Sedimentary 15N/14N ratios can be used as a unique measure of past changes in surface ocean nutrient utilization which in turn is a function of past changes in productivity and nutrient input from deeper waters. Due to isotopic fractionation during nitrate uptake by phytoplankton, partial nutrient utilization produces substantial 15N enrichment in particulate matter reaching the seafloor. Examples are given from the N. Atlantic, Equatorial Pacific, and Southern Ocean. In the latter two regions large variations in nutrient utilization with latitude are observed which go along with gradients in both near-surface ocean and core top 15N/14N. Thus isotopic signals generated in surface waters are transferred and preserved in sediments. First down core results from the Southern Ocean indicate that only modest increases in nutrient utilization and perhaps productivity occured in Subantarctic waters uring the last glacial maximum.
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- The Use of Nitrogen Isotopic Ratio for Reconstruction of Past Changes in Surface Ocean Nutrient Utilization
M. A. Altabet
- Springer Berlin Heidelberg