Auxiliary Material for Paper 2010PA001936

A box model test of the freshwater forcing hypothesis of abrupt climate change
and the physics governing ocean stability

Charles S. Jackson,1 
1Institute for Geophysics, University of Texas at Austin, Austin, Texas, USA.

Olivier Marchal,2 
2Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA.

Yurun Liu,3 Shaoping Lu,3 
3Department of Physics, University of Texas at Austin, Austin, Texas, USA.

William G. Thompson2
2Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA.

Jackson, C. S., O. Marchal, Y. Liu, S. Lu, and W. G. Thompson (2010), A box model test of the freshwater forcing hypothesis of abrupt climate change and the physics governing ocean stability, Paleoceanography, 25, PA4222, doi:10.1029/2010PA001936.

Introduction.

The Auxiliary material includes three figures of results discussed in the text. 

2010PA001936-fs01.eps Comparison between solutions from 4-box model inversions 
(dashed) and results of Knutti et al. [2004] (solid). Knutti et al [2004] found
 a simple relationship between Greenland temperature anomalies and freshwater 
anomalies to the North Atlantic and a model dependent sensitivity scaling 
parameter. Panel (a) shows freshwater forcing versus box sea surface temperature 
anomalies, (b) time series of inferred freshwater forcing, and (c) implied sea 
level anomalies. 

2010PA001936-fs02.eps Equilibrium solutions of the 4-box ocean model with a 
parameterization of the Southern Ocean according to Gnanadesikan [1999]. The 
meridional overturning circulation in the northern hemisphere is shown as a 
function of the meridional moisture transport in the atmosphere. Arrows indicate 
the direction of hysteresis. The different lines refer to different mixing 
assumptions: constant vertical mixing (solid line), stability dependent mixing 
(short dashed line), and constant mixing energy (long dashed line).

2010PA001936-fs03.eps Inversion solutions for the 6-box model, with two boxes in 
each polar region and a stability threshold for deep convection in these regions. 
Panel (a) compares the solutions for the polar northern temperature (black lines) 
to the scaled Greenland record (gray lines) [Grootes et al., 1993; Meese et al., 
1997]. Panel (b) gives the corresponding estimate for MOC strength. Panel (c) 
compares sea level anomalies inferred from the Greeland record and estimated from 
oxygen isotope records from the Red Sea [Siddall et al., 2003]. The solid dashed 
lines correspond to different rates of deep convection: 5 Sv (solid) and 1 Sv 
(dashed).

References

Knutti, R., J. Flückiger, T. F. Stocker, A. Timmermann (2004), Strong hemispheric 
coupling of glacial climate through freshwater discharge and ocean circulation, 
Nature, 430(7002), 851–856, doi:10.1038/nature02786.

Gnanadesikan, A. (1999), A simple predictive model for the structure of the 
oceanic pycnocline, Science, 283(5410), 2077–2079.

Grootes, P. M., M. Stuvier, J. W. C. White, S. J. Johnsen, and J. Jouzel (1993), 
Comparison of oxygen isotope records from GISP2 and GRIP Greenland ice cores, 
Nature, 366, 552–554.

Meese, D. A. et al. (1997), The Greenland ice sheet project 2 depth-age scale: 
methods and results, J. Geophys. Res., 102(C12), 26411–26423.

Siddall, M., E. J. Rohling, A. Almogi-Labin, C. Hemleben, D. Meischner, I. 
Schmelzer, D. A. Smeed (2003), Sea-level fluctuations during the last glacial 
cycle, Nature, 423, 853–858.