050428 Carbonate Solubility Lecture 20 DM 2701
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Transcript of 050428 Carbonate Solubility Lecture 20 DM 2701
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Carbonate Solubility
Solubility
Dissolution mechanisms
Dissolution rate expressions
Saturation state in the oceanT, P, and CO
2release
In situ [CO32 and the saturation hori!on
Sedimentary e"idence o# carbonate dissolution
$inetic and%or thermodynamic controls
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p& scales
'ree
Total
Sea(ater
)eebe and *ol#+ladro(
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p& scale comparisons
p$ comparisons
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Carbonate Solubility
CaCO3-./ Ca02
0 CO32
De#ine satauration state as1
. IP % $sp
*ith IP 4ion acti"ity product5
. [Ca02[CO32 #or the solution,
and (ith the apparent solubility product1
#or a solution in e6uilibrium (ith solid CaCO34T,P,S5
02 +27 3sp
[Ca [CO $
8=
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$9sp depends on mineralo:y 4calcite - ara:onite - ;:+calcite,
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O#ten, (e ta=e [Ca02 as a constant #unction o# salinity,
and express in terms o# the saturation carbonate ion concentration
so, i# [Ca02 constant,
De#ine CO32 as 4[CO
32
in situ+ [CO
32
sat5
02 +2 02 +2
3 in situ 3 in situ
7 02 +2
sp 3 saturation
[Ca [CO [Ca [CO
$ [Ca [CO = =
+2
3 in situ
+2
3 saturation
[CO
[CO
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Controls on saturation state1
Pressureand temperature e##ects on carbonate solubility
Solubility hi:her in deeper and colder (ater
Pressure, temperature, and respiratione##ects on [CO32
in situ
[CO32 lo(er in deeper, colder, and >older? (ater
@roec=er and Pen:
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@en+Aa=o" et alB,
in situ saturometer
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Pro#ile o# saturation
carbonate ion concentration,
based on in situ saturometerE
stron: increase in solubility
(ith increasin: depthB
@roec=er and Pen:
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Sayles, 8FGH
se obser"ed
$9sp in J+8H cm
inter"al o# in situ
pore (ater pro#iles4l= 0 p&, . Ca5
to estimate
solubilityB
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Solubility "s depth #or Sayles9 pore
(ater data and lab solubility studies
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Solubility "s depth
comparisonB
@roec=er and Pen:
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*hat is the relationship bet(een de:ree o# undersaturation and
dissolution rateK
CaCO3-./ Ca020 CO
32
De#ine the mass+normali!ed dissolution rate1
>=L? is the reaction rate 4M%day5
>n? is the reaction order
>L? to account #or M CaCO3in bul= sediments, and #or sur#ace area
Can express dissolution rate in terms o# carbonate ion concentration
N . =L 4[CO32
sat+ [CO
32
in situ5n
*here 4[CO32
sat is the saturation carbonate ion concentration 4T,P5
+8 LN 4M d 5 48 5nk=
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n unresol"ed pu!!le1
aboratory dissolution studies 4$eir, 8FGJ5 and
theoretical ar:uments 4;orse5 su::est that
=L 8JJJ % day
and
n . BH
stron:ly non+linear
#ast dissolution
really #ast at lo(
@ut all pore(ater dissolution studies :i"e
=L 8 + 8J % day48J2to 8J3slo(er5
and
n . 3, or e"en 8
4&ales and Qmerson, 8FF5
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;orse and r"idson + &i:h order
=inetics consistent (ith controlo# dissolution by one o# the
sur#ace processes
4adsorption, mi:ration, reaction,
mi:ration, desorption5
&ales and Qmerson, Sayles and ;artin
Shallo( depth at (hich pore(aters
reach saturation implies lo(+order
=ineticsE other(ise #inal approach tosaturation (ould ta=e much
lon:er 4deeper5B
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&ales and Qmerson
Necalculate (ith ne(
constants1 n . 3B2
Neassess solubiliy
too1 n . 8B3
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*hy do (e careK
In#luences o# dissolution rate la( include1"ertical pro#ile o# dissolution in sediments
impact o# CO2 release by benthic decomposition
total dissolution rate
shape o# lysocline
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Saturation state in the ocean
In#luence o# T, P, and CO2release
In situ [CO32 and the saturation hori!on
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Pressure,temperature, and
respiration e##ects
on [CO32
in situB
[CO32
lo(er indeeper, colder, and
>older? (aterB
:in: dominatesB
Temperature
0 5 10 15 20 25 30
CO3=umol/kg
200
250
Const Alk (2320) and DIC (19!)
Dept" (m)
0 1000 2000 3000 #000 5000
CO3=umol/kg
200
250T = 25 C
T = 3 C
$ = sur%a&e
'espraton DIC n&rease (umol/kg)
0 100 200
CO3=um
ol/kg
0
100
200
3 C 3*5 km no dssoluton
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&o( does [CO32 respond to chan:es in l= or DICK
CT . [&2CO3L 0 [ &CO3 0 [CO32
~ [ HCO3] + [CO
32] 4an approximation5
l= . [O& 0 [&CO3 0 2[CO
32 0 [@4O&5
+ [&0
~ [HCO3] + 2[CO
32] 4aB=BaB >carbonate al=alinity?5
So 4rou:hly51
[CO32] ~ Alk CT
CT , [CO
32] Alk , [CO
32]
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Photosynthesis
CO20 &
2O ./ >C&
2O? 0 O
2
CO2
. +8
l= . J
So [CO32 . l= + CO
2. J 4+85 . 08
[CO3
2] increases, increasesB
Nespiration
>C&2O? 0 O
2 ./ CO
20 &
2O
CO2 . 08l= . J
So [CO32 . l= + CO
2. J 8 . +8
[CO32] ecreases, ecreases!
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)eebe and *ol#+ladro(
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Calci#ication
Ca020 CO32 ./ CaCO
3
CO2
. +8
l= . +2
So [CO32 . +2 4+85 . +8
[CO3
2] ecreases, ecreasesB
Dissolution1
CaCO3 ./ Ca020 CO
32
CO2
. 08
l= . 02
So [CO32 . 2 8 . 08
[CO32] increases, increases!
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% CaCO3vs. water depth
lysocline onset ofdissolution
calcite compensation
depth
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Ta=ahashi and @roec=er 9GJE QOSQCS data
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Calcite
saturation
ra:onite
in situ
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@et!er et alB, 8FG
nother pu!!le1
RPac sediment traps loss o#
carbonate abo"e the
ara:onite saturation hori!onB
&i:h ara:onite%calcite ratio
in sin=in: #lux1
JB2 to 2J, most / 8
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Carbonate #lux in Rtl
sediment traps loss o#
carbonate abo"e the
ara:onite saturation hori!onB
;illiman et alB, 8FFF
ThermodynamicsK &i:h+
solubility phase4s5K
;a:nesian+calcite5
rti#actsK
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Sedimentary e"idence o# carbonate dissolution
$inetic and%or thermodynamic controls
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Sediment
e"idence #or
dissolutionK
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&ere, core+top ara:onite
distribution seems to
match the depth o# theara:onite saturation
hori!onB
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'arrell and Prell
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delsec= 8F
lab study o#
selecti"edissolution o#
plan=tonic
#oramini#era
ssembla:e chan:e
only a#ter substantial
carbonate dissolutionE
not a sensiti"eindicator
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@er:er et alB, 8FG2 Selecti"e dissolution in Q6Pac
Di##erential dissolution1 a ran:e o# susceptibility
ThermodynamicsK 4di##erent solubilitiesK5
$ineticsK 4di##erent area%:, crystallinityK5
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M radiolaria
M (hole menardii
M benthic
M (hole plan=tBM CoarseM CaCO3
Peterson and Prell a
>composite dissolution index?
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Peterson and Prell a>composite dissolution index? compared
(ith (ater column saturation stateB
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ohmann si!e+normali!ed
shell (ei:htB
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Si!e+normali!ed shell
(ei:ht su::estsdissolution startin: (ell
abo"e the calcite
saturation hori!onB
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