5. geochemicalcycles

8/16/2019 5. GeochemicalCycles

1/53

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%


2/53

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


3/53

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+(


4/53

Marine Cycles

$pen Uni!ersity, MBC* -ig. .


5/53

Marine Cycles


" 0 particulate inputs 0 dissol!ed inputs G 0 gas inputs

"

"&ir/sea

e1change"

"

" cosmogenicG

G


6/53

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


7/53

MBC* -ig. .

Marine Cycles

C 0 internal cycling 'recycling(

C

C

C


8/53

Marine Cycles

• Cycling

– Cyclic salts# from ocean atmosphere

ri!ers or rainout oceans• &erosols '8ea spray(

– Biological cycling

• nutrients – 8ediment cycling


9/53

MBC* -ig. .

Marine Cycles

$ 0 $utputs

$$

$ $

$

$

&ir/sea

e1change


10/53

Marine Cycles

• $utputs – 8edimentation 'biogenic* lithogenic* chemical(

• Burial• 9e!erse 4eathering

• Lithification

• 8ubduction

– iagenetic reactions

– 5ydrothermal reactions '8eafloor 4eathering of basalt(

– Gas e1change


11/53


12/53

Marine Cycles

• 5ydrothermal and diagenetic cycles

– Both process add and remo!e cations

– 5ydrothermal

• Mg/


13/53

Marine Cycles


""

&ir/sea

e1change"

"

"G

G

C

C

C

$$

$ $

$


14/53

Marine Cycles

$B* -ig. >.


15/53

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


16/53

Marine Cycles

• Weathering

CaC$= < C$ < 5$ Ca


17/53

Marine cycles

• 3o close the loop

– -rom the marine realm back to

continent/atmosphere/'biosphere( – Burial and metamorphism

– Uplift

– 6olcanism


18/53

Marine Cycles

$B* -ig. >.


19/53

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


20/53

• 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


21/53

8alinityMajor Constituents of Seawater

Chlorine Cl# AAA

8odium Ha< @K

Mg< A@

8ulfate

Calcium Ca< ?.A

"otassium I < ?

Bicarbonate 5C$=

#

mmol/kg

Magnesium

8$@

#


22/53

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


23/53

• Conser!ati!e Beha!ior 'mostly maDor elements( – &ltered 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( – &ltered by physical* chemical or biological

processes 4ithin the ocean

– 71amples# nutrients* silica* dissol!ed o1ygen

issol!ed Constituents


24/53

Conser!ati!e # Hon#conser!ati!e

$C* -ig. .?

Conser!ati!e Hon#conser!ati!e

Ca


25/53

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


26/53

"ermian/3riassic 7!aporites

9uddiman* A#?A


27/53

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


28/53

Mg and Ca

8eas

9idge4ell and Oeebe. A


29/53

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


30/53

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.


31/53

• 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


32/53

"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


33/53

"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(


34/53

"article 8ca!enging

depth

concentration

3ypical 8ca!enged

7lement "rofile

'3h* "b* -e(


35/53

"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(


36/53

Marine -lu1

W5$2 4ebsite

8ediment trap material

Marine :sno4;

-ecal pellet


37/53

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


38/53

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


39/53

$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


40/53

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


41/53

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


42/53

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


43/53

Hutrient "rofiles

Broecker and "eng* -ig. >#?@

onJt al4ays consume all nutrients at the surface

"reformed nutrients# can be ad!ected into deep ocean


44/53

Hutrient "rofiles

Chester* Marine Geochemistry* -ig. .=


45/53

"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(


46/53

5igh Hutrient#Lo4 Chlorophyll

9egions

Levitus World Ocean Atlas 199


47/53

• "$@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


48/53

$ "rofiles

P air/sea e1change

P photosynthesis

regeneration of nutrients

$ added

$ remo!ed

bo1 model


49/53

&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


50/53

issol!ed

$

Broecker and "eng* -ig. =#Q and -ig. .># MBC

8upersaturation in

surface 4aters,•"hotosynthesis•Wa!es/bubbles


51/53

&$U

Broecker and "eng* -ig. =#K

8urface0 supersaturated


52/53

$ "rofile

$ minimum

corresponds to

nutrient ma1imum

Combination of

biological pump <

circulation 'age# timea4ay from surface(

MBC* -ig. .K# Horth "acific

8urface0 supersaturated


53/53

issol!ed "rofiles# 8ummary

5. geochemicalcycles

Documents