The Royal Society report.Statement of what ocean “acidification\” means. Present pH of the oceans.Likely pH change so far, and to come.Caldeira’s picture. Why is this a problem? Picture of the natural carbon cycle/interaction with sediments/buffering by sediments. (RS report has a simple one)Past changes – Andy Ridgwell’s picture.CalcificationPicture coral reefs, cold water corals, open ocean calcifying organisms.Coral reefs

The basics: carbon cycle, ocean-atmosphere near equilibrium, ocean sink, land sink

Ocean Acidification due to increasing atmospheric CO2

Andrew Watson

School of Environmental SciencesU. East Anglia

Norwich NR4 7TJ, UK

Atmospheric CO2 variations since 1000 AD

Prior to the industrial revolution the carbon cycle, fluxes into and out of the atmosphere were closely balanced. Anthropogenic fluxes to the atmosphere are small compared to natural fluxes (a few percent) but they are a cumulative disturbance from the previous steady state.

The changing carbon cycle

• Nearly half of the CO2 released by fossil fuel burning since the industrial revolution has dissolved into the surface ocean.

• A good thing! It has helped to slow the process of global warming.

• But as a result the surface ocean is becoming more acidic….

Fluxes in gigatonnes of carbon per year

Royal Society Report, June

2005

"Basic chemistry leaves us in little doubt that our burning of fossil fuels is changing the acidity of our oceans. And the rate change we are seeing to the ocean's chemistry is a hundred times faster than has happened for millions of years.”

“We just do not know whether marine life which is already under threat from climate change   can adapt to these changes.”

John Raven FRS FRSE, chair of the Royal Society Working group on Ocean Acidification.

Caldeira K, Wickett ME, Anthropogenic carbon and ocean pH, NATURE 425: 365-365, 2003

• Rising atmospheric CO2 has so far caused about 0.1 unit decrease in surface ocean pH.

• “Business as usual” release will cause ~0.5 unit decrease by 2100, and further decreases beyond that depending on the total amount of fossil fuel ulimately burned.

Present-day surface ocean pH

• Surface ocean pH is restricted to a narrow range, (~0.3 pH units)• Why is this?

1) “Fast” buffer: Hydrogen carbonate/ bicarbonate/ carbonate chemistry

2) “Slow” buffer: dissolution / formation of carbonate sediments

H2CO3 H+ + HCO3- 2H+ + CO3

--

Range of Sea water pH

Fast buffer: seawater carbon chemistryAdding H+ lowers pH, converts some carbonate to bicarb, which takes up H+ and resists the change.

Slow buffer: transformation of minerals from continental rock to ocean sediment.

CaCO3 sediment

lysocline

Input of Ca, Mg and bicarbonate from rivers

Weathering of carbonates and silicates on land

“Rain” of biologicallygenerated CaCO3

• Ca and Mg carbonates dissolve in rivers and wash to the sea.• Surface waters are supersaturated in carbonates. Organisms precipitate a “rain”

of carbonate particles.• Deep waters are undersaturated. Carbonate sediment accumulates above the

lysocline, but dissolves below it, Input to the ocean balances output.• Over thousands of years, if pH change causes increase (decrease) in saturation,

the lysocline depth adjusts to allow more (less) carbonate sediment formation – so resisting the pH change.

A (disputed) reconstruction of surface pH, from boron isotope analysis.(Pearson and Palmer, 2002).

Carbon-cycle reconstruction of atmospheric CO2 and ocean pH over the past 500 Myr.

Figure courtesy of Andy Ridgwell, U.B.C., Canada

Predicted range next 250 yr

Modelled range last 108 yr

Large future change because the rapidity of the CO2 increase overwhelms the slow buffering due to interaction with sediments.

Possible biological effects of acidification

• sub-lethal hypercapnia in some metazoans, (particularly mollusca, including cephalopods…. ).

• Inhibition of calcification by a wide variety of organisms– Coral reefs (warm and cold water types)– Diverse calcifying plankton– Molluscs – Echinoderms

• Increase in photosynthesis rate in some marine primary producers.

Hypercapnia (CO2 poisoning) in marine animals

• CO2 is much more soluble than oxygen• Gills require a high throughput of water to extract

sufficient oxygen.• Water-breathing animal’s internal CO2 concentrations are

brought much closer to equilibrium with the external environment than is the case for air-breathing animals.

• Potentially therefore they are much more sensitive to changes in ambient CO2 pressure.

• Most fish exhibit compensation mechanisms to adjust their internal pH/pCO2 against external changes.

• Some organisms (molluscs, echinoderms, for instance) don’t have these mechanisms and are more sensitive to hypercapnia induced by increases in ambient CO2

Uncompensated acidosisand metabolic depression in several invertebrates

…contributing to lower resistance and enhanced mortality?

Compensated acidosis and, therefore, no metabolic depression in most fish

…a reason for enhanced resistance to high CO2?

Sepia officinalisSepia officinalis Sipunculus nudusSipunculus nudus

PachycaraPachycarabrachycephalumbrachycephalum

Gadus morhuaGadus morhua

©CephBase

see Poster Heisler, 1986, Larsen et al. 1997, Ishimatsu et al., 2004

MytilusMytilus

galloprovincialisgalloprovincialis

55 % growth reduction inMytilus galloprovincialis under

hypercapnia

0 20 40 60 80 10012

14

16

18

20

22

24

26

28

30

Time (days)

Mea

n sh

ell l

engt

h (m

m) Water pH 7.3:

Maximum pH drop as expected from business as usual scenarios by 2300(Caldeira and Wickett, 2003)

hypercapniahypercapnia

controlcontrol

© M.S. Calle

Michailidis et al. (2004)

Calcification Calcite and aragonite

• … mineral forms of calcium carbonate

• Calcite is less soluble, made by some planktonic organisms (foraminifera, coccolithophores) and coralline algae.

• Aragonite, more soluble, made by most corals and molluscs.

Biological calcification

• Taxonomically very diverse: – Red algae, green algae, protists, animals

• Great range of functions– Sometimes obvious (eg protective shells, anchoring to

substrate)– frequently unknown/obscure function (e.g.

foraminifera, coccolithophores)

• Surprising consistency in response to pH change: 10-30% decrease for a doubling of CO2

Approx percent change in calcification when CO2 is

Organism/system Mineralogy

2X preindust 3X preindust

references

Coccolithophores Emiliana. Huxleii Calcite -25 Sciandra et al. 2003, cultures grown under 400ppm

and 700 ppm Calcite -9 -18 Riebesell et al., 2000, Sondervan et al., 2001;

decrease in CaCO3 / cell Gephyrocapsa oceanica Calcite -29 -66

Foraminifera

Orbicula universa Calcite -4 to -6 -6 to -8 Bijma et al., 1999, 2002

Scleractinian corals

Turbinaria reniformes Aragonite –13 Pavona cactus Aragonite –18 Galaxea fascicularia Aragonite –16 Acropora verweyi Aragonite –18

Marubini et al., 2003); corals grown at pCO2 = 412 ppm and 866 ppm

Porites compressa Aragonite 14 to –20 Marubini et al., 2001 (S33) Porites porite Aragonite –16 Marubini and Thake, 1999 Stylophora pistillata

Aragonite

0 to –50

Reynaud et al., 2003; Corals grown at pCO2 = 460 and 760 ppm; level of response is temperature-

dependent

Inhibition of calcification in plankton and some corals (Feely et al., 2004)

Most organisms show a decrease in calcification, in the range 5 to 30% for a doubling of CO2.

K/T boundary

coralsalgaebivalves

Kiessling et al. 1999

Coral/algal reef development over time

Pearson & Palmer 2000

Mill

ions

of y

ea

rs B

P

Coralline Red Algae

Halimeda Corals

Trophic Level autotrophic autotrophic* both

Mineral Form hi-mag calcite aragonite aragonite

Generation Time days weeks months-years

No. Species ~20 genuses 25-30 > 1000

Nancy Sefton

NOAA

Some Major Benthic Calcifiers

Coccolithophores Foraminifera Pteropods

Trophic Level autotrophic heterotrophic* heterotrophic

Mineral Form calcite calcite aragonite

Generation Time days weeks months

No. Species 250 4000 30

Major Planktonic Calcifiers

Function Planktonic BenthicProtection All groups All groups

Buoyancy regulation coccolithophores foraminifera

Light modification coccolithophores corals

Provide protons for conversion of HCO3

– to CO2 for photosynth.coccolithophores calcareous algae?

Facilitate bicarbonate-based photosynthesis

coccolithophores

Aid in capture of prey foraminifera

Reproduction pteropods corals?

Prevention of osmotically induced volume changes

coccolithophores

Extension into hydrodynamic regime

corals, calc. algae, bryozoans

Anchoring to substrate corals, calc. algae, bryozoans

Competition for space corals, calc. algae, bryozoans

Possible Functions of CaCO3 in Organisms

Warm water corals: •Some of the most productive (and beautiful) ecosystems on the planet.

•Important for tourism, fisheries.•100 million people are estimated to depend directly on coral reefs for their livelihood.

Environmental limits to coral reef development

Kleypas et al. (1999) Am Zool 39: 146-159

TEMPERATURE

Average min/max: 24.8 – 27.6oC

Min: 16oC

SALINITY

Average min/max: 34.3 – 35.3 ppt

MIN LIGHT PENETRATION

Range: -7 to -72

ARAGONITE SATURATION

Average min/max: 3.28 – 4.06

NITRATE

Average: 0.25 M

PHOSPHATE

Average: 0.13 M

TEMPERATURE

Average min/max: 24.8 – 27.6oC

Min: 16oC

SALINITY

Average min/max: 34.3 – 35.3 ppt

MIN LIGHT PENETRATION

Range: -7 to -72

ARAGONITE SATURATION

Average min/max: 3.28 – 4.06

NITRATE

Average: 0.25 M

PHOSPHATE

Average: 0.13 M

Mass coral bleaching caused by thermal stress

• 95% correlation with increases in sea temperature (1-2oC above long-term summer sea temperature maxima) and bleaching.

1998

Strong, Hayes, Goreau, Causey and others

Estimated loss of living coral colonies

from reefs in 1997-98:16% world wide.

Estimated loss of living coral colonies

from reefs in 1997-98:16% world wide.

Aragonite Saturation State of the Surface Oceanfr

om

C.

Sab

ine

1800

1994

Coral distribution, and Change in Aragonite saturation 1800-1994.

Coral reefs Deep-water corals

from C. Sabine

Combined effects of temperature and acidification on calcification:

Reynaud et al. 2004

Suggests that pH change has more effect at higher temperatures.

Cold/deep water corals:

poorly documented compared to warm-water varieties.

Potentially fragile ecosystems, since they live at lower aragonite saturations.

•Coccoliths alter the appearance of the ocean: 15% of the light scattered out of the ocean surface is due to coccoliths.

Coccolithophores and the Earth system.

•Geological impact of coccolithophores.

•99% of the carbon on the planet is locked up in rocks.

•Important for the long-term habitability of Earth (c.f. Venus).

Coccolithophores and the Earth system.

190190370370

700700

pCOpCO22 (ppmv)(ppmv)

Large Scale Facilities, Bergen, NorwayLarge Scale Facilities, Bergen, Norway

Effect of increased COEffect of increased CO22 on Emiliana Huxleii blooms, on Emiliana Huxleii blooms,

Mesocosm experiments: B. Dellille et al., GBC Mesocosm experiments: B. Dellille et al., GBC 1919, (2005)*., (2005)*.

*Response of primary production and calcification to changes of pCO2 during experimental blooms of the coccolithophorid Emiliania huxleyi. Delille B, Harlay J, Zondervan I, Jacquet S, Chou L, Wollast R, Bellerby RGJ, Frankignoulle M, Borges AV, Riebesell U, Gattuso JP. GBC 19, art. no. GB2023 2005

pCO2 normalised

0 5 10 15 200

200

400

600

800

Day

µatm

0

2

4

6

8

10

12

14

0 5 10 15 20

Chlorophyll a

pCO2 (normalized)ppm

Vµ

g L

-1

Year 2100PresentLGM

Emiliania huxleyiEmiliania huxleyi

Initial nutrient concentrations:Initial nutrient concentrations: NONO33

-- 15.5 mmol m 15.5 mmol m-3-3

POPO443-3- 0.51 mmol m 0.51 mmol m-3-3

Si(OH)Si(OH)44 ~0 ~0

NONO33-- and PO and PO44

3-3- exhausted on day 13 exhausted on day 13

Primary production and calcification during a bloom of Emiliania huxleyi

Calcification

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)Production

Dissolution

Respiration -10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d2

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d4d3

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)d10

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d11

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d12

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d13

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

) d14

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

) d15

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)d18

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d21-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d21-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d21-10

10

20

30

(µmolC.kg-1.d-1)

(µm

olC

.kg-1

.d-1

)

d23

B. Delille et al. in prep.B. Delille et al. in prep.

CO2-Calcification feedback

10 20 30

-10

10

20

30

d11

d13

d15

d17

d2

d7

d23

(µm

olC

.kg-1

.d-1

)

d11

d13

d15

d17

d23

d2

d7

d11

d13

d15d17

d23

d7

d2

d11

d13

d15

d17d2

d7

d23

d11

d13

d15

d7

d23

d2

10 20 30-5

-10

10

20

30

d11

d13

d15 d17

d23

d7

(µmolC.kg-1.d-1)

10 20 30-5

d7

d11

d13

d15

d23

(µmolC.kg-1.d-1)

10 20 30-5

d11

d13

d15d17

d2

d7

d23

(µmolC.kg-1.d-1)

Year 2100(700 ppmV)

Present(370 ppmV)

LGM(190 ppmV)

Calcification

Pro

du

cti

on

Resp

ir.

Dissol.

-10

10

20

30

d11

d13 d15

d17

d19

d21

d2

d9

(µm

olC

.kg-1

.d-1

)(µ

mol

C.k

g-1.

d-1)

B. Delille et al. in prep.B. Delille et al. in prep.

-10

10

20

30

d11

d13

d15

d17

d2

d7

d23

(µm

olC

.kg-1

.d-1

)

10 20 30-5

-10

10

20

30

d11

d13

d15 d17

d23

d7

(µmolC.kg-1.d-1)

Year 2100(700 ppmV)

Present(370 ppmV)

LGM(190 ppmV)

Calcification

Pro

du

cti

on

Resp

ir.

Dissol.

-10

10

20

30

d11

d13 d15

d17

d19

d21

d2

d9

(µm

olC

.kg-1

.d-1

)(µ

mol

C.k

g-1.

d-1)

B. Delille et al. (2005).B. Delille et al. (2005).

Increasing pCOIncreasing pCO22 from from

190 ppmV to 700 ppmV caused190 ppmV to 700 ppmV caused

24-48 h delay in the 24-48 h delay in the onset of calcificationonset of calcification

40% decrease in 40% decrease in CaCOCaCO33 production production

“gla

cial

”

“pre

sent

”

“Yea

r 210

0”

“gla

cial

”

“pre

sent

”

“Yea

r 210

0”

With increasing CO2:

• No change in net organic carbon fixation

• Decrease in calcification

• Increase in “carbon loss” – difference between fixed carbon and POC in water column – ascribed to faster-sinking particles

Carbon budget from day 10 to day 15; (Delille et al, 2005)

• Some early attempts have been made* to model the global effect for future anthropogenic CO2;

• Potentially large change in calcification (50% decrease by 2250)

• Very small net effect on atmospheric CO2

*Heinze, C. Geophys. Res Lett 31 art. no. L16308, 2004.

Global change in calcification rates

“Earth-systems” feedbacks involving climate, CO2, and ocean pH.

Ratio of CaCO3 to organic carbon production

Climate

Atmospheric CO2

anthropogenicemissions

Ocean pH / pCO2Stratification/

circulationNutrients

(Fe, nitrate?)

?

Engineering solutions?

• Other than by decreasing CO2 emissions, could ocean acidification be reversed by a “technological fix”

• Dissolving limestone rock in ocean water would increase the pH.

• Problems: – The rock would have to be dissolved under

pressure/chemical treatment, since it doesn’t spontaneously dissolve in surface sea water.

– An awful lot is needed; about 20 Gt CaCO3 to counteract the effect of the 2 Gt C of carbon that the ocean takes up each year.

– This is a volume of rock 60 km2 x 100m thick; the mining operation would be formidable, energy-intensive and almost certainly non-feasible.

Summary• Ocean acidification is a consequence of the pollution of the global

environment with carbon dioxide. • It’s effects are chronic, impacting all marine ecosystems.• Future pH changes will be larger than any in the global oceans in

the last >100 million years.• Substantial, but sub-lethal, effects can be shown on a wide variety

of organisms. – Hypercapnia in many inverterbrates– Decrease in calcification in many species

• The degree to which individual species or ecosystems, including the global ocean ecosystem, will adapt to these changes is almost completely unknown.

• Likewise the overall impact on the planetary environment is difficult to assess.

• The only feasible way to prevent substantial ocean acidification is to curb emissions of CO2