THE DYNAMIC INTERACTION BETWEEN INTERNAL WAVES AND KRILL:HOTSPOT GENERATION IN THE GULF OF MAINE

Food in the ocean is often distributed in a very patchy manner and in order for large organisms, like whales, to feed efficiently (i.e. consume more calories than burned finding the food), they often rely on physical mechanisms that concentrate their food. In the summertime in the Gulf of Maine, the days are long and the heat from the sun warms the surface layer of the ocean. The deeper water, however, remains colder. If you were to swim deep enough, you could feel the temperature change between the layers. The line that defines the change from one layer to the other is called a pycnocline and waves can move along the pycnocline, very much like waves move along the surface of the ocean. Because waves moving along such a layer occur within the ocean, they are called internal waves. We examined the relationship between internal waves and krill, small (1-10cm) critters that live in the ocean. Krill are eaten by everything from herring to humpback whales. When krill interact with an internal wave, they become more concentrated, and when krill are concentrated enough, whales, seabirds, and other large animals will come to eat them. To look at how krill respond to the passing of an internal wave we used a mathematical model. We found that swimming krill are concentrated by a passing internal wave and we looked at several other variables such as the depth of the pycnocline, how intense the temperature change was between the warm surface water and the cold deep water, or whether the presence of an offshore bank changed the concentration of krill in the waves.