1. A new calibrated deglacial drainage history for North America and evidence for an Arctic trigger for the Younger Dryas Lev Tarasov and W. R. Peltier University of Toronto

2. Outline The issue: meltwater, Bolling-Allerod (B-A) and Younger Dryas (YD) Model and data Drainage results Implications for climate dynamics

3. Inferred Greenland temperature

4. Thermohaline (THC) record (57W, 33N), McManus et al.,(Nature, 2004)

5. Barbados sea-level record

6. More challenges Champlain Sea was at highest salinity during YD onset (Rodrigues and Vilks, QSR, 1994) High surface salinity for Gulf of St. Lawrence during YD (de Vernal et al., Nature,1996) Muddy water sinks (Parsons et al., Sed., 2001) With sediment loads as low as 1 kg/m^3

7. Deglacial drainage

8. Glacial Systems Model (GSM) Margin forcing (Dyke, 2003) Large ensemble approach Bayesian calibration of 22 model parameters against a large set of paleo proxies

9. Drainage topography Fast down-slope/storage surface drainage solver: dt=100 years Coarse grained topography derived from HYDRO-1K DEM

10. Drainage ensembles 50 member sub-ensembles Best from Bayesian calibration: 92A, but strandline misfits -> Further hydrological tuning: 11P, 11Y Red River (RR) Wampum (W) Lake Athabasca (A) Great Slave Lake (GS) Great Bear Lake (GB)

11. Deglacial eustatic sea-level chronology

12. Gulf of Mexico discharge 0.2 dSv present- day flow Largest pulse during mwp1-a inferred from observations

13. Gulf of Mexico discharge comparison

14. mwp1-a drainage map Mississippi drainage NW Arctic drainage Labrador Sea drainage Gulf of St. Lawrence drainage Hudson River drainage Pacific drainage -14.6 kyr Mississippi discharge: 0.34 dSv -14.4 kyr Mississippi : 1.7 dSv

15. Hudson River discharge

16. Gulf of St. Lawrence discharge

17. Gulf of St. Lawrence sensitivity

18. NW arctic discharge

19. Arctic discharge sensitivity

20. Arctic discharge

21. YD onset drainage basins Mississippi drainage NW Arctic drainage Labrador Sea drainage Gulf of St. Lawrence drainage Hudson River drainage Pacific drainage

22. NW routing for Lake Agassiz

23. NW routing for Lake Agassiz sensitivity

24. Lake Agassiz choke point elevations

25. Where does the meltwater go? Bauch et al (QSR, 2001): evidence of a low salinity event at or before YD onset in western Fram Strait

26. Climate and meltwater phasing

27. Summary Largest (1.7 to 2.3 dSv over 100 years) discharge into the NW Arctic Basin during YD onset Most of NW discharge is due to the reduction of the Keewatin ice dome: thus independent of Lake Agassiz routing uncertainties Trigger for YD? Ensemble NA contributions to mwp-1a range from 7.2 to 11.4 m eustatic Large (1.5-2 dSv over 100 years) meltwater pulses into both the Gulf of Mexico and Eastern seaboard GSM + calibration = data and physics integration