DETECTING INCLINATION ANGLE


The geomagnetic parameter that is most strongly correlated with latitude is field line inclination. In the diagram below, a map of inclination angles is superimposed on a map of the North Atlantic gyre. The red lines are referred to as isoclinics. An isoclinic is a line along which the magnetic inclination angle is constant. Thus, the inclination angle is 75 everywhere along the 75 isoclinic, 60 along the 60 isoclinic, and so on. The map also shows that the northern border of the North Atlantic gyre has an inclination angle of about 60-65 associated with it, whereas the southernmost border of the gyre has an inclination angle somewhere between about 15 and 30.



To determine whether loggerhead sea turtle hatchlings could detect and respond to different inclination angles, they were tested in two experimental situations:




In the open ocean, these responses would aid the hatchlings in maintaining their position in the North Atlantic Gyre. This response would seem to be particularly important at the 60 degree inclination angle, as it is experienced at the northern edge of the gyre. Swimming to the southwest in such a case would prevent the loggerhead sea turtle hatchlings from entering colder waters, where they might die.