Arctic ocean change: what changes and what doesn't

Water properties in the Arctic Ocean have changed, perhaps most markedly from pre-1990 into the 1990s. Do these changes reflect reorganization of Arctic Ocean circulation? It will be suggested, following a simple scheme supported from theory and modeling, that changes occur in three distinct ways. Near-surface direct forcing modifies the sea ice / ocean mixing layer. Thermodynamics are accommodated in a localized way. Below the mixing layer down to a main halocline, circulation changes respond to changes in large scale windstress / sea level pressure. None of this is surprising and research efforts strive to quantify myriad details. The picture gets more interesting below the main halocline where water properties also have evidenced large change. It is suggested that mid- and deep-circulations change very little except at a few key branching points where even subtle changes of circulation lead to large changes of mid-depth heat, salt and tracer distributions.