Gold
Gold is mentioned frequently in the text and we might therefore see it as an important commodity for Columbus. For example, upon arriving at Lucayos, Columbus immediately "strove to learn if they had any gold," meaning it is a key motivation for him. Ultimately, gold represents wealth and access to power.
Islands
Islands are a key motif in Columbus' journals, as he is constantly moving between them. On each new island, he hopes to find valuable resources, gold, and spices.
Discovery
As we might expect, discovery is a key motif of this text. During his life, Columbus completed many voyages across the Atlantic Ocean, and in this text, we learn about his ventures from his perspective.
Uncertainty
Uncertainty is a key feature of Columbus' voyages, as his crew is frequently facing the unpredictability of the weather and the sea. As such, the uncertainty of navigating the natural world and the uncertainty of exploring are key motifs in this text.
The Unknown
When Columbus and the crew are voyaging, they have no idea what they will find. They hope to find land and resources, but truly they have no idea what awaits them when they dock. In this way, "the unknown" becomes a place in itself, onto which Columbus and his crew project their fantasies and fears. Ultimately, the unknown is seen as a formidable entity, which leads to fear and mutiny.