September 5, 2005
Today we saw a record number of sightings for this leg of CSCAPE. We had twenty-one by the end of the day! Most of the sightings were blue whales and fin whales. We also had a couple of dolphin sightings. These cetaceans seemed to popping up all over the place. Why? Did something change?
Candy Hall and Liz Zele, the oceanographers on board, continually monitor the surface water temperature. For this entire leg, the temperature has been approximately 18° Celsius. At 9:00 A.M. this morning, it remained at 18° C. However, they noticed by 1:00 P.M., the temperature dropped to 15.5° C. A three degree change in temperature is quite sufficient in such a short period of time. The water's temperature and conductivity at four meters below the surface is monitored with a TSG (thermosalinograph). What did this temperature change mean? It meant we hit a temperature front, where warm and cold water meet. These events can be caused by headlands, subtidal topography, storms, or prevailing offshore currents. Given our position, Candy believes the temperature front was caused by a boundary of currents, which causes upwelling to occur. 'Upwelling' is the movement of cool nutrient-rich waters from the deep towards the ocean's surface. An abundance of plankton is generally found in cooler waters, and therefore, possibly providing food for whales. This could be the reason for all the sightings we had today.
All cetaceans are classified in the order Cetacea. Scientists recognize two suborders: Odontoceti and Mysticeti. Fin and blue whales are both baleen whales so they are mysticetes. Instead of having teeth like the odontocetes, they have plates of baleen rooted in the gums of the upper jaw. The plates are used to strain food (plankton and small fish) from the water. So the nutrient-rich, plankton abundant water would be a great place for the blue and fin whales to be.
As with many scientific studies, it is a combination of the chemical, physical, and biological components that help scientists answer questions and learn more about the Earth's ecosystems.