CHAPTER 6: GEOCHEMICAL CYCLES

• Most abundant elements: oxygen (in solid earth!), iron (core),

silicon (mantle), hydrogen (oceans), nitrogen, carbon, sulfur…

• The elemental composition of the Earth has remained essentially

unchanged over its 4.5 Gyr history

– Extraterrestrial inputs (e.g., from meteorites, cometary

material) have been relatively unimportant

– Escape to space has been restricted by gravity

• Biogeochemical cycling of these elements between the different

reservoirs of the Earth system determines the composition of the

Earth’s atmosphere and oceans, and the evolution of life

THE EARTH: ASSEMBLAGE OF ATOMS OF THE 92 NATURAL ELEMENTS

BIOGEOCHEMICAL CYCLING OF ELEMENTS:

examples of major processes Physical exchange, redox chemistry, biogeochemistry are involved

Surface

reservoirs

EVOLUTION OF O2 AND O3 IN EARTH’S ATMOSPHERE

NOAA Greenhouse Gas records

http://www.esrl.noaa.gov/gmd/aggi/

OXIDATION STATES OF NITROGEN N has 5 electrons in valence shell a9 oxidation states from –3 to +5

-3 0 +1 +2 +3 +4 +5

NH3

Ammonia

NH4+

Ammonium

R1N(R2)R3

Organic N

N2 N2O

Nitrous

oxide

NO

Nitric

oxide

HONO

Nitrous acid

NO2-

Nitrite

NO2

Nitrogen

dioxide

HNO3

Nitric acid

NO3-

Nitrate

Decreasing oxidation number (reduction reactions)

Increasing oxidation number (oxidation reactions)

Nitrogen: Nitrogen is a major component of the atmosphere, but an essential nutrient in short

supply to living organisms. Why is "fixed" nitrogen in short supply? Why does it stay

in the atmosphere at all?

free radical free radical

THE NITROGEN CYCLE: MAJOR PROCESSES

ATMOSPHERE N2 NO

HNO3

NH3/NH4+ NO3

-

orgN

BIOSPHERE

LITHOSPHERE

combustion

lightning

oxidation

deposition

assimilation

(bacteria or

host plants

decay

(bacteria)

nitrification

(bacteria, aerobic)

denitrification

(bacteria,

anaerobic)

biofixation

(bacteria)

burial weathering

free radical

"fixed" or "odd" N is less stable globally N2

Kunstgjødsel

http://iconbazaar.com/bars/contributed/pg04.html

IPCC WGI, 2013

Box 6.2, Figure 1 |

Anthropogenic reactive

nitrogen (Nr) creation rates

(in TgN yr–1) from fossil fuel

burning (orange line),

cultivation-induced biological

nitrogen fixation (blue line),

Haber–Bosch process

(green line) and total

creation (red line). Source:

Galloway et al. (2003),

Galloway et al. (2008). Note

that updates are given in

Table 6.9. The only one with

significant changes in the

more recent literature is

cultivation-induced BNF)

which Herridge et al. (2008)

estimated to be 60 TgN yr–

1. The data are only

reported since 1850, as no

published estimate is

available since 1750.

I 1926 krevde lysbueprosessen i snitt 61000 kWh for å produsere

1 tonn fiksert nitrogen, Frank-Caro-prosessen krevde rundt 12-

14000 kWh, mens Haber-Bosch-prosessen kun krevde 4000 kWh

https://no.wikipedia.org/wiki/KWh

Økning i N2O konsentrasjonen de siste 2000 år.

Fra 270 ppbv til 325 ppb (+20%)

FAST OXYGEN CYCLE: ATMOSPHERE-BIOSPHERE

• Source of O2: photosynthesis

nCO2 + nH2O g (CH2O)n + nO2

• Sink: respiration/decay

(CH2O)n + nO2 g nCO2 + nH2O

O2

CO2

orgC

orgC litter

Photosynthesis

less respiration

decay

O2 lifetime: 5000 years

http://iconbazaar.com/bars/contributed/pg04.html

…however, abundance of organic carbon in

biosphere/soil/ocean reservoirs is too small to control

atmospheric O2 levels

Atmosfære

Atmosfære

∑ C

SLOW OXYGEN CYCLE: ATMOSPHERE-LITHOSPHERE

O2 CO2

Compression

subduction

Uplift

CONTINENT OCEAN

FeS2 orgC

weathering Fe2O3 H2SO4

runoff

O2 CO2

Photosynthesis

decay

orgC

burial

SEDIMENTS

microbes

FeS2 orgC

CO2 orgC: 1x107 Pg C

FeS2: 5x106 Pg S

O2: 1.2x106 Pg O

O2 lifetime: 3 million years

The heavier temperature lines 160,000 BP to present reflect more data points, not necessarily greater variability.

Source: Climate and Atmospheric History of the past 420,000 years from the Vostok Ice Core, Antarctica, by Petit

J.R., Jouzel J., Raynaud D., Barkov N.I., Barnola J.M., Basile I., Bender M., Chappellaz J., Davis J. Delaygue G.,

Delmotte M. Kotlyakov V.M., Legrand M., Lipenkov V.M., Lorius C., Pépin L., Ritz C., Saltzman E., Stievenard M.,

Nature, 3 June 1999.

Antarctic Ice Core Data

CO2 varies over geologic time, within the range 190 – 280 ppm for the last

420,000 years. The variations correlate with climate: cold low CO2 . Is

CO2 driving climate or vice versa?

Det Global karbonbudsjettet

1 Pg = 1015 g = 1000 mill tonn

Det Global karbonbudsjettet

1 Pg = 1015 g = 1000 mill tonn

Fotosyntes

e

Respirasjo

n/nedbrytni

ng

Det Global karbonbudsjettet

Det Global karbonbudsjettet

Det Global karbonbudsjettet

Det Global karbonbudsjettet

• Stor utveksling

mellom atmosfære

og planter/hav

• Levetid CO2:

820(PgC)/(100+100

PgC/år) = 4 år

• Mye karbon i

dyphavet

• Veldig tregt tap av

karbon til

olje/kull/gass Kilde: https://www.carboncyclescience.us/what-is-carbon-cycle

Le Quere, 2016

Jacob (1999): FF: 6 Pg(C)/yr

Avskoging: 1.6 Pg(C)/yr

Økning atm: 4 Pg(C)/yr

Opptak (hav/land): 3.6 Pg(C)/yr

FF: 9.5 Pg(C)/yr

Avskoging: 1.0 Pg(C)/yr

Økning atm: ≈ 5 Pg(C)/yr

Opptak hav: ≈ 3 Pg(C)/yr

Opptak land: ≈ 2.5 Pg(C)/yr

Forskjell NH/SH skyldes mer utslipp fra fossile

kilder i nord.

IPCC, 2013

Carbon Cycle on Land

•Photosynthesis:

CO2 + H2O + light => "H2CO" + O2

•Respiration:

"H2CO" + O2 => CO2 + H2O + energy

Very little organic matter is stored, on average.

Carbon Cycle in the ocean

•Dissolution/evasion

CO2(g) + H2O + CO3(aq) = 2 HCO3

¯

https://www.google.no/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiIn_qPjvDXAhVEYZoKHQNgBloQjRwIBw&url=https%3A%2F%2Fwww.huffingtonpost.com%2Fjose-maria-figueres%2Fwhats-working-inspiring-a_b_10331436.html&psig=AOvVaw26LInujZHt4dK76QdJOisl&ust=1512468425629577

Karbonkjemi i havet

• CO2 løses i vannet og danner CO2·H2O

– Likevekt ved Henrys lov

KH = [CO2·H2O]/PCO2 = 3·10-2 M/atm

• CO2·H2O dissosierer og danner HCO3- og H+

– K1 = [HCO3-][H+]/[CO2·H2O] = 9·10

-7 M

• HCO3- dissosierer og danner CO3

2- og H+

– K2 = [CO32-][H+]/[HCO3

- ] = 7·10-10 M

pH = -log [H+]

Lav pH [H+] høy

[H+] høy R5 og R4 forskjøvet

mot venstre

pH i havet (pre-industrielt): 8.2

Ønsker å finne

F(Ki, [H+])

M=mol/liter (Molar)

Oppløst karbon i havet

https://www.google.no/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjc7cC9kPDXAhWGHJoKHY46APgQjRwIBw&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FOceanic_carbon_cycle&psig=AOvVaw0ZUVZGvIm8NRFI7vOJ8leK&ust=1512469063395027

Ønsker å finne F(Ki, [H+])

= 0.03 Betyr dette at 97% av

ekstra tilført CO2 blir

tatt opp i havet?

Oppløst karbon i havet

pH=8 [H+]=10-8 M

DIC = 2·10-3 M

https://www.google.no/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjc7cC9kPDXAhWGHJoKHY46APgQjRwIBw&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FOceanic_carbon_cycle&psig=AOvVaw0ZUVZGvIm8NRFI7vOJ8leK&ust=1512469063395027https://www.google.no/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjKy5e2kfDXAhWpBZoKHW0OBDwQjRwIBw&url=https%3A%2F%2Fwattsupwiththat.com%2F2013%2F11%2F27%2Fco2-in-the-air-co2-in-the-seawater%2F&psig=AOvVaw0ZUVZGvIm8NRFI7vOJ8leK&ust=1512469063395027

Buffereffekten av HCO3- og CO3

2-

Nei, mer CO2 betyr mer H+ slik at F øker

NB! Buffereffekten hindrer ikke at [H+]

øker, men demper økningen betydelig

Ved en ekstra tilførsel

av CO2 til atmosfæren

(dN), hvor mye blir

værende ?

k’= kH k1 / k2 For R6

Lang utregning ……. (se side 102 i boka)

= 0.28

Betyr dette at 72% av ekstra tilført CO2 blir tatt opp i havet?

Ja, men ikke umiddelbart!

- VOC er volumet av hele havet, og blandingen ned i dyphavet er treg.

- Høyere temperatur ved overflaten (?) varmere vann på overflaten

tregere blanding

Dersom vi bare tar med

overflatelaget blir f=0.94

Hvordan tas resten av CO2 opp?

CO2(g) + CaCO3 ↔ 2HCO3- + Ca2+

f=7%

IPCC, 2013

CaCO3 : I sedimenter fra bl.a skjell

IPCC, 2013

Hvordan blir CO2 fjernet på enda lengre tidsskalaer?

• Forvitring av mineraler som består av kalsiumsilikat (CaSiO3)

CO2 opptak i havet til nå

IPCC, 2013

IPCC, 2013

Arrows indicate

El Nino events

Notice:

• atmospheric increase is ~50% of fossil fuel emissions

• significant interannual variability

EVIDENCE FOR LAND UPTAKE

OF CO2 FROM TRENDS IN O2,

1990-2000

Dagens CO2

budsjett.

IPCC, 2013

http://www.google.no/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwisgPiFlfDXAhWJF5oKHWbEAfEQjRwIBw&url=http%3A%2F%2Feuanmearns.com%2Fco2-emissions-reduction-renewables-and-recession%2F&psig=AOvVaw1QJ7EU3LZ3o4_Il5oQSNHX&ust=1512470245545693

CYCLING OF CARBON WITH TERRESTRIAL BIOSPHERE

Inventories in PgC

Flows in PgC yr-1

Relatively small reservoirs a Short time scales

Biogeokjemiske tilbakekoblinger

• T øker økt/redusert plantevekst økt/red CO2 opptak

negativ/positiv tilbakekobling

• CO2 øker økt plantevekst økt CO2 opptak negative

tilbakekobling (såkalt non-climate feedback)

Feedback parameter

𝑪𝒅𝑻

𝒅𝒕= 𝑸 + 𝜶𝒊 𝑻

En-boks klimamodell:

αi: Feedback parametere

Q: Strålingspådriv (Wm-2)

C: Global varmekapasitet

Kilde: IPCC 2013.

https://www.google.no/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjhl7ui_czXAhVoYZoKHa8aBmsQjRwIBw&url=https://wattsupwiththat.com/2016/09/03/feet-of-clay-the-official-errors-that-exaggerated-global-warming-part-2/&psig=AOvVaw2jslIbr-d3VD-JhvVXiNkf&ust=1511261288885131

IPCC, 2013

Mer CO2 i

atmosfæren

høyere opptak i

hav og på land

Høyere temperatur

høyere/lavere

opptak i hav og på

land

Uendret

klima, høyere

CO2

Varmere klima,

uendret CO2

CO2 utslipp og Paris-avtalen

https://blogs.agu.org/geospace/2016/06/27/capping-warming-2-degrees-new-study-details-pathways-beyond-paris/

https://www.google.no/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjN1pmvmPDXAhVmIJoKHSLXAPcQjRwIBw&url=https%3A%2F%2Fblogs.agu.org%2Fgeospace%2F2016%2F06%2F27%2Fcapping-warming-2-degrees-new-study-details-pathways-beyond-paris%2F&psig=AOvVaw0aXcOEY66IWvkMDRvhgHAg&ust=1512471182698349

Varmekraftverk basert biobrensel og CCS: En

mulighet for negative CO2 utslipp?

UPTAKE OF CO2 BY THE OCEANS

CO2(g)

CO2.H2O

CO2.H2O HCO3

- + H+

HCO3- CO3

2- + H+

KH = 3x10-2 M atm-1

K1 = 9x10-7 M

K2 = 7x10-10 M

Net uptake:

CO2(g) + CO32-

+ H2O 2HCO3

-

CO2.H2O HCO3

- CO32-

OCEAN

ATMOSPHERE

EQUILIBRIUM PARTITIONING OF CO2 BETWEEN ATMOSPHERE AND GLOBAL OCEAN

Equilibrium for present-day ocean:

only 3% of total inorganic carbon is currently in the atmosphere

But CO2(g) k [H+] k F k

… positive feedback to increasing CO2

Pose problem differently: how does a CO2 addition dN partition between

the atmosphere and ocean at equilibrium?

28% of added CO2 remains in atmosphere!

2

2 2

( )0.03

( ) ( )

CO

CO CO

N gF

N g N aq

varies roughly as [H+]

2

2 2

( )0.28

( ) ( )

CO

CO CO

dN gf

dN g dN aq

varies roughly as [H+]2

FURTHER LIMITATION OF CO2 UPTAKE:

SLOW OCEAN TURNOVER (~ 200 years)

Inventories in 1015 m3 water

Flows in 1015 m3 yr-1

Uptake by oceanic mixed layer only (VOC= 3.6x1016 m3)

would give f = 0.94 (94% of added CO2 remains in atmosphere)