EFFECTS OF CHANGES IN CARBONATE CHEMISTRY

ON NUTRIENT AND METAL SPECIATION

Hein De Baar Loes GerringaHein De Baar, Loes Gerringaand Charles-Edouard Thuroczy

Biological Elements in SeawaterC N

Al Si PGe

Ca Mn Fe Co Ni Cu ZnAg Cd

Ba La

L C Nd S E Gd Tb D H E T Yb LLa Ce Nd SmEu Gd Tb Dy Ho Er Tm Yb Lu

Element in biochemical function (soft tissue)Element in biochemical function (soft tissue)

Element in skeletal part (hard shell, frustule)

Apparent coupling with ocean biological cycle

Metals Abundance & Biological Evolution

Zn1260

Cu522

Ni49300

Co2250

Fe900000

Mn9550

Cd ?Ag

12605224930022509000009550

PbH

Cd ?1.61

Ag0.49

Pb315

Hg0.34

Biological Evolution used abundant metals: essentialL b d t t l bi f ti t i

numbers of atoms versus 1 million Si atoms

Low abundant metals no bio-functions: toxic

De Baar & La Roche (2003)Case studies for Fe, Cu, Zn, Cd

Contents

• Small changes in CO2 chemistry are significant– effects on underwater sound– effects on biology

• Small changes in nutrient chemistry– Silicate

• sidestep: AluminiumPh h t– Phosphate

• Speciation of trace metals Zn, Cu, CdS i ti f i F• Speciation of iron Fe

• Future work• Summary

What is SpeciationWhat is Speciation

Different physical chemical states of a• Different physical-chemical states of a chemical element in seawater

t l di l d ll id l ti l– truly dissolved, colloids, larger particles– oxidation state, Fe(II) versus Fe(III)– weak acid (H2CO3) or weak base (NH4OH)– inorganic complexation (e.g. NaHCO3

0)– organic complexation (e.g. Fe(III)Lorganic)

DIC and Alkalinity at the Zero Meridian

50 0S station Steven van Heuven, unpubl. data, 2008

Zero Meridian Station 10700 16 13’ S 01026 1’ W500 16.13’ S, 01026.71’ W

2100.0 2200.0 2300.0 2400.00

7.8 7.9 8.0 8.1020.0 30.0

0

500

0

500

1000

0

500

1000 CO21000

1500

2000

Dept

h (m

)

1000

1500

2000

Dept

h (m

) pH 1500

2000Dept

h (m

)

2000

2500

DICAlk

2000

2500

3000

2500

3000

3000

3500

3000

35003500

deep waters already are natural laboratory for low pH

Steven van Heuven, unpubl. data, 2008

Today and future scenario at 49 m depthStation 107 (50 0S 01 0W)Station 107 (50 0S, 01 0W)

year DIC ALK pCO2 pHy p p

2008 2144 2287 360 8.07

Future:

2100 ? 2249 2287 800 7.76

2300 ? 2325 2287 1500 7.5DIC and ALK above units micromol per kg seawater

these were converted to micromol per Liter for Mineql+ Version 4.6 (2007) simulations

CO2 System Speciation ith M j I i S twith Major Ions in Seawater

CO2 System Speciation at pCO2=360 ppm and pH=8.07

CO3(2-)

CaHCO3+

H2CO3 (aq)

HCO3HCO3-

MgHCO3+

NaHCO3 (aq)NaHCO3 (aq)

CaCO3 (aq)

MgCO3 (aq)Mineql+ g ( q)

NaCO3-

MineqlVersion 4.6(2007)

Unanticipated Consequences of Ocean Acidification: A Noisier Ocean at Lower pH

Keith Hester, Edward Peltzer, William Kirkwood and Peter BrewerGeophysical Research Letters (2008)

Decrease in ocean sound absorption for frequencies lower than 10 kHz Decrease in ocean sound absorption for frequencies lower than 10 kHz.

This effect is due to known pH-dependent chemical relaxations in theB(OH) /B(OH) - and HCO -/CO 2- systems B(OH)3/B(OH)4 and HCO3 /CO3 systems.

The pH change of 0.3 units anticipated by mid-century, results in adecrease of sound absorption by almost 40% decrease of sound absorption by almost 40%.

Simplified scheme is a coupled exchange reaction with ion-pairing:

In fact the species CaCO3(aq) and CaHCO3+ as well as MgCO3(aq) and MgHCO3

+ are involved

Also Presentation by D. Browning at Wednesday morning

Will marine mammals adapt ?

U d t d i l d Underwater sound is already increasing due to human activity (ships, sonar, etc.)

The additional decrease of sound absorption is an extra concern59 oSouth, February 2008

Simplified CO2 System in SeawaterCO2 System in Seawater

at pCO2=360 ppm and pH=8.07

CO2

HCO3-HCO3

CO32-

CO2 System Speciation at pCO2=360 ppm and pH=8.07

CO3(2-)

CaHCO3+

H2CO3 (aq)

HCO3-HCO3

MgHCO3+

NaHCO3 (aq)

CaCO3 (aq)

MgCO3 (aq)

NaCO3-

Future changes CO2 system:changes of minor players can make a difference

2500

2000

2500

1500

= [1

0-6

M]

CO2(aqueous)

1000

[Mic

rom

ol] = CO32-

HCO3-

500

01 2 38.07 7.76 7.5 pH

360 800 1500 pCO2

M j l HCO i it t blMajor player HCO3- remains quite stable

Minor players CO2 and CO32- change more

this is our concern for photosynthesis and calcification, respectively

Equilibrium Thermodynamics in Mineql+4.6(2007)

The thermodynamic equilibrium simulation only mimics The thermodynamic equilibrium simulation only mimics the existing or predicted situation

The rate or kinetics of any chemical reaction is notassessed

Conversion between chemical species:H2O + CO2 = HCO3

- + H+H2O + CO2 = HCO3 + HThis is a slow reaction

Therefore chemical speciation is importantTherefore chemical speciation is important(acceleration by enzyme Carbonic Anhydrase)

When the rates of conversion reactions are fast, then chemical speciation in seawater may be less important

15Si(OH)4 [10-6M]

Silicate Speciation

10

or P

erce

nt

Si(OH)4 [10 6M]H3SiO4- [10-6M]H3SiO4- [%]

0

5

[10-

6 M

]

pH 8.07 7.76 7.5

Si(OH) [10 6 M] 12 0 12 1 12 2

%%%

1 2 3

pH

8.07 7.76 7.50

At tenfold expanded scale:

Si(OH)4 [10-6 M] 12.0 12.1 12.2

H3SiO4- [10-6 M] 0.151 0.074 0.041

1

1.5

Perc

ent

Total Si [10-6 M] 12.2 12.2 12.2

Percent H3SiO4- 1.2 % 0.6 % 0.3 %

%

0.5

0-6

M]

or P

Si(OH)4 [10-6M]H3SiO4- [10-6M]

%

%

01 2 3

pH

[1 H3SiO4- [%]

8.07 7.76 7.50

Silicate speciation: does it matter ??(who cares ?)( )

Milligan et al (2004)Si uptake and dissolution by diatomsconditions pH = 8.5 and pH = 7.8Si uptake rate not affected by pHSi dissolution rate is 6-7 fold higher at low pHat low pH more Si efflux from cell: lower Si/C ratioeffect on Si stable isotope fractionation yet to be assessed

Del Amo & Brzezinski (1999)4 diatoms at pH 8.0 and pH 9.2Si(OH)4 is by far the preferred Si species for diatom uptakeone diatom P. tricornutum behaves different from other 3 diatoms

Recommendation:assess conceivable effect on fractionation of stable isotopes of Si

With gratitude to Damien Cardinal for responding to my questions

use more realistic pH value ranges in diatom studies

Biological Elements in SeawaterC N

Al Si PGe

Ca Mn Fe Co Ni Cu ZnAg Cd

Ba La

L C Nd S E Gd Tb D H E T Yb LLa Ce Nd SmEu Gd Tb Dy Ho Er Tm Yb Lu

Element in biochemical function (soft tissue)Element in biochemical function (soft tissue)

Element in skeletal part (hard shell, frustule)

Apparent coupling with ocean biological cycle

Titanium ultraclean sampling systemwith Kevlar hydrowirefor trace elements in seawater(De Baar et al., 2008, Marine Chemistry)

Ultra Clean Sub-sampling inside clean containers de c ea co a e

Al in high latitude Arctic Ocean Steady increase of dissolved Al with increasing depth

Looks like silicate

Rob Middag, unpublished data, Arctic Geotraces, Polarstern 2007

Aluminium Speciation 70

65 69

Aluminium: major shiftsp

at pH = 8.07 and pCO2 = 360 ppm

50

60

44

53

65

Al(OH)2+Al(OH)3 (aq)Al(OH)4- 30

40

Perc

enta

ge [%

]

Al(OH)2+Al(OH)3 (aq)Al(OH)4-27( )

10

20

P

3

15

8

16

01 2 3

pH

3

8.07 7.76 7.5

pH = 8.07 pH = 7.76 pH = 7.5

Al(OH)2+

Al(OH)3 (aq)

Al(OH)4-

Major shifts Al speciation: does it matter ?

Thalassiosira nordenskjioldiiAl Si 1 3 1000

Gehlen et al (2002); Al incorporation in growing diatoms

Al : Si = 1.3 : 1000Al : Si = 3.8 : 1000

uptake ratio varies with Al/Si ratio in t diseawater medium

Dissolution of opal diatom frustules decreases significantly with higher Al:Si decreases significantly with higher Al:Si ratio of the biogenic opal (Van Bennekom)

Speciation changes of Al in seawater likely affect the uptake ratio Al:Si by diatoms

The 6-7 fold higher opal dissolution at l H (Milli t l 2004) ll b lower pH (Milligan etal 2004) may well be due to shifts in Al speciation affecting the Al:Si ratio of opal hence the dissolution

Phosphate speciationPhosphate Speciation with Major IonsPhosphate Speciation with Major Ions

at pH = 8.07

MgHPO4 (aq)

NaHPO4-

H2PO4-

Phosphate Speciation at pH = 8.07Simplified in 3 Categories

HPO4-2

CaPO4-

H2PO4-

HPO42-

PO43-PO43

Phosphate speciation with ocean acidification100

pH 8.07 7.76 7.5

H2PO4- 2 2 % 4 4 % 7 8 %

60

80

tage

[%]

H2PO4-HPO42- H2PO4 2.2 % 4.4 % 7.8 %

HPO42- 96.2 % 94.8 % 91.7 %20

40

Perc

ent HPO42

PO43-

At tenfold expanded scale:

PO43- 1.6 % 0.8 % 0.4 %

01 2 3

pH8.07 7.76 7.5

• major shifts of two minor species• (just like the CO2 system)8

10

%]

• does it matter ?• probably not ?

onl 1 stable isotope 31P2

4

6

Perc

enta

ge [% H2PO4-

HPO42-PO43-

• only 1 stable isotope 31P• who cares ?

01 2 3

pH8.07 7.76 7.5

Acidification effect on third major nutrient NitrogenNitrogen

• Nitrate is strong ion• Nitrate is strong ion– only one species NO3

- and this will not be affected

• Ammonia is weak ion– speciation obviously will be affected

Zinc, Copper and Cadmium

Zn1260

Cu522

Ni49300

Co2250

Fe900000

Mn9550

Cd Ag

12605224930022509000009550

PbH

Cd 1.61

Ag0.49

Pb315

Hg0.34

numbers of atoms versus 1 million Si atoms

Zinc Inorganic SpeciationZn is key element in enzyme Carbonic Anhydrasey y y

Zinc Inorganic Speciation at pH = 8.07 Total Zn = 0.4 nM

Zn(2+)

ZnHCO3+ Zn Inorganic Speciation

ZnCO3 (aq)

Zn(SO4)2-2

ZnSO4 (aq) 70

80

90

100

%]

Zn(2+)

ZnHCO3+

30

40

50

60

Perc

enta

ge [%

ZnCO3 (aq)

Zn(SO4)2-2

0

10

20

1 2 3

ZnSO4 (aq)

decrease of ZnCO3(aq) species

pH

Zn Inorganic Speciation

15Zn(2+)

10

ge [%

] ZnHCO3+

ZnCO3 (aq)10

5Perc

enta

g ( q)

Zn(SO4)2-26

5P

ZnSO4 (aq)3

01 2 3

pH

8.07 7.76 7.5

pH

ZnCO3(aq) would decrease from 10 % to 6% to 3 % with ocean acidification

Zinc Speciation with Natural Organic LigandZinc Organic SpeciationT t l Z 0 4 M Zinc Organic Speciation

100 ZnLZn(2+)

96.6 97.297Total Zn = 0.4 nM

Total Ligand = 2.2 nMK(ZnL) = 10.8

[%]

( )

le

This Ligand also binds Cd and Cu at same time

Sum (Zn+Cd+Cu)=1.2 nM

10

Perc

enta

ge

Lo

g s

cal

Assumption:L binding strength does not

h ith H

18 07 7 76 7 5

1.6 1.6 1.6change with pH

Zinc-binding Ligand after Ellwood 2004; Lohan et al., 2005;

Very strong organic complexation stabilizes everything

1 2 3

pH

8.07 7.76 7.5Bruland 1989

Very strong organic complexation stabilizes everythingNo impact of ocean acidification on Zn speciationNo tipping point manuscript to Nature/Science

Copper (Cu) Inorganic SpeciationCu Inorganic Speciation

at pH = 8.07 at pCO2 =360 ppm

Cu(2+)70

80

90

Cu(2+)Cu(2+)

CuOH+

Cu(OH)2 (aq)

CuCl+40

50

60

erce

ntag

e [%

]

Cu(2+)CuOH+Cu(OH)2 (aq)CuCl+CuCO3 (aq)

CuCl+

CuCO3 (aq)

Cu(CO3)2-210

20

30

Pe Cu(CO3)2-2

Cu Inorganic Speciation mostly carbonatesand also OH species

Very promising for major changes ??

01 2 3

pH8.07 7.76 7.5

Very promising for major changes ?? pH 8.07 7.76 7.5

Free Cu(2+) 6 % 11 % 17 %

CuCO3 (aq) 81 % 80 % 72 %

Cu(CO3)22- 7 % 4 % 2 %

Copper speciation with natural organic ligandTotal Cu = 0.6 nM

Total Ligand = 2.2 nMK(CuL) = 13.8

80

100

This Ligand also binds Cd and Cu at same time

Sum (Zn+Cd+Cu)=1 2 nM

60

80

tage

[%]

CuLSum (Zn+Cd+Cu)=1.2 nM

Assumption:L binding strength does not 20

40

Perc

ent CuL

change with pH

Cu binding Ligand after Gerringa et al 1995;

01 2 3

H8.07 7.76 7.5

Gerringa et al., 1995; Laglera & Van Den Berg, 2003; Moffett, 2007

Full 100% organic complexation at every pH value

pH

Full 100% organic complexation at every pH valueNo impact of ocean acidification on Cu speciationNo tipping point manuscript to Nature/Science

80

Cadmium Speciation without and with Organic Ligand

60

80

[%]

Free Cd(2+)

Cd Inorganic Speciation

40

5064% 64% 64%

40

erce

ntag

e [ ( )

CdCl+CdCl3-CdCl2 (aq)CdL20

30

40

cent

age

[%]

Free Cd(2+)CdCl+CdCl3-

0

20

1 2 3

P CdL

0

10

20

Per CdCl2 (aq)

8.07 7.76 7.5

pH1 2 3

pH

8.07 7.76 7.5

3 % free Cd2+ ionFor the rest only Chlorine species

Total Cd = 0.2 nMTotal Ligand = 2.2 nMFor the rest only Chlorine species

No pH dependence at all

64 % Cd-L organic complex

K(CdL) = 10.8 after Ellwood, 2004

This Ligand also binds Zn and Cu at same timeSum (Zn+Cd+Cu)=1.2 nM

64 % Cd L organic complex1 % free Cd2+ ion

For the rest only Chlorine speciesNo pH dependence at all

Gold is for the mistressSilver for the maid

Copper for the craftsmanCopper for the craftsmancunning at his trade.

“Good” said De BaaronGood said De Baaronsitting in this hall:

“But iron – cold iron –is master of them all ”is master of them all.

free after Rudyard Kipling (1910)

Surface Ocean: Iron Speciation crucial for biological uptake by phytoplankton in the euphotic zone

photoreduction

solidsFe2O3

colloids

[FeCO ]0

Fe2O3Fe(OH)3FeOOH

[Fe ] [Fe ]? ?

[Fe(OH) ][Fe(OH) ]2+

+23+2+

[FeCO ]3

[FeOH ]+

[Fe(II)L]?

sidero-

[ ( ) ]

cell

[Fe(III)L]? ?

siderophoresphotoreduction

[Fe(III)L]organic complexes

Gerringa et al, 2000

Deep Ocean: Competition between Stabilization by Organic Complexation versus Removal via Colloids controls Residence Time of Fe in the Oceans

upper ocean

eanstabilization removal

eep

oce

dissolvedstable fine colloids

Fe-particles

000m

dedissolved[Fe3+]dissolved

[Fe3+]-organiccomplex

colloidsFe-

particles

particles

> 0.2 micron

40

complex

sedimentation

seafloor

Case 1: inorganic speciation, no light (dark ocean)

photoreduction

solid

colloids

[FeCO ]0

FeOOHgoethite

[Fe ] [Fe ]? ?

[Fe(OH) ][Fe(OH) ]2+

+23+2+

[FeCO ]3

[FeOH ]+

[Fe(II)L]?

sidero-

[ ( ) ]

cell

[Fe(III)L]? ?

siderophoresphotoreduction

[Fe(III)L]organic complexes

Gerringa et al, 2000

Case 1: inorganic speciation, no light (dark ocean)

Surface sample at 49 m depth:< 0.2 micron

[Fe] = 0.096 nM = 96 pM 1.E-10 Fe'[Fe] 0.096 nM 96 pMAssume no Ligand

7.E-11

8.E-11

9.E-11 GOETHITE88 pM82 pM

72 pM

4.E-11

5.E-11

6.E-11

Con

cent

ratio

nDissolved Inorganic Iron

Fe(OH)2+

1.E-11

2.E-11

3.E-11

8 pM

24 pM

14 pM

Fe(OH)2+

Fe(OH)3 (aq)

Fe(OH)4-

0.E+001 2 3

pH

90 % of the dissolved Fe would precipitate

8.07 7.76 7.5

( )

S f ll i i iSum of all inorganic species:Fe’ = Fe(OH)2

+ + Fe(OH)3 + Fe(OH)4-

Case 2: include organic ligand, delete solid FeOOH, no light (dark ocean)

photoreduction

solid

colloids

[FeCO ]0

FeOOHgoethite

[Fe ] [Fe ]? ?

[Fe(OH) ][Fe(OH) ]2+

+23+2+

[FeCO ]3

[FeOH ]+

[Fe(II)L]?

sidero-

[ ( ) ]

cell

[Fe(III)L]? ?

siderophoresphotoreduction

[Fe(III)L]organic complexes

Gerringa et al, 2000

Case 2: include organic ligand, delete solid FeOOH, no light (dark ocean)

Surface sample at 49 m depth:< 0 2 micron

100

Prediction of speciation model:

< 0.2 micron[Fe] = 0.096 nM = 96 pMLigand = 0.668 nM = 668 pM

80

96pM

96pM

96pM

40

60

FeL

[pM

]

FeL

20

01 2 3

pH

8.07 7.76 7.5

All the dissolved Fe is bound by the ligand, thus stable in seawater

Case 2: Measure the organic complexation in real samplecomplexation in real sample

• deep water sample (2500m depth)– measurement onboard: Fe=0.95 nM, L=1.64 nMmeasurement onboard: Fe 0.95 nM, L 1.64 nM

• adjusted to 3 different pH values 7.75, 8.05, 8.25 in laboratory• measure ligand concentration L and its stability constant K

pH L [nM] error (L) logK error logKOnboard 1.638 0.110 22.42 0.18

8.057.75 1.686 0.067 22.52 0.118 05 1 734 0 081 22 82 0 158.05 1.734 0.081 22.82 0.158.25 1.694 0.065 22.84 0.10

Ligand concentration L does not change significantlyLigand concentration L does not change significantlyStability constant logK does not change significantlyThis supports modeling assumption that K is independent of pH

Case 3: include organic ligand, dissolve FeOOH as much as possible, no light (dark ocean)

photoreduction

solid

colloids

[FeCO ]0

FeOOHgoethite

[Fe ] [Fe ]? ?

[Fe(OH) ][Fe(OH) ]2+

+23+2+

[FeCO ]3

[FeOH ]+

[Fe(II)L]?

sidero-

[ ( ) ]

cell

[Fe(III)L]? ?

siderophoresphotoreduction

[Fe(III)L]organic complexes

Gerringa et al, 2000

Case 3: include organic ligand, dissolve FeOOH as much as possible, no light (dark ocean)

700

800Total Dissolved Fe = Fe’ + FeLSurface sample:

Ligand = 0.668 nM =

698674

522 712688

500

600

Dis

s Fe

[pM

]Fe'

FeL

668 pM

Original Fe = 96 pM514

300

400

FeL

or T

otal

D FeL

TotalDissolved Fe

100

200

Fe' o

r Dissolved Fe

8 14 24Original Fe = 96 pM

01 2 3

pH8.07 7.76 7.5

8 14 24

The Excess Ligand of Todays Ocean Can Accomodate more dissolved FeBy Ocean Acidification the dissolved Fe in Seawater can increase even more

Dissolution of solid phase Fe and Mn is much Dissolution of solid phase Fe and Mn is much more a function of low oxygen conditions than of pHthan of pH

Strong Fe and Mn maxima exist in subsurface i i f E t i l E t oxygen minimum zones of Equatorial East

Pacific, Northwest Indian Ocean (L di t l 1987 S t l 1989)(Landing et al. 1987, Saager et al. 1989)

... however this meeting happens to be about pH not oxygen

How about photoreduction to Fe(II) in open ocean ?How about the fine colloids in open ocean ?

photoreduction

solidsFe2O3

colloids

[FeCO ]0

Fe2O3Fe(OH)3FeOOH

[Fe ] [Fe ]? ?

[Fe(OH) ][Fe(OH) ]2+

+23+2+

[FeCO ]3

[FeOH ]+

[Fe(II)L]?

sidero-

[ ( ) ]

cell

[Fe(III)L]? ?

siderophoresphotoreduction

[Fe(III)L]organic complexes

Gerringa et al, 2000

Photochemistry in upper euphotic zoneof the open oceanof the open ocean

Photoreduction of Fe(III) to Fe(II)only in upper euphotic zoneonly in upper euphotic zonebeyond chemical thermodynamics predictionrapid re-oxidation but slower in cold polar waters

ll ti f th d i t F (III)L i di i tsmall portion of the dominant Fe(III)L species dissociatesinto free Fe(II) and free L

the free Fe(II) likely is more available for uptake by algae

Photochemical breakdown of organic ligand Lyes but only of small labile portion of total L poolyes but only of small labile portion of total L poolligand L is very stable and uniform throughout world ocean

this supports the notion of long term chemical stability li d b i f d i f t f bi tnew ligand being formed in surface waters from biota

surface waters tend to have large excess of ligand versus Fe

Future work in open ocean waters

• response of Fe colloids size class to acidification• response of Fe-colloids size class to acidification– adjust 0.2 micron filtered seawater to different pH values– wait some timewait some time– ultrafiltration and then measure Fe and L in size fractions– physical-chemical modeling ?

• Acidification effects on other metals– Mn manganese– lanthanides series (dominated by CO3

2- species)• but who cares about the lanthanides ?

Summary• shifts in Silicate speciation may affect fractionation of Si stable

isotopesf ff• major shifts in Aluminium speciation may affect its uptake in

diatom frustules, hence dissolution of biogenic Silicon• major shifts of two minor species of Phosphate any effects onmajor shifts of two minor species of Phosphate, any effects on

biota unknown• Zn, Cu and Cd are strongly stabilized by organic complexation• excess organic ligand in modern ocean may accomodate more

dissolved Fe than is currently present• if so then in the future more acidic ocean somewhat more Fe• if so, then in the future more acidic ocean somewhat more Fe

may dissolve• caveats:

– in fact the open ocean ligand does not carry as much Fe as it could