Escanaba Trough Expedition: Gravity Coring
Seafloor features such as sulfide mounds and chimneys are prominent evidence of hydrothermal activity. These features, whether active or dormant, are just the tip of the iceberg, so to speak; much of the “plumbing” of hydrothermal systems exists beneath the seafloor surface.
To collect this subsurface data, scientists can push hollow tubes, or cores, into the seafloor, extracting cylinders of sediment that preserve its various layers, or stratigraphy. With its robotic arms, the ROV Jason can collect cores up to a meter long—but rough weather can sometimes keep Jason on deck.
To collect even longer cores and when seas are heavier, scientists use gravity-driven sediment coring, or gravity coring, a straightforward and effective method to delve deeper beneath the seafloor.
The principle behind gravity coring is simple: lower a heavy metal barrel surrounding an empty polybutyrate tube—the core—down to the seafloor at a desired location, letting the weight of the barrel drive the core into the sediment. The barrel used during the Escanaba Trough expedition is 4.5 meters (15 feet) long, weighs about 570 kilograms (1,250 pounds), and typically descends more than 3,000 meters (9,800 feet) to reach the seafloor.
At the downward end of the barrel is a check-valve with upward-pointing teeth, allowing sediment to fill the core but preventing its escape as the barrel is winched back to the surface.
Once the barrel is back on deck, researchers extract the sediment-filled polybutyrate core and cut it into 1.5-meter lengths, to fit analytical instruments onshore. The core segments are then labeled, capped, and kept under refrigeration until they can be transported to laboratories for analysis.
Music: "SRY" by Twelwe, used with permission by Epidemic Sound.