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The 8.2Kyr event Julia Tindall Freshwater hosing experiments Ron Kahana

The 8.2Kyr event Julia Tindall Freshwater hosing experiments Ron Kahana. The 8.2Kyr event. Introduction and motivation The 8.2Kyr event in data Cause of the event Modelling the 8.2Ka event using other models Modelling the 8.2Ka event using HadCM3L. The 8.2Ka event in Greenland ice cores.

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The 8.2Kyr event Julia Tindall Freshwater hosing experiments Ron Kahana

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  1. The 8.2Kyr eventJulia TindallFreshwater hosing experiments Ron Kahana

  2. The 8.2Kyr event • Introduction and motivation • The 8.2Kyr event in data • Cause of the event • Modelling the 8.2Ka event using other models • Modelling the 8.2Ka event using HadCM3L

  3. The 8.2Ka event in Greenland ice cores • Largest rapid climate change • event of the Holocene • (cooling of 3oC-6oC) • Useful for understanding • the sensitivity of the climate • and the likelihood of a similar • future event • The ideal test for climate • models

  4. Data from Greenland ice core Figure from Alley and Ágústsdóttir 2005

  5. The 8.2Kyr event globally?

  6. Timing and structure in Greenland(δ18O from GRIP(red) and GISP2(black)) From Thomas et al 2006

  7. Summary of evidence for 8.2Ka event globally • Recent review (Morrill et al. 2005) found a statistically significant • signal at 8.2Ka in 40% of records considered in both the Northern • Hemisphere and the tropics • Important to separate a clear ~150yr 8.2Ka signal from • millennial scale variability in the Holocene • Was sharp 150year event superimposed on a longer (millennial scale) • weaker event • No evidence for event over Southern Hemisphere, or southward shift • of ITCZ • Some evidence of a slowdown in NADW formation at 8.2Ka, • although this evidence is weak as many proxy records • contain no signal

  8. Cause of the 8.2Ka event

  9. Details of outflow from Glacial Lake Agassiz • 151,000km3 of freshwater • 5.2Sv over 6months/1year • Reasonably well dated and occurred at 8.45Ka

  10. Legrande et al 2006 • GISS (model E) • Ensemble of experiments with 2.5Sv – 5.0Sv added over 6 months to 1 year • Large differences between ensemble members • All ensemble members, had a full recovery of the THC within 30 years although sometimes there were secondary shutdowns. Temperature precip δ18O in precipitation δ18O in seawater

  11. Modelling the 8.2Ka event using other models • Wiersma et al 2006 • ECBilt-Clio model (intermediate complexity) • Flood equivalent to 5.2Sv With baseline flux of 0.172Sv Without baseline flux

  12. Other of previous modelling results • NCAR model has full recovery in ~10 years (Carrie Morill 8.2Ka workshop) • Vellinga and Wood 2001; HadCM3 forced with ~16Sv years – recovery in ~120years • Bauer et al 2004: CLIMBER-2, multi-century weak freshwater pulse (0.04Sv) required (associated with melting of LIS)

  13. Experiments with HadCM3

  14. HadCM3 5Sv added over North Atlantic for 1 year First 10 years of model run show cooling over much of the Northern hemisphere however δ18O signal is more noisy.

  15. Atlantic MOC

  16. First 10 years Next 10 years Last 20 years (yr 57-yr 77) Temperature Changes δ18O Changes

  17. What could improve model results? • 8.2Ka boundary conditions • Extra freshwater forcing (e.g. preflood=0.055Sv, flood=2.5Sv, routing=0.172Sv rerouting=0.104Sv ????) • Other initial conditions

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