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The Royal Society report.

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1 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

2 Ocean Acidification due to increasing atmospheric CO2
Andrew Watson School of Environmental Sciences U. East Anglia Norwich NR4 7TJ, UK

3 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.

4 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

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: 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.

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 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-- Range of Sea water pH

9 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 “Rain” of biologically generated CaCO3 lysocline 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 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

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 (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

14 Uncompensated acidosis and metabolic depression in several invertebrates
Mytilus galloprovincialis Sipunculus nudus …contributing to lower resistance and enhanced mortality? Sepia officinalis ©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

15 55 % growth reduction in Mytilus galloprovincialis under hypercapnia
© M.S. Calle control Water pH 7.3: Maximum pH drop as expected from business as usual scenarios by 2300 (Caldeira and Wickett, 2003) hypercapnia 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 CO2

18 Inhibition of calcification in plankton and some corals (Feely et al
Most organisms show a decrease in calcification, in the range 5 to 30% for a doubling of CO2.

19 Coral/algal reef development over time
corals algae bivalves Millions of years BP This plots relative reef abundance over time (Kiessling et al. 1999) versus CO2 time series derived from Pearson & Palmer ( from previous slide). CO2 concentrations exceed those of past 420 Ka, probably past 24 Ma. Corals survived the KT extinction (65 Ma), but did not build reefs until Miocene (~20 Ma) Conditions of last 4-5 Ma are unusual in Earth’s history, and coral reefs have thrived during this period of “ice-house” conditions which has included: low CO2 fluctuating sea level There are many reasons why reef development may have been slow to get started at the KT extinction. I don’t propose to put this forward as the only explanation, but simply to illustrates that the pattern of coral reef development is not inconsistent with changes in atmospheric CO2 . K/T boundary Pearson & Palmer 2000 Kiessling et al. 1999

20 Some Major Benthic Calcifiers
Coralline Red Algae Halimeda Corals Trophic Level autotrophic autotrophic* both Mineral Form hi-mag calcite aragonite Generation Time days weeks months-years No. Species ~20 genuses 25-30 > 1000 NOAA Nancy Sefton

21 Major Planktonic Calcifiers
Coccolithophores Foraminifera Pteropods Trophic Level autotrophic heterotrophic* heterotrophic Mineral Form calcite aragonite Generation Time days weeks months No. Species 250 4000 30

22 Possible Functions of CaCO3 in Organisms
Planktonic Benthic Protection All groups Buoyancy regulation coccolithophores foraminifera Light modification coccolithophores corals Provide protons for conversion of HCO3– to CO2 for photosynth. calcareous algae? Facilitate bicarbonate-based photosynthesis Aid in capture of prey foraminifera Reproduction pteropods corals? Prevention of osmotically induced volume changes Extension into hydrodynamic regime corals, calc. algae, bryozoans Anchoring to substrate Competition for space

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.


25 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 Joanie Kleypas and others have carefully reviewed the environmental data for more than 6,000 coral reefs. After inspecting these data – a number of other co-variables can be found. Kleypas et al. (1999) Am Zool 39:

26 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 Estimated loss of living coral colonies from reefs in : 16% world wide. Strong, Hayes, Goreau, Causey and others

27 Aragonite Saturation State of the Surface Ocean
1800 1994 From 1991 thru 1998 the first comprehensive study of CO2 species in the all of the Ocean basins was conducted as part of the WOCE/JGOFS/OACES Global CO2 Survey. At least 2 of the 4 CO2 species and related tracers were measured on approximately 100,000 samples with a precision of about +- 3 umolkg-1 for DIC. from C. Sabine

28 Coral distribution, and Change in Aragonite saturation 1800-1994.
The workshop participants also had a lot of discussion about WHERE to conduct field experiments. The criteria fell into several camps: High latitudes, in regions where saturation states are expected to go from saturated to undersaturated Across natural gradients (problem is the covariation of sat. state with temperature and light) Regions with naturally high pCO2 (upwelling regions of the Galapagos) Regions of convenience: existing time-series stations, regions that are already well-characterized Coral reefs Deep-water corals from C. Sabine

29 Combined effects of temperature and acidification on calcification:
Suggests that pH change has more effect at higher temperatures. Reynaud et al. 2004

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

31 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.

32 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).

33 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. GB

34 Chlorophyll a pCO2 (normalized) Emiliania huxleyi
Initial nutrient concentrations: NO mmol m-3 PO 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

35 CO2-Calcification feedback
Primary production and calcification during a bloom of Emiliania huxleyi Production Respiration Dissolution Calcification B. Delille et al. in prep.

36 Year 2100 Present LGM (700 ppmV) (370 ppmV) (190 ppmV)
-10 10 20 30 d11 d13 d15 d17 d19 d21 d2 d9 (µ -1 .d ) LGM (190 ppmV) (µ Production Dissol. Calcification Respir. B. Delille et al. in prep.

37 Year 2100 Present LGM Increasing pCO2 from 190 ppmV to 700 ppmV caused
 h delay in the onset of calcification  40% decrease in CaCO3 production Present (370 ppmV) -10 10 20 30 d11 d13 d15 d17 d19 d21 d2 d9 (µ -1 .d ) LGM (190 ppmV) (µ Production Dissol. Calcification Respir. B. Delille et al. (2005).

38 Carbon budget from day 10 to day 15; (Delille et al, 2005)
“Year 2100” “Year 2100” “glacial” “present” “glacial” “present” 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

39 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.

40 “Earth-systems” feedbacks involving climate, CO2, and ocean pH.
anthropogenic emissions Climate Atmospheric CO2 ? Ocean pH / pCO2 Nutrients (Fe, nitrate?) Stratification/ circulation Ratio of CaCO3 to organic carbon production

41 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.

42 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



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