Greenhouse Climates: the Paleocene- Eocene Thermal Maximum

Transcription

1 Greenhouse Climates: the Paleocene- Eocene Thermal Maximum

2 Main Points a) We know Earth was warm (a Greenhouse) several times over the past 1900 my. Was this the result of elevated CO 2 concentrations? b) Why was sea level higher 100 mya? Did this affect climate? c) What were the environmental effects of the K/T boundary asteroid impact?

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4 Main Points a) We know Earth was warm (a Greenhouse) several times over the past 1900 my. Was this the result of elevated CO 2 concentrations? b) Why was sea level higher 100 mya? Did this affect climate? c) What were the environmental effects of the K/T boundary asteroid impact? Drastic in short term Inconsequential in long term

5 Large and abrupt greenhouse episode ca. 55 mya: Paleocene-Eocene Thermal Optimum cavorting on an Eocene beach

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7 It had all happened before, but the PETM is closest in geological time. Eocene Temperature trends based on oxygen isotope ratios as measured in fossils, reported by Veizer et al. (1999), and updated online in 2004

8 PETM Greenhouse summarized a) Lasted ca. 70,000 to 200,000 years b) Very brief relative to the speed of tectonic factors c) Evidenced by poleward spread of warm-loving flora and fauna d) Accompanied acidification of oceans (1/2 of benthic forams extinct) e) Possibly a enormous burb of CH 4 stored in ocean sediment (methane clathrates?) and/or release of C from deep-sea reservoir

9 the Paleocene-Eocene Thermal Maximum (PETM) Röhl, U.; Bralower, T.J.; Norris, R.D.; Wefer, G. (2000). "New chronology for the late Paleocene thermal maximum and its environmental implications". Geology 28 (10):

10 Zachos et al (2008) NATURE

11 mean annual temperatures at poles were >>> freezing latitude

12 Eocene metasequoia forests in High Arctic Hope Jahren

13 Estimates of the carbon addition needed to have these effects during the PETM range from about 2500 to > 6800 gigatons (rem: about 800 Gt of C held in atmosphere today) Panchuk, K.; Ridgwell, A.; Kump, L.R. (2008). "Sedimentary response to Paleocene-Eocene Thermal Maximum carbon release: A model-data comparison". Geology 36 (4):

14 Estimates of the carbon addition needed to have these effects during the PETM range from about 2500 to > 6800 gigatons (rem: about 800 Gt of C held in atmosphere today) Panchuk, K.; Ridgwell, A.; Kump, L.R. (2008). "Sedimentary response to Paleocene-Eocene Thermal Maximum carbon release: A model-data comparison". Geology 36 (4):

15 What caused the Paleocene-Eocene Thermal Maximum? Massive release of carbon into the atmosphere/ocean. continents were in similar positions as today except for the Southern Ocean Gateways

16 1)Evidence = negative excursion in carbon and oxygen isotopes in forams del 13 C del 18 O Zachos et al (2008) NATURE

17 2) Evidence = sharp increase in carbonate dissolution in the deep-sea.

18 Brief aside to ocean acidification: Ocean acidification: decrease in ph of the oceans caused by uptake of CO 2 from the atmosphere.

19 30 40% of the carbon dioxide from human activity released into the atmosphere dissolves in oceans, rivers and lakes.

20 To achieve chemical equilibrium, some of the dissolved CO 2 reacts with the water to form carbonic acid.

21 Some of these carbonic acid molecules then react with water to produce bicarbonate and hydronium ions

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23 Estimated change in sea water ph caused by human created CO 2 between the 1700s and the 1990s, from the Global Ocean Data Analysis Project (GLODAP) and the World Ocean Atlas By Plumbago - Own work, CC BY-SA 3.0,

24 What does ocean acidification look like in the geological record? Zachos et al (2008) NATURE Difficult time for hermit crabs?

25 What caused the PETM? Massive release of carbon into the atmosphere/ocean. continents were in similar positions as today except for the Southern Ocean Gateways

26 A brief aside into methane geochemistry Intergovernmental Panel on Climate Change (IPCC) 2013: CH 4 is 84x more potent as a greenhouse gas than CO 2 over a 20-yr timeframe. and 25x more potent over a centurytimespan.

27 CH 4 is a potent greenhouse gas. Atmospheric CH 4 concentrations have increased 150% since the Industrial Era (IPCC, 2013).

28 1800 Gt current stocks of methane Review of Geophysics (2017)

29 methane clathrate: natural-gas hydrate methane (CH 4 ) molecule trapped inside a water molecule (CH 4 ) 4 (H 2 O) 23

30 clathrates: cage compounds : one substance trapped inside the crystal lattice of another Structure of the clathrate consisting of cadmium cyanide host and carbon tetrachloride guest,cd(cn)2.ccl4. Blue = Cd(CN)2 framework, gray = C, green = disordered Cl.

31 Methane hydrate stabilized in its clathrate cage by different combinations of temperature and pressure

32 worldwide amounts of methane hydrate: estimated 2x the amount of carbon contained in all other fossil fuel deposits. methane hydrate reservoir probably contains 2 10 times the known reserves of conventional natural gas

33 -966 m Ruppell and Kessler (2017) What are these mussels eating?

34 anaerobic methanotrophs archaea energy release electron acceptor

35 Methane hydrates form by migration of gas along geological faults, then crystallization on contact of the gas stream with cold sea water.

36 methane clathrate common: Onshore in polar sedimentary rocks where surface temperatures are less than 0 C Alaska and Siberia Beaufort Sea, East Siberian Sea Offshore in sediment at water depths >300 m where the temperature is around 2 C.

37 Ruppell and Kessler (2017)

38 The clathrate gun hypothesis : increases in sea temperatures (and/or drops in sea levels) trigger the sudden release of CH 4 from methane clathrate in sea bed. Why not a Nobel Prize in Paleontology? Kennett, James P.; Cannariato, Kevin G.; Hendy, Ingrid L.; Behl, Richard J. (7 April 2000). "Carbon Isotopic Evidence for Methane Hydrate Instability During Quaternary Interstadials". Science. 288 (5463):

39 Ruppell and Kessler (2017): No conclusive evidence that hydrate-derived methane is now reaching the atmosphere.

40 At present in the Arctic, methaneclathrates are minor emitter of CH 4. Ruppell and Kessler (2017) Review Geophysics

41 And clathrate releases unlikely to have driven ice-age climates either Sowers, Todd. "Late Quaternary Atmospheric CH 4 Isotope Record Suggests Marine Clathrates Are Stable". Science. 311 (5762): but I keep hoping. nonetheless

42 What if there was a huge, undersea landslide? Ruppell and Kessler (2017).

43 Or what if widespread volcanism occurred under a polar sea? Siberian Traps By derivative work: Jo (talk)sibirien_topo2.png: Ulamm 21:06, 18 April 2008 (UTC) - Sibirien_topo2.png, CC BY-SA 3.0,

44 Odd carbon isotopes characterize the time of the End Permian Extinction..evidence for methane-clathrate release then?

45 Coming back to the Eocene

46 During the PETM, thousands of petagrams of carbon were released into the ocean-atmosphere system, and this isotopic composition is consistent with methane. McInerney and Wing (2011)

47 How could a burb of CO 2 and/or CH 4 occur?

48 CO 2 gas clouds, tsunamis aftermath of a CO 2 -driven limnic eruption in 1986 in Lake Nyos, Cameroon

49 exploding lakes Nyos and Monoun are both in western Cameroon

50 Another of the 3 known exploding lakes Lake Kivu contains approximately 56 Rwanda billion cubic kilometers of dissolved methane and 260 billion cubic kilometers of CO 2.

51 Several million people live on the shores of Lake Kivu

52 How does a lake explode? Deep, cold water saturated with CO 2 or CH 4. Gases held in solution by low temperature and high pressure. beer bottles provide excellent analogy. Some sort of trigger (landslide, volcanism,?) causes upwelling.

53 which releases gases from solution violent bubbling ensues. PNAS 2005

54 Did the PETM greenhouse result from a limnic/oceanic explosion of CO 2 and/or CH 4?

55 Undersea landslides along the outer continental shelves? uk/research/hyd rate/hydrates_

56 Eocene Greenhouse (PETM) summarized a)lasted 70, ,000 years b)very brief relative to the speed of tectonic factors c)evidenced by poleward spread of warm-loving flora and fauna

57 Eocene Greenhouse summarized d) Accompanied acidification of oceans (1/2 of benthic forams extinct) e) Possibly a enormous burb of CH 4 stored in ocean sediment (methane clathrates?) and/or release of C from deep-sea reservoir

58 Recovery from the mid-eocene Greenhouse Required about 100,000 years Onset and recovery probably slower than the climate changes driven by CO 2 that we are now experiencing.

59 Ruminant livestock can produce 250 to 500 L of methane per day. This level of production results in estimates of the contribution by cattle to global warming that may occur in the next 50 to 100 yr to be a little less than 2%. Johnson and Johnson (1995) Journal of Animal Science, Vol 73

60 1) How has Earth remained habitable in the face of a warming sun, large changes in its biota, and significant perturbations from Outer Space? How could O 2 go from <1 % to >21% and NOT throw a monkey wrench into the climate system?

61 2. What processes have controlled Earth s climate at the time scale of millions to billions of years? Earth is 4.5 billion years old

62 3. What were the causes and effects of seal-level changes through deep time?

63 4. How did that apocalyptic asteroid impact 65 mya ago affect global climate? I m trying to eat here!

64 Next: descent into the ice house