Holocene sea-surface temperature as a regional driver of environmental shifts and its effects on humans of La Paz Bay, Gulf of California

Past oceanic characteristics can be reconstructed via δ 18 O in bivalve shells, enabling the study of climatic patterns that affected marine and human communities. Through the novel analysis of δ 18 O in Pinctada mazatlanica shells from a 14 C dated Holocene coastal camp we calculated Holocene summer SSTs of La Paz Bay, Baja California Sur, México. Presently summer δ 18 O of P. mazatlanica is −1.8 ± 0.2‰, varying between −1.3‰ and −1.9‰ during the last 8.4 ka. For the years 8413 BP, 7726 BP and 7046 BP, δ 18 O was 0.2–0.1‰ higher than current values, suggesting slightly colder sea surface temperature (SST), while in 7795 BP, values were 0.1‰ lower, suggesting slightly warmer SST. In 6936 BP and 2093 BP, values were 0.4–0.5‰ higher, suggesting significantly colder SSTs. Periods of low (high) SST were characterized by arid (humid) conditions and high (low) marine primary productivity (MPP), favouring human presence (absence) throughout the Holocene. Our results, like those of other paleoceanographic studies, align with orbital forcing and its effects on SST and MPP, which affected human settlement patterns at regional and global scales.