A COARSE RESOLUTION NORTH-ATLANTIC OCEAN CIRCULATION MODEL - AN INTERCOMPARISON STUDY WITH A PALEOCEANOGRAPHIC EXAMPLE

Paleoreconstructions suggest that during the Last Glacial Maximum (LGM ) the North Atlantic circulation was noticeably different from its pre sent state. However, the glacial salt conveyor belt is believed to be similar to the present-day's conveyor, albeit weaker and shallower bec ause of an increased freshwater flux in high-latitudes. We present her e the investigation of the conveyor operation based on ocean circulati on modelling using two numerical models in parallel. The GFDL primitiv e equation model and a planetary geostrophic model are employed to add ress the problem of the paleocirculation modelling in cases of uncerta in and sparse data comprising the glacial surface boundary conditions. The role of different simplifications that may be used in the ocean c limate studies, including the role of grid resolution, bottom topograp hy, coast-line, etc., versus glacial-interglacial changes of the ocean surface climatology is considered. The LGM reverse conveyor gyre appe ared to be the most noticeable feature of the glacial-to-interglacial alteration of the ocean circulation. The reversed upper-ocean conveyor , weaker and subducting 'normal' conveyor in the intermediate depths, and the change of the deep-ocean return flow route are robust signatur es of the glacial North Atlantic climate. The results are found to be 'model-independent' and fairly insensitive to all factors other than t he onset of the glacial surface conditions.