These biogeochemists are getting smarter everyday. Now they have determined how to identify different species of nitrogen that have been created in different areas. Tropical waters create one kind of nitrogen, polar waters create another. Deep water corals utilize nitrogen in growth. These researchers have sampled deep water corals in the northwest Atlantic off of Nova Scotia and found that their nitrogen source since the early 1970s has been that of the tropical variety. For the last 1600 years prior to the early 1970s though, the deep water corals off of Nova Scotia obtained their nutrients from polar waters. The authors of the paper conclude that it is likely that recent (the 1970s is recent in climate life) climate changes have impacted ocean circulation.
Sherwood et. al., Nutrient regime shift in the western North Atlantic indicated by compound-specific δ15N of deep-sea gorgonian corals, Proceedings of the National Academy of Science, November 2010.