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- The earlier rapid changes (reflected in 6180 profile of Greenland ice cores) might have 
the same cause, i-e., shifts in the North Atlantic sea ice extension and iceberg influence. 
- The system's bistable mode might be the result of lower sea level and higher continental 
ice mass, influencing ocean circulation in various ways (deep water formation, seabed topography 
influence). 
- "Milankovitch" forcing probably responsible for longer term climatic cycle, e.g., continen- 
tal ice covers; superimposed undoubtedly are the phenomena of rapid climatic oscillations related 
to events in the North Atlantic Ocean. 
- Deglaciation starting ~15,000 BP, still enabling transitions between cold and warm system 
states; however, after the last transition around 10,000 BP the system could no longer switch 
back to the cold state, and the North Atlantic continued its mode of operation till today. 
- Changes in North Atlantic circulation might trigger other ocean circulation changes which 
together might lead to a change in ocean surface chemistry (CO, and alkalinity) leading to 
changes of pCO, in the ocean surface water and changes of atmospheric COg concentration. 
Recommendations 
- Importance of paleo-information for understanding of complex environmental system mecha- 
nisms is underlined by these ice core, ocean and lake sediment data. They should be continued 
with high priority. 
- Attempts to model isotopic ratios (2H/H and 180/160 in H2O) using physical information 
derived from GCM's. Also modelling of transport of sea salts and continental dust etc. to com- 
pare results with ice core information. 
- North Atlantic probably crucial area for triggering of general oceanic circulation changes. 
Study of propagation of North Atlantic changes into the entire oceanic system should not be 
neglected (equatorial upwelling and mixing of water around Artarctica). 
- More realistic modeling of ocean circulation in GCM's, especially regarding heat transport 
(horizontal). 
