Together with the expansion of the ice cover, this leads to an increase in the annual sea-ice volume of 20,000 km ³ (Table  2 ).

The increase in the sea-ice thickness in the central Arctic produces a large increase in the southward sea-ice transport through Fram Strait (Table  2 ), contributing to the sea-ice expansion east of Greenland.

The strength of meridional overturning circulation in the Nordic Seas slightly decreases by 0.4 Sv or 12% (Fig.  14 and Table  2 ), consistent with the noted expansion of winter sea-ice cover here (Fig.  13 c).

After 4 kyr BP, the temporal variability of this circulation is notably enhanced (Table  2 ).

Simultaneously, however, deep convection is enhanced in the Labrador Sea, which is coherent with the small increase in the overall North Atlantic overturning circulation as expressed by a slightly larger NADW export at 20°S (Table  2 ).

This is clearly evident in the temperatures in Scandinavia and North America (Figs.  5 , 6 and Table  1 ), in the different components of the ocean circulation in the Nordic Seas (Fig.  14 and Table  2 ) and in the sea-ice evolution (Table  2 ).

The simulated increase in variability depends partly on southward sea-ice transport through Fram Strait, which in our experiment shows an increase in both the volume flux as in the variability (Table  2 ).