A new calibrated deglacial drainage history for North America and

evidence for an Arctic trigger for the Younger Dryas

Lev Tarasov and W. R. PeltierUniversity of Toronto

Outline The issue: meltwater, Bolling-Allerod (B-A) and Younger

Dryas (YD) Model and data Drainage results Implications for climate dynamics

Inferred Greenland temperature

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

Barbados sea-level record

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

Deglacial drainage

Glacial Systems Model (GSM)

Margin forcing (Dyke, 2003)

Large ensemble approach

Bayesian calibration of 22 model parameters against a large set of paleo proxies

Drainage topography

Fast down-slope/storage surface drainage solver: dt=100 years

Coarse grained topography derived from HYDRO-1K DEM

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)

Deglacial eustatic sea-level chronology

Gulf of Mexico discharge 0.2 dSv present-

day flow Largest pulse

during mwp1-a inferred from observations

Gulf of Mexico discharge comparison

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

Hudson River discharge

Gulf of St. Lawrence discharge

Gulf of St. Lawrence sensitivity

NW arctic discharge

Arctic discharge sensitivity

Arctic discharge

YD onset drainage basins

Mississippi drainage NW Arctic drainage Labrador Sea drainage Gulf of St. Lawrence

drainage Hudson River drainage Pacific drainage

NW routing for Lake Agassiz

NW routing for Lake Agassiz sensitivity

Lake Agassiz choke point elevations

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

Climate and meltwater phasing

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