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Morrill: Model sensitivity to North Atlantic freshwater forcing at 8.2 ka

2013 April 15


Fig. 3. Time series of AMOC intensity anomalies following the MWP, expressed as a fraction of the long-term control mean. The MWP of 2.5 Sv for one year was added at Model year 1. AMOC intensity is defined as the maximum value of the overturning streamfunction below 500 m water depth (excludes shallow wind-driven overturning). Heavy lines are decadal averages. Vertical lines on the right show the 2-sigma range of interannual variability in the control simulations, and are not shown for ModelE-R since only 30 yr control averages are available.

Model sensitivity to North Atlantic freshwater forcing at 8.2 ka

We compared four simulations of the 8.2 ka event to assess climate modelsensitivity and skill in responding to North Atlantic freshwaterperturbations. All of the simulations used the same freshwater forcing, 2.5 Sv for one year, applied to either the Hudson Bay(northeastern Canada) or Labrador Sea (between Canada’s Labrador coast and Greenland). Thisfreshwater pulse induced a decadal-mean slowdown of 10–25% in theAtlantic Meridional Overturning Circulation (AMOC) of the models and causeda large-scale pattern of climate anomalies that matched proxy evidence forcooling in the Northern Hemisphere and a southward shift of theIntertropical Convergence Zone. The multi-model ensemble generatedtemperature anomalies that were just half as large as those fromquantitative proxy reconstructions, however. Also, the duration of AMOC andclimate anomalies in three of the simulations was only several decades,significantly shorter than the duration of ~150 yr in thepaleoclimate record. Possible reasons for these discrepancies includeincorrect representation of the early Holocene climate and ocean state inthe North Atlantic and uncertainties in the freshwater forcing estimates.

Model sensitivity to North Atlantic freshwater forcing at 8.2 ka
C. Morrill, A. N. LeGrande, H. Renssen, P. Bakker, and B. L. Otto-Bliesner
Clim. Past, 9, 955-968, 2013
http://www.clim-past.net/9/955/2013/
doi:10.5194/cp-9-955-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.

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