The Beckman Coulter LS 13320 Laser Diffraction Particle Size Analyzer is a key tool in understanding the sediment we bring back to the lab. By passing a sample through a laser beam and measuring the diffraction (bending of light), the device can tell us what percent of the sediment is of what grain size. Knowing the relative amounts of sand, silt, and clay in the sediment can be useful in a wide range of applications. Larger particles are heavier and take more energy to transport, meaning high winds or fast moving water. Based on this principle, a layer with a high percentage of sand in an otherwise silty area indicates a storm event in a normally calm area, while a whole region of larger grains could indicate a beach with large waves or a strong current.
The primary limitation of the Beckman Coulter machine is that it cannot distinguish between organic and rock-derived particles. Knowing what the sediment is made of can tell researchers a lot about where it came from, how it was transported, and what kind of chemical environment it has been in. Separate analysis must be applied to samples where we care about these factors, and usually results in the sediment being sieved by hand to determine grain size.