the 8 2kyr event julia tindall freshwater hosing experiments ron kahana
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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
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
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
slide4

Data from Greenland ice core

Figure from Alley and Ágústsdóttir 2005

slide7

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
details of outflow from glacial lake agassiz
Details of outflow from Glacial Lake Agassiz
  • 151,000km3 of freshwater
  • 5.2Sv over 6months/1year
  • Reasonably well dated and occurred at 8.45Ka
slide10

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

modelling the 8 2ka event using other models
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

other of previous modelling results
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)
slide14

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.

slide17

First 10 years

Next 10 years

Last 20 years

(yr 57-yr 77)

Temperature Changes

δ18O Changes

what could improve model results
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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