Ocean Acidification: Cause, Impact and mitigation

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Ocean Acidification and the battle for Carbonate. …

Ocean Acidification and the battle for Carbonate.
In this presentation the points covered are detailed briefing of ocean acidification, its causes, its impact on marine ecosystems and measures to mitigate this.

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  • Why does the seasonal trend fluctuate?Low in the summer when uptake of CO2 by plants for photosynthesis is highest, and high in the winter when rates of photosynthesis are lower.Trend follows seasons in the NORTHERN hemisphere because that is where there is more land and thus plant biomass there than in the southern hemisphere
  • Why does the seasonal trend fluctuate?Low in the summer when uptake of CO2 by plants for photosynthesis is highest, and high in the winter when rates of photosynthesis are lower.Trend follows seasons in the NORTHERN hemisphere because that is where there is more land and thus plant biomass there than in the southern hemisphere
  • Figure 2. Changes in the concentrations of the three different chemical species constituting dissolvedinorganic carbon (DIC). As the influx of extra CO2 acidifies the surface ocean and raises DIC,the carbonate ion concentration (dark grey) falls strongly, the concentration of dissolved CO2gas (black) increases strongly and the bicarbonate ion concentration (light grey) increases slightly.Surface ocean pH was on average about 8.2 in the pre-industrial ocean, is about 8.1 on average todayand could drop to as low as about 7.4 if all available fossil fuels are burnt. Graph calculated for anaverage surface ocean of temperature 15◦C, salinity 35 and alkalinity 2310 mmol kg−1. Black-shadedregion, [CO2(aq.)]; light grey-shaded region, [HCO−3 ]; dark grey-shaded region, [CO2−3 ].
  • This figure shows the relationship between changes in ocean carbon dioxide levels (measured in the left column as a partial pressure—a common way of measuring the amount of a gas) and acidity (measured as pH in the right column). The data come from two observation stations in the North Atlantic Ocean (Canary Islands and Bermuda) and one in the Pacific (Hawaii). The up-and-down pattern shows the influence of seasonal variations.
  • This map shows changes in the amount of aragonite dissolved in ocean surface waters between the 1880s and the most recent decade (2003-2012). Aragonite is a form of calcium carbonate that many marine animals use to build their skeletons and shells. Aragonite saturation is a ratio that compares the amount of aragonite that is actually present with the total amount of aragonite that the water could hold if it were completely saturated. The more negative the change in aragonite saturation, the larger the decrease in aragonite available in the water, and the harder it is for marine creatures to produce their skeletons and shells.
  • Representative Concentration Pathways (RCPs) are four greenhouse gas concentration (not emissions) trajectories adopted by the IPCC for its fifth Assessment Report (AR5).[1]The pathways are used for climate modeling and research. They describe four possible climate futures, all of which are considered possible depending on how much greenhouse gases are emitted in the years to come. The four RCPs, RCP2.6, RCP4.5, RCP6, and RCP8.5, are named after a possible range of radiative forcing values in the year 2100 relative to pre-industrial values (+2.6, +4.5, +6.0, and +8.5 W/m2, respectively)
  • Grey lines shows mass of water coming.Black lines shows potential density.
  • In august ocean acidification coincides with the seasonal stratification. Due to low buffering action, the impact of pH is higher at shallower part in the august than in january.
  • The 3 major gps of…..Relative abundance of each group varies by region;These 3 gps are diverse with respect to mineralogy, trophic level and other attributesFor eg, Pteropods&forams are heterotrophs; coccosautotrophs; Pteropods secrete aragonite which is about 50% more soluble in seawater than the calcite formed by forams and coccos---Generation times are particularly impt when considering the capacity of these gps to adapt to the future high CO2 ocean – Coccos have generation times on the order of days….

Transcript

  • 1. Ocean Acidification and the battle for carbonate Presented by-  Shubham Gupta  Sajal Mittal  Kumar Saurav  Kunal Ghosh  Gyanesh K. Singh
  • 2. What is ocean acidification…? “A reduction in ocean pH due to the uptake of anthropogenic CO2.” (Hofmann et al 2010) • Ocean Acidification is a term used to describe the change in chemistry of the Earth’s Ocean i.e. ongoing decrease in pH and increase in acidity, caused by the anthropogenic CO2 uptake 26% 29% 45% Fate of Anthropogenic CO2 Emissions Source: Le Quéré et al 2013 Sources Sinks
  • 3. Mauna Loa , Hawaii (13,677 ft = 4169 m) Key concepts: 1. Atmospheric CO2 is increasing
  • 4. Key concepts: 1. Atmospheric CO2 is increasing Mauna Loa , Hawaii (13,677 ft = 4169 m) Currently 30% higher than since last 650,000 years (Feely et al 2009)
  • 5. Key concepts: 2. CO2 sink in the Oceans
  • 6. Key concepts: 2. CO2 sink in the Oceans • Water naturally absorbs CO2 from the air • The more atmospheric CO2, the more the ocean absorbs
  • 7. Key concepts: 3. Water becomes more acidic the more CO2 it contains.
  • 8. Key concepts: 3. Water becomes more acidic the more CO2 it contains. CO2 reacts with H20 to produce: bicarbonate ion (HCO- 3) hydrogen ion (H+)
  • 9. Key concepts: 3. Water becomes more acidic the more CO2 it contains. CO2 reacts with H20 to produce: bicarbonate ion (HCO- 3) hydrogen ion (H+) this H+ ion is making ocean more acidic
  • 10. Key concepts: 4. Increased ocean acidity affects marine organisms’ abilities to make and keep their hard parts (calcium carbonate (CaCO3) shells, skeletons, etc.)
  • 11. Key concepts: 4. Increased ocean acidity affects marine organisms’ abilities to make and keep their hard parts (calcium carbonate (CaCO3) shells, skeletons, etc.) Many marine organisms have CaCO3 hard parts • Carbonate ion is used for the formation of the hard part(shell, skeleton, etc.) which they get from the sea-water BUT, hydrogen also naturally reacts with CO32-
  • 12. Key concepts: 4. Increased ocean acidity affects marine organisms’ abilities to make and keep their hard parts (calcium carbonate (CaCO3) shells, skeletons, etc.) Many marine organisms have CaCO3 hard parts • Carbonate ion is used for the formation of the hard part(shell, skeleton, etc.) which they get from the sea-water BUT, hydrogen also naturally reacts with CO32- • The more acidic the ocean, the more CO32- reacts with hydrogen, and the LESS CO3 left for marine organisms to convert into their hard parts “Battle” for carbonate!
  • 13. Key concepts: 4. Increased ocean acidity affects marine organisms’ abilities to make and keep their hard parts (calcium carbonate (CaCO3) shells, skeletons, etc.) Many marine organisms have CaCO3 hard parts • Carbonate ion is used for the formation of the hard part(shell, skeleton, etc.) which they get from the sea-water BUT, hydrogen also naturally reacts with CO32- • The more acidic the ocean, the more CO32- reacts with hydrogen, and the LESS CO32- left for marine organisms to convert into their hard parts “Battle” for carbonate! • Organisms must use more energy or make less hard part material •Existing hard parts dissolve (chemical reaction goes “the wrong way”)
  • 14. Chemistry of Ocean Acidification • Relative proportion of these species vary with pH; increase of CO₂ invasion into seawater leads to increased concentration of CO₂(aq.) and HCO₃¯ and a decreased concentration of CO₃²¯ (91% of DIC exists as HCO₃¯ 8% as CO₃²¯ and 1 % as CO₂)
  • 15. Change in the concentration of DIC Dissolve Inorganic Carbon (DIC) Bicarbonate ion (91%) Carbonate ion (8%) CO2 (1%) pH 8.2 : Pre Industrial Value pH 8.1 : Present Value pH 7.4 : When all fossil fuel burnt (Tyrrell et. Al. 2011) CO3 2- (8%) HCO3 - (91%) CO2 (1%)
  • 16. Indicators • Shows pH values and levels of dissolved carbon dioxide at three locations • Data come from two stations in the Atlantic Ocean (Bermuda1 and the Canary Islands2) and one in the Pacific (Hawaii3) • Measured directly or calculated from related measurements such as dissolved inorganic carbon and alkalinity. Source: Bates et al., 20121 , González- Dávila, 20122, University of Hawaii, 20123
  • 17. Indicators Source: Feely et al., 2009 Related Information at http://sos.noaa.gov/Datasets /list.php?category=Ocean • Amount of aragonite dissolved in ocean water, which is called aragonite saturation • Aragonite saturation measurements done only at selected locations • But it can be calculated reliably for different times and locations based on the relationships scientists have observed among aragonite saturation, pH, dissolved carbon, water temperature, concentrations of carbon dioxide in the atmosphere, and other factors that can be measured •So this is indirectly based on actual measurements
  • 18. Feely, Doney and Cooley, Oceanography (2009) pH distribution in surface waters pH from the NCAR CCSM3 model projections using the IPCC A2 CO2 Emission Scenarios Projections
  • 19. Ocean Acidification in the Past • 55 million yr ago Earth went to the same change, this ancient catastrophe is known as Paleocene-Eocene thermal maximum, or PETM • 5X CO2 in the atmosphere • 0.8 pH unit lower • Temp was 60C to 100C high • So corrosive that it ate away at the shells, along with other species with calcium carbonate in their bodies • It took hundred of thousand of years to recover from this crisis and seafloor from red black to white How is present OA differ from PETM…? • Acidification rates is 10X • Anthropogenic CO2 blast
  • 20. IPCC Projections for 2100 • Anthropogenic Ocean acidification is currently in progress and its measurable • Reducing CO2 emission will slow the process of ocean acidification Global temperature increase likely by 2100: 0.9°C – 2.3°C 3.2°C – 5.4°C 0.3-0.4 pH unit drop expected
  • 21. Revelle factor is defined as • Describes how partial pressure of CO2 in seawater changes for a given change in DIC )/()( / 22 DICDIC PP COCO • Proportional to ratio btwn DIC and alkalinity (oceanic charge balance). • Low Revelle factors generally in warm tropical and subtropical waters • High Revelle factors in cold high latitude waters
  • 22. Capacity for ocean waters to take up anthropogenic CO2 is inversely related to the Revelle factor • Highest anthropogenic CO2 concentrations found in subtropical Atlantic due to low Revelle factor • North Pacific has high Revelle factor  lower anthropogenic CO2 concentrations
  • 23. CAUSES OF OCEAN ACIDIFICATION
  • 24. Main Causal factors affecting Ocean Acidification  Rivers  Anthropogenic  Volcanic Vents  Ships
  • 25. SATURATION INDEX OF ARAGONITE (Ω) Ω = [Ca2+] [CO3 2-] /Ksp Saturation Index of aragonite, or degree of saturation relative to aragonite stoichiometric solubility product Ω=1, Saturation Ω>1, Oversaturation (required to form shell) Ω<1, under saturation • Aragonite is 1.5 times more soluble than calcite. • Increase in acidity cause carbonate equilibrium towards lower CO3 2- and lowers the saturation index of aragonite (Ω) .
  • 26. EFFECT OF RIVERS ON SHELL GROWTH Fig. 1. Effect of increased acidification on soft- shelled clam larvae. • The increase in alkalinity with time at Ω = 0.5, indicates that shell dissolution is occurring, as the gain in alkalinity of the solution is proportional to the decrease in shell material. •At Ω = 2.0, the decrease of alkalinity indicates shell formation and growth. •When seawater is supersaturated at Ω = 1.6, the rate of alkalinity change (CO3 2- uptake) is effectively zero. The early spawn coincides with the river discharge which unable larvae to incorporate aragonite at Ω=1. 6.
  • 27. COASTALACIDIFICATION BY RIVERS Fig. 2. Mapped Ω for the surface waters of the Kennebec plume and Casco Bay, Gulf of Maine. Contours of Ω = 1.0 (inner) and Ω=1.6 (outer) are shown as black curves. Source: BY J. SALISBURY (2005) Fig.3. The Gulf of Mexico (above) has a large dead zone due to excess nitrogen. Source: NASA
  • 28. Fig. 4.(a) Estimated Ω versus salinity of several major world rivers: 1, Mississippi; 2, Yangtze; 3, Nile; 4, Congo; 5, Amazon; 6, Mekong; 7, Orinoco; 8, Yenisey; 9, Amur; 10, MacKenzie; 11, Ob. Note the strong patterns in grouping by alkalinity and latitude. (b) A look at Ω as a function of salinity for the region of the Amazon and Orinoco plumes. Black contour shows the estimated extent of the combined plumes. Source:BY J. SALISBURY(2005) •Climate and river chemistry are the main factors determining Ω, with low temperatures and carbonate favouring lower Ω. • To consider the potential threat to marine species (specially shellfish) on a global scale, we estimated Ω from the low-salinity region near the river mouth out into the open ocean for several of the world’s major rivers.
  • 29. IMPACT OF ANTHROPOGENIC CO2 • CO2 increase from 280ppm to 398.03ppm from the industrial period due to several human activities. • 45% remain in atmosphere • 26% has been taken up by ocean • 29% by the terrestrial biosphere Fig.5. Atmospheric CO2 emissions, historical atmospheric CO2 levels and predicted CO2 concentrations from this emissions scenario, together with changes in ocean pH based on horizontally averaged chemistry Source: Feely.et.al(2004)
  • 30. Fig.6. Relation between the CO3 2-, pCO2 and DIC. The solid vertical light green line shows the range of carbonate ion concentrations observed in the present-day oceans, and the solid vertical magenta line shows the range of dissolved inorganic carbon concentrations. Source: Feely.et.al(2004) • Surface-water dissolved inorganic carbon (DIC) increase by more than 12%, and the carbonate ion concentration would decrease by almost 60%. • The corresponding pH drop would be about 0.4 pH units in surface waters. EFFECT ON SATURATION DEPTH
  • 31. • The primary production carbonate shells occur in euphotic zone. • Initially we think dissolution occur after CCD, but 60 to 80% of the CaCO3 dissolves in the upper 1000 m. Fig.7. Distribution of (A) aragonite and (B) calcite saturation depth. This depth is significantly shallower for aragonite than for calcite, because aragonite is more soluble in seawater than calcite. Source: Feely.et.al(2004) • Pronounced shoaling from Atlantic through the Indian to the Pacific Oceans. • The higher DIC/TA in the deep waters of the Indian and Pacific. • DIC > TC, due to respiration processes and water circulates along Deep Conveyor Belt.
  • 32. IMPRINTS OF ANTHROPOGENIC CO2 ON THE OCEANS Fig.8. Representative sections of anthropogenic CO2(µmol kg-1) from (A) the Atlantic, (B) Pacific, and Indian (C) oceans. Source: Sabine et al. (2004)
  • 33. Fig.9. Vertical distributions of anthropogenic CO2 concentrations in mol kg–1 and the supersaturation/ undersaturation horizons for aragonite and calcite along north- south transects in the (A) Atlantic, (B) Pacific, and (C) Indian Oceans. Present-day (solid line) Preindustrial (dashed line) Source: Feely.et.al(2004) Present saturation horizon is same as pre-industrial 80-150m 100-200m Aragonite-: 30-100m Calcite-: 40-100m
  • 34. VOLCANIC CO2 VENTS IMPACTS Fig.10. Variation in pH, cover of algae and abundance of species at CO2 vents. calcareous (triangles) and noncalcareous algae (circles) is shown. Source: Jason M. Hall-Spencer (2008) PercentageAlgalCoverpH(TotalScale)
  • 35. c Fig.11. Posidonia oceanica with heavy overgrowth of Corallinaceae at pH 8.2 (a) and lacking Corallinaceae at mean pH7.6. (b); arrow indicates bubbles from the CO2 vent field. (c) Sea-grass shoot density and amount of CaCO3 on leaves growing at differing pH levels. Source: Jason M. Hall-Spencer (2008)
  • 36. IMPACTS OF SHIPS Fig.12. Calculated surface water pH changes arising from shipping-derived inputs of SOX and NOX. • The largest effects of SOX and NOX are in parts of the Northern Hemisphere 85%. •Annual acidifications of 0.0014, 0.00046, and 0.0008 for the North Sea, Baltic Sea and South China Sea, respectively. • The Baltic Sea has a lower buffer capacity, making it especially sensitive to strong acids. •A maximum annual acidification of 0.0004 pH. Source: Hassellöv et.al. (2013)
  • 37. Fig.13. Calculated shipping-derived acidification (ΔpH) with surface water (a) pCO2 (30,688 data points) (b) SOX , NOX (30,675 data points). • The calculated near-coastal seasonal acidification of 0.0015–0.002 pH • Heavily trafficked trade routes more acidic, and may contribute to local acidification. •Shipping acidification could be a concern where high traffic occurs near fisheries or biodiversity. Source: Hassellöv et.al. (2013)
  • 38. IMPACT ON CALCIFYING ORGANISMS  Reduced calcification and growth of the corals.  The most absolute impact is the decrease in the linear extension rate and skeletal density of coral colonies.  Loss of structural complexity- which will affect the reefs to absorb wave energy and thereby impairs coastal protection.  Mass coral Bleaching and loss of rugosity.  Increased erosion by the activities of grazing fishes such as parrotfish which removes carbonates from low density substrates.  Reduced larval output from reefs.  Loss of habitat quality and diversity.  Loss of ecological resilience.
  • 39. Stony coral Sea urchins Pteropods Coralline algae Calcium carbonate part Coral skeleton Skeleton & test Shell Component of fronds Fish Ear bones and other structures Organism
  • 40. • 10-50% decrease in the calcification rate of reef-building corals and coralline algae. (Kleypas and Langdon,2006) • The calcifying macro algae like coralline red and calcifying green contains high Mg calcite and has shown slow calcification rate. • Rhodoliths calcification decreased as much as 250% in mesocosms and successful recruitment by coralline algae was diminished. (Kuffner et al.,2008) • Mollusks are reef organisms in shelled forms it is expected that some species will produce thinner shells and suffer reduced recruitment rates. ( Green et al.,2004,Miller et al.,2009) • One of the most interesting effects of OA concerns “endolithic” algae that bore into reef skeletal material. At double CO2 level, these algae bore more deeply into skeletal material, dissolving nearly 50% carbonate in oceans. (Tribollet et al.,2009) Mollusks Rhodoliths EFFECTS ON CALCIFYING ORGANISMS
  • 41. Echinoderms • The greater solubility of high Mg calcite skeletons of echinoderms suggests that they are highly vulnerable to OA. (Kurihara 2008,Miles et al.,2007) • Calcareous benthic foraminifera produces bulk of carbonate sands in shallower environment and are sensitive to high CO2 concentrations. (Bernhard et al.,2009)
  • 42. Major planktonic calcifers Coccolithophores Foraminifera Pteropods algae protists snails ~ 200 calcite days ~ 30 weekscalcite ~ 32 months to year? aragonite Extant species Mineral form Generation Time
  • 43. • Characteristics: – Free drifting photosynthetic Phytoplankton (phylum Haptophyta) – One of the most abundant marine calcifying phytoplankton – Building of calcium carbonate scales (coccoliths) Ca2+ + CO3 2- ↔ CaCO3 Ca2+ + 2HCO3 - ↔ CaCO3 + H2O + CO2 • Occurrence: – Mostly in upper layers of sub polar regions – Nutrient poor and mild temperature waters COCCOLITHOPHORES
  • 44. E. huxleyi G. oceanica C. braarudii aarudii C. . C.quadriperforatus pH DISRUPTS SHELL FORMATION Ambient pH Decrease in pH Coccolithophores largest producer of calcite on Earth Source-Riebesell et al. 2000 Langer et al. 2006 Coccolithophore bloom in the English Channel off the coast of Plymouth [NASA Image]
  • 45. FORAMINIFERA SHELLED PTEROPODS (single-celled protists)  -4 to -8% decline in calcification at pCO2= 560 ppm  -6 to -14% decline in calcification at pCO2= 780 ppm Source-Bijma et al. (2002) (planktonic snails) Shell dissolution in a live pteropod (Clio pyramidata) Source-Orr et al. (2005)
  • 46. Loss of marine biodiversity Coral reefs harbor more than 25% of the ocean’s biodiversity – provide a refuge and feeding ground for countless marine organisms. > 50% of all corals reefs are in cold, deep waters – more impacted by ocean acidification. (Source-NOAA)
  • 47. Coral Bleaching Unbleached coral Bleached coral CaCO3 → CaO + CO2 Coral Bleaching is a stress condition in coral reefs that involves the breakdown of zooxanthellae. Source: buceandoelmundo.wordpress.com
  • 48. (A) Linkages between the buildup of atmospheric CO2 and the slowing of coral calcification due to ocean acidification. (B)Temperature, [CO2] atm, and carbonate-ion concentrations reconstructed for the past 420,000 years. (O. Hoegh-Guldberg et al. 2007) Coral Calcification Scenario
  • 49. • Reduction in the resilience of Caribbean forereefs as coral growth rate declines by 20%. • Reef recovery is only feasible above or to the right of the unstable equilibria (open squares). • The “zone of reef recovery”(pink) is therefore more restricted under reduced coral growth rate and reefs require higher levels of grazing to exhibit recovery trajectories. Shift in Equilibrium of corals (Source: O. Hoegh-Guldberg et al. 2007)
  • 50. • Changes in coral community calcification rate in the Biosphere 2 coral reef mesocosm as a function of decreasing aragonite saturation state. • Note that once Ωarg value reached a value of 1.0-2.0 the coral community shifted from net calcification to net dissolution. Change in coral calcification rate with Aragonite Saturation Fig. Atmospheric pCO2 levels that roughly correspond to Ωarg values (Langdon et al., 2003)
  • 51. (A) Reef slope communities at Heron Island. (B) Mixed algal and coral communities associated with inshore reefs around St. Bees Island near Mackay. (C) Inshore reef slope around the Low Isles near Port Douglas. Plot showing the variation of calcification (grams per square centimeter per year) in Porites corals over time. (modified from De’ath et al, Science, 2008). The Great Barrier Reef Scenario • Calcification has declined with 14.2%, from 1.76 g/cm2/y to 1.51 g/cm2/y. Source: (O. Hoegh-Guldberg et al. 2007) Coral Reef Scenarios CRS-A, CRS-B, and CRS-C from the Great Barrier Reef
  • 52. Calculated changes in reef building of coral reefs worldwide at four different atmospheric pCO2 stabilization levels, based on the combined changes in saturation state and temperature on coral community calcification. The values are expressed as a percentage of pre-industrial calcification rates ; PIR=Pre-Industrial rate; TGgross = temperature dependent Gross calcification. Note that this calculation assumes constant coral cover=50% Change in Reef Building of Corals (Silverman et al. (2009)
  • 53. Fig. Effects of experimental ocean acidification (CO2level) and warming on three key performance variables of three major coral reef builders: Effects of experimental ocean acidification • (A–C) crustose coralline algae (CCA,Porolithononkodes), • (D–F) branching Acropora (A. intermedia), and • (G–I) massivePorites(P. lobata). • Gray and black bars show low- and high- temperature treatments, respectively. • Levels of CO2 represented the present-day control condition (380 ppm atmospheric CO2) and projected scenarios for high categories IV (520 –700 ppm) and VI (1000 –1300 ppm) by the IPCC. (Source: Anthony et al.)
  • 54. Impact pathway for OA Socio-Economic Activity CO2 Emissions Ocean Acidification  Food Webs  Fish Stocks Coral Reefs  Fish Catch  Aquaculture  Tourism  Coastal Protection  Biodiversity  Population  Income  Welfare  Distribution  Vulnerability  Food Security  Adaptation Marine Ecosystems Ecosystem Services Socio-economic impacts Source: Moore et al. (2011)
  • 55. Socio-Economic Impacts Economic value of corals : • Act as a habitat and nursery for commercial fish stocks. • Act as a natural barrier for coastlines. • Provides recreation and tourism opportunities  The global economic value associated with reefs is of the order of $30 billion per year.  Loss of coral reefs will amount to a loss of tens of billions of dollars.  The economic value of damage to coral reefs has been estimated and losses were found to be of the order of 0.18% of global GDP in 2100.(European Science foundation)
  • 56. Global Economic Losses Source: Brander et al. (2009)
  • 57. Ecosystem Effects of Ocean Acidification in Times of Ocean Warming: A Physiologist’s View Portner.et.al., 2008
  • 58. Overview of Processes and Mechanisms Affected By CO2 In a Generalized Water-breathing Animal Portner.et.al., 2008
  • 59. Heat Tolerance Of The Edible Crab Cancer Pagurus Under Normocapnia And Hypercapnia 1. Discontinuities in the curve depicting arterial oxygen tensions (pO2) under normocapnia were identified as thermal limits. 2. Highly elevated CO2 levels (1% hypercapnia) cause heat tolerance to decrease dramatically by about 5 C. Portner.et.al., 2008
  • 60. Conceptual Model of How Ocean Acidification, Hypoxia And Temperature Extremes Interact Mechanistically. Temperature Portner.et.al., 2008
  • 61. Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms Kristy j. Kroeker. et.al., 2010
  • 62. Effect of Near-future (2100) Ocean Acidification on Different Response Variables Of Marine Organisms from Weighted, Random Effects Meta-analyses Kristy j. Kroeker. et.al., 2010
  • 63. Impact of Anthropogenic Atmospheric Nitrogen and Sulphur Deposition on Ocean Acidification and the Inorganic Carbon System  Basic Principles of The Effects of Atmospheric C, S and N Deposition on Seawater Chemistry Scott C. Doney. et.al., 2007
  • 64. Model-estimated Anthropogenic (1990–2000 Minus Preindustrial) And Preindustrial Atmospheric Deposition Fluxes Integrated anthropogenic deposition Teq/y (preindustrial) Flux Global Ocean-only Model Observed 138 0.10 to 0.20 4.11(0.00) 1.99(0.00) 0.00 to 0.03 0.02 1.84(1.18) 0.67(0.73) 0.00 to 0.03 0.02 2.21(0.58) 0.78(0.49) 0.00 to 0.03 0.01 -2.15(-2.34) -0.24(-1.71) -0.01 to +0.01 -10.37(-2.34) -4.22(-1.71) -0.01 to +0.01 Scott C. Doney. et.al., 2007
  • 65. OCEAN ACIDIFICATION MITIGATION Source: Adelsman and Binder, 2012
  • 66. SYNOPSIS OF MITIGATION STRATEGIES BY EUROPEAN SCIENCE FOUNDATION AND UNITED STATES BLUE RIBBON PANEL ON OCEAN ACIDIFICATION • Co-ordinating at various levels (local to global scale) to reduce CO2 emissions and sharing research for a sustainable policy development • Strengthening monitoring abilities: more field and lab studies • Using Earth’s past to understand OA: PETM • Understanding biogeochemical feedbacks and relationships with OA • OA Integrated Climate models with different feedbacks • Understanding the relationship with climate change and the cost additions in mitigation Source: Adelsman and Binder, 2012 Monitoring BuoyLocal air emissions Wave Glider
  • 67. • Adopting measures to reduce land based contributions to OA: nutrients & organic carbon • Developing strategies keeping in mind the socio- economic impacts on natural resources and human communities: Communicating with the stake- holders, fund providers and other researchers • Adapting to the changing OA: shellfish farms & phytoremediation Source: Adelsman and Binder, 2012 Seaweed growing on oyster longlines: Phytoremediation Waste water dumped directly into water bodies Centre for Microbial Oceanography, Hawaii
  • 68. IRON FERTILIZATION • Increase of biological production by addition of iron to the upper ocean layer • “Iron Hypothesis” : Iron acts as a fertilizer in increasing the growth of phytoplankton in high-nutrient, low-chlorophyll (HNLC) regions thereby increasing the ability of oceans to store more atmospheric CO2 After Martin, 1990 • Commercially supported as Carbon Credit generation method • Method Adopted: Zero phosphate concentration in near surface ocean denoting the maximum macronutrient decrease by iron fertilization • Scenarios: • A2_emission • A2_emission + Ocean Iron Fertilization (OIF) • A2_conc + OIF: generates carbon credit Source: Cao and Caldeira, 2010
  • 69. OBSERVATIONS and RESULTS Source: Cao and Caldeira, 2010 Slight mitigation of surface ocean acidification at the cost of increased deep ocean acidification Fig: Simulated surface ocean pH Fig: Simulated temporal evolution of pH Deep Ocean Accelerated acidification Shoaling of saturation zones More effect in Southern Oceans Surface Ocean Minor mitigation effect (lowering of pH reduced by 0.06 units) Lag by a decade
  • 70. LIMESTONE ADDITION TO UPWELLING REGIONS • Enhancement of CO2 absorption from the atmosphere • Partial Reversal of OA CO2(g) + H2O(l) → H2CO3(aq) H2CO3(aq) → H+ + HCO3 - CO3 2- + H+ → HCO3 - _____________________________ H2O + CO2 + CO3 2- → 2HCO3- CaCO3 → Ca2+ + CO3 2- ______________________________ CaCO3 + H2O + CO2 → Ca2+ + 2HCO3- Source: Harvey, 2008 Fig: Distribution of the limestone powder addition rate for total application rate of 4gt/a
  • 71. OBSERVATIONS pH recovery of 0.06 by 2200 and 0.12 by 2500 Scenario 1: global CO2 emission grows to 17.5 Gt C/a in 2100 and then declines at 1%/a Scenario 2: global CO2 emission grows to 7.5 Gt C/a by 2010, return to 2010 level by 2020 and continue to go down to 0 by 2100 Source: Harvey, 2008
  • 72. RESULT AND DISCUSSION Feasibility of the process • Economic cost: 40-45 billion dollars per annum for 4 Gt/a application rate • Energy requirements in terms of transport, crushing and sprinkling of limestone • Comparisons with iron fertilization: Limestone process dependent on inorganic chemical reactions. • Increase in ocean surface albedo: slight cooling • Decrease of solar radiation penetration: reduce biological pump strength Switch from the increasing CO2 path to one with zero emission Preindustrial pH level 8.31 pH by 2100 with Zero emissions : 8.12 pH by 2100 if peak emission is 17.5 Gt C/a : 7.78 Addition of Limestone at 4 Gt/a : difference between Pre-industrial level and minimum pH restored by 20% by 2200 and 40% by 2500 Source: Harvey, 2008
  • 73. • Clear evidence of Ocean Acidification • Main Cause: Anthropogenic CO2 emission • Impacts on marine ecosystem and shell organisms • Economic impacts on fish industry • Mitigation strategies needed in collaboration with climate models CONCLUSION OCEAN ACIDIFICATION: A CHALLENGE THAT “CAN” AND “MUST BE” MET
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