By Phebe Pierson
We probably all know that if you dig down deep in the earth, you can find out about the planet’s past. Dirt, artifacts, and fossils can teach us all about human history, climate history, and more. But when you think about archaeological digs or studying sediment, perhaps you think primarily of dry land and dinosaur bones. What about the ocean? Underneath all that water is mud, and it’s filled with fascinating microfossils and sediment that can tell us about the past.
That’s where the Core Repository at Columbia’s Lamont-Doherty Earth Observatory comes in. Over the course of the last 70 years, the Lamont Core Repository has become the go-to place for samples of deep-sea sediment from all over the world. Beginning in 1947, scientists working out of LDEO collected cores during field expeditions on research vessels. Maurice Ewing, Lamont’s founding director, encouraged researchers to collect “a core a day,” no matter where in the world they were. The repository is now home to more than 19,500 cores from all major ocean basins, and new cores come in every year.
So how do scientists collect cores from the ocean floor? And what do they do with them? To find out, we visited the Core Repository and spoke with Nichole Anest, curator of the repository, and Claire Jasper, research staff assistant at the repository and lab. Based on these interviews, we’ve compiled a list of tools used in the “repository of mud,” as Anest calls it, what they are used for, and a glossary of terminology.
One of two kinds of corers used, this one is basically a long pipe (called the barrel) with a weight at the top called a core head.
This is a gravity corer with a piston inside the barrel. When this kind of corer is pulled up from underwater, the first thing that gets pulled up is the piston, which eases a bit more mud into the barrel than you would get with a gravity corer. Bonus!
The weighted part of the corer is located towards the top. This is the only thing (along with gravity) that drives the barrel of the corer into the mud, so it’s heavy—it can weigh up to 1 ton, depending on the type of sediment the researchers are anticipating
The hard and pointy tip of the corer that helps it penetrate the mud.
This captures the top few feet of mud. Piston cores tend to over-penetrate, which means the corer goes deeper than the length of the barrel and the topmost layer of mud is lost. When that happens a trigger weight can be used to regain the top layer.
These can be dropped off the side of the ship and dragged along the ocean floor to collect surface rocks.
Orange Peel Grab Sampler
As the name suggests, this grabs a surface sample from the ocean floor—kind of like those claw games at arcades and movie theaters, but for science.
The barrel of each corer is steel, and inside that is a PVC pipe that fills with the mud sample. Anest and Jasper slide the PVC pipe out of the barrel and chop it into five-foot sections, each of which is then split in half lengthwise using the core splitter. The splitter is essentially two small routers that cut through the PVC pipe as it’s pulled along a track. Once the tube is cut, the mud inside is still intact. Jasper and Anest then pull a wire through the length of the mud, like you’d cut through a chunk of clay at a pottery studio. This slices the tube-shaped mud sample in half lengthwise. Then the two halves can be stored in two long trays so that the inside is visible.
Used for looking at samples up close.
Small spoons used to scoop out samples.
A cutting tool used to cut out U-shaped sections of dried cores. The wire used as the blade is coated with industrial diamond dust, so no matter how lithified (solidified into stone) the core has become, the saw can cut through it.
A small measuring tool used to accurately locate sections of core. When the repository gets a core, the team marks it in 10-centimeter intervals. When they do this, the core is usually wet. But when a core dries, it shrinks, so in order to locate the sections accurately, they use the 10-point, which will divide the shrunken interval into 10 equal parts.
When the scroll saw isn’t working, the team uses these to cut samples.
iTrax Core Scanner aka XRF Machine
The X-ray Fluorescence machine bombards a sample with X-rays to determine how much of each element is in the sample. Each element deflects X-rays in a different and predictable wavelength, so by plotting the wavelengths that result from the bombarding, the Core Lab team can see what elements are present.
The X-ray Diffraction machine is similar to the XRF—it also bombards a sample with X-rays to learn more about its composition. Instead of looking at the elements, though, the XRD looks at the structure of a sample (its mineral composition). (For more about the difference between these two machines visit here.)
GeoTek Multisensor Track
Measures density, sound wave velocity through the sample, and sensitivity to magnets. This tool is also used to photograph cores once they are split in half.
For drying samples of mud. It consists of a cooling coil and a vacuum pump. The cooling coil goes down to -48 degrees C, which ensures that any liquid that’s sucked out of the sample is trapped in the freezer coils so as not to break the pump.
A particle size analyzer for grains smaller than 70 microns. The machine uses X-ray attenuation, meaning it analyzes the amount of X-rays that get blocked by the material to infer how much of the material is in a certain sample.
An undisturbed core will have distinct layers of sediment, which are made up of the material that has fallen to the ocean floor over time. When there’s an earthquake, those layers get all mixed up due to the disturbance of the earth shaking. This means that any cores that are taken from an area that has been disturbed by an earthquake will be mixed up and will not have distinct layers.
A strong underwater current that can cut valleys into the ocean floor—similar to the way rivers cut through land to create canyons and valleys. Most cores have layers of sediment with varying consistencies like sand or clay. A core taken from an area with a turbidity current will have lots of larger rocks in it. These rocks come from underwater landslides on the slopes of underwater hills and valleys, and are then caught up by turbidity currents, settling on the abyssal plains. The heaviest rocks settle first, then the finer clays and sand settle on top.
The flat, deep parts of the ocean floor that are covered in sediment, between continents and oceanic ridges.
When a core is collected incorrectly or there’s some air caught in the tube, the sediment that is from the bottom of the sample can flow up the side, disturbing the barcode-look that undisturbed layers can have. Cores with flow-in can’t be reliably used for research, so the Core Lab gives them to school groups to study the minerals and microfossils in them.
Coccolithophores are a type of single-celled algae with calcium carbonate scales, called coccoliths, that are abundant in the sunlight zone of the ocean (the topmost layer that’s exposed to the sun during the day).
Short for foraminifera, a single-celled organism with a shell made of calcium carbonate that lives on the sea floor.
A type of single-celled algae with cell walls made of silica. These are found in oceans, other bodies of water, and soil.
Any kind of fossil that’s only visible with the use of a microscope (not visible to the naked eye). Coccoliths, forams, and diatoms are all microfossils.
All photos by Phebe Pierson