Russia submitted its claim in 2001 to an international commission, which has ruled that the available data is not sufficient to support it. But Russia has pressed on.

“We must determine the border, the most northerly of the Russian shelf,” Mr. Chilingarov said on national television before the dive, which was billed as the first of its sort — a descent into the inky darkness far beneath a large window cut into the ice sheet by a nuclear-powered ice breaker.

After resurfacing more than eight hours later, Mr. Chilingarov spoke as if he had been the first to the moon. “If a hundred or a thousand years from now someone goes down to where we were, they will see the Russian flag,” he said. The flag is reproduced in titanium. He later added, “Our task is to remind the world that Russia is a great Arctic and scientific power.”

The day’s events underscored both Russia’s restored sense of confidence and the international competition for access, influence and extraction rights in the far north, which has intensified as oil and gas prices have surged and as trends in global warming have encouraged speculation that the region could become more navigable.

President Vladimir V. Putin called the members of the expedition to thank them personally, an unmistakable sign of the significance of the claim to the Kremlin, which has reestablished itself as a world power in recent years in part through its control of its oil, gas, minerals and other commodities.