Sampling

Piston coring is a popular method in marine geology for getting relatively undisturbed sediment samples, known as "core samples." The piston creates a stable environment at the top of the core, which reduces disturbance and compaction.

How it works: The corer is lowered near the seabed. A trigger weight hits the bottom first, taking a small 1-metre core sample. This action releases the main corer, allowing it to freefall into the sediment.

Best for: Soft sediment environments. It cannot be used on sandy or rocky seabeds.

Capabilities: Core lengths: 6, 9, 12, 15, 18, 21, and 24 metres, Water depth: 70 to 6,500 metres on a NERC vessel (deeper with a higher capacity winch), Liner: 110mm O.D., 5mm wall thickness, PVC-U material.

Operation: Requires two technicians per 12-hour shift. Operates in weather up to Force 6-8, depending on the ship's movement.

A gravity core is a simpler, yet still very effective, way to get sediment samples. Like the piston core, it uses a weighted pipe to pierce the seabed. However, it doesn't have a piston or freefall mechanism; instead, it is simply lowered at speed into the seabed.

When to use: Deployment and recovery are faster and simpler than piston coring. It is used when minimal sediment disturbance isn't the highest priority.

Best for: Softer sediments. It cannot be used on sandy or rocky seabeds.

Capabilities: Core lengths: 1, 2, and 3 metres (barrels can be joined for longer samples in very soft sediment), Weight: Variable from 100kg to 800kg to aid penetration without damaging the sample.

• Barrels: Stainless steel (unlike piston cores).
• Standard liner: Polycarbonate clear liner, 63mm diameter.

Operation: Requires one technician per 12-hour shift. Operates in weather up to Force 6-8.

The megacore collects multiple high-quality, undisturbed samples that include the water/sediment interface. This is especially valuable for studying things like microplastics, benthic layer interactions, and pore water chemistry.

Specifications: Up to 12 core tubes, with outer diameter options of 110mm or 65mm. The tubes are clear polycarbonate for easy visual inspection.

Best for: Soft sediment. It can be used in sandy sediment (with sub-optimal recovery) but not on rocky or gravel seabeds.

Operation: Requires one technician per 12-hour shift. Operates in weather up to Force 6-8.

SMBA box cores capture undisturbed soft sediment samples using a square box design (500mm x 500mm). The corer sits on the seabed and lowers the box into the sediment. A spade then cuts through the bottom to seal the sample.

Like the megacore, it captures the water/sediment interface, making it great for detailed analysis.

Best for: Soft sediment and sandy seabeds. Not suitable for rocky ground.

Operation: Requires at least one technician per 12-hour shift. Operates in weather up to Force 6-8.

A rock dredge is a large chain-mail bag held open by a heavy frame. It is towed along the seabed to gather geological samples like rocks and gravel. A finer net inside can capture smaller samples.

When to use: Rough and hard seafloor areas.

Deployment: It is towed. We often use a "sacrificial wire" of up to 500 metres before attaching to the ship's wire to reduce damage.

Capabilities: Works in depths up to 6,500 metres.

Operation: Requires one technician per 12-hour shift.

A Day grab is a small sediment sampler comprising two scoops. Once landed on the seabed, they snap together like a pincer to capture the sample.

Best for: Shallower waters, where its weight and size are most effective.

Capabilities: Collects about 10 litres of sediment.

Operation: Requires one technician per 12-hour shift.

OTSB (Otter Trawl Semi Balloon): Used to collect biological samples from the seabed or mid-water. It has a funnel-shaped net kept open by heavy "otter boards" (doors).

Operation: Requires four technicians.

Agassiz Trawl: Also used for biological samples but held open by a steel frame (2.5m x 1m). Unlike the OTSB, it can be used vertically through the water and is towed using the ship's wire directly.

Operation: Requires two technicians per 12-hour shift.

Operational Details:

• Deployment: All coring systems are deployed mid-ship on the core wire to minimise ship movement effects.
• Weather: Most systems operate in conditions up to Force 6-8, depending on ship stability and wave height.
• Additional Services: OEG offers core splitting (for piston/gravity cores) and positioning support using the ship's USBL units.