BEIJING — Bitter maritime disputes between China and its neighbors have recently sent fighter jets scrambling, ignited violent protests, and seen angry fishermen thrown in jail. But beneath all the bellicose rhetoric and threatening posture, China also has been waging a quiet campaign — using ancient documents, academic research, maps, and technical data — to bolster its territorial claims.
The frenetic pace of such research — and the official appetite for it — comes after decades of relative quiet in the field and has focused heavily on the two hottest debates: China’s quarrel with six other nations over a potentially oil-rich patch of the South China Sea, and its tense feud with Japan over a small sprinkling of land, which is called the Diaoyu Islands by the Chinese and the Senkaku Islands by the Japanese.
For some Chinese academics, the now-heavy demand for such work marks a near reversal of what they experienced early in their careers.
In past decades, some say, territorial disputes were often considered too sensitive a topic because China was leery of disrupting its relations with its neighbors.
‘‘The government always emphasized the stability of bilateral relationships in the past, so doing public research on the Diaoyu Islands, for example, was not practical,’’ said one Chinese professor.
‘‘You couldn’t write a thesis on it . . . there would be nowhere to publish such articles publicly.’’
Even now, the topic remains sensitive. The professor spoke on the condition of anonymity because, he said, others have been punished in the past for speaking too openly on such matters.
But after an especially bitter dust-up in 2010 between China and Japan, some Chinese scholars say, officials worried that the limited research had hurt China’s ability to make strong territorial claims, leaving it at
a disadvantage with others, such as Japan, whose research community faced fewer constraints.
China’s attention to maps and other documents has intensified since — bringing with it spats of a new kind.
The most recent began shortly after Christmas when a Japanese publication posted what it claimed was a 1950 Chinese government document unearthed in China’s own archives calling the disputed islands by their Japanese name, implying that Beijing then regarded the islands as Japanese.
China’s embassy in Japan sidestepped the question of the document’s authenticity, saying that ‘‘even if the document exists, it won’t change the consistent position of the Chinese government.’’
The embassy later dismissed the whole thing as a ‘‘Japanese attempt to support their wrong stance with an anonymous reference document.’’
But just weeks afterward, with little explanation, China’s Ministry of Foreign Affairs shut down access to a large portion of its archival documents.
A staffer at the archive said the closure was ‘‘due to an upgrading of the system’’ but was unable to say when the work would be complete.