USING TIME SERIES AND MULTIVARIATE TECHNIQUES TO ANALYZE CHANGES IN THE OCEAN NITROGEN CYCLE THROUGHOUT HISTORY

Abstract

Nitrogen is a limiting resource in marine ecosystems that directly impacts the productivity of marine life. Values of δ15N extracted from down core sediments are used as a proxy measure of nitrogen in past marine environments. We analyzed historic δ15N records from around the world, covering time periods that ranged 125,000 to 5000 years ago. The Kalman smoother was used to extract the true signal of δ15N from the noisy observations. Applying multivariate techniques, we found both global and regional signals of δ15N. From the principal components analysis we found global signals characterized by sharp increases in δ15N values that began 60,000 and 20,000 years ago. Using k-means clustering, we identified cores with statistically similar δ15N signals that were in close geographical proximity. These findings suggest that there may be both global and regional forcing of the marine nitrogen cycle.