Holocene Climate Variability on Centennial-to-Millennial Time Scales: 2. Internal and Forced Oscillations as Possible Causes

Abstract

The climate of Western and Northern Europe is closely linked to the meridional circulation of the Atlantic Ocean, and climate variability on centennial-to-millennial time scales. in this realm may well be caused by fluctuations in the associated heat transport. The sensitivity of the meridional circulation is determined by a number of feedbacks in the climate system, which can also interact to sustain internal oscillations. Another source of climate variability is (quasi-) periodic external forcing of the climate system, which gives rise to forced oscillations. A climate model is used to generate internal oscillations of one sort (i.e. deep-decoupling oscillations) with periods ranging approximately from 1600-2000 years. During all phases of these oscillations, there is active deep water formation and export from the North Atlantic to the Southern Ocean, and the maximum of the meridional overturning does never drop below 6 x 10(6) m(3) s(-1).