1 / 23

WAIS collapsed before GIS collapse!

WAIS meeting, October, 2008. WAIS collapsed before GIS collapse!. Reed Scherer Northern Illinois University Analytical Center for Climate & Environmental Change & Department of Geology & Environmental Geosciences. Strong Obliquity-forced cyclicity. AND-1B 000-600m.

tender
Download Presentation

WAIS collapsed before GIS collapse!

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. WAIS meeting, October, 2008 WAIS collapsed before GIS collapse! Reed Scherer Northern Illinois University Analytical Center for Climate & Environmental Change & Department of Geology & Environmental Geosciences

  2. Strong Obliquity-forced cyclicity AND-1B000-600m Diatomites and diatomaceous muds • 48% of upper 600 m • 53%, excluding volcanic facies • Loads of stories from diatom-based proxies: • Sea-ice • SST • Milankovitch & sub-Milankovitch cyclicity • Glacial processes at transitions

  3. Marine Isotope Stage 31 100ka MPT 41ka N. Atlantic S. Atlantic

  4. Late Pleistoceneterminations are triggered by rising NH insolation • Orbital-scale Antarctic climate change lags NH insolation by a few millennia True for all terminations?

  5. Highest high latitude insolation of the last 3 Ma • High, obl. & ecc. • One intense NH insolation peak (1.072 Ma), 2 SH peaks • Perihelion in SH summer at 1.082 Ma

  6. “Better bring your sunblock”- Rob DeConto, Oct 8, 2008 • Insolation at 70°S at 1.082 Ma ~50 watts/m2 > today • ~100 watts/m2 difference between 1.08 Ma and 1.072 Ma!

  7. Raymo et al., 2006

  8. You’ll soon hear a bit of Rob D & Dave P’s latest model runs for MIS-31!

  9. Laskar inso. 65ºN&S 18O cib. & pachy. 18O 1094 – pachy. 13C 1094 Calc. nanno Diatoms Site 1094 Scherer et al. 2008

  10. CRP-1 Lithostratigraphic Unit 3.2 Up to 80% biogenic carbonate (mostly benthic) Unequivocally dated as MIS-31 (Ar/Ar, Sr/Sr, diatoms, paleomag.) Shallow mixed layer, ~1% sea-ice diatoms Abundant local IRD, 5-7% sea-ice diatoms Abundant pelagic diatoms

  11. 0.99Ma Jaramillo 84.97 ANDRILL MIS: MIS-31 is present but incomplete Comparble diatoms to CRP-1 <<1% sea-ice diatoms Ar/Ar: 1.01 Ma ~~~~~~~ 91.13 1.072 Ma Rare calc-nannofossils Bioturbated diatomaceous mud with volcanic sand but no IRD (90.8 mbsf) Bioturbated diatomite with local-source IRD (87.2 mbsf)

  12. CRP-1 & ANDRILLInterpretation • Little or no sea-ice • Low salinity shallow mixed layer • Surface waters ~2-3° (current surface waters -1.8°) NO RIS – early collapse, in phase with insolation NO WAIS (probably)

  13. Gavin Dunbar’s work at VUW: Laser-ablation ICPMS (in prep.) Mg/Ca ratios from N. pachyderma shows Ross Sea ~2-4°C

  14. Red: NH Blue: SH

  15. Marine Isotope Stage 311.08-1.06 Ma ago • Warmer surface waters than any time in the last 2.4 Ma • RIS absolutely retreated and WAIS almost certainly collapsed (my opinion) • Much better documented than the late Pleistocene events that I’ve discussed before • WAIS collapse preceded GIS collapse by ~10ka (1/2 precession cycle) (my opinion)

  16. Conclusions: • It was a different world “One Million Years BC” • MIS-31 further demonstrates the fragility of sea-ice and the RIS/WAIS system to insolation

  17. Questions: • Was it unique? • What does this mean in terms of future CO2 forcing, rather than insolation forcing?

  18. Pilot study with Tim Naish & colleagues at VUW/GNS: MIS-31, Wanganui Basin, New Zealand sensitive SL record, >20 m thick Does it show the 2-stepped SL rise with max SL coincident with regional cooling around the base of the Jaramillo?

  19. Ice sheet variation and Milankovitch cyclicity: two views (Science, 313, 2006) • Huybers: Duration of summer • higher mean annual temperature (# +degree days/yr) • Obliquity (41kyr) dominated • In phase between poles • Typically relatively warm winter and cool summers (which wouldn’t cause Antarctic melting) • Raymo et al.: Intensity of summer insolation • Precession (23 kyr) dominated • out of phase between poles – strong influence on local insolation • Short but potentially intense summers • Threshold melting affects ice margins on land • Indicates a larger SL contribution from Antarctica than widely recognized

  20. But CO2 highs are synchronous with Antarctic warming on lower amplitude, millennial cycles • CO2 ↑ during NH stadials, several ka before abrupt warming in Greenland

More Related