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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.Caldeiras picture.

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Presentation on theme: "The Royal Society report. Statement of what ocean acidification\ means. Present pH of the oceans. Likely pH change so far, and to come.Caldeiras picture."— Presentation transcript:

1 The Royal Society report. Statement of what ocean acidification\ means. Present pH of the oceans. Likely pH change so far, and to come.Caldeiras 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 Ridgwells 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

2 Ocean Acidification due to increasing atmospheric CO 2 Andrew Watson School of Environmental Sciences U. East Anglia Norwich NR4 7TJ, UK

3 Atmospheric CO 2 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.

4 The changing carbon cycle Nearly half of the CO 2 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

5 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.

6 Caldeira K, Wickett ME, Anthropogenic carbon and ocean pH, NATURE 425: , 2003 Rising atmospheric CO 2 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.

7 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

8 H 2 CO 3 H + + HCO 3 - 2H + + CO 3 -- 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.

9 Slow buffer: transformation of minerals from continental rock to ocean sediment. CaCO 3 sedimentlysoclineInput of Ca, Mg and bicarbonate from rivers Weathering of carbonates and silicates on land Rain of biologically generated CaCO 3 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.

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

11 Carbon-cycle reconstruction of atmospheric CO 2 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 10 8 yr Large future change because the rapidity of the CO 2 increase overwhelms the slow buffering due to interaction with sediments.

12 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.

13 Hypercapnia (CO 2 poisoning) in marine animals CO 2 is much more soluble than oxygen Gills require a high throughput of water to extract sufficient oxygen. Water-breathing animals internal CO 2 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 CO 2 pressure. Most fish exhibit compensation mechanisms to adjust their internal pH/pCO 2 against external changes. Some organisms (molluscs, echinoderms, for instance) dont have these mechanisms and are more sensitive to hypercapnia induced by increases in ambient CO 2

14 Uncompensated acidosis and 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 CO 2 ? Sepia officinalis Sipunculus nudus Pachycarabrachycephalum Gadus morhua ©CephBase see Poster Heisler, 1986, Larsen et al. 1997, Ishimatsu et al., 2004 Mytilus galloprovincialis

15 55 % growth reduction in Mytilus galloprovincialis under hypercapnia Water pH 7.3: Maximum pH drop as expected from business as usual scenarios by 2300 (Caldeira and Wickett, 2003) hypercapnia control © M.S. Calle Michailidis et al. (2004)

16 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.

17 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 CO 2

18 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 CO 2.

19 K/T boundary corals algae bivalves Kiessling et al Coral/algal reef development over time Pearson & Palmer 2000 Millions of years BP

20 Coralline Red Algae Halimeda Corals Trophic Level autotrophicautotrophic*both Mineral Form hi-mag calcitearagonite Generation Time daysweeksmonths-years No. Species ~20 genuses25-30> 1000 Nancy Sefton NOAANOAA Some Major Benthic Calcifiers

21 CoccolithophoresForaminiferaPteropods Trophic Level autotrophicheterotrophic*heterotrophic Mineral Form calcite aragonite Generation Time daysweeksmonths No. Species Major Planktonic Calcifiers

22 FunctionPlanktonicBenthic ProtectionAll groups Buoyancy regulationcoccolithophores foraminifera Light modificationcoccolithophorescorals Provide protons for conversion of HCO 3 – to CO 2 for photosynth. coccolithophorescalcareous algae? Facilitate bicarbonate-based photosynthesis coccolithophores Aid in capture of preyforaminifera Reproductionpteropodscorals? Prevention of osmotically induced volume changes coccolithophores Extension into hydrodynamic regime corals, calc. algae, bryozoans Anchoring to substratecorals, calc. algae, bryozoans Competition for spacecorals, calc. algae, bryozoans Possible Functions of CaCO 3 in Organisms

23 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.

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25 Environmental limits to coral reef development Kleypas et al. (1999) Am Zool 39: TEMPERATURE Average min/max: 24.8 – 27.6 o C Min: 16 o C 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 – 27.6 o C Min: 16 o C 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

26 Mass coral bleaching caused by thermal stress 95% correlation with increases in sea temperature (1-2 o C above long-term summer sea temperature maxima) and bleaching Strong, Hayes, Goreau, Causey and others Estimated loss of living coral colonies from reefs in : 16% world wide. Estimated loss of living coral colonies from reefs in : 16% world wide.

27 Aragonite Saturation State of the Surface Ocean from C. Sabine

28 Coral distribution, and Change in Aragonite saturation Coral reefs Deep-water corals from C. Sabine

29 Combined effects of temperature and acidification on calcification: Reynaud et al Suggests that pH change has more effect at higher temperatures.

30 Cold/deep water corals: poorly documented compared to warm-water varieties. Potentially fragile ecosystems, since they live at lower aragonite saturations.

31 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.

32 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.

33 pCO 2 (ppmv) Large Scale Facilities, Bergen, Norway Effect of increased CO 2 on Emiliana Huxleii blooms, Mesocosm experiments: B. Dellille et al., GBC 19, (2005)*. *Response of primary production and calcification to changes of pCO 2 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. GB

34 Chlorophyll a pCO 2 (normalized) ppmV µg L -1 Year 2100 Present LGM Emiliania huxleyi Initial nutrient concentrations: NO mmol m -3 NO mmol m -3 PO mmol m -3 PO mmol m -3 Si(OH) 4 ~0 Si(OH) 4 ~0 NO 3 - and PO 4 3- exhausted on day 13

35 Primary production and calcification during a bloom of Emiliania huxleyi Calcification Production Dissolution Respiration B. Delille et al. in prep. CO 2 -Calcification feedback

36 Year 2100 (700 ppmV) Present (370 ppmV) LGM (190 ppmV) Calcification Production Respir. Dissol d11 d13 d15 d17 d19 d21 d2 d9 (µmolC.kg.d ) (µmolC.kg-1.d-1) B. Delille et al. in prep.

37 Year 2100 (700 ppmV) Present (370 ppmV) LGM (190 ppmV) Calcification Production Respir. Dissol d11 d13 d15 d17 d19 d21 d2 d9 (µmolC.kg.d ) (µmolC.kg-1.d-1) B. Delille et al. (2005). Increasing pCO 2 from 190 ppmV to 700 ppmV caused h delay in the h delay in the onset of calcification 40% decrease in 40% decrease in CaCO 3 production

38 glacial present Year 2100 glacial present Year 2100 With increasing CO 2 : 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)

39 Some early attempts have been made* to model the global effect for future anthropogenic CO 2 ; Potentially large change in calcification (50% decrease by 2250) Very small net effect on atmospheric CO 2 *Heinze, C. Geophys. Res Lett 31 art. no. L16308, Global change in calcification rates

40 Earth-systems feedbacks involving climate, CO 2, and ocean pH. Ratio of CaCO3 to organic carbon production Climate Atmospheric CO 2 anthropogenic emissions Ocean pH / pCO 2 Stratification/ circulation Nutrients (Fe, nitrate?) ?

41 Engineering solutions? Other than by decreasing CO 2 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 doesnt spontaneously dissolve in surface sea water. –An awful lot is needed; about 20 Gt CaCO 3 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 km 2 x 100m thick; the mining operation would be formidable, energy-intensive and almost certainly non-feasible.

42 Summary Ocean acidification is a consequence of the pollution of the global environment with carbon dioxide. Its 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 CO 2

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