Grab sampling is the simple process of bringing up surface sediments from the seafloor. It cannot be used to characterize different sedimentary layers since a mixture of sediments is produced when they are brought up, therefore, it is only used for the surface. This method has neither the ability nor the ergonomic qualities to penetrate the ground to depth. How does it work?

Once it is launched, the jaws of the grab sampler open and it descends to the seafloor. A spring closes the jaws, and they trap sediments or loose substrate. The grab sampler is then brought up to the surface where its contents are studied in detail.

grab sample

grab sampling

Coring

Coring is a technique used to bring sediments from the seafloor up to the surface for analysis. There are several types of coring; three types were used to obtain samples from the Georgia Basin, they are:

• Gravity coring
• Piston coring
• Vibrocoring

How does it work?

The three types function similarly. They all have a tube which penetrates the ground and pulls a core of sediments out. This core is used in studying the physical structure of the seafloor, its history, and the nature of the sediments. What distinguishes the three types of coring is the penetration mechanism of the tube. The basic principles of each are described below, gravity being an important driving force in each.

1. Gravity Coring

   This type of coring penetrates the ground due to the force of gravity. Since the speed of penetration is the same as the sampling speed, it barely disrupts the sedimentary layers. A cable attached to the ship pulls the core once it has penetrated the ground to its maximum capacity. The contents are retracted and the sedimentary layers may be studied.
   

2. Piston Coring

   Along with the force of gravity, this type of coring uses a piston mechanism to penetrate deeper ground. Connected to the tube is a weight which reaches the seafloor before the tube and lifts the lever to release the piston.This exerts a force that pulls the sediments up into the tube. The force disrupts the physical structure of the layers of sediments because the speed of penetration and the sampling speed differ.
   

3. Vibrocoring

   Vibrocoring uses vibration to facilitate ground penetration. With the force of gravity, and sometimes a piston, it can penetrate much deeper layers. The vibration provokes a slight mixing of the sediments.