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The Royal Society report. Statement of what ocean “acidification\” means. Present pH of the oceans. Likely pH change PowerPoint Presentation
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slide1

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.

Calcification

Picture 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 co 2

Ocean Acidification due to increasing atmospheric CO2

Andrew Watson

School of Environmental Sciences

U. East Anglia

Norwich NR4 7TJ, UK

slide3

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
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
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.

slide6

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.
slide7

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
slide8

Range of

Sea water

pH

Fast buffer: seawater carbon chemistry

Adding H+ lowers pH, converts some carbonate to bicarb, which takes up H+ and resists the change.

H2CO3  H+ + HCO3-  2H+ + CO3--

slow buffer transformation of minerals from continental rock to ocean sediment

Input of Ca, Mg and bicarbonate from rivers

Weathering of carbonates and silicates on land

CaCO3 sediment

lysocline

“Rain” of biologically

generated CaCO3

Slow buffer: transformation of minerals from continental rock to ocean sediment.
  • 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.
slide10

A (disputed) reconstruction of surface pH, from boron isotope analysis.

(Pearson and Palmer, 2002).

slide11

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

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.

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

possible biological effects of acidification
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 co 2 poisoning in marine animals
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 acidosis and metabolic depression in several invertebrates
Uncompensated acidosisand metabolic depression in several invertebrates

Mytilus

galloprovincialis

Sipunculus nudus

Sepia officinalis

…contributing to lower resistance and enhanced mortality?

©CephBase

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

…a reason for enhanced resistance to high CO2?

Pachycara

brachycephalum

Gadus morhua

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

see Poster

55 growth reduction in mytilus galloprovincialis under hypercapnia
55 % growth reduction inMytilus galloprovincialis under hypercapnia

© M.S. Calle

control

WaterpH 7.3: Maximum pH drop as expected from business as usual scenarios by 2300

(Caldeira and Wickett, 2003)

hypercapnia

Michailidis et al. (2004)

calcification calcite and aragonite
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
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
slide18

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.

slide19

Coral/algal reef development over time

corals

algae

bivalves

Millions of years BP

K/T boundary

Pearson & Palmer 2000

Kiessling et al. 1999

slide23

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
Environmental limits to coral reef development

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 mM

PHOSPHATE

Average: 0.13 mM

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

mass coral bleaching caused by thermal stress

1998

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.

Estimated loss of living coral colonies from reefs in 1997-98:

16% world wide.

Strong, Hayes, Goreau, Causey and others

slide28

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

Coral reefs

Deep-water corals

from C. Sabine

slide29

Combined effects of temperature and acidification on calcification:

Suggests that pH change has more effect at higher temperatures.

Reynaud et al. 2004

slide30

Cold/deep water corals:

poorly documented compared to warm-water varieties.

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

slide31

Coccolithophores and the Earth system.

  • Coccoliths alter the appearance of the ocean: 15% of the light scattered out of the ocean surface is due to coccoliths.
slide32

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).
slide33

Effect of increased CO2 on Emiliana Huxleii blooms,

Mesocosm experiments: B. Dellille et al., GBC 19, (2005)*.

pCO2(ppmv)

190

370

700

Large Scale Facilities, Bergen, Norway

*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

slide34

Chlorophyll a

Initial nutrient concentrations:

NO3- 15.5 mmol m-3

PO43- 0.51 mmol m-3

Si(OH)4 ~0

NO3- and PO43- exhausted on day 13

µg L-1

Year 2100

pCO2 (normalized)

Present

LGM

ppmV

Emiliania huxleyi

primary production and calcification during a bloom of emiliania huxleyi
Primary production and calcification during a bloom of Emiliania huxleyi

CO2-Calcification feedback

Production

10 20 30

Respiration

Calcification

Dissolution

B. Delille et al. in prep.

slide36

30

d13

)

d15

20

-1

.d

d11

-1

d17

10

(µmolC.kg

d19

d9

d2

d21

-10

Year 2100

(700 ppmV)

Present

(370 ppmV)

LGM

(190 ppmV)

(µmolC.kg-1.d-1)

Production

Calcification

Dissol.

Respir.

B. Delille et al. in prep.

slide37

30

d13

)

d15

20

-1

.d

d11

-1

d17

10

(µmolC.kg

d19

d9

d2

d21

-10

Year 2100

(700 ppmV)

Increasing pCO2 from

190 ppmV to 700 ppmV caused

 24-48 h delay in the

onset of calcification

 40% decrease in

CaCO3 production

Present

(370 ppmV)

LGM

(190 ppmV)

(µmolC.kg-1.d-1)

Production

Calcification

Dissol.

Respir.

B. Delille et al. (2005).

slide38

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

“Year 2100”

“Year 2100”

“present”

“present”

“glacial”

“glacial”

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
slide39

Global change in calcification rates

  • 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.

earth systems feedbacks involving climate co 2 and ocean ph

Stratification/

circulation

Nutrients

(Fe, nitrate?)

Ocean

pH / pCO2

Climate

Ratio of CaCO3 to organic

carbon production

Atmospheric

CO2

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

anthropogenic

emissions

?

engineering solutions
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
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