Climatic fluctuations on a decadal timescale in the North Atlantic in
a global ocean general circulation model were considered. The analysis
was carried out for the 3800-year stochastic forcing simulation of Mi
kolajewicz and Maier-Reimer in which the Hamburg Large-Scale Geostroph
ic ocean model was driven by monthly climatologies of wind stress, air
temperature, and freshwater flux with superimposed white noise freshw
ater fluxes with an amplitude of about 16 mm/month. We applied a Princ
ipal Oscillation Pattern analysis to the vector time series of the upp
er level salinity fields, so that the examined fluctuations appear as
estimated eigenmodes of the system. In addition to an oscillation with
a period of 320 years as already described by Mikolajewicz and Maier-
Reimer, we found a broadband Principal Oscillation Pattern with a time
scale of the order of 10 to 40 years. It describes the generation of s
alinity anomalies in the Labrador Sea and the following discharge into
the North Atlantic. In sensitivity experiments we clarified that the
source of the variability lies in the Labrador Sea and showed that the
generation of the salinity anomalies is mainly due to an undisturbed
local integration of the white noise freshwater fluxes.