A day before the Japanese attacked Pearl Harbor, the USS Arizona received a fresh supply of about 1.2 million gallons of Bunker C oil.

When a 1,760-pound bomb tore through the ship’s deck during the attack, the resulting explosion destroyed a section of the ship’s bow and continued backward and out of the smokestack. The ship burned for more than two days, consuming a great deal of the loaded oil.

What remains of the oil, roughly a half-million gallons, has been leaking to the surface for the last 75 years in dribs and drabs of one to eight quarts a day, the so-called “black tears” of a black day forming iridescent circles atop the waters of Pearl Harbor.

The National Park Service made the first concerted effort to assess the leaking oil and its potential environmental impact when it took over management of the Arizona in 1980.

Archaeologists from the NPS Submerged Resources Center and Navy divers completed the first mapping of the ship.

Oil was first detected coming from hatches on two barbettes (armored housings at the base of a gun turret). Subsequent assessments have identified leaks in at least six other locations on the ship.

The current rate of leakage has minimal impact on the harbor’s ecosystems, but concern has periodically been raised that as the ship continues to slowly degrade, a significant rupture or collapse could result in a catastrophic release of the remaining oil within the ship — an amount five times more than the 100,000 gallons of jet fuel that spilled from a pipeline into the harbor in 1987, which took two months to clean up.

Scott Pawlowski, chief of cultural and natural resources for the World War II Valor in the Pacific National Monument, said such a massive release is highly unlikely given the physical properties of the oil and its location within the ship.

According to Pawlowski, the oil is gelatinlike in consistency and thus too dense to rise en masse. More significantly, the remaining oil is housed within roughly 100 individual fuel cells in the ship’s lower decks; all would need to rupture at the same time to produce the sort of environmental disaster speculated upon in a catastrophic release scenario.

Pawlowski, who along with other divers routinely examines the ship for signs of change, said efforts are underway to quantify their observations that wind and wave conditions affect the rate of leakage from day to day.