The oceanographers said yesterday that the unusual accumulation has been caused by Siberian and Canadian rivers dumping more water into the Arctic and from melting sea ice. Both are consequences of global warming.

If it flushes into the Atlantic, the infusion of fresh water could, in the worst case, change the ocean current that brings warmth from the tropics to European shores, said Laura De Steur of the Royal Netherlands Institute for Sea Research.

German researcher Benjamin Rabe, of the Alfred Wegener Institute, said the Arctic’s fresh water content had increased 20 percent since the 1990s — about 8,400 cubic kilometers. That is the equivalent of Lake Michigan and Lake Huron together

Increased runoff from the great northern rivers “could potentially impact the large-scale ocean circulation in the Atlantic Ocean,’’ said De Steur. “This is important for us in Western Europe because our climate is pretty much dictated by the thermohaline ocean circulation.’’

The thermohaline current loops like a conveyor belt from the tropics to the North Atlantic, driven by differences in temperature, salt content and wind patterns.

Rabe cautioned that scientists do not yet know enough to predict what may happen, and the results of model simulations also were inconclusive.