Nitrogen isotopic variations in the Gulf of California since the Last Deglaciation: Response to global climate change

Abstract

High‐resolution records of the nitrogen isotopic composition of organic matter (δ 15 N org ), opal content, and opal accumulation rates from the central Gulf of California reveal large and abrupt variations during deglaciation and gradual Holocene changes coincident with climatic changes recorded in the North Atlantic. Homogenous sediments with relatively low δ 15 N org values and low opal content were deposited at the end of the last glacial period, during the Younger‐Dryas event, and during the middle to late Holocene. In contrast, laminated sediments deposited in the two deglacial stages are characterized by very high δ 15 N org values (>14‰) and opal accumulation rates (29–41 mg cm −2 yr −1 ). Abrupt shifts in δ 15 N org were driven by widespread changes in the extent of suboxic subsurface waters supporting denitrification and were amplified in the central gulf record due to variations in upwelling, vertical mixing, and/or the latitudinal position of the Intertropical Convergence Zone.