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Marine
Geochemical/Biogeochemical
Cycles
• Working up to sedimentation
– Understanding chemistry of the oceans – Lead to biogenic and chemical sedimentation
• Cycles – issol!ed constituents
– "articulate# $rganic and inorganic
– Colloidal material# dissol!ed% particulate%
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Marine Geochemical Cycles
• &lmost entire periodic table of elements can
be found in the ocean 'ions in solution(
– Concentrations are not e)ui!alent to ri!erine
input
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Marine Geochemical Cycles
• &lmost entire periodic table of elements can
be found in the ocean 'ions in solution(
– Concentrations are not e)ui!alent to ri!erine
input
– $ther sources# inputs 'hydrothermal* diagenetic+(
– Must also consider outputs and output rates'sedimentation* hydrothermal+(
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Marine Cycles
$pen Uni!ersity, MBC* -ig. .
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Marine Cycles
$pen Uni!ersity, MBC* -ig. .
" 0 particulate inputs 0 dissol!ed inputs G 0 gas inputs
"
"&ir/sea
e1change"
"
" cosmogenicG
G
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Marine Cycles
• 2nputs, – "articulate
• 3errestrial# ri!erine* eolian* !olcanic
• Cosmogenic
– issol!ed constituents• Continental 4eathering 'including ground 4ater flu1(
• 5ydrothermal reactions 'ocean crust 4eathering(
• iagenetic reactions 'sediment(
– Gases• 6olcanic
• &ir/sea e1change
• 71cess !olatiles
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MBC* -ig. .
Marine Cycles
C 0 internal cycling 'recycling(
C
C
C
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Marine Cycles
• Cycling
– Cyclic salts# from ocean atmosphere
ri!ers or rainout oceans• &erosols '8ea spray(
– Biological cycling
• nutrients – 8ediment cycling
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MBC* -ig. .
Marine Cycles
$ 0 $utputs
$$
$ $
$
$
&ir/sea
e1change
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Marine Cycles
• $utputs – 8edimentation 'biogenic* lithogenic* chemical(
• Burial• 9e!erse 4eathering
• Lithification
• 8ubduction
– iagenetic reactions
– 5ydrothermal reactions '8eafloor 4eathering of basalt(
– Gas e1change
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Marine Cycles
• 5ydrothermal and diagenetic cycles
– Both process add and remo!e cations
– 5ydrothermal
• Mg/
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Marine Cycles
$pen Uni!ersity, MBC* -ig. .
""
&ir/sea
e1change"
"
"G
G
C
C
C
$$
$ $
$
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Marine Cycles
$B* -ig. >.
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Marine Cycles
• "rocess approach
• Global cycle# includes passage through
oceans?( Weathering
( 9emo!al to sediments
=( Cycling through hydrothermal systems ormarine sediments
@( Uplift or burial/metamorphism
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Marine Cycles
• Weathering
CaC$= < C$ < 5$ Ca
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Marine cycles
• 3o close the loop
– -rom the marine realm back to
continent/atmosphere/'biosphere( – Burial and metamorphism
– Uplift
– 6olcanism
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Marine Cycles
$B* -ig. >.
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issol!ed Constituents
• 8alinity#
– 3he sum of all the dissol!ed salts in sea4ater
– &mount of dissol!ed inorganic solids
– &!erage =A
• =Ag salt in ?g 4ater 'g/kg(
• =A ppt• =A per mil ' (
• =A psu 'practical salinity units(
o
o
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• 8alts di!ided into
– maDor constituents 'E ? ppm(
– minor constituents '? ppb – ? ppm( – trace constituents 'F ? ppb(
•> MaDor constituents account for E. ofthe salts
– Cl#* Ha
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8alinityMajor Constituents of Seawater
Chlorine Cl# AAA
8odium Ha< @K
Mg< A@
8ulfate
Calcium Ca< ?.A
"otassium I < ?
Bicarbonate 5C$=
#
mmol/kg
Magnesium
8$@
#
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8alinity
• La4 of constant proportions
– 8alinity 4ill !ary 4ith e!aporation and
precipitation 'add and remo!e 5/$(* but theratio of the maDor salts does not change
• conser!ati!e beha!ior# not altered by biological or
chemical reactions 4ithin the ocean
Mg/Ca A
# 3hroughout the oceans
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• Conser!ati!e Beha!ior 'mostly maDor elements( – <ered only by processes at the boundaries
– Within the ocean only altered by mi1ing – 71amples –maDor elements salinity* potential
temperature and pressure
• Hon#conser!ati!e Beha!ior 'most minor and trace( – <ered by physical* chemical or biological
processes 4ithin the ocean
– 71amples# nutrients* silica* dissol!ed o1ygen
issol!ed Constituents
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Conser!ati!e # Hon#conser!ati!e
$C* -ig. .?
Conser!ati!e Hon#conser!ati!e
Ca
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8teady 8tate
• 8teady 8tate
– 2nputs 0 outputs
– Chemical budget is balanced
• Belie!ed to be true in a gross sense for maDor
constituents and many minor/trace for the
"haneroNoic – 8ediment/organisms ha!enJt changed
– -luid inclusions
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"ermian/3riassic 7!aporites
9uddiman* A#?A
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8teady 8tate
• Balanced cycles
• 71ample# Mg cycle
– 2f 53 circulation decreases 'less seafloorspreading(
– Less Mg uptake at the ridge
– 2ncreased Mg uptake else4here 'carbonates*e!aporites+(
– 9elated to distribution coefficient• I 0 conc in solid/conc in sea4ater
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Mg and Ca
8eas
9idge4ell and Oeebe. A
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9esidence 3ime
• 2f elements are in steady state* it is possible
to determine ho4 long they stay in
dissol!ed form# the residence time – 9eacti!ity of an element
τ'yrs( 0 &bundance 'total number of moles(-lu1 'input or output rate(
molesmoles/yr
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9esidence 3ime
8r 71ample
τ 0'K> µm( P '?.=> 1 ?? l(
'= < ?. < .=( 1 ?? mol/yr ri! 53 diag
Mi1ing time of the ocean 0 ?A yrs
Well mi1ed
0 .Q m.y.
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• MaDor constituents tend to ha!e long
residence times
9esidence 3ime
7lement Conc 'mM(
'millimoles/l(
9esidence time
'm.y.(
Ha< @K ?=Mg< A@ ?A
Ca< ?.A ?.
I <
? K.Cl# AAA =A
8$@#
5C$=# .KK
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"articulate -lu1es
• Most of the organic matter and particulate cycles
takes place in the upper 4ater column
– "hotic None ?# m
– "hytoplankton photosynthesiNe 'most of the biomass(
– Oooplankton eat phytoplankton 'fecal pellets(
– Bacteria consume and decompose small particles and pellets
– 2nput of eolian material
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"article 8ca!enging
• Metal ions and ionic comple1es areadsorbed on particles and transferred to theseafloor – &dsorption 0 ionic attraction
– Bacteria# small siNe* large surface area sitesof adsorption
– Clays# charged surfaces
• 7lements that are commonly sca!enged – 3h* "b* Co
– 5a!e short residence times 'F? – ? yrs(
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"article 8ca!enging
depth
concentration
3ypical 8ca!enged
7lement "rofile
'3h* "b* -e(
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"articulate -lu1es
• 3ransfer to the seafloor
– 8ettle at ?m/hr* ?QQ days to reach seafloor
• Ret sediment on seafloor reflects particles in
o!erlying 4ater column
• "ackaged as,
– -ecal pellets '?#m/day(
– Marine sno4 'aggregates(
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Marine -lu1
W5$2 4ebsite
8ediment trap material
Marine :sno4;
-ecal pellet
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Hutrient Cycles
• Biological "ump
– o4n4ard mo!ement of nutrients out of the
photic None as particles – 9elease into deeper 4aters by decay
– Combines particle and dissol!ed flu1es
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Biological "ump# Hutrient Cycles
"hotosynthesis
9espiration
9egeneration
9emineraliNation'ecay(
bo1 model
?Q C$ < ?Q 5H$= < 5="$@
< ? 5$
'C5$(?Q'H5=(?Q'5="$@( <
?=K $
9edfield 9atio 'marine organic matter(
C,H,",
?Q,?Q,?
Biological Pump
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$C* -ig. .=
S organic matter
recycled in
upper ? m
'abo!e the
thermocline(? of sinking
organic matter
'.A units(
makes it to theseafloor
'repacked
multiple times(
Biological "article -ormation
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Biological "article -ormation
$f the A units Corg that
sink belo4 the photic
None '? m(
# =#@ recycled abo!e
the thermocline#only .A makes it to
the seafloor
$rganic matter is rare
in the deep seaT
8keletal/organic
matter increases4ith depth
MBC -ig. .=
6ertical -lu1es and Cycling of issol!ed
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6ertical -lu1es and Cycling of issol!ed
and "articulate Constituents
MBC* -ig. .
Mi1ed layer
3hermocline
8traight arro4s
0 dissol!ed
flu1es
Wa!y arro4s 0
particle flu1es
:Biological "ump;
eep $cean
photosynthesis
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Hutrient "rofilesMicromoles per liter
Can be Nero at the surface 'limiting(# consumed
" and H# mid depth ma1ima 0 oldest 4ater
8i# ma1imum slightly deeper* high at seafloor# dissolution
from sediment
5ard part profile8ee -ig. .? MBC
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Hutrient "rofiles
Broecker and "eng* -ig. >#?@
onJt al4ays consume all nutrients at the surface
"reformed nutrients# can be ad!ected into deep ocean
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Hutrient "rofiles
Chester* Marine Geochemistry* -ig. .=
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"reformed Hutrients
• "reformed nutrients# Hutrients that aread!ected into the deep ocean rather than
produced by decay
• Common in 8outhern $cean '5HLC areas( – Lo4 light le!els
– Lack of biolimiting trace elements# -e%
"$@ meas 0 "$@ preformed < "$@ o1 'recycled(
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5igh Hutrient#Lo4 Chlorophyll
9egions
Levitus World Ocean Atlas 199
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• "$@P 'Broecker( initial phosphate 'relatedto preformed phosphate(
– istinct !alue for HCW and 8CW
– 8CW EHCW
– Conser!ati!e property
"reformed Hutrients
"$@P 0 "$@ < $/?>A – ?.A µm/kg
2ncrease in "$@ due to o1idation of organic matter
Balanced by decrease in $/?>A
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$ "rofiles
P air/sea e1change
P photosynthesis
regeneration of nutrients
$ added
$ remo!ed
bo1 model
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&pparent $1ygen UtiliNation
'&$U(• Ino4 dissol!ed o1ygen content of 4ater 4hen
it sinks
• 3hat !alue decreases through o1idation of organicmatter
• ifference bet4een e1pected !alue at saturation
and obser!ed !alue 0 amount used for o1idation
&$U 0 $ sat – $ meas
Used to calculate preformed nutrients
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issol!ed
$
Broecker and "eng* -ig. =#Q and -ig. .># MBC
8upersaturation in
surface 4aters,•"hotosynthesis•Wa!es/bubbles
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&$U
Broecker and "eng* -ig. =#K
8urface0 supersaturated
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$ "rofile
$ minimum
corresponds to
nutrient ma1imum
Combination of
biological pump <
circulation 'age# timea4ay from surface(
MBC* -ig. .K# Horth "acific
8urface0 supersaturated
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issol!ed "rofiles# 8ummary