The influence of the closure of the Panamanian Gateway during the late Cenozoic on climate in and around the North Pacific is investigated by using a coupled ocean-atmosphere general circulation model with an open and closed gateway. In the case of an open (closed) gateway, deep convection is present (absent) in the North Pacific. The deep convection is associated with surface saline water transported from the subtropical Atlantic through the open gateway to the North Pacific. On the other hand, with the closed gateway, the lack of saline water transport from the Atlantic induces halocline formation over the subarctic Pacific with cold climate. The deep convection in the North Pacific leads to a vigorous thermohaline circulation with larger meridional heat transport, and causes warmer climate in and around the North Pacific. These results are generally consistent with paleoceanographic and paleoclimatic estimates related to the closure of the Panamanian Gateway.