Dark circle on horizon above sea moving up and down above the horizon.

Place of observation was near Amble in Northumberland and lasted for approx 15 minutes. I saw a dark solid object on the horizon. Due to the distance it appeared spherical. The object changed altitude constantly, sometimes at sea level sometimes above. This was north east from the beach between Amble and High Hauxley. It was very dark in colour and had no distinguishing features. It slowly moved south until eventually out of site. I took 4 videos ( over 1 min in total) and 15 photographs on my camera phone. 2 videos and 2 images are attached to this report. I am happy to be contacted by email.