1. 1 Climate Records from Ice Cores Major Points Ice cores have provided the best record of climate change over the last 700K years. The most important climate characteristics recovered from ice cores are air temperature, atmospheric CO 2 and CH 4 concentrations and dust. One key unanswered question is the cause of the atmospheric CO 2 shifts between glacial and interglacial periods. Another key question, still not completely answered, is the sequence of events that occur that cause the earth to shift from glacial to interglacial periods.

2. 2 Ice Core Drilling Depths

3. 3 Dome C, Antarctica

4. 4 Tools of the Trade LLLLLLLLLL

5. 5 Ice Core Drill

6. 6 Ice Core Recovery

7. 7 Ice Cores from Greenland Firn Ice Compact Ice Bedrock

8. 8 Antarctica Drilling Sites

9. 9 Ice Cores and Ice Sheet Flow Age of Ice: annual layers (Greenland) and ice flow models (Antarctica)

10. 10  18 O of Today’s Precipitation vs Air Temperature  18 O (‰) ΔTemp/Δ  18 O = ~1.4ºC / 1‰ ΔTemp/Δ  D = ~0.2ºC / 1‰

11. 11 Effect of Condensation on the  18 O (and  D) of Precipitation

12. 12 Borehole Temperature Record in Ice Cores Scientists measure the temperature of an ice sheet directly by lowering a thermometer into the borehole that was drilled to retrieve the ice core. Like an insulated thermos, snow and ice preserve the temperature of each successive layer of snow, which reflects general atmospheric temperatures when the layer accumulated.

13. 13  18 O versus Borehole Paleothermometry a controversy in Greenland Ice Cores  emp/  18 O= 1.5 ºC / ‰) Current Precipitation  emp/  18 O= 3 ºC / ‰ Borehole Temps Climate scientists favor the borehole temperature changes.

14. 14 Greenland Drilling Sites

15. 15 Greenland Ice Core  18 O and Temperature Record Using borehole temperature vs  18 O calibration

16. 16 Temperature Swings between Glacial and Interglacial Conditions ΔTemp/Δ  18 O about equal for borehole and precipitation in Antarctica ΔT* 36 24 21 *BH corr’n

17. 17 Reconstructing Atmospheric Gas Concentrations from Ice Cores Use trapped air bubbles as preserved samples of atmosphere. Measure the concentration of important (greenhouse) atmospheric gases on the trapped air bubbles (e.g., CO 2, CH 4, N 2 O)

18. 18 Trapping Air Bubbles in Ice Snow Accumulation Rates Greenland = 0.5 m/yr Antarctica = 0.05 m/yr

19. 19 How does age of air bubbles compare to age of ice? Determine the age of the ice (annual layer or flow model). Determine the age of the trapped air bubble. -bubble age doesn’t equal ice age, it’s younger. How long does it take for the ice to seal? - ~50 meters divided by snow accumulation rate - 50m / 0.5 m/yr = ~100 yrs in Greenland - 50m / 0.05 m/yr = ~1000 yrs in Antarctica Why is this lag between ice and bubble ages important?

20. 20 Industrial Era Changes in Atmospheric CH 4 and CO 2 Extending the record of industrial era change Test of accuracy of ice core gas measurements

21. 21 Atmospheric Methane (CH 4 ) A greenhouse gas and climate indicator. Natural (pre-anthropogenic) CH 4 sources are dominated by emissions from wetlands (swamps, tundra, bogs, etc.). Biogenic methane is produced by microbes under anoxic (no oxygen) conditions. CO 2 + H 2  CH 4 + H 2 O CH 2 COOH  CH 4 + CO 2 Methane Hydrates (?)

22. 22 Atmospheric Methane The primary sink for atmospheric CH 4 is reaction with OH radicals in the atmosphere. CH 4 + OH  CO 2 + H 2 O Currently, CH 4 has a ~10 year lifetime in atmosphere. Methane is a reactive gas in the atmosphere, in contrast to CO 2 which is a non-reactive gas.

23. 23 Methane as Climate Indicator Source strength depends on extent of wet soil conditions (opposite of aridity) Extent of wet soils controlled primarily by precipitation rates and patterns (climate). In cold (tundra) regions, temperature likely has major role on CH 4 emission strength. The ocean has small role in the CH 4 cycle (in contrast to CO 2 ).

24. 24 Atmospheric Methane from Antarctic Ice Cores CH 4 concentration doubles between glacial and interglacial conditions CH 4 changes correlate strongly with temperature changes

25. 25 Methane as Climate Indicator During interglacial times, the earth was generally wetter (higher precipitation) than during glacial times, which increased the spatial extent of flooded soils and in turn the biogenic production rate of methane and its concentration in the atmosphere. Currently unclear whether this increase in precipitation was global or regionally specific (e.g., role of monsoons?). Where did increased methane production occur (tropics, temperate, polar latitudes)? Methane concentration in atmosphere contributes to greenhouse gas warming effect.

26. 26 Atmospheric Carbon Dioxide (CO 2 ) Dominant greenhouse gas that has played a key role in changing the earth’s climate in the past (e.g., Snowball Earth, Cretaceous Hothouse). What can we learn about our future climate change, in a world of high atmospheric CO 2 levels, from climate changes over the last 700K years when atmospheric CO 2 levels oscillated by ~40%?

27. 27 Atmospheric CO 2 and Temperature from an Antarctic Ice Core Atmospheric CO 2 levels increase by 40% between glacial and interglacial times. Strong correlation between CO 2 and temperature changes.

28. 28 Atmospheric CO 2 and Ice Volume Records - CO 2 from Ice Cores - Ice Volume from  18 O of marine CaCO 3 - What is implication of strong correlation?

29. 29 What causes the Glacial-Interglacial shifts in atmospheric CO 2 ? No clear answer yet. (one of the Holy Grails) Involves a change in the earth’s carbon cycle. Very likely that changes in the ocean are involved.

30. 30 Carbon Reservoir Changes and Exchange Rates Changes in Reservoir Sizes (Pg, %) Interglacial to Glacial Carbon Exchange Rates (Pg/yr) Deep Ocean accumulates the carbon lost from the atmosphere and land biota during glacial times.

31. 31 Ocean- Atmosphere CO 2 System There is much more CO 2 in the ocean (38,000 Pg C) compared to the atmosphere (600 Pg C). Thus the concentration of CO 2 in the ocean controls the concentration of CO 2 in the atmosphere. (CO 3 = + CO 2 + H 2 O  2HCO 3 - ) Air-sea CO 2 gas exchange is the process that links the CO 2 concentrations in the atmosphere and ocean.

32. 32  13 C as a Tracer of Changes in the Earth’s Carbon Cycle  18 O and  13 C in CaCO 3 SedimentsSize and  13 C of C Reservoirs  13 C (‰)= [( 13 C/ 12 C) sample /( 13 C/ 12 C) standard – 1)*1000 (Standard = PDB carbonate)

33. 33 Correlation between  13 C and  18 O changes in CaCO 3 Record Benthic = open circle Pelagic = filled circle  13 C is lower during Glacial versus Interglacial conditions

34. 34 Using  13 C as a Carbon Cycle Tracer Changes in the  13 C of the ocean CaCO 3 record indicate that there was a significant change in the earth’s carbon cycle during Glacial vs Interglacial times. The  13 C of CaCO 3 in benthic forams decreased by ~ -0.3 to -0.4 ‰ (avg. Ruddiman) during glacial times. If this glacial ocean  13 C decrease was the result of a transfer of terrestrial organic carbon to the ocean, we can calculate how much carbon was transferred using  13 C. (How was it transferred?)

35. 35 Quantify the Amount of Terrestrial Carbon Transferred to Ocean Carbon Mass and Isotope Budget Interglacial Ocean Carbon + Terr Carbon Added = Glacial Ocean Carbon (38,000 PgC) (0 ‰) + ( Terr C added) (-25 ‰) = (38000+ Terr C added)(-0.35 ‰) Terrestrial Carbon added = 524 Pg C This estimate roughly agrees with estimates based on the loss of vegetation and soils during the growth of continental ice sheets.

36. 36 Effect on Atmospheric CO 2 What effect will this ocean inorganic carbon increase have on atmospheric CO 2 concentrations? -increases CO 2 in the atmosphere (~ 2 ppm) (Remember: ocean CO 2 controls atmospheric CO 2 ) This is opposite to the trend observed in ice cores Interglacial CO 2 = 280 ppm Glacial CO 2 = 190 ppm Some other change in Earth’s carbon cycle caused lower CO 2 levels during Glacial times.

37. 37 Why did the atmospheric CO 2 decrease by 90 ppm during glacial times? Don’t know yet…. but a lot of smart people are trying to figure it out. It’s very likely that the mechanism lies in the ocean. It is likely a combination of physical, biological and chemical changes to the ocean that cause the CO 2 level in the ocean (and thus atmosphere) to change.

38. 38 Mechanism: Change CO 2 Solubility in Seawater CO 2 gas solubility depends inversely on temperature –Increases by ~4% per 1ºC cooling –Cool surface ocean by 2.5 ºC lowers pCO 2 by –22 ppm CO 2 gas solubility depends inversely on salinity –Increase salinity by ~ 1 ppt increases pCO 2 by ~11 ppm –Why does ocean salinity increase during Glacial times? Net Effect: – 11 ppm

39. 39 Mechanism: Increase the Ocean’s Photosynthesis Rate during Glacial Times Photosynthesis consumes CO 2 CO 2 + H 2 O  CH 2 O (sugar) + O 2 Currently there are a lot of nutrients in the surface waters of the Southern Ocean that could be utilized Hypothesis: Increase supply rate of iron to the ocean -iron is a trace nutrient that plankton need and is thought to limit photosynthesis rates in the Southern Ocean “Give me half a tanker of iron, and I’ll give you the next Ice Age” (John Martin, ~1990)

40. 40 Current Distribution of Photosynthesis in the Ocean estimated from Satellite Data

41. 41 Current Distribution of Nitrate in Surface Pacific Ocean Purple = high nitrate Green = low nitrate Unused nutrients in Southern Ocean

42. 42 Increase in Dust in Ice Cores Prior to Glacial to Interglacial Transition Dust contains iron

43. 43 Possible Ocean Photosynthesis effects on Atmospheric CO 2 Current CO 2 Level

44. 44 Mechanism: Make the Surface Ocean More Alkaline during Glacial Times Key Reaction: CO 2 + H 2 O + CO 3 =  2 HCO 3 - -an increase in CO 3 = concentration will decrease CO 2 Change CO 3 = by changing the ratio of biological organic carbon (CH 2 O) to CaCO 3 production and sedimentation -if diatoms were favored over forams during glacial times there would be less CaCO 3 (s) production and an increase in CO 3 = concentration (iron supply favors diatoms) Change CO 3 = by increasing supply of CO 3 = ion to the surface of Southern Ocean by a change in ocean circulation rates and/or pathways

45. 45 Possible Ocean Mechanisms to Reduce Atmospheric CO 2

46. 46  13 C as a tracer of Ocean Photosynthesis

47. 47 Record of  13 C depth gradient in the Ocean  13 C of pelagic CaCO 3 minus  13 C of benthic CaCO 3 Some evidence for increased ocean productivity during glacial times.

48. 48 What effect would these ocean changes have on atmospheric pCO 2 ? pCO 2 (Glacial) = 190ppm pCO 2 (Interglacial) = 280 ppm - (Qualitative)

49. 49 Where do we stand? Currently, model calculations that attempt to simulate the biological, chemical and physical changes in the ocean during the LGM cannot reproduce the glacial concentrations of atmospheric CO 2 found in ice cores and independent evidence of ocean change. Thus our current understanding of the processes controlling the earth’s carbon (CO 2 ) cycle on glacial to interglacial time scales is incomplete.

50. 50 Ice Core Records over last 750K years Critical climate record: –air temperature –atmospheric gas concentrations (CO 2, CH 4, N 2 O, O 2 ) –Dust (iron supply?) –Marine aerosols What do ice core records tell us about links between temperature change and forcing? What do ice core records tell us about sequence of climate events during transition from glacial to interglacial conditions?

51. 51 Ice Core Records from Vostok, Antarctica Petit et al., 1999 (Petit et al., 1999) Repeating ‘sawtooth’ patterns. Why? Consistent limits for temp and gases. Why?

52. 52 Glacial Terminations What was sequence of climate events that ended glacial eras? What about gas age vs ice age offset? Termination II at 120K yrs

53. 53 Higher Resolution Record during Termination Monnin EPICA Dome C (Science 2001) Does temperature rise in Antarctica precedes global CO 2 and CH 4 rise?

54. 54 Timing during Termination I Röthlisberger et al., GRL, 2004 Does temperature change precede CO 2 change? How important is dust?

55. 55 Sequence of Events during Termination Insolation increase at high latitudes Dust increases, then Temperature, CO 2, CH 4 increases Ice Volume decreases No single change (e.g., insolation, greenhouse gases, albedo) can account for the observed temperature change. Several processes must act together to amplify initial climate change trigger.

56. 56 EPICA Antarctic Ice Core (going back to 750K yrs)

57. 57 Reduced Temperature Cycles >400K yrs Interglacials were less warm at > 400K yrs

58. 58 Weak Interglacials have lower CO 2 Siegenthaler et al., Science 2005 (EPICA gas consortium) Vostok

59. 59 Weak Interglacials have lower CH 4 Spahni et al., Science 2005, EPICA gas consortium

60. 60 Mudelsee (based only on Vostok data): pCO 2 = 922 + 1.646 * δD t-2000 What does ability to accurately predict CO 2 from Antarctic temperatures tell us about the role of CO 2 in temperature change? Temperature and CO 2 are tightly coupled

61. 61 Tight Coupling between Temperatures in Antarctica and global CO 2 levels Why are temperature and CO 2 so tightly (linearly) coupled when other feedbacks (albedo, ocean heat transfer, etc.) are needed to explain temp change? Global CO 2 levels controlled by ocean. Unused surface nutrients present in Southern Ocean. Air temperatures in Antarctica impacted by heat released in Southern Ocean. Does a change in circulation and productivity in Southern Ocean provide the link between earth’s radiation budget and CO 2 cycle?

62. 62 Termination V (450K yrs BP) CO 2 increase precedes temperature and CH 4 increase and dust decrease. Different from 20K termination sequence. Errors in ice age and bubble age?

63. 63 Where do we stand? Glacial/Interglacial changes in temperature and atmospheric CO 2 and CH 4 levels show an extremely tight correlation. Change sequence looks like Solar Insolation, Dust, Temperature, CO 2 /CH 4 and, finally, Ice Volume (except Termination V at 450K). Earth’s climate feedback system has keep range in temperatures very consistent over the last 750K yrs. Increasing evidence that Southern Ocean may be an important feedback factor in controlling global CO 2 and temperatures. What is the implication for future climate change?