The wrecks were found in 2015 seven months and 36 kms apart, 2,300 kms southwest of Australia in debris fields scattered with coal more than 3.7 kms below the ocean's surface.
The searchers had a closer look with underwater drones that took photographs of both sites and retrieved a coal sample from one. Analysis showed the coal was probably from Britain, a Western Australian Museum report said.
The museum's examination of the images of the scattered remnants of a ship discovered on May 19, 2015, found it was possibly the brig W Gordon or the barque Magdala, according to incomplete records of ships lost in that period.
W Gordon was on a voyage from Scotland to Australia when it disappeared in 1877 with 10 crew aboard. Magdala was lost in 1882 while sailing from Wales to Indonesia.
The report found the splintered wreck was most likely sunk by an explosion. Coal cargoes in the era exploded through sparking of methane gas accumulating below deck or the spontaneous combustion of overheated coal.
An iron wreck found on December 19, 2015, was most likely the barque West Ridge, which vanished while sailing from England to India with 28 sailors in 1883, the report said. A coal sample from that wreck suggested the cargo was from Britain.
There was no evidence of what caused the disaster, but the wreck's location east of the trade route from Europe to Asia suggested it might have been heading to the closest port in Australia for help.
The museum's curator of maritime archaeology, Ross Anderson, said the new data about the two 19th century sinkings was a significant byproduct of the search for Flight 370, which was flying from Malaysia to China when communications with it were lost.
But Anderson doubted that the identities of the two deepest wrecks found in the Indian Ocean would ever be confirmed without a wealthy private benefactor because of their depth and remoteness.
"If it was a shipwreck that we could dive on ... we'd be looking for any artifacts like ceramics or bottles or anything that could confirm providence," Anderson said.
"These are the deepest wrecks so far located in the Indian Ocean, they're some of the most remote shipwrecks in the world, so we try to maximize any information," he added.
The initial underwater sonar probe scoured remote seabed at depths of up to 6,000 metres (20,000 feet) before Malaysia, China and Australia agreed to end the state-funded search for Flight 370 last year. The wrecks were found during that search.
The wrecks of two trawlers sunk the late 20th century were also discovered, but the Australian Transport Safety Bureau, which supervised the search, did not ask the museum to research them.
Ocean Infinity, a US technology company conducting a new search, said this week it had covered nearly 80,000 square kms since January without finding any sign of the plane's wreckage.
In January, the Malaysian government pledged to pay Texas-based Ocean Infinity up to USD 70 million if it could find the wreckage or black boxes of the aircraft within 90 days.
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