the royal society report. statement of what ocean acidification\ means. present ph of the oceans....
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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