Effects of Climate Change on Ocean Acidification. Knut Yngve Børsheim

Transcription

1 Effects of Climate Change on Ocean Acidification Knut Yngve Børsheim

2 Ocean acidification: Increased CO 2 in the atmosphere leads to lower seawater ph. Station Mike Simultaneously, carbonate ion concentration decreases, and the solubility of calcium carbonates increases. CO 2 + H 2 O = HCO H + HCO 3 - = CO H + Equilibrium winter ph at 62 N 2 E in the Norwegian Sea at constant temperature as a function of carbon dioxide in the atmosphere. IPCC scenarioes:

3 The winter carbonate system in surface water at 62 N 2 E in the Norwegian Sea. Estimates based on data in Skjelvan et al μmol/kg CO 2 14,95 17,46 19,98 HCO , , ,08 CO ,35 131,34 118,53 ph 8,20 8,14 8,09

4 One aspect of ocean acidification: CO 2 + H 2 O + CO HCO 3 - The uptake of CO 2 in seawater generates bicarbonate, and consumes carbonate ions. As the sum of total dissolved inorganic carbon accumulates, the readiness for uptake of CO 2 will decrease. However, the total capacity of seawater for uptake of CO 2 is large enough to take up all the carbon in the known resources of fossil fuel.

5 Calcification: Ca HCO 3 - CaCO 3 + CO 2 + H 2 O Supersaturation of calcium carbonate minerals drive calcification in many organisms. Station Mike Some organisms have calcifying mechanisms that are independent on supersaturation. Saturation state is a linear function of CO 3 2- concentration. Positive saturation state (Ω>0) means supersaturation, negative means undersaturation. Calcification represents a net contribution to ocean acidification. When temperature increase, the solubility of calcites decrease. Effect of increased pco 2 and temperature on aragonite saturation state (Ω arg ). Blue line: Temperature unchanged. Red line: Gradual 2 change.

6 Climate change effects on the ocean Temperature Stratification Circulation Ocean-atmosphere exchange rates

7 The biological carbon pump Surface Primary producton CO 2 + H 2 O (CH 2 O) org + O 2 Sedimentation Deep water CO 2 + H 2 O Mineralization (CH 2 O) org + O 2

8 The solubility pump Atmosphere CO 2 Surface water CO 2(aquous) DIC Deep water formation, thermohaline circulation Deep water

9 Trends and projections of changes in the properties of the marine CO2 system in cold (blue) and warm (red) surface waters between 1750 and 2100 under the prescribed atmospheric CO2 increase. A. Increase in pco 2 is based on a modest release scenario reaching 700 ppm by Warmer water will take up less CO 2. Acidification will be smaller in warmer scenarioes. B. Total alkalinities in the polar regions are much lower in than in the tropics, this is not expected to change. However, DIC in warm water will increase more than in cold water (because it starts from a lower concetration). C. Note the decrease in carbonate ion concentration. Riebesell U et al. PNAS 2009;106: by National Academy of Sciences

10 Trends and projections of changes in the properties of the marine CO2 system in cold (blue) and warm (red) surface waters between 1750 and 2100 under the prescribed atmospheric CO2 increase. D. The saturation state for calcium carbonates (stipled) is and will continue to be much lower in cold than in warm areas. Solid lines depict the uptake factor, showing that the willingness for uptake of CO 2 from the atmosphere will decrease in all kinds of seawater. E. The sensitivity of pco 2 and ph to change in temperature increases as pco 2 increases. F. The sensitivity of pco 2 and ph to change in DIC increases. This will have consequences for the annual cycles of seawater carbon chemistry in euphotic waters. Riebesell U et al. PNAS 2009;106: by National Academy of Sciences

11 Seasonal cycle of pco2 (A) and ph (B) anomalies at present (year 2004, continuous lines) and in the future (year 2100, dashed lines) at a location in the central Labrador Sea (56.5 N, 52.6 W). A. The blue line represent the change (anomaly) in pco 2 over the year, the green line shows how much chemical forcing (biology) contributes, the red shows the contribution from temperature. Extrapolating the same biology to the year 2100 carbon scenario (stipled curves), the amplitude of the anomaly is amplified. The winter anomaly at 100µatm changes imply this water will act as a source of CO 2 to the atmosphere in the future scenario, whereas it is at present neutral in winter and a sink in summer. Riebesell U et al. PNAS 2009;106: by National Academy of Sciences

12 Seasonal cycle of pco2 (A) and ph (B) anomalies at present (year 2004, continuous lines) and in the future (year 2100, dashed lines) at a location in the central Labrador Sea (56.5 N, 52.6 W). B. The blue line represent the ph change (anomaly), the green line shows what chemical forcing (biology) contribute, the red shows the contribution from temperature. Extrapolating the same biology to the year 2100 carbon scenario (stipled curves), the amplitude of the ph anomaly is amplified. Riebesell U et al. PNAS 2009;106: by National Academy of Sciences

13 Monthly mean air sea disequilibrium at a location in the central Labrador Sea (56.5 N, 52.6 W) in years 2004 (continuous line) and 2100 (broken line). Green line: Present monthly mean air-sea disequilibrium, broken line Yellow dots: Mean wind speed. Riebesell U et al. PNAS 2009;106: by National Academy of Sciences

14 Schematic model illustrating the effect of sea-surface warming on upper-ocean processes in low (Upper) and high (Lower) latitudes. At low latitudes, warming is expected to decrease circulation, and difusivity will increase. At high latitudes, decreased circulation is also expected, both from warming and increased supply of freshwater. This may or may not increase total production. Riebesell U et al. PNAS 2009;106: by National Academy of Sciences

15 Crustacean physiology Heartbeat frequency (Hyas araneus). At high CO 2 a critical temperature appears. Above the critical temperature heartbeat frequency decreases. Walther et al. 2007

16 Combined effect of temperature and CO 2 Grean algae with calsiom carbonate shells: Comparison of today s and future s conditions: Doubling of CO 2 in the atmosphere, combined with three degrees higher temperature Upper panel: Necrosis expressed as percentage of surface Lower panel: Mortality as percentage dead indiviuals. From: Martin S, Gattuso JP (2009) Response of Mediterranean coralline algae to ocean acidification and elevated temperature. Global Change Biology 15:

17 A natural laboratory not far from Mt. Vesuvius Locations exist where CO 2 - acidification of seawater has been the normal condition for a long time ( years). At the island Ischia SW of Naples almost pure CO 2 is emitted from volcanic vents on the seafloor. Hall-Spencer et al. (2008) described flora and fauna as a function of distance to the volcanic vents CO 2. This distance represents a gradient both in ph og calsite saturation. The island Ischia SW of Naples : Sampling stations in a natural ph gradient. Note: 0 meter denotes no influence of CO 2, 300 meter is the vent center. Jason M. Hall-Spencer, Riccardo Rodolfo-Metalpa, Sophie Martin, Emma Ransome, Maoz Fine, Suzanne M. Turner, Sonia J. Rowley, Dario Tedesco & Maria-Cristina Buia (2008) Volcanic carbon dioxide vents show ecosystem effects of ocean acidification. Nature 454, 96-99

18 Results from a natural ph gradient. Upper panel: ph as afunction of distance to the CO 2 source b: Seagrass with and without chalk, c: Sea urchins d: Osilinus turbinata e: Limpets F: Barnacles Friske eksemplarer av Osilinus turbinata

19 1) Encrusted epiphytes were dependennt on normal ph 2) Seagrass thrive wonderfully at reduced ph Posidonia oceanica (a seagrass of the Mediterranean) Seagrass with and without epifytes. Black columns: calsified epiphytes on the leaves of grass. Open colomns: Production of seagrass measured as density of fresh leaves.

20 Friskt eksemplar av Hexaplex trunculus Kalkskall i oppløsning a: Posidonia oceanica with aufwuchs (ph 8.2) b: Posidonia oceanica without calcified algae (ph 7.6) c : Ihealthy Osilinus turbinata at ph 8.2 d: Osilinus turbinata at ph 7.2, older parts of the shell are eroded. e: Patella caerulea at ph 7.4, the animal is alive but the shell is eroded f: Hexaplex trunculus at ph 7.4, highly eroded

21 We urge policymakers to launch four types of initiatives: to help improve understanding of impacts of ocean acidification by promoting research in this field, which is still in its infancy; to help build links between economists and scientists that are needed to evaluate the socioeconomic extent of impacts and costs for action versus inaction; to help improve communication between policymakers and scientists so that : i) new policies are based on current findings and ii) scientific studies can be widened to include the most policy-relevant questions;

22 And we must descellerate the release of CO 2 to the atmosphere