLOGICAL UPTAKE PROCESSES AND SCAVENGING OF ELEMENTS BY PARTICLES BIOLOGICALLY DRIVEN PARTICLE CYCLE IN THE UPPER OCEAN The third class of elemental pro le has an excess in the surface waters and less at depth This is the result of rapid scavenging onto sinking particles As a result the residence time of such elements is typically short lt ocean stirring time emup Transition Elements Peria d Pr A tinides 92 91 3 7 Pa U Np 231 1 380 237 95 Am 241 96 9 98 Cm Bk Cf 99 100 101 Es Fm 102 103 No Lr 239 FIGURE 4 Scavenged elements The majority of the material is removed from the upper ocean by particles generated in biological processes Only a limited number of elements are actually essential for life 1G however in addition to deliberate processes involving the transfer of the element through the cell membrane biological uptake and release there are other adventitious ones in which the element is simply adsorbed onto the surface of the cell To understand this we will examine the role of bonding in surface reactivity and the kinetics of the scavenging of elements by particles A simplistic view of particle cycle in the upper ocean is shown in the following gure The catch all compartment Biological Packaging includes the effects of zooplankton grazing and excretion on the particle cycle Typically almost all of the particles exported from the euphotic zone are rem ineralized by bacterial processes below the euphotic zone and only about 1 of the particles leaving the euphotic zone reach the bottom see Figure 6 Innoduc on Group Transition Elements Period Ce Pr Actinides 90 91 92 93 94 95 6 97 98 99 100101 102103 Pa Np Pu Am Cm Bk Cf Es Fm Md No Lr n 1 FIGURE 5 Biologically active elements SPECIATION OF THE ELEMENTS Why study speciation A belief that the form of an element in solution controls the IN SEA WATER nature and extent of its participation in the various biological and geochemical processes that regulate the composition of natural waters The equilibrium speciation of elements in sea water is calculated from thermodynamic information about the formation of a Wide variety of possible complexes A broa summary of the inorganic speciation of the elements in sea water is shown in Figure 7 11 Introduction Aeolian Rivers dust I A L 39 Dermal mjngms 39 gt PhotoOXIdatIon D solved PhotosyntheSI EUPHOTIC of m ZONE ma nces B m39quot 3939s 5 25 70 Biological packaging production particulate material exported from the euphotic zone FIGURE 6 Schematic of the particle cycle in the upper ocean Group Transition Elements Period Fe Co Ni Cu Zn Ru Rh Pd Cd Os Ir Pt Hg FIGURE 7 Summary of the inorganic speciation of the elements in sea water Yellow water magenta noble gases green cations orange simple anions blue fully hydrolyzed elements and red radioactive elements Introduction CELL MEMBRANE TRANSPORT BINDING PROCESSES FOR AN ELEMENT IN A CELL PER PRO IODIC TABLE OF OCEANIC FILES The uptake of materials by a biological system typically involves transfer through a cell membrane Figure 8 N 5quot F 9 L1 Synthesis Ener MH LHM 9 ML2 ML2 m Pump Kinetic ML1 ML1 trap pHout39 Eoout pHin39 Eoin FIGURE 8 Schematic of the various processes involved in transfer of an element through a cell membrane The cell membrane is used as a physical barrier to diffusion of a free or bound ion e g Na K An element can be stored free or bound Within an internal vesicle after passing a second membrane 6 g Na K Internal polymers can bind an element at equilibrium e g Mg Ca2 transition In eta s Internal polymers can incorporate an element forming thermodynamically unstable but kinetically stable bonds 6 g nonmetals Two trapped elements can combine to form a precipitate at equilibrium 139 e biominerals The net result of all these various processes when combined with oceanic mixing processes is to provide a Wide variety of oceanic pro les for the distribution of the various elements in sea water A periodic table of the elements displaying the distribution of elements in the North Paci c has been complied by Nozaki 1997 and was published as an article in E05 7 see overleaf The article is also available on the W at http www agu orgeoselecas97025e i html 13
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