| Abstract: This study examines the responses of the
simulated modern climate of a coupled ocean-atmosphere model to the
discharge of freshwater into the North Atlantic Ocean. Two
numerical experiments were conducted. In the first numerical
experiment in which freshwater is discharged into high North Atlantic
latitudes over the period of 500 years, the thermohaline circulation
(THC) in the Atlantic Ocean weakens. This weakening reduces
surface air temperature over the northern North Atlantic Ocean and
Greenland and, to a lesser degree, over the Arctic Ocean, the
Scandinavian peninsula, and the Circumpolar Ocean and the Antarctic
Continent of the Southern Hemisphere. Upon termination of the
water discharge at the 500th year, the THC begins to reintensify,
gaining its original intensity in a few hundred years. As a
result, the climate of the northern North Atlantic and surrounding
regions resumes its original distribution. However, in the Pacific
sector of the Circumpolar Ocean of the Southern Hemisphere, the initial
cooling and recovery of surface air temperature is delayed by a few
hundred years. In addition, the sudden onset and the termination
of the discharge of freshwater induces a multidecadal variation in the
intensities of the THC and convective activities, which generate large
multidecadal fluctuations of both sea surface temperature and salinity
in the northern North Atlantic. Such oscillation yields almost
abrupt changes of climate with rapid rise and fall of surface
temperature in a few decades. In the second experiment, in which
the same amount of freshwater is discharged into the subtropical North
Atlantic over the period of 500 years, the THC and climate evolve in a
manner of qualitatively similar to the first experiment. However,
the magnitude of the THC response is 4-5 times smaller. It appears
that freshwater is much less effective in weakening the THC if it is
discharged outside high North Atlantic latitudes. The results from
numerical experiments conducted earlier indicate that the intensity of
the THC could also weaken in response to a future increase of
atmospheric CO2, thereby moderating the
CO2-induced warming over the northern
North Atlantic and surrounding regions. |