A "heat stain" has been detected in the search for the missing Argentine submarine with sailors trapped on-board.
A number of nations have joined in the search for the sub in the South Atlantic.
Two Argentinean ships picked up sounds from the ocean that some thought could be signals from the crew, though navy officials said Monday that they do not believe the noises to be Morse code or another attempt at rescue from the crew.
The ARA San Juan would have enough oxygen for its crew to survive underwater for seven days, if there was no hull breach, according to officials.
Peter Layton, a visiting fellow at the Griffith Asia Institute at Australia's Griffith University, offered a scenario similar to Balbi's: If the vessel had sunk but was still intact, Layton said, the crew would have about a week to 10 days of oxygen. Given that five days have passed since it went missing, there are now only two days left to locate it. It is unclear whether the boat is underwater or on the surface.
The San Juan entered service in the Argentine Navy in 1985, but underwent an extensive "mid-life update" from 2008 to 2013 - a refit that was reportedly plagued by delays due to a shortage of funds.
The Argentinian diesel-electric vessel made its last contact with authorities to report a mechanical breakdown.
The submarine was traveling from a base in far southern Tierra del Fuego archipelago to its home base in Mar del Plata, a city hundreds of miles to the northeast, when the navy lost contact with it last week. "At this time, we have not received a request for military assistance", he added.
The US Navy was preparing on Tuesday to deploy rescue equipment, including a remote-operated vehicle.
Relatives of the crew members have gathered at the base to receive psychological counseling and wait for news about their loved ones. "I am hopeful that with the help of God soon we'll hear the news we've all been waiting for".
The governments of Brazil, Canada, Chile, Colombia, France, Germany, France, Norway, Peru, the United Kingdom and the United Stated have sent ships, airplanes and submarines to provide logistic support and information exchange during the search for the missing submarine.
"We know it's been really rough, so even though the Argentinian navy protocol is to surface, it makes no sense with 6-8m waves to be sitting on the surface", he said.
Among the crew on board the San Juan is Eliana Maria Krawczy, Argentina's first female submarine officer.
The waters of the Atlantic ocean, where the sounds were said to originate from, said the U.S. official, are extremely deep. No other missing vessels have been reported in the area, Balbi said.