Chocolate Milk Anyone?
If you prepare chocolate milk and let it sit, you’ll see that the chocolate starts to sink to the bottom, creating a “chocolate” gradient from top to bottom. If you sip from the top of the glass, it tastes most like milk, and from the bottom it tastes most like chocolate, however it is all chocolate milk.
In the sea, for the most part, we can’t see the gradients like we can in chocolate milk, but we do have ways to study them. Brendan Roark and Nancy Prouty are studying the variations in water between the Norfolk and Baltimore Canyons and hoping to learn what water masses (layers) are present in and outside the Canyons, as well as describe the characteristics of those water masses — “yum, that layer tastes like milk,” “yummmmmm, that layer tastes like chocolate!”
We expect to find layers that include water from the warm Gulf Stream and the colder Labrador Current. By using a CTD (Conductivity, Turbidity and Density) outfitted with 12 Niskin bottles we can sample the ocean water at different depths, and create a graph of how the water differs from the top to the bottom. We are running CTD transects from the head of the canyon to the mouth, examining the differences that we find along the length of the canyon.
The water samples collected at standard depths (so scientists can compare their data from cruise to cruise) are used for a wide variety of measurements. For example they are using the element Neodymium (Nd) which is dissolved in the water to try and identify the different water masses like the Gulf Stream (milk layer) verses the Labrador sea water (chocolate layer). Neodymium is delivered to the ocean by weathering and erosion of the continent. It is used in making extremely strong magnets. Different water masses have different Neodymium signatures. So the scientists can trace where the water may have come from.
One of the layers that we can “see” is the nepheloid layer. First discovered in the 1950s, this area of the sea contains lots of suspended sediment. Its name comes from the Greek “nephos” which means “cloud.” And it appears as a cloudy area in otherwise clear water. The sediment can be particles that are settling from the upper ocean or from sediment that is being stripped from the bottom by undersea currents. Preliminary results suggest this layer is rich in elements such as iron and aluminum. Through their work, these scientists hope to characterize the nepheloid layer and determine its origin and extent in the canyons.
Ship time is expensive and no scientist can do it all alone, so they work as teams to collect and analyze samples. Water collected from the surface and bottom are run through a very fine filtration system – much finer than the coffee filters you find at home. The particulate organic matter, or marine snow, is trapped on the filter. These separate water filters of the undissolved particles are being studied by Marc Lavaleye and Craig Robertson who are looking at the chlorophyll pigments, and Amanda Demopoulos is analyzing the isotopes of the particulate organic matter. Using these pigments they can figure out the origin of the chlorophyll, where food from photosynthesis is being produced, and from where in the food chain the material is originating.
So go prepare a glass of chocolate milk and let it sit for a few minutes. As you drink down to the thick chocolate at the bottom, think about what we can learn about our ocean by studying its layers.