Nitrogen isotopic variations in the Gulf of California since the last deglaciation: Response to global climate change

High-resolution records of the nitrogen isotopic composition of organic mat ter (delta(15)N(org)), opal content, and opal accumulation rates from the c entral Gulf of California reveal large and abrupt variations during deglaci ation and gradual Holocene changes coincident with climatic changes recorde d in the North Atlantic. Homogenous sediments with relatively low delta(15) N(org) values and low opal content were deposited at the end of the last gl acial 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 delta(15)N(org) values (>14 parts per thousand) and opal accumulation rates (29-41 mg cm(-2) yr(-1)). Abrupt shi fts in delta(15)N(org) were driven by widespread changes in the extent of s uboxic subsurface waters supporting denitrification and were amplified in t he central gulf record due to variations in upwelling, vertical mixing, and /or the latitudinal position of the Intertropical Convergence Zone.