I am sure the Master told him about His departure from this world and that because of it he threw himself into the sea.

That morning [after the cold] Mirza Abul Hassan Afnan dismissed his servant and said he was going away. He wrote a supplication to the Beloved. Then the Afnan went to the seashore, about two hours walk, and threw himself into the sea. Some fisherman nearby took him out and notified the authorities. Abdul-Baha sent his automobile. I went with the Afnans and Dr. Lotfullah and helped to bring his body home. The next day when we carried the body from his house, the Beloved approached and assisted in carrying the casket to the carriage. I am sure the Master told him about His departure from this world and that because of it he threw himself into the sea.

Mirza Abu'l Hasan Afnán (a noble gentleman from the family of the Báb, for many years living near Abdu'l-Baha), realizing the approach of the most great calamity - the Master's ascension - could not wait to see it, and therefore he drowned himself here, in the sea.

http://bahai-library.com/pdf/m/merrick_abdulbaha_ascension_1921.pdf