SCIENCE

The vertical migration of brine shrimp causes substantial mixing of the water column. (Science)

Learn more about this “marine mix” with our student-friendly article.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

Discussion Ideas

• The brine shrimp studied in the new article engage in diel vertical migration. What is diel vertical migration?
  • Diel vertical migration describes a daily pattern of movement from the colder, darker, deeper part of the ocean (the mesopelagic zone) to the slightly warmer, brighter, and shallower part of the ocean (the epipelagic zone). Diel vertical migration can also apply to microscopic migrations in freshwater—from a lake’s dark hypolimnion to its sunny surface.
    • The brine shrimp’s diel vertical migration is fairly short (measured in tanks of just two meters (six feet)), but the shrimp are pretty tiny! They’re what researchers call “centimeter-scale swimmers.”
      • Nat Geo Explorer Kakani Katija explains it like this: “We are pretty big, so when we swim through water it feels like water. But . . . if we were something smaller, like a worm, it will feel more like swimming through honey. This difference is called fluid viscosity.”

• How do “centimeter swimmers” mix waters on an oceanic scale?
  • They work together! Brine shrimp tend to migrate in huge swarms. “The individual eddies created by each shrimp don’t do much, but as they swirl together, they add up to a significant downward flow. The difference is akin to what happens when you stir cream into coffee rather than letting the cream just sink in.”
    • The swirling water surrounding the shrimp “caused the two layers of water to mix 1000 times faster than they would if left to their own devices.”

• Why is ocean mixing so important for marine ecosystems? Read through our short article on the work of bioengineer Kakani Katija for some help.
  • Ocean mixing is important for two reasons: marine life and climate.
    • marine life. “If you want to get oxygen, that comes from the surface or the atmosphere. If you want nutrients, a lot of those nutrients settle to the bottom of the ocean. Somehow you need to spread oxygen as well as these nutrients through the ocean fast enough to sustain life. That’s where ocean mixing is very important.”
    • climate. The ocean is one of the primary agents distributing heat on Earth, and so is largely responsible for climate. The 1,000-year-long ocean conveyer belt transports warm water from the equator toward the poles, and cold water from the poles back to the tropics. In the tropics, the of evaporation helps distribute temperature in the atmosphere. Learn more from our video here.

• The process studied in the new research is called biogenic ocean mixing, describing physical changes (ocean mixing) resulting from the activity of living organisms. Besides biogenic ocean mixing, what are some other phenomena and factors that contribute to vertical mixing of ocean waters?
  • temperature. Warmer water is found near the surface of the ocean, where it is warmed by the sun. Sunlight cannot penetrate the bathypelagic or midnight zone of the ocean, where water is very cold and very dark. Ice cover on the surface of the ocean can also impact how ocean mixing occurs.
  • salinity and density. Salinity is the primary contributor to seawater’s density. Saltier water tends to sink.
  • wind. Wind is the primary mixing agent in the upper layers of the ocean.
  • waves and tides. Both the regular and irregular (stormy) movements of the ocean can mix temperatures, organisms, and nutrients.
  • currents. Local and regional currents distribute water to different areas of the globe. The global system of currents known as the ocean conveyor belt distributes water from the surface to the seafloor all around the world.
  • topography and bathymetry. The shape of the seafloor can have a huge impact on how ocean waters mix. In the waters surrounding Antarctica, for instance, “there is no land mass to block [the current]. So it builds and builds, until it ultimately flows with the volume of 100 Amazon rivers.” Learn more with our short video here.
  • upwelling. The forces of wind, waves, and underwater features contribute to upwelling, the process in which cold, deep, nutrient-rich water is forced toward the surface.
  • geology. Geologic features such as hydrothermal vents and underwater volcanoes can really mix things up by radically changing ocean chemistry, topography, and temperature.

TEACHERS TOOLKIT

Science: Tiny shrimp may be mixing ocean water as much as the wind and waves

Nat Geo: Marine Mix

(extra credit!) Nature: Vertically migrating swimmers generate aggregation-scale eddies in a stratified column