More Q & A

Ms. Pfaff’s 6th grade Earth science class (period 3) asks, “Why are internal waves so important, that you decided to research them?”

Internal waves are important from two perspectives.  First, they have the ability to distribute ocean energy from lunar tides to various parts of the ocean.  Energy (both heat and turbulence) is moved around the ocean by either tides or surface waves.  Normally the moon driven tides distribute energy on the order of about 12 hrs (the semidiurnal tidal cycle).  Internal tides have shorter periods (the wave created by the water hitting a deep ridge is kind of like a ripple in the larger tide) and therefore can distribute energy more quickly. Scientists believe that internal tides may be the source of high turbulence areas that are important for mixing ocean waters globally.  The Tasman Sea tide is one of these (some others occur in Hawaii, the Aleutian Islands, and Africa), but special because the internal tide is so regular and the “beam” of the tide (the area of highest energy) occurs mostly in one direction across the very flat bottom of the Tasman Sea.  This allows scientists to study the how an internal tide propagates across an ocean basin, and also how it interacts with smaller scale processes like eddies.  The eddies have the potential to reduce or break up the energy of the tide.  Scientists can also study what happens once the internal tide hits the continental shelf of Tasmania – does it bounce back directly?, does it get reflected in other directions?, does it just dissipate?  The likely answer is that it probably does all of these, but we don’t know how and to what extent.  Knowing all of this information about internal tides will help scientists better understand ocean mixing, which is an important component of predicting how climate change may affect different areas of the planet (since the oceans are so important in distributing heat energy absorbed from the atmosphere).

The other reason that internal tides are important is because they have the potential to affect fisheries, which I mentioned in my last response.  Both sediments and cold water may be brought up to surface waters due to the tide breaking on the continental shelf.  Generally, surface waters of the ocean have less nutrients than deeper waters (and sediments).  If these nutrients are brought up closer to the surface, they will be available to phytoplankton, which will use them to grow and reproduce.  More phytoplankton means more food for zooplankton and small fishes, which in turn means more food for larger fishes.  Areas that have lots of nutrients coming up in the water are considered “high productivity” areas because they “produce” a lot of biomass (lots of organisms).

– Judy Lemus, The Falkor