What are magnetic anomalies? how do they relate to seafloor spreading?

Magnetic anomalies is is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks.

The relationship between magnetic anomalies and seafloor spreading is that the strength of the geomagnetic field is alternately anomalously high and low with increasing distance away from the axis of the mid-ocean ridge system.

answerformal;