Saline circulation forced by fresh water alone is studied for a broad
region of parameter space by varying the amplitude and profile of evap
oration minus precipitation, the vertical and horizontal mixing of sal
t, vertical and horizontal dissipation of momentum, and the horizontal
resolution. The model is a modified Bryan-Cox model with a freshwater
flux as the natural boundary condition for the salinity balance. For
a model forced by a linear freshwater flux profile, as the amplitude o
f freshwater flux is increased from 0.01 m year-1 to 1 m year-1 with o
ther parameters fixed, the system evolves from a steady state of no os
cillation to a state of periodic oscillation whose frequency increases
almost linearly with the amplitude of freshwater flux. When the fresh
water flux is fixed and the vertical mixing coefficient is increased f
rom 0.5 to 2.5 cm2s-1, the system evolves from a steady state to a sta
te of single-period oscillation, chaotic, a single period, and finally
to a chaotic state when the vertical mixing coefficient is larger tha
n 2 cm2s-1. One set of numerical experiments forced by a cosine shape
of freshwater flux clearly reveals the transition from a state of sing
le period oscillation to period doubling, period quadrupling, and a st
ate of chaotic oscillation. Simple scaling analysis and numerical expe
riments indicate that the strength of the meridional overturning incre
ases with the square-root of the vertical mixing and the 1/4 power of
the freshwater flux. The mean sea surface salinity (deviation from 35
psu) increases with the 3/4 power of the freshwater flux and decreases
with the 1/2 power of the vertical salt mixing.