Climatic patterns and changes in marine N isotope pools

Background/Question/Methods

Several recent studies have documented changes in N isotopes at upper trophic levels of the marine food web.  Such changes integrate both ecological transfers occurring over large spatial scales, as well as climatic changes in the nutrient supply to the base of the food web.  Ocean biogeochemical model simulations provide an important means for untangling the superposition of these processes.  We developed a model of the global ocean cycle of N and its isotopes, with a nested high-resolution regional climate-ecosystem model.  We use these tools to examine the relationships between local variations in N isotopes and the large-scale patterns and climatic trends in nutrient cycling.

Results/Conclusions

We use global model simulations to demonstrate how the isotopic enrichment from marine denitrification in the tropical Pacific responds to climate change, ultimately through the wind-driven circulation.   High-resolution regional model shows that these signals are propagated away from their origin in tropical anoxic zones, into the California Current where the isotope anomalies can be transferred through the higher trophic levels of the marine ecosystem.  Our results imply that the large amplitude of decadal and longer climate trends in the tropical ocean may have a significant impact on remote N isotope signals.