1 / 54

The Icehouse and Miller’s Magic Line (1.8‰ in Cibicidoides )

The Icehouse and Miller’s Magic Line (1.8‰ in Cibicidoides ) If all of the modern ice sheets were melted  w change from -0.28‰ to -1.2‰

cindy
Download Presentation

The Icehouse and Miller’s Magic Line (1.8‰ in Cibicidoides )

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Icehouse and Miller’s Magic Line (1.8‰ in Cibicidoides) If all of the modern ice sheets were melted w change from -0.28‰ to -1.2‰ If there were no ice sheets (w = -1.2‰ ‰), 18O values greater than 1.8‰ in Cibicidoides (2.4‰ in Uvigerina) would require bottom-water temperatures be colder than today! This is not compatible with an ice-free world. Thus, Cibicidoides values >1.8‰ require high-latitude ice sheets. For the early record, this must have been primarily the East Antartic ice sheet The most significant 18O changes occurred at mid-Pliocene ca. 2.5 Ma, growth of large northern hemisphere ice sheets mid-Miocene, 14.8-12.8 Ma, development of a permanent EAIS earliest Oligocene, ca. 33 Ma, an EAIS~90% present from the early/middle Eocene boundary to late middle Eocene From -0.5 to 1.0‰. This must reflect primarily high-latitude cooling Why? Either a 6°C cooling or development of an ice sheet 1.5x today Ample geological evidence for warm high latitudes during Eocene

  2. Earliest Oligocene Oi1 event major change in state “initiation EAIS” Not presence/absence but influence on global climate Greenhouse: ephemeral EAIS not seen (IRD; SST) by oceans Icehouse: ice sheet directly influenced the oceans Middle Miocene development of a “permanent” EAIS

  3. Earliest Oligocene Oi1 ~1‰ benthic 18O increase; 60 m sea-level fall Large ice sheetHow much ice? ~0.66‰ (97% EAIS) How much cooling? <2°C [60 m* 0.11‰/10 m (Fairbanks and Mathews, 1977) = 0.66‰] 50 m sea-level rose 1 m.y. later, near collapse of the ice sheet (Pekar et al., 2001)

  4. The gateway school Kennett (1977): opening of Antarctic gateway cause thermal isolation of Antarctica “This notion is supported by ocean general circulation model (OGCM) simulations, showing that the opening of Drake Passage and the organization of an ACC reduces southward oceanic heat transport and cools Southern Ocean sea surface temperatures (SSTs) by 3°C” DeConto and Pollard (2003) Toggweiler, J. R. & Bjornsson, H. Drake Passage and paleoclimate. J. Quat. Sci. 15, 319–328 (2000); Nong, G. T., Najjar, R. G., Seidov, D. & Peterson,W. Simulation of ocean temperature change due to the opening of Drake Passage. Geophys. Res. Lett. 27, 2689–2692 (2000). http://www-odp.tamu.edu/publications/189_IR/chap_01/images/01_f01.jpg

  5. Kennett now (Leg 189 results) “By the early Oligocene, warm currents from the tropics were cut off from some parts of Antarctica by the developing Antarctic Circumpolar Current, leading to cooling and some ice-sheet formation. These events contributed to global cooling. “ “The Drake Passage opened early in the Neogene, and the Tasmanian Seaway continued to open, strengthening and widening the Antarctic Circumpolar Current and strongly isolating Antarctica from warm-water influences from lower latitudes. At ~15 Ma, the east Antarctic cryosphere evolved into ice sheets comparable to those of present day. This intensified global cooling and thermohaline circulation. The "Icehouse" world had arrived.”

  6. Oi1 Ice sheet causes more vigorous ocean circulation “spin up” Increased deep-ocean circulation: NCW & SCW pulses Decreased age bottom water Less corrosive to calcite Earliest Oligocene (33.7 Ma) drop in CCD New data from Leg 199 confirms Van Andel et al. (1975) classic paper Miller, & Tucholke, 1982 Mountain, Miller, Wright Modified after Mountain and Miller (1992) http://www-odp.tamu.edu/publications/199_IR/

  7. The Earliest Oligocene Big Chill Falkowski Grass-Horse coevolution hypothesis Grasses and horses expand More phytoliths, hence more dissolved SiO2 Enhanced diatom productivity, burial TOC Drawdown CO2 Cooler climate Greater latitudinal thermal gradients More oceanic turnover CCD drop, benthic foraminiferal turnover Miller circulation hypothesis A “spinning up” event due to large ice sheets Turns on deep-sea circulation NCW & SCW Spinning up increases upwelling, diatoms Aridity on land Grasses and horses expand

  8. Earliest Oligocene Diatom Diversification Earliest OligoceneIncrease Diatom Diversity Katz et al., in prep.

  9. Paleocene/Eocene Oceanography peak warmth in early Eocene: Miller et al. 18O summary 13°C early Eocene low vertical and latitudinal 18O gradients; warm high latitudes where tropics actually cooler? problem: how to convert 18O to temperature Zachos et al. (1994) reconstructions low latitude not cooler

  10. Low latitudinal thermal gradients in the past Modern planktonic foraminiferal d18O data is in shaded circles Absolute latitude combines both hemispheres Note the extremely low d18O in high latitudes, but the remarkably high values in the tropics Interpreted as warm high latitude surface waters and deep waters ~13° but cool tropics (20-24°C in the Eocene, 16° in the Oligocene???????) Is this true? Must correct for “salinity”

  11. Zachos et al. (19994) assumed modern salinity differences and obtained more reasonable values (similar to or only 1% (4°) cooler than today’s 28°C Low latitudinal gradients persisted throughout the Paleogene, but were lowest in the early Eocene Nearly flat thermal gradient (1.5‰; ~6-7°C) How can this planet have such a low thermal gradient?

  12. Pearson et al., Nature, 2001 Took a different approach to high tropical d18O values of the Paleogene Diagensis. Though usually thought to lower d18O values, they noted that recrystallization on the bottom/shallow burial resulted in overprinting of planktonic d18O with high benthic foram. d18O They tested this by measuring pristine planktonic foraminifera found entombed in clays and found very low d18O values They concluded the tropical SST’s were 28°C or higher and that much of DSDP/ODP planktonic foram. d18O were overprinted by diagensis Still does not explain away the very warm high latitudes required by stable isotopes and faunal/floral data

  13. The Geologic RecordEllesmere Island

  14. How do you warm high latitudes so much high CO2 high ocean heat and/or atmospheric transport high CO2 should warm tropics too!! Rind and Chandler model output Sloan, Feb. 1995 Paleoceanography): ocean heat transport not enough atmosphere can't do it either so what did it? high CO2, warming clouds at high latitudes, cooling clouds at low latitudes??? Miller’s Magic Line (1.8‰ in Cibicidoides)

  15. Late middle Eocene and younger (<42 Ma) hiatuses correlate w/ d18O increases Backstripped eustatic estimates consistent with d18O

  16. Glacioeustatic Control of Late Cretaceous Sequences • Large (10’s m), rapid (<< 1 m.y.) eustatic changes: only known mechanism is ice • d18O record: • 71.2 Ma event, • ice-volume changes • Other events consistent with glacioeustasy

  17. Early Eocene -Cretaceous Ice? Yet high latitudes were warm

  18. Visions of Ice Sheets in a Greenhouse World Modeling results of Deconto and Pollard (2003)

  19. Greenhouse & Icehouse Glacials Benthic foraminiferal oxygen isotopes, past 100 m.y.Miller et al. (in press)

  20. Enigma highlighted: Cenomanian/Turonian peak warmthmid Ceno. & mid Tur. falls: 33% modernlate Cenomanian falls: 20% modern

  21. Maas./Camp. 71 Ma: 50% modernOther Late K falls: 33% modern

  22. Oligocene: near modern volumemiddle Miocene-Recent: EAIS

  23. 50 m Greenhouse & Icehouse Glacials 35 m 25 m 0 m middle Miocene-Recent Oligocene-middle Miocene glacials 40 m Maas/Camp. glacial mid-Cenomanian mid-Turonian glacials late Cenomanan glacial

  24. 50 m 35 m 25 m 0 m Antarctic Interglacial Climates http://www.geographie.uni-freiburg.de/ipg Late Oligocene- middleMiocene mossy tundra King George Is. today http://biology.queensu.ca/~arnoldh/Torres%20del%20Paine%20photos.htm Early Oligocene Nothofagus woodland So. Chile today Eocene presume K also Nothofagus-conifer fern-Proteacea Cool, temperate rainforest http://www.tarkine.org/ Tasmania today Vegetation inferences from pollen data (Askin, 2002)

  25. 50% extinction in deep-sea benthic foraminifera at the end of the Paleocene

  26. PETM Paleocene/EoceneThermal Maximum CIE Carbon Isotopic Excursion First reported by Kennett and Stott (1990) from Maude Rise Site 690 This huge (>2‰), rapid (<10 k.y.) decrease cannot be explained by normal transfers of organic carbon vs. carbonate carbon amongst reservoirs http://earth.usc.edu/~stott/ProjectsFolder/ProjectsII.htm

  27. Dickens et al. (1995) the only means of changing d13C by >1‰ in <10 k.y. is the release of methane (CH4, -60‰) Methane stored on continental slopes and upper rises in the form of clathrates (methane popsicles): “Methane burp”

  28. Methane initially released through slumping? Katz et al. (1999)

  29. PETM Katz et al. (1999) Science Linked the CIE to a clast layer: smoking gun for massive CH4 release? d13C recovery time of ~200 k.y.

  30. Cretaceous: “The Chalk” White Cliffs Dover K = Cretaceous K/T or K/P (Paleogene) boundary One of the big 5 mass extinctions

  31. K/T Cretaceous/Tertiary boundary One of the largest mass extinctions in history Sepkowki (1994) extinction 25% of families, 50 % species

  32. Cretaceous/Tertiary (K/T) boundary extinction of 25% of families, 50 % species Dinosaurs, marine reptiles, flying reptiles ammonites and belmnites, rudists 75% marsupials planktonic foraminifers: three species survived out of >23 Nannofossils similar 90+% extinction coral, bivalves, gastropods, bryozoans severely affected not affected: most land plants?? mammals (1/9 extinction's) crocodiles, lizards, snakes, turtles survived ?most benthic organisms

  33. Iridium Element 77 Iridium is found enriched in extraterrestrial material (comets, asteroids) and deep within the Earth http://www.planetary.org/html/news/Italy/whyitaly.html

  34. Iridium Anomaly at Gubbio Extraterrestrial impact Asteroid or comet 10 km in diameter http://palaeo.gly.bris.ac.uk/Communication/Lee/irspike.html

  35. Alvarez team measured hoping to find slight enrichment due to hiatus but found very dramatic increase. Could not be explained by hiatus postulated impact of ~6-10 km asteroid; Ir anomaly found throughout the world, including terrestrial sections impact yields dust block out sun for part of year, disrupt food chain,

  36. Slide 9 Impact supported by spherules (impact glass), shocked quartz (very high pressure mineral) soot at boundary Chixulub structure: huge buried crater in Mexico: smoking gun

  37. counter hypothesis: great outpouring of basalt lava (Deccan Traps) caused outpouring of CO2 and warming that killed dinosaurs? cause outpouring of dust which blocked out sun for part of year, disrupt food chain most scientist now discredit volcanic cause, favor impact

  38. what happened to ocean productivity? evidence for a dramatic shutdown in ocean productivity: Strangelove Ocean benthic and planktonic 13C difference maintained by the biological pump of productivity. planktonics have high 13C values due to photosynthesis, benthics low due to organic C regeneration in deep water This surface to deep 13C difference (i.e., the biological pump) disappeared in the earliest Paleocene: shutdown of primary export productivity confirmed at Bass River

  39. Collapse of the vertical d13C gradient after impact: Strangelove oceans Global warming 65.5-65.0 Ma; Deccan trap CO2?

  40. Gradstein et al. (1995) Late Cretaceous time scale 98.9-65 Ma Ages: Most Contrite Sinners Come To Church Note the long normal polarity interval that continues to 120 Ma “Cretaceous Quiet Zone”

  41. Plate Tectonics & Paleogeography: Separation of the continents North Atlantic opening 165 Ma oldest definitely dated seafloor Middle Jurassic (Callovian) may have occurred older than this at ca. 180 Ma 2. opening of South Atlantic ca. 120 Ma Hauterivian-Aptian

  42. The unusual Late Cretaceous Tethys seaway “circum-equatorial” flow Flooded epicontinental Seas (e.g., western US New Jersey, NW Europe) http://www.umich.edu/~newsinfo/MT/95/Dec95/fo08bd95.gif

  43. Spreading rate changes control 10-100 m.y. scale eustatic changes Faster spreading rates, higher global sea level (tectonoeustasy) ~250 m above present

  44. Widespread shallow and no-so shallow marine deposits on cratons highest stand of global sea level: flood epicontinental sea (Hudson Bay, Barents Sea modern analog) Larsen, 1991, Geology revisited a time-honored hypothesis (Sheridan, 1988) Late Cretaceous high eustatic level caused by high seafloor spreading rates Associated with magnetic quiet zone Associated with mantle superplume and large igneous provinces (LIPs)

  45. Unusual warmth Warmest interval 80-100 Ma: not just due to high sea-level or contintental position (these factors are minor contributions to warm) 2. Modelers require high CO2 to explain extremely warm climates. a. may be due to higher flux of CO2 from seafloor spreading and huge hot spot volcanism (e.g., Darwin Rise; superplumes) b. superplume explains both large volcanic edifices such as Darwin R. and high rates of seafloor spreading Widespread black shale and oil source rocks associated with lower O2 oceans (higher T, less soluable; Less vigorous bottom-water circulation (no NADW, ?AABW) low latitude deepwater sources?

  46. IV. Black Shales and other sedimentary cycles • Ocean Anoxic Events (AOE) - widespread black shales • massive extraction of organic carbon resulted in high global 13C values • 1. OAE1a Albian-Aptian (ca. 120 Ma) Selli bed • 2. OAE2 Cenomanian/Turonian (ca. 93 Ma boundary Bonarelli bed CAUSE? Productivity B. deep-water O2 a. expanded O2 min. b. whole basin anoxia?

  47. Bonarelli Bed 93 MaOrganic rich oil sourcebottom water anoxia (w/o oxygen)

More Related