Red abalone collecting and marine water temperature during the Middle Holocene occupation of Santa Cruz Island, California

► Oxygen isotope analysis was performed on prehistoric mussel shells dating to 6300-5300 cal BP. ► The analysis revealed that waters of the Santa Barbara Channel, CA, were cooler than historically. ► The results are consistent with those of previous regional oxygen isotope analyses. ► Collection of red abalone during the 6300-5300 cal BP period was facilitated by cool waters. ► Intertidal and subtidal water temperature variation is important in isotope data interpretation.