In October, winds are generally light and upwelling events are rare. Sun warms the waters near the sea surface, while cold water remains below this surface layer.
Meanders in the California current bring offshore water toward shore. Pennate diatoms, dinoflagellates, and picoplankton dominate the phytoplankton. Tongues of water from the California Current flow toward the coast, bringing clear, salty oceanic water and oceanic animals such as albacore tuna, jellies, and leatherback sea turtles.
Krill are still abundant, but become less numerous by the end of the month, as blue whales, pelicans, and other summer visitors begin to leave the area.
The kelp canopy grows slowly because few nutrients are available. Kelp blades begin to rot, especially in protected coastal areas. Other algae also begin to release spores and decompose. Kelp bed animals reach peak abundance, as young from the summer grow and seek out new territory.
The waves are generally very small except when occasional large swells from the south tear up the rotting kelp blades.
Young crabs, worms, sea stars, and other tide-pool animals are abundant, especially those that feed on algae. Many intertidal seaweeds form reproductive structures, release gametes, and begin to decompose.
Huge numbers of migrant birds use estuaries as feeding stops on their return from nesting in Canada and Alaska. Sandy beaches also see beach birds returning from nesting in the far north.