In the last decade, sea-ice cover in the Arctic Ocean has experienced dramatic changes. In the eastern Eurasian Basin, these changes are partially due to a regime shift in vertical oceanic mixing associated with weakening stratification and stronger currents and an increase in current shear. These changes have provided means for unprecedented winter ventilation of the ocean interior, making this region similar to the western Eurasian Basin. An associated enhanced release of oceanic heat has reduced winter sea-ice formation at a rate comparable to sea-ice loss due to local atmospheric thermodynamic forcing, explaining the observed recent reduction in sea-ice cover in the eastern Arctic. This “atlantification” of the eastern Arctic Ocean represents an essential step toward a new Arctic climate state. In contrast, stronger stratification in the central Amerasian Basin precluded exchanges between the ocean interior and upper ocean and sea ice. However, numerous changes associated with influxes of anomalous Pacific water were found at the basin’s periphery. Changes in geochemical and biological components as a response to changes in physical component of the Arctic Ocean system will be discussed.